ALBERT

Description: Minerals, Vol. 8, Pages 315: Biomineral Reactivity: The Kinetics of the Replacement Reaction of Biological Aragonite to Apatite Minerals doi: 10.3390/min8080315 Authors: Martina Greiner Lurdes Férnandez-Díaz Erika Griesshaber Moritz N. Zenkert Xiaofei Yin Andreas Ziegler Sabino Veintemillas-Verdaguer Wolfgang W. Schmahl We present results of bioaragonite to apatite conversion in bivalve, coral and cuttlebone skeletons, biological hard materials distinguished by specific microstructures, skeletal densities, original porosities and biopolymer contents. The most profound conversion occurs in the cuttlebone of the cephalopod Sepia officinalis, the least effect is observed for the nacreous shell portion of the bivalve Hyriopsis cumingii. The shell of the bivalve Arctica islandica consists of cross-lamellar aragonite, is dense at its innermost and porous at the seaward pointing shell layers. Increased porosity facilitates infiltration of the reaction fluid and renders large surface areas for the dissolution of aragonite and conversion to apatite. Skeletal microstructures of the coral Porites sp. and prismatic H. cumingii allow considerable conversion to apatite. Even though the surface area in Porites sp. is significantly larger in comparison to that of prismatic H. cumingii, the coral skeleton consists of clusters of dense, acicular aragonite. Conversion in the latter is sluggish at first as most apatite precipitates only onto its surface area. However, the process is accelerated when, in addition, fluids enter the hard tissue at centers of calcification. The prismatic shell portion of H. cumingii is readily transformed to apatite as we find here an increased porosity between prisms as well as within the membranes encasing the prisms. In conclusion, we observe distinct differences in bioaragonite to apatite conversion rates and kinetics depending on the feasibility of the reaction fluid to access aragonite crystallites. The latter is dependent on the content of biopolymers within the hard tissue, their feasibility to be decomposed, the extent of newly formed mineral surface area and the specific biogenic ultra- and microstructures.

Description: Minerals, Vol. 8, Pages 318: Mapping Surface Quartz Content in Sand Dunes Covered by Biological Soil Crusts Using Airborne Hyperspectral Images in the Longwave Infrared Region Minerals doi: 10.3390/min8080318 Authors: Shahar Weksler Offer Rozenstein Eyal Ben-Dor Biological soil crusts (BSCs), composed of cyanobacteria, algae, mosses, lichens, and fungi, are important ecosystem engineers that stabilize the quartz-rich dunes in the Nitzana study area near the Israel–Egypt border. The longwave infrared (LWIR) region of the electromagnetic spectrum is very useful for quartz identification since quartz reflectance in the visible, near infrared, and shortwave infrared (VIS-NIR-SWIR, 0.4–2.5 µm) spectral regions lacks identifying features, whereas in the LWIR region, the quartz emissivity spectrum presents a strong doublet feature. This emissivity feature can be used as a diagnostic tool for BSCs development in desert environments, because BSCs attenuate the quartz feature as a function of their successional development. A pair of day and night airborne hyperspectral images were acquired using the Specim AisaOWL LWIR sensor (7.7–12 µm) and processed using an innovative algorithm to reduce the atmospheric interference in this spectral domain. The resulting day and night apparent emissivity products were used to produce a surface quartz content map of the study area. The significant reduction in atmospheric interference resulted in a high correlation (R2 = 0.88) between quartz content in field samples determined by X-ray powder diffraction analysis and emissivity estimations from the airborne images. This, in turn, served as the ground truth to our quartz content map of the surface, and by proxy to the BSC.

Description: Minerals, Vol. 8, Pages 313: Reverse Flotation Separation of Fluorite from Calcite: A Novel Reagent Scheme Minerals doi: 10.3390/min8080313 Authors: Jianjun Wang Zihan Zhou Yuesheng Gao Wei Sun Yuehua Hu Zhiyong Gao Fluorite (CaF2), as an important strategic mineral source, is usually separated from calcite by the common froth flotation method, but this separation is still not selective enough. The development of a selective collector and/or depressant is the key to achieving high selective separation. 1-Hydroxyethylidene-1,1-diphosphonic acid (HEDP or H4L) is widely used as an environmentally friendly water treatment reagent due to its low cost and excellent anti-scaling performance in an aqueous solution. In this study, a novel reagent scheme was developed using HEDP as a fluorite depressant and sodium oleate (NaOL) as a calcite collector for the first time. When 3 × 10−5 mol/L of HEDP and 6 × 10−5 mol/L of NaOL were used at pH 6, the optimal selective separation for single minerals and mixed binary minerals was obtained. Zeta potential measurements indicated that HEDP possessed a stronger adsorption on fluorite than calcite, while NaOL did the opposite. This novel reagent scheme is of low cost, uses a small dosage, and is friendly to the environment, which makes it a promising reagent scheme for fluorite flotation in industrial application.

Description: Minerals, Vol. 8, Pages 323: (10.4) Face of Ordered and Disordered Dolomite, MgCa(CO3)2: A Computational Study to Reveal the Growth Mechanism Minerals doi: 10.3390/min8080323 Authors: Marco Bruno Erica Bittarello In this study, the stability of the (10.4) face of dolomite was systematically investigated. The surface energies at 0 K of the different (10.4) surfaces resulting from the cut of both ordered and disordered bulk structures were determined and compared, to establish how different atomic configurations (surface terminations) can affect the stability of the investigated face. To study the thermodynamic behavior of a surface, a 2D periodic slab model and the ab initio CRYSTAL code were adopted. The surface energies of the (10.4) faces of calcite and magnesite were also calculated in order to compare them with those of the different terminations of the (10.4) face of dolomite. Our calculations showed that the bulk of the dolomite crystal must have an ordered structure to reach the minimum of the energy, whereas the (10.4) surface is more stable when its structure is disordered. A growth model of the (10.4) face has been proposed: the peculiarity of this model consists in the existence of some disordered layers forming at the interface crystal/solution, which arrange in an ordered structure once covered by others disordered layers resulting by the spiral steps propagation.

Description: Minerals, Vol. 8, Pages 322: Particle Size Distribution Effects on the Strength Characteristic of Cemented Paste Backfill Minerals doi: 10.3390/min8080322 Authors: Jiangyu Wu Meimei Feng Zhanqing Chen Xianbiao Mao Guansheng Han Yiming Wang It is of great significance, for economic, environmental and security reasons, to investigate the strength characteristic of underground cemented paste backfill (CPB). Consequently, an ultrasonic test, uniaxial and triaxial compression experiment, and acoustic emission (AE) monitoring were carried out on CPB, for which the particles satisfied Talbot gradation. The homogeneity of CPB specimens was evaluated by ultrasonic pulse velocity (UPV). The stress–strain behavior and AE characteristic of CPB specimens under different Talbot indices and confining pressures were investigated. The effects of the particle size distribution and the confining pressure on the peak strength of CPB were analyzed. The strength parameter model of CPB under the coupled influence of the particle size distribution and the confining pressure was constructed based on the Mohr–Coulomb strength criterion. The results show that the peak strength of CPB is positively linear with confining pressure, however, the relationship between its strength parameters and the Talbot index can be characterized by a quadratic polynomial function. This suggests that there is an optimal gradation of particles reflected in the maximum strength of CPB.

Description: Minerals, Vol. 8, Pages 319: Fault Zone Evolution and Development of a Structural and Hydrological Barrier: The Quartz Breccia in the Kiggavik Area (Nunavut, Canada) and Its Control on Uranium Mineralization Minerals doi: 10.3390/min8080319 Authors: Alexis Grare Olivier Lacombe Julien Mercadier Antonio Benedicto Marie Guilcher Anna Trave Patrick Ledru John Robbins In the Kiggavik area (Nunavut, Canada), major fault zones along, or close to, where uranium deposits are found are often associated with occurrence of thick quartz breccia (QB) bodies. These bodies formed in an early stage (~1750 Ma) of the long-lasting tectonic history of the Archean basement, and of the Proterozoic Thelon basin. The main characteristics of the QB are addressed in this study; through field work, macro and microscopic observations, cathodoluminescence microscopy, trace elements, and oxygen isotopic signatures of the quartz forming the QB. Faults formed earlier during syn- to post-orogenic rifting (1850–1750 Ma) were subsequently reactivated, and underwent cycles of cataclasis, pervasive silicification, hydraulic brecciation, and quartz recrystallization. This was synchronous with the circulation of meteoric fluids mixing with Si-rich magmatic-derived fluids at depth, and were coeval with the emplacement of the Kivalliq igneous suite at 1750 Ma. These processes led to the emplacement of up to 30 m thick QB, which behaved as a mechanically strong, transverse hydraulic barrier that localized later fracturing, and compartmentalized/channelized vertical flow of uranium-bearing fluids after the deposition of the Thelon Basin (post 1750 Ma). The development and locations of QB control the location of uranium mineralization in the Kiggavik area.

Description: Minerals, Vol. 8, Pages 326: Hydrotalcite and Hydrocalumite in Mortar Binders from the Medieval Castle of Portilla (Álava, North Spain): Accurate Mineralogical Control to Achieve More Reliable Chronological Ages Minerals doi: 10.3390/min8080326 Authors: Graciela Ponce-Antón Luis Angel Ortega Maria Cruz Zuluaga Ainhoa Alonso-Olazabal Jose Luis Solaun Mortars from different stratigraphic units at Portilla Castle (Alava, North Spain) have been analyzed for mineralogical characterization before radiocarbon dating. The mortar binder at Portilla Castle is composed not only of neoformation calcite but also of double-layered hydroxide (LDH) minerals such as hydrotalcite and hydrocalumite. The mineralogy of several fractions of the binder has been analyzed to determine the granulometric distribution of minerals in the binder. The continuous monitoring of mineralogy during the extraction of different grain size fractions has been performed by using a scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermogravimetric analyses (TGA). Hydrotalcite and hydrocalumite-bearing mortar binders give older ages than expected since they introduce dead carbon into the system.

Description: Minerals, Vol. 8, Pages 312: Leaching of Primary Copper Sulfide Ore in Chloride-Ferrous Media Minerals doi: 10.3390/min8080312 Authors: Karina E. Salinas Osvaldo Herreros Cynthia M. Torres Copper extraction from primary copper sulfide ore from a typical porphyry copper deposit from Antofagasta, Chile, was investigated after leaching with a chloride-ferrous media at two temperatures. The study focused on whether this chemical leaching system could be applied at an industrial scale. Leaching tests were conducted in columns loaded with approximately 50 kg of agglomerated ore; the ore was first cured for 14 days and then leached for 90 days. The highest copper extraction, 50.23%, was achieved at 32.9 °C with the addition of 0.6 kg of H2SO4 per ton of ore, 0.525 kg of NaCl per ton of ore, and 0.5 kg of FeSO4 per ton of ore. In respect to copper extraction, the most effective variables were temperature and the addition of NaCl.

Description: Minerals, Vol. 8, Pages 332: Kurchatovite and Clinokurchatovite, Ideally CaMgB2O5: An Example of Modular Polymorphism Minerals doi: 10.3390/min8080332 Authors: Yulia A. Pankova Sergey V. Krivovichev Igor V. Pekov Edward S. Grew Vasiliy O. Yapaskurt Kurchatovite and clinokurchatovite, both of ideal composition CaMgB2O5, from the type localities (Solongo, Buryatia, Russia, and Sayak-IV, Kazakhstan, respectively) have been studied using electron microprobe and single-crystal X-ray diffraction methods. The empirical formulae of the samples are Ca1.01Mg0.87Mn0.11Fe2+0.02B1.99O5 and Ca0.94Mg0.91Fe2+0.10Mn0.04B2.01O5 for kurchatovite and clinokurchatovite, respectively. The crystal structures of the two minerals are similar and based upon two-dimensional blocks arranged parallel to the c axis in kurchatovite and parallel to the a axis in clinokurchatovite. The blocks are built up from diborate B2O5 groups, and Ca2+ and Mg2+ cations in seven- and six-fold coordination, respectively. Detailed analysis of geometrical parameters of the adjacent blocks reveals that symmetrically different diborate groups have different degrees of conformation in terms of the δ angles between the planes of two BO3 triangles sharing a common O atom, featuring two discrete sets of the δ values of ca. 55° (B’ blocks) and 34° (B” blocks). The stacking of the blocks in clinokurchatovite can be presented as …(+B’)(+B”)(+B’)(+B”)… or [(+B’)(+B”)], whereas in kurchatovite it is more complex and corresponds to the sequence …(+B’)(+B”)(+B’)(−B’)(−B”)(−B’)(+B’)(+B”)(+B’)(−B’)(−B”)(−B’)… or [(+B’)(+B”)(+B’)(−B’)(−B”)(−B’)]. The B’:B” ratios for clinokurchatovite and kurchatovite are 1:1 and 2:1, respectively. According to this description, the two minerals cannot be considered as polytypes and their mutual relationship corresponds to the term modular polymorphs. From the viewpoint of information-based measures of structural complexity, clinokurchatovite (IG = 4.170 bits/atom and IG,total = 300.235 bits/cell) is structurally simpler than kurchatovite (IG = 4.755 bits/atom and IG,total = 1027.056 bits/cell). The high structural complexity of kurchatovite can be inferred from the modular character of its structure. The analysis of structural combinatorics in terms of the modular approach allows to construct the whole family of theoretically possible “kurchatovite”-type structures that bear the same structural features common for kurchatovite and clinokurchatovite. However, the crystal structures of the latter minerals are the simplest and are the only ones that have been observed in nature. The absence of other possible structures is remarkable and can be explained by either the maximum-entropy of the least-action fundamental principles.

Description: Minerals, Vol. 8, Pages 331: Textural Characteristics of Noncrystalline Silica in Sinters and Quartz Veins: Implications for the Formation of Bonanza Veins in Low-Sulfidation Epithermal Deposits Minerals doi: 10.3390/min8080331 Authors: Tadsuda Taksavasu Thomas Monecke T. James Reynolds Silica sinters forming at the Wairakei geothermal power plant in New Zealand are composed of noncrystalline opal-A that deposited rapidly from cooling geothermal liquids flashed to atmosphere. The sinter is laminated with alternating layers of variably compacted silicified filamentous microbes encased by chains of fused silica microspheres. Microscopic inspection of bonanza quartz vein samples from the Buckskin National low-sulfidation epithermal precious metal deposit in Nevada showed that colloform bands in these veins exhibit relic microsphere textures similar to those observed in the silica sinters from the Wairakei power plant. The textural similarity suggests that the colloform bands were originally composed of noncrystalline opal-A that subsequently recrystallized to quartz. The colloform bands contain dendrites of electrum and naumannite that must have grown in a yielding matrix of silica microspheres deposited at the same time as the ore minerals, implying that the noncrystalline silica exhibited a gel-like behavior. Quartz bands having other textural characteristics in the crustiform veins lack ore minerals. This suggests that ore deposition and the formation of the colloform bands originally composed of compacted microspheres of noncrystalline silica are genetically linked and that ore deposition within the bonanza veins was only episodic. Supersaturation of silica and precious metals leading to the formation of the colloform bands may have occurred in response to transient flashing of the hydrothermal liquids. Flashing of geothermal liquids may thus represent a key mechanism in the formation of bonanza precious metal grades in low-sulfidation epithermal deposits.

Description: Minerals, Vol. 8, Pages 337: The Compressive Strength and Microstructure of Alkali-Activated Binary Cements Developed by Combining Ceramic Sanitaryware with Fly Ash or Blast Furnace Slag Minerals doi: 10.3390/min8080337 Authors: Juan Cosa Lourdes Soriano María Victoria Borrachero Lucía Reig Jordi Payá José María Monzó The properties of a binder developed by the alkali-activation of a single waste material can improve when it is blended with different industrial by-products. This research aimed to investigate the influence of blast furnace slag (BFS) and fly ash (FA) (0–50 wt %) on the microstructure and compressive strength of alkali-activated ceramic sanitaryware (CSW). 4 wt % Ca(OH)2 was added to the CSW/FA blended samples and, given the high calcium content of BFS, the influence of BFS was analyzed with and without adding Ca(OH)2. Mortars were used to assess the compressive strength of the blended cements, and their microstructure was investigated in pastes by X-ray diffraction, thermogravimetry, and field emission scanning electron microscopy. All the samples were cured at 20 °C for 28 and 90 days and at 65 °C for 7 days. The results show that the partial replacement of CSW with BFS or FA allowed CSW to be activated at 20 °C. The CSW/BFS systems exhibited better mechanical properties than the CSW/FA blended mortars, so that maximum strength values of 54.3 MPa and 29.4 MPa were obtained in the samples prepared with 50 wt % BFS and FA, respectively, cured at 20 °C for 90 days.

Description: Minerals, Vol. 8, Pages 250: Effect of Ammonium Chloride on the Efficiency with Which Copper Sulfate Activates Marmatite: Change in Solution Composition and Regulation of Surface Composition Minerals doi: 10.3390/min8060250 Authors: Shengdong Zhang Dongxia Feng Xiong Tong Bo Yang Xian Xie Zinc sulfide minerals are the primary choice for zinc extraction and marmatite is one of the two most common zinc sulphide minerals (sphalerite and marmatite), therefore it is of great significance to study and optimize the flotation of marmatite. To improve the activation of copper sulfate on marmatite, a method involving the addition of ammonium chloride is devised. The method has been proven to be an effective way of improving the activation efficiency of copper sulfate towards marmatite under alkaline conditions. The strengthening mechanism was studied using micro-flotation, adsorption test, X-ray photoelectron spectroscopy, and by analyzing changes in solution composition. Flotation test results show that the activation effect of the copper sulfate towards marmatite is enhanced with the addition of ammonium chloride. According to the results of the adsorption measurements and X-ray photoelectron spectroscopy analysis, when the marmatite surface is activated using copper sulfate with added ammonia chloride, it adsorbs more copper sulfide and less copper hydroxide and zinc hydroxide. These changes in surface composition are believed to occur via the following process: NH3(aq) promotes the dissolution of zinc hydroxide and then facilitates the conversion of surface copper hydroxide to copper sulfide. In addition, the occurrence of Cu(NH3)n2+ can promote the adsorption of copper ions (Cu2+ can be stored as Cu(NH3)n2+ via complexation, and then, when the concentration of copper ions decreases, Cu2+ can be released through the decompositionof Cu(NH3)n2+. Hence, the copper ion concentration can be maintained and this can facilitate the adsorption of Cu2+ on marmatite). Based on a comprehensive analysis of all our results, we propose that adding ammonium chloride to the copper sulfate changes the solution components (i.e., the presence of NH3(aq) and Cu(NH3)n2+) and then regulates the surface composition of marmatite. The change in surface composition improves the hydrophobicity of mineral surface and this leads to an improvement in activation of marmatite.

Description: Minerals, Vol. 8, Pages 263: Effect of TiO2 on the Sintering Behavior of Chromium-Bearing Vanadium–Titanium Magnetite Minerals doi: 10.3390/min8070263 Authors: Weidong Tang Songtao Yang Gongjin Cheng Zixian Gao He Yang Xiangxin Xue The sintering pot test was used to investigate the effect of TiO2 on the sintering behavior of chromium-bearing vanadium–titanium magnetite (CVTM) sinter. The main characterization methods of X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy-energy disperse spectroscopy (SEM-EDS), and metallographic microscopy were employed. In this study, yield, tumbler index (TI), vertical sintering speed, productivity, reduction degradation index (RDI), and reduction index (RI) were tested and calculated. The yield first increases from 82.87% to 84.37% and then decreases to 83.65%, vertical sintering speed first increases from 17.00 mm·min−1 to 23.45 mm·min−1 and then decreases to 20.61 mm·min−1, and productivity first increases from 2.33 t·m−2·h−1 to 3.14 t·m−2·h−1 and then decreases to 2.69 t·m−2·h−1 with increasing TiO2 content. The TI increases from 45.81% to 52.09%, and RDI increases from 74.99% to 96.74%, while RI decreases from 67.92% to 47.15% with increasing TiO2 content.

Description: Minerals, Vol. 8, Pages 270: Multi-Stage Deformation of the Khangalas Ore Cluster (Verkhoyansk-Kolyma Folded Region, Northeast Russia): Ore-Controlling Reverse Thrust Faults and Post-Mineral Strike-Slip Faults Minerals doi: 10.3390/min8070270 Authors: Valery Y. Fridovsky Maxim V. Kudrin Lena I. Polufuntikova This study reports the results of the analysis of multi-stage deformation structures of the Khangalas gold ore cluster, northeast Russia. Four Late Mesozoic-Early Eocene deformation stages were identified. The first deformation event (D1) was characterized by the development of NW-striking tight to isoclinal folds of the first generation (F1) and interstratal detachment thrusts. Major folds, extensive thrusts, boudinage, cleavage, auriferous mineralized fault zones and quartz-vein gold mineralization were formed in the reverse and thrust fault stress field during the progressive deformation stage (D1), with NE-SW-oriented σ1. Post-ore deformation is widely manifested in the region. Structures D2 and D3 are coaxial. Sinistral strike-slip motions (D2 and D3) occurred along NW-trending faults under prevailing W-E compression. They were accompanied by the formation of NS- and NE-striking F2–3 folds with steep hinges and by bending of the earlier formed structures, among them ore-controlling ones. The last deformation event (D4) was represented by normal-dextral strike-slip faulting, refolding of rocks, pre-existing structures and ore bodies and by the development of folds with steep hinges. Key structural elements of varying age are described, the chronology of deformation events and mineralization reconstructed and their relation to geodynamic events in northeast Asia established.

Description: Minerals, Vol. 8, Pages 329: The Impact of Secondary Phyllosilicate Minerals on the Engineering Properties of Various Igneous Aggregates from Greece Minerals doi: 10.3390/min8080329 Authors: Petros Petrounias Panagiota P. Giannakopoulou Aikaterini Rogkala Paraskevi Lampropoulou Eleni Koutsopoulou Dimitrios Papoulis Basilios Tsikouras Konstantin Hatzipanagiotou This paper investigates the effect of alteration on the physicomechanical properties of igneous rocks used as aggregates, from various areas from Greece. The studied lithologies include serpentinized dunites, serpentinized harzburgites, serpentinized lherzolites, metamorphic gabbros, diabases, dacites and andesites. Quantitative petrographic analysis shows that the tested samples display various percentages of secondary phyllosilicate minerals. Mineral quantification of the studied rock samples was performed by using the Rietveld method on X-ray diffraction patterns. The samples were also tested to assign moisture content (w (%)), total porosity (nt (%)), uniaxial compressive strength (UCS (MPa)) and Los Angeles abrasion test (LA (%)). The influence of secondary phyllosilicate minerals on the physicomechanical behavior of the tested samples was determined using regression analysis and their derived equations. Regression analysis shows a positive relationship between the percentage of the phyllosilicate minerals of the rocks and the moisture content as well as with the total porosity values. In mafic and ultramafic rock samples, the relationships between the secondary phyllosilicate minerals and their physicomechanical properties have shown that the total amount of the secondary phyllosilicate minerals results negatively on their physicomechanical properties. On the other hand, the low percentage of phyllosilicate minerals in volcanic rocks can’t be able to define their engineering properties.

Description: Minerals, Vol. 8, Pages 327: Assessment of the Mineral Resource Potential of Atlantic Ferromanganese Crusts Based on Their Growth History, Microstructure, and Texture Minerals doi: 10.3390/min8080327 Authors: Isobel A. Yeo Kate Dobson Pierre Josso Richard B. Pearce Sarah A. Howarth Paul A. J. Lusty Tim P. Le Bas Bramley J. Murton The decarbonisation of our energy supply is reliant on new technologies that are raw material intensive and will require a significant increase in the production of metals to sustain them. Ferromanganese (FeMn) crusts are seafloor precipitates, enriched in metals such as cobalt and tellurium, both of which have a predicted future demand above current production rates. In this study, we investigate the texture and composition of FeMn crusts on Tropic Seamount, a typical Atlantic guyot off the coast of western Africa, as a basis for assessing the future mineral resource potential of Atlantic Seamounts. The majority of the summit is flat and covered by FeMn crusts with average thicknesses of 3–4 cm. The crusts are characterized by two dominant textures consisting of either massive pillared growth or more chaotic, cuspate sections of FeMn oxides, with an increased proportion of detrital and organic material. The Fe, Mn, and Co contents in the FeMn oxide layers are not affected by texture. However, detrital material and bioclasts can form about 50% of cuspate areas, and the dilution effect of this entrained material considerably reduces the Fe, Mn, and Co concentrations if the bulk samples are analyzed. Whilst Tropic Seamount meets many of the prerequisites for a crust mining area, the thickness of the crusts and their average metal composition means extraction is unlikely to be viable in the near future. The ability to exploit more difficult terrains or multiple, closely spaced edifices would make economic feasibility more likely.

Description: Minerals, Vol. 8, Pages 328: Mesozoic High- and Low-SiO2 Adakites and A-Type Granites in the Lower Yangtze River Belt, Eastern China: Implications for Petrogenesis and Metallogeny Minerals doi: 10.3390/min8080328 Authors: Lei Liu Geng Chu Yanguang Li Xiaoyong Yang Madhava Warrier Santosh Qing Hu The Lower Yangtze River Belt (LYRB) is one of the important magmatic and metallogenic belts in China and hosts abundant Mesozoic calc-alkaline magmatic rocks and economic mineral deposits. Anqing orefield in the southwestern of the LYRB received less attention during the last two decades. Here, we present an integrated study of whole-rock major and trace elements, zircon U-Pb dating and Lu-Hf isotopes on late Mesozoic adakites and A-type granites from the Anqing orefield. The adakites emplaced during 138–136 Ma and can be further subdivided into two types: high-SiO2 adakites (HSA) with SiO2 >60 wt % from the Zongpu intrusion, and low-SiO2 adakites (LSA) <60 wt % from the Yueshan intrusion. The rocks display mid- to high-K calc-alkaline features and have consistent arc-like trace element characteristics with enrichment in LREE and LILE, and depletion in HREE and HFSE. The distinct zircon εHf(t) values for the LSA (from −27 to −20) and HSA (from −15 to −5) preclude a magma mixing model, yet suggest a subduction-related setting with partial melting of the subducted slab and overlying metasomatic mantle wedge. The A-type granites dated at 124 Ma from the Dalongshan intrusion characterized by LILE and LREE enrichment and slightly negative Eu anomalies, with lower MgO, CaO but higher K2O and Na2O contents. Their zircon εHf(t) values and geochemical features suggest that the parent magma was produced by the partial melting of Neoproterozoic crustal components, followed by variable degrees of fractional crystallization under a back-arc extensional setting, together with minor juvenile crust input. The adakites and A-type granites investigated in this study record a tectonic transition from compressive to extensional setting during 138–124 Ma. The transitional magmatic pulses are associated with distinct metallogenic signature with the adakites hosting copper deposits and the A-type granites linked to uranium mineralization.

Description: Minerals, Vol. 8, Pages 334: Water Structure, Dynamics and Ion Adsorption at the Aqueous {010} Brushite Surface Minerals doi: 10.3390/min8080334 Authors: Natalya A. Garcia Paolo Raiteri Elias Vlieg Julian D. Gale Understanding the growth processes of calcium phosphate minerals in aqueous environments has implications for both health and geology. Brushite, in particular, is a component of certain kidney stones and is used as a bone implant coating. Understanding the water–brushite interface at the molecular scale will help inform the control of its growth. Liquid-ordering and the rates of water exchange at the brushite–solution interface have been examined through the use of molecular dynamics simulation and the results compared to surface X-ray diffraction data. This comparison highlights discrepancies between the two sets of results, regardless of whether force field or first principles methods are used in the simulations, or the extent of water coverage. In order to probe other possible reasons for this difference, the free energies for the adsorption of several ions on brushite were computed. Given the exothermic nature found in some cases, it is possible that the discrepancy in the surface electron density may be caused by adsorption of excess ions.

Description: Minerals, Vol. 8, Pages 338: Synthesis of 4A Zeolite from Kaolinite-Type Pyrite Flotation Tailings (KPFT) Minerals doi: 10.3390/min8080338 Authors: Yating Cui Yu Zheng Weiqing Wang As a solid waste, kaolinite-type pyrite flotation tailings (KPFT) are a type of low-quality kaolin that contain impurities, such as iron and titanium. In this study, KPFT were calcined at 800 °C for two hours. The calcined production (CKPFT), which is mainly metakaolin, was used as the silicon and aluminum source to synthesize 4A zeolite (Na12[(AlO2)12(SiO2)12]·27H2O) via hydrothermal synthesis. The optimal hydrothermal synthesis conditions were determined from X-ray diffraction phase analysis, relative crystallinity (RC), and cation ion exchange capacity (CEC). The optimal hydrothermal synthesis conditions were determined to be a ratio of 5 g CKPFT, 6.5 g NaOH, 65 mL H2O, crystallization temperature 110 °C, and crystallization time of three hours. Under the optimal hydrothermal synthesis conditions, the RC and CEC of the synthesized 4A zeolite were 40.77% and 210.32 mg CaCO3·g−1, respectively. Further characterizations including pore size distribution, scanning electron microscopy, energy dispersive X-ray, thermogravimetry-differential scanning calorimetry, and Fourier transform infrared spectroscopy were performed. The results revealed that impurities in KPFT do not affect the synthesis of 4A zeolite. The surface morphology of the synthesized 4A zeolite was composed of chamfered-edged cubes with a particle size of one to three μm that was thermally stable up to approximately 890 °C.

Description: Minerals, Vol. 8, Pages 344: Mineralogy and Geochemistry of Mud Volcanic Ejecta: A New Look at Old Issues (A Case Study from the Bulganak Field, Northern Black Sea) Minerals doi: 10.3390/min8080344 Authors: Ella Sokol Svetlana Kokh Olga Kozmenko Sofya Novikova Pavel Khvorov Elena Nigmatulina Elena Belogub Maxim Kirillov We characterise the mineralogy and geochemistry of Oligo-Miocene Maykopian shales that are currently extruded by onshore mud volcanoes of the Kerch-Taman Province (the Northern Black Sea) from the depths of ~2.5–3 km. The ejected muds are remarkable by highly diverse authigenic mineralogy that comprises glauconite, apatite, siderite, mixed Fe–Mg–Mn–(Ca) and Mn–Ca–Fe-carbonates, pyrite, marcasite, sphalerite, cinnabar, chalcopyrite, nukundamite, akantite, native Cu, Au and Au–Ag alloys. Precise geochemical techniques and high-resolution methods are applied to study the composition of bulk rocks, sulphide and carbonate fractions, as well as individual mineral species, including trace element and isotopic compositions of carbonates (C, O) and pyrite (S). Mineralogy of clastic and heavy fractions is used as a provenance tracer. Oxygen-deficient to weakly sulphuric deposition conditions are inferred for the parent sediments proceeding from trace element partitioning between carbonate, sulphide, and metallic phases. The main conclusion of the study is that onshore mud volcanoes of the region only transport buried sedimentary material and authigenic minerals they store to the ground surface.

Description: Minerals, Vol. 8, Pages 343: The Evolution, Current Status, and Future Prospects of Using Biotechnologies in the Mineral Extraction and Metal Recovery Sectors Minerals doi: 10.3390/min8080343 Authors: D. Barrie Johnson The current global demand in terms of both the amounts and range of metals for industrial and domestic use greatly exceeds that at any previous time in human history. Recycling is inadequate to meet these needs and therefore mining primary metal ores will continue to be a major industry in the foreseeable future. The question of how metal mining can develop in a manner which is less demanding of energy and less damaging of the environment in a world whose population is increasingly aware of, and concerned about, the environment, requires urgent redress. Increased application of biotechnologies in the mining sector could go some way in solving this conundrum, yet, biomining (harnessing microorganisms to enhance the recovery of base and precious metals) has remained a niche application since it was first knowingly used in the 1960s. This manuscript reviews the development and current status of biomining applications and highlights their limitations as well as their strengths. New areas of biotechnology that could be applied in the mining sector, and their potential impact in terms of both their potential environmental and economic benefits, are also discussed.

Description: Minerals, Vol. 8, Pages 346: Metal Sequestration through Coupled Dissolution–Precipitation at the Brucite–Water Interface Minerals doi: 10.3390/min8080346 Authors: Jörn Hövelmann Christine V. Putnis Liane G. Benning The increasing release of potentially toxic metals from industrial processes can lead to highly elevated concentrations of these metals in soil, and ground- and surface-waters. Today, metal pollution is one of the most serious environmental problems and thus, the development of effective remediation strategies is of paramount importance. In this context, it is critical to understand how dissolved metals interact with mineral surfaces in soil–water environments. Here, we assessed the processes that govern the interactions between six common metals (Zn, Cd, Co, Ni, Cu, and Pb) with natural brucite (Mg(OH)2) surfaces. Using atomic force microscopy and a flow-through cell, we followed the coupled process of brucite dissolution and subsequent nucleation and growth of various metal bearing precipitates at a nanometer scale. Scanning electron microscopy and Raman spectroscopy allowed for the identification of the precipitates as metal hydroxide phases. Our observations and thermodynamic calculations indicate that this coupled dissolution–precipitation process is governed by a fluid boundary layer at the brucite–water interface. Importantly, this layer differs in composition and pH from the bulk solution. These results contribute to an improved mechanistic understanding of sorption reactions at mineral surfaces that control the mobility and fate of toxic metals in the environment.

Description: Minerals, Vol. 8, Pages 356: Geology and Mineralogy of Rare Earth Elements Deposits and Occurrences in Finland Minerals doi: 10.3390/min8080356 Authors: Thair Al-Ani Ferenc Molnár Panu Lintinen Seppo Leinonen Rare earth elements (REE) have critical importance in the manufacturing of many electronic products in the high-tech and green-tech industries. Currently, mining and processing of REE is strongly concentrated in China. A substantial growth in global exploration for REE deposits has taken place in the recent years and has resulted in considerable advances in defining new resources. This study provides an overview of the mineralogical and petrological peculiarities of the most important REE prospects and metallogeny of REE in Finland. There is a particularly good potential for future discoveries of carbonatite hosted REE deposits in the Paleozoic Sokli carbonatite complex, as well as in the Paleoproterozoic Korsnäs and Kortejärvi Laivajoki areas. This review also provides information about the highest known REE concentration in the alkaline intrusions of Finland in the Tana Belt and other alkaline rock hosted occurrences (e.g., Otanmäki and Katajakangas). Significant REE enrichments in hydrothermal alteration zones are also known in the Kuusamo Belt (Uuniniemi and Honkilehto), and occurrences of REE-rich mineralisation are also present in granite pegmatite bodies and greisens in central and southern Finland (Kovela monazite granite and the Rapakivi Granite batholith at Vyborg, respectively). REE minerals in all of the localities listed above were identified and analyzed by scanning electron microscopy (SEM) and electron microprobes (EMPs). In localities of northern and central Finland, both primary rock forming and epigenetic-hydrothermal REE minerals were found, namely phosphates (monazite-Ce, xenotime-Y), fluorcarbonates (bastnäsite-Ce, synchysite), and hydrated carbonates (ancylite-Ce), hydrated aluminium silicates (allanite-Ce, Fe-allanite, cerite, chevkinite), oxides (fergusonite, euxenite) and U-Pb rich minerals. The chondrite normalized REE concentrations, the La/Nd ratios and the REE vs. major element contents in several types of REE bearing minerals from prospects in Finland can be used to identify and define variable REE fractionation processes (carbonatites), as well as to discriminate deposits of different origins.

Description: Minerals, Vol. 8, Pages 357: Aqueous Fe(II)-Induced Phase Transformation of Ferrihydrite Coupled Adsorption/Immobilization of Rare Earth Elements Minerals doi: 10.3390/min8080357 Authors: Yingheng Fei Jian Hua Chengshuai Liu Fangbai Li Zhenke Zhu Tangfu Xiao Manjia Chen Ting Gao Zhiqi Wei Likai Hao The phase transformation of iron minerals induced by aqueous Fe(II) (Fe(II)aq) is a critical geochemical reaction which greatly affects the geochemical behavior of soil elements. How the geochemical behavior of rare earth elements (REEs) is affected by the Fe(II)aq-induced phase transformation of iron minerals, however, is still unknown. The present study investigated the adsorption and immobilization of REEs during the Fe(II)aq-induced phase transformation of ferrihydrite. The results show that the heavy REEs of Ho(III) were more efficiently adsorbed and stabilized compared with the light REEs of La(III) by ferrihydrite and its transformation products, which was due to the higher adsorptive affinity and smaller atomic radius of Ho(III). Both La(III) and Ho(III) inhibited the Fe atom exchange between Fe(II)aq and ferrihydrite, and sequentially, the Fe(II)aq-induced phase transformation rates of ferrihydrite, because of the competitive adsorption with Fe(II)aq on the surface of iron (hydr)oxides. Owing to the larger amounts of adsorbed and stabilized Ho(III), the inhibition of the Fe(II)aq-induced phase transformation of ferrihydrite affected by Ho(III) was higher than that by La(III). Our findings suggest an important role for the Fe(II)aq-induced phase transformation of iron (hydr)oxides in assessing the mobility and transfer behavior of REEs, as well as for their occurrence in earth surface environments.

Description: Minerals, Vol. 8, Pages 355: On the Chemical Composition and Possible Origin of Na–Cr-Rich Clinopyroxene in Silicocarbonatites from Samalpatti, Tamil Nadu, South India Minerals doi: 10.3390/min8080355 Authors: Ondřej Krátký Vladislav Rapprich Martin Racek Jitka Míková Tomáš Magna Mineralogical and chemical data are presented for a suite of Na–Cr-rich clinopyroxenes associated with chromite, winchite (sodium-calcium amphibole), titanite and calcite in Mg-Cr-rich silicocarbonatites from the Samalpatti carbonatite complex, Tamil Nadu, South India. The Mg-Cr-rich silicocarbonatites occur as 10–30 cm large enclaves in pyroxenites. The chemical composition of the pyroxenes differs among individual enclaves, with variable proportions of diopside, kosmochlor and jadeite-aegirine end-members. These compositions fill a previously unoccupied space in the kosmochlor-diopside-jadeite+aegirine ternary plot, indicating a distinct origin of kosmochlor-rich pyroxene compared with previous findings from diverse settings. The Na–Cr-rich clinopyroxene has low ΣREE = 9.2 ppm, with slight enrichment in LREE (LaN = 7), coupled with low HREE (YbN = 0.6), and flat HREE, paralleled by a significant fractionation of Nb/Ta (2408) and Th/U (26.5). Sodic metasomatism (fenitization) associated with either carbonatite emplacement at shallow levels or during carbonatite ascent through the upper mantle most likely was the major process operating in the area. We suggest two scenarios of the formation of Na–Cr-rich pyroxene: (1) from mantle-derived chromian mineral phases (spinel and/or garnet) through fenitization, with subsequent corrosion by growing winchite due to volatile influx; (2) via metasomatic reaction of Cr-rich garnet in mantle peridotite due to reaction with Na-rich carbonatite melt. Collectively, the appearance of kosmochlor may play an important role in deconvolving metasomatic processes, and fenitization in particular. If combined with petrologic experiments, it could improve our understanding of the origin and subsequent history of chemical signatures of carbonate-rich materials in the mantle.

Description: Minerals, Vol. 8, Pages 364: The Arsenic Fault-Pathfinder: A Complementary Tool to Improve Structural Models in Mining Minerals doi: 10.3390/min8090364 Authors: Daniel Carrizo Carlos Barros German Velasquez In a mining operation, the structural model is considered as a first-order data required for planning. During the start-up and in-depth expansion of an operation, whether the case is open-pit or underground, the structural model must be systematically updated because most common failure mechanisms of a rock mass are generally controlled by geological discontinuities. This update represents one of the main responsibilities for structural geologists and mine engineers. For that purpose, our study presents a geochemically-developed tool based on the tridimensional (3-D) distribution of arsenic concentrations, which have been quantified with a very high-density of blast-holes sampling points throughout an open pit operation. Our results show that the arsenic spatial distribution clearly denotes alignments that match with faults that were previously recognized by classical direct mapping techniques. Consequently, the 3-D arsenic distribution can be used to endorse the existence and even more the real persistence of structures as well as the cross-cutting relationships between faults. In conclusion, by linking the arsenic fault-pathfinder tool to direct on field fault mapping, it is possible to improve structural models at mine scale, focusing on geotechnical design and management, with a direct impact in the generation of safety mining activities.

Description: Minerals, Vol. 8, Pages 367: Cr Release from Cr-Substituted Goethite during Aqueous Fe(II)-Induced Recrystallization Minerals doi: 10.3390/min8090367 Authors: Jian Hua Manjia Chen Chengshuai Liu Fangbai Li Jian Long Ting Gao Fei Wu Jing Lei Minghua Gu The interaction between aqueous Fe(II) (Fe(II)aq) and iron minerals is an important reaction of the iron cycle, and it plays a critical role in impacting the environmental behavior of heavy metals in soils. Metal substitution into iron (hydr)oxides has been reported to reduce Fe atom exchange rates between Fe(II)aq and metal-substituted iron (hydr)oxides and inhibit the recrystallization of iron (hydr)oxides. However, the environmental behaviors of the substituted metal during these processes remain unclear. In this study, Fe(II)aq-induced recrystallization of Cr-substituted goethite (Cr-goethite) was investigated, along with the sequential release behavior of substituted Cr(III). Results from a stable Fe isotopic tracer and Mössbauer characterization studies show that Fe atom exchange occurred between Fe(II)aq and structural Fe(III) (Fe(III)oxide) in Cr-goethites, during which the Cr-goethites were recrystallized. The Cr substitution inhibited the rates of Fe atom exchange and Cr-goethite recrystallization. During the recrystallization of Cr-goethites induced by Fe(II)aq, Cr(III) was released from Cr-goethite. In addition, Cr-goethites with a higher level of Cr-substituted content released more Cr(III). The highest Fe atom exchange rate and the highest amount of released Cr(III) were observed at a pH of 7.5. Under reaction conditions involving a lower pH of 5.5 or a higher pH of 8.5, there were substantially lower rates of Fe atom exchange and Cr(III) release. This trend of Cr(III) release was similar with changes in Fe atom exchange, suggesting that Cr(III) release is driven by Fe atom exchange. The release and reincorporation of Cr(III) occurred simultaneously during the Fe(II)aq-induced recrystallization of Cr-goethites, especially during the late stage of the observed reactions. Our findings emphasize an important role for Fe(II)aq-induced recrystallization of iron minerals in changing soil metal characteristics, which is critical for the evaluation of soil metal activities, especially those in Fe-rich soils.

Description: Minerals, Vol. 8, Pages 372: Geometallurgical Flowsheet as a Tool for Designing and Communicating Geometallurgical Programs Minerals doi: 10.3390/min8090372 Authors: Aleksandra Maria Lang Steinar Løve Ellefmo Kurt Aasly This paper introduces the concept of using a geometallurgical flowsheet as a tool to design, visualize and communicate a geometallurgical program. The development of the concept is carried out using a case study of an industrial mineral mining operation. A modified Integration Definition for Function Modeling (IDEF0) technique is proposed as a methodology to develop the geometallurgical flowsheet. The geometallurgical program is defined as a summary of the operations necessary to develop and validate the geometallurgical model. The geometallurgical model is defined as the function that links georeferenced in-situ geological characteristics and a georeferenced measure of performance in a processing plant. The geometallurgical flowsheet in this study is developed both as a general concept as well as a case-specific illustration based on the example of the Verdalskalk AS industrial mineral operation.

Description: Minerals, Vol. 8, Pages 375: Quantitative and Qualitative Research on the Waste from the Mining of Rock Raw Materials in Lower Silesia Minerals doi: 10.3390/min8090375 Authors: Urszula Kaźmierczak Jan Blachowski Justyna Górniak-Zimroz Herbert Wirth The Lower Silesia area in SW Poland is characterized by a geological structure that is conducive to mining activity. The exploitation of rock raw materials plays an important role in this sector of the economy. By the end of 2017, there were in total approximately 400 current concessions for the exploitation of rock raw materials in the analysed area (Polish Geological Institute, MIDAS database—Management and Protection System of Polish Mineral Resources). The conducted mining activity results in waste, which in the greatest amount occurs in the process of obtaining crushed road and construction aggregates, natural aggregates, carbonate raw materials for the cement and lime industry, as well as stone elements for construction and road engineering. At the end of 2016, the mining plants accumulated 26,569,600 Mg of waste. As part of the European Regions Toward Circular Economy (CircE) project, research was conducted on the volume and composition of the mining waste of rock raw materials in the years 2010–2016 within Lower Silesia. This research used the methods of statistical, descriptive and spatial analysis to identify mining plants with the highest potential for using their wastes. In the course of this study, 6 mining plants with the highest potential of using their waste for industrial production purposes were selected. In order to objectively select these plants, the methodology of qualitative multi-criteria analysis was developed, and 7 criteria were selected for assessing the economic potential of using waste from the mining of rock raw materials. An additional result of this research is a database and graphical presentation of changes in the spatial distribution of generated waste in the Lower Silesia region in the years ranging from 2010 to 2016.

Description: Minerals, Vol. 8, Pages 377: Column Leaching of Greek Low-Grade Limonitic Laterites Minerals doi: 10.3390/min8090377 Authors: Kostas Komnitsas Evangelos Petrakis Olga Pantelaki Anna Kritikaki In this study, column leaching experiments were carried out to investigate the extraction of Ni and Co from low-grade limonitic laterites from Agios Ioannis mines in central Greece. Tests were carried out in laboratory Plexiglas columns using H2SO4 as leaching solution. Parameters determining the efficiency of the process, i.e., acid concentration (0.5 M or 1.5 M) and addition of 20 or 30 g/L of sodium sulfite (Na2SO3) in the leaching solution, were also studied. Upflow transport of the leaching solution with the use of peristaltic pumps was carried out, while the pregnant leach solution (PLS) was recycled several times over the entire test duration. The concentration of Ni, Co, Fe, Ca, Al, Mg, and Mn in the PLS was determined by Atomic Absorption Spectroscopy (AAS). The ore and the leaching residues were characterized by different techniques, i.e., X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and differential scanning calorimetry and thermogravimetry (DSC/TG). The experimental results showed that (i) Ni and Co extractions increased with the increase of H2SO4 concentration—60.2% Ni and 59.0% Co extractions were obtained after 33 days of leaching with 1.5 M H2SO4; (ii) addition of 20 g/L Na2SO3 in the leaching solution resulted in higher extraction percentages for both metals (73.5% for Ni and 84.1% for Co, respectively), whereas further increase of Na2SO3 concentration to 30 g/L only marginally affected Ni and Co extractions; and (iii) when leaching was carried out with 1.5 M H2SO4 and 20 g/L Na2SO3, its selectivity was improved, as deduced from the ratios Ni/Mg, Ni/Ca and Ni/Al in the PLS; on the other hand, the ratio Ni/Fe dropped as a result of the higher Fe extraction compared with that of Ni.

Description: Minerals, Vol. 8, Pages 378: Metal Removal from Acid Waters by an Endemic Microalga from the Atacama Desert for Water Recovery Minerals doi: 10.3390/min8090378 Authors: Marcela Martínez Yanett Leyton Luis A. Cisternas Carlos Riquelme The environmental problems generated by waste from the mining industry in the mineral extraction for business purposes are known worldwide. The aim of this work is to evaluate the microalga Muriellopsis sp. as a potential remover of metallic ions such as copper (Cu2+), zinc (Zn2+) and iron (Fe2+), pollutants of acid mine drainage (AMD) type waters. For this, the removal of these ions was verified in artificial acid waters with high concentrations of the ions under examination. Furthermore, the removal was evaluated in waters obtained from areas contaminated by mining waste. The results showed that Muriellopsis sp. removed metals in waters with high concentrations after 4–12 h and showed tolerance to pH between 3 and 5. These results allow proposing this species as a potential bioremediator for areas contaminated by mining activity. In this work, some potential alternatives for application in damaged areas are proposed as a decontamination plan and future prevention.

Description: Minerals, Vol. 8, Pages 389: Induration Process of MgO Flux Pellet Minerals doi: 10.3390/min8090389 Authors: Qiangjian Gao Xin Jiang Haiyan Zheng Fengman Shen The induration process of oxidized pellet, containing the oxidation of magnetite phase (Fe3O4) and the sintering of oxidized magnetite phase (hematite–Fe2O3), is significant to obtain sufficient pellet strength. The current study focuses on the induration mechanisms of MgO flux pellet in terms of the oxidation process of Fe3O4 and densification process of the pellet. It is found that MgO dosage negatively affects the oxidation of Fe3O4 into Fe2O3. The number of recrystallized grain of Fe2O3 in the MgO flux pellet is less than that in the Non-MgO flux pellet. Additionally, an unreacted core model was applied to consider and clarify the oxidation of Fe3O4. According to the verification experiments, the experimental data and calculated results fit well. Therefore, the unreacted core model can describe the oxidation of Fe3O4 in the pellet induration process. Moreover, based on the development of pore parameters during the pellet induration process, a new index, the so-called oxide densification index (ODI) was defined to profoundly specify the densification degree of the pellet. The results show that the ODI of the MgO flux pellet maintains at a lower level compared with that of the Non-MgO flux pellet. It illustrates that MgO can substantially restrain the pellet densification process.

Description: Minerals, Vol. 8, Pages 388: Ore-Forming Processes at the Xiajinbao Gold Deposit in Eastern Hebei Province: Constraints from EPMA and LA-ICPMS Analysis Minerals doi: 10.3390/min8090388 Authors: Cheng Wang Yongjun Shao Kuanxin Huang Haodi Zhou Jianguo Zhang Zhongfa Liu Qingquan Liu The Xiajinbao gold deposit is located at the northern margin of the North China Craton. Hydrothermal pyrites belonging to three stages were identified: Py1; Py2; and Py3. Geochemical study of these pyrites was conducted using electron probe microanalysis and laser ablation inductively coupled plasma mass spectrometry to investigate the distributions of minor and trace elements, constrain pyrite genesis, and to obtain an improved understanding of the ore-forming processes. Py1 and Py2 contain high concentrations of Au and are interpreted to have been deposited from fluids from a dominantly magmatic source. Py3 grains have the lowest Co/Ni ratios. All generations of pyrite were deposited by mixing of meteoric waters with magmatic-hydrothermal fluids. Boiling of early ore-forming fluids led to the precipitation of Py1 and gold. Decreasing fO2 in the ore-forming system resulted in the formation of Py2 and gold. Fluid mixing was the dominant controlling factor for the precipitation of Py3 together with small amounts of gold.

Description: Minerals, Vol. 8, Pages 383: Towards Greener Lixiviants in Value Recovery from Mine Wastes: Efficacy of Organic Acids for the Dissolution of Copper and Arsenic from Legacy Mine Tailings Minerals doi: 10.3390/min8090383 Authors: Richard A. Crane Devin J. Sapsford In many cases, it may be possible to recover value (e.g., metals, land) from legacy mine wastes and tailings when applying leaching-based remediation such as dump/heap leaching or in-vessel soil washing. However, if the lixiviant used has the potential to cause environmental damage upon leakage, then this approach will have limited practicability due to actual or perceived risk. This study focused on comparing the efficacy of organic acids, namely methanesulfonic (CH3SO3H) and citric (C6H8O7) acid, with mineral acids, namely sulfuric (H2SO4) and hydrochloric (HCl) acid, for the dissolution of Cu and As from mine tailings. The advantage of the former acid type is the fact that its conjungate base is readily biodegradable which should thereby limit the environmental impact of accidental spill/leakage (particularly in non-carbonate terrain) and might also be directly useful in capture/recovery systems coupled with percolation leaching (e.g., as an electron donor in sulphate-reducing bioreactors). The operational factors acid concentration, leaching time, mixing intensity and solid–liquid ratio, were tested in order to determine the optimum conditions for metal dissolution. HCl, H2SO4, and CH3SO3H typically exhibited a relatively similar leaching ability for As despite their different pKa values, with dissolutions of 58%, 56%, 55%, and 44% recorded for H2SO4, HCl, CH3SO3H, and C6H8O7, respectively, after 48 h when using 1 M concentrations and a 10:1 L:S ratio. For the same conditions, H2SO4 was generally the most effective acid type for Cu removal with 38% compared to 32%, 29% and 22% for HCl, CH3SO3H and C6H8O7. As such, CH3SO3H and C6H8O7 demonstrated similar performances to strong mineral acids and, as such, hold great promise as environmentally compatible alternatives to conventional mineral acids for metal recovery from ores and waste.

Description: Minerals, Vol. 8, Pages 381: Effects of Superplasticizer on the Hydration, Consistency, and Strength Development of Cemented Paste Backfill Minerals doi: 10.3390/min8090381 Authors: Jian Zhang Hongwei Deng Abbas Taheri Junren Deng Bo Ke The strength and consistency of cemented paste backfill (CPB) are of key concerns in the stope stability and cost control for underground mines. It is common practice to use additives, such as superplasticizer, to improve the performance of CPB. This study mainly focuses on the effects of superplasticizer on the hydration, consistency, and strength of CPB. In this study, a polynaphtalene sulfonate was used as the superplasticizer. The binder is a mix of 33.3% ordinary Portland cement and 66.7% fly ash. The CPB specimens with a tailings-binder ratio of 3:1 and a solid concentration of 70% were then tested by a low field nuclear magnetic resonance system after different hydration times. Effects of polynaphtalene sulfonate on the hydration, fluidity, and strength were investigated. Results showed that the polynaphtalene sulfonate has a strong influence on short-duration hydration, which may contribute to the strength increase of CPB. It has been demonstrated that the polynaphtalene sulfonate improved the fluidity of the CPB mixture. With the increased dosage of polynaphtalene sulfonate, the slump increased. It was also found that the polynaphtalene sulfonate dosage has a negligible effect on the 1 day (d) strength while it has a strengthening effect on the 7 d, 14 d, and 28 d strength of CPB specimens.

Description: Minerals, Vol. 8, Pages 382: Synchrotron Radiation Based Study of the Catalytic Mechanism of Ag+ to Chalcopyrite Bioleaching by Mesophilic and Thermophilic Cultures Minerals doi: 10.3390/min8090382 Authors: Zhenyuan Nie Weiwei Zhang Hongchang Liu Jinlan Xia Wei Zhu Duorui Zhang Lei Zheng Chenyan Ma Yidong Zhao Wen Wen The catalytic mechanism of Ag+ for chalcopyrite bioleaching by mesophilic culture (at 30 °C) and thermophilic culture (at 48 °C) was investigated using synchrotron radiation-based X-ray diffraction (SR-XRD) and S K-edge and Fe L-edge X-ray absorption near edge structure (XANES) spectroscopy. Bioleaching experiments showed that copper extraction from chalcopyrite bioleaching by both cultures was promoted significantly by Ag+, with more serious corrosion occurring on the minerals surface. SR-XRD and XANES analyses showed that the intermediates S0, jarosite and secondary minerals (bornite, chalcocite and covellite) formed for all bioleaching experiments. For these secondary minerals, the formation of bornite and covellite was promoted significantly in the presence of Ag+ for both cultures, while Ag+ has almost no effect on the formation of chalcocite. These results provided insight into the catalytic mechanisms of Ag+ to chalcopyrite bioleaching by the mesophilic and thermophilic cultures, which are both probably due to the rapid formation of bornite by Ag+ and the conversion of bornite to covellite.

Description: Minerals, Vol. 8, Pages 391: Interpretation of Hydrophobization Behavior of Dodecylamine on Muscovite and Talc Surface through Dynamic Wettability and AFM Analysis Minerals doi: 10.3390/min8090391 Authors: Hao Jiang Ya Gao Sultan Ahmed Khoso Wanying Ji Yuehua Hu In this study, a new approach, “dynamic wettability”, and atomic force microscopy (AFM) imaging analysis techniques were successfully used to characterize the hydrophobization mechanism of the collector dodecylamine (DDA) on muscovite and talc surfaces. The attachment of bubbles to the minerals was studied through the dynamic contact angle to gain a detailed understanding of the hydrophobization mechanism of DDA on a muscovite and talc surface. AFM imaging and interaction forces were performed to explain the DDA adsorption mechanism on both minerals. Finally, flotation tests were performed to verify the effectiveness of these techniques. After treatments with DDA, the contact angles became much larger compared to initial angles, particularly for muscovite, and the attachment of bubbles on the talc surface was much easier than muscovite due to its natural hydrophobicity. From AFM imaging, both the muscovite and talc showed a similar tendency; the higher the DDA concentration, the more the adsorbed amount. However, the adsorbed amount of DDA on talc surface was obviously more than that on muscovite. As far as interaction forces are concerned, the maximum attractions occurred at certain different concentrations respectively for muscovite and talc and agreed well with the AFM-imaging results. Moreover, results obtained from flotation tests were promising and quite in agreement with the phenomenon of these techniques.

Description: Minerals, Vol. 8, Pages 397: The Saint-Honoré Carbonatite REE Zone, Québec, Canada: Combined Magmatic and Hydrothermal Processes Minerals doi: 10.3390/min8090397 Authors: Alexandre Néron Léo Paul Bédard Damien Gaboury The Saint-Honoré carbonatite complex hosts a rare earth element (REE) deposit traditionally interpreted as being produced by late-stage hydrothermal fluids that leached REE from apatite or dolomite found in the early units and concentrated the REE in the late-stage units. New evidence from deeper units suggest that the Fe-carbonatite was mineralized by a combination of both magmatic and hydrothermal crystallization of rare earth minerals. The upper Fe-carbonatite has characteristics typical of hydrothermal mineralization—polycrystalline clusters hosting bastnäsite-(Ce), which crystallized radially from carbonate or barite crystals, as well as the presence of halite and silicification within strongly brecciated units. However, bastnäsite-(Ce) inclusions in primary magmatic barite crystals have also been identified deeper in the Fe-carbonatite (below 1000 m), suggesting that primary crystallization of rare earth minerals occurred prior to hydrothermal leaching. Based on the intensity of hydrothermal brecciation, Cl depletion at depth and greater abundance of secondary fluid inclusions in carbonates in the upper levels, it is interpreted that hydrothermal activity was weaker in this deepest portion, thereby preserving the original magmatic textures. This early magmatic crystallization of rare earth minerals could be a significant factor in generating high-volume REE deposits. Crystallization of primary barite could be an important guide for REE exploration.

Description: Minerals, Vol. 8, Pages 406: Comparative Analysis of Attachment to Chalcopyrite of Three Mesophilic Iron and/or Sulfur-Oxidizing Acidophiles Minerals doi: 10.3390/min8090406 Authors: Qian Li Baojun Yang Jianyu Zhu Hao Jiang Jiaokun Li Ruiyong Zhang Wolfgang Sand Adhesion plays an important role in bacterial dissolution of metal sulfides, since the attached cells initiate the dissolution. In addition, biofilms, forming after bacterial attachment, enhance the dissolution. In this study, interactions between initial adhesion force, attachment behavior and copper recovery were comparatively analyzed for Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, and Leptospirillum ferrooxidans during bioleaching of chalcopyrite. The adhesion forces between bacteria and minerals were measured by atomic force microscopy (AFM). L. ferrooxidans had the largest adhesion force and attached best to chalcopyrite, while A. ferrooxidans exhibited the highest bioleaching of chalcopyrite. The results suggest that the biofilm formation, rather than the initial adhesion, is positively correlated with bioleaching efficiency.

Description: Minerals, Vol. 8, Pages 409: The Lengenbach Quarry in Switzerland: Classic Locality for Rare Thallium Sulfosalts Minerals doi: 10.3390/min8090409 Authors: Thomas Raber Philippe Roth The Lengenbach quarry is a world-famous mineral locality, especially known for its rare and well-crystallized Tl, Pb, Ag, and Cu bearing sulfosalts. As of June 2018, it is the type locality for 44 different mineral species, making it one of the most prolific localities worldwide. A total of 33 thallium mineral species have been identified, 23 of which are type minerals. A brief description of several thallium species of special interest follows a concise and general overview of the thallium mineralization.

Description: Minerals, Vol. 8, Pages 408: Structural Control on Clay Mineral Authigenesis in Faulted Arkosic Sandstone of the Rio do Peixe Basin, Brazil Minerals doi: 10.3390/min8090408 Authors: Ingrid B. Maciel Angela Dettori Fabrizio Balsamo Francisco H.R. Bezerra Marcela M. Vieira Francisco C.C. Nogueira Emma Salvioli-Mariani Jorge André B. Sousa Clay minerals in structurally complex settings influence fault zone behavior and characteristics such as permeability and frictional properties. This work aims to understand the role of fault zones on clay authigenesis in arkosic, high-porosity sandstones of the Cretaceous Rio do Peixe basin, northeast Brazil. We integrated field, petrographic and scanning electron microscopy (SEM) observations with X-ray diffraction data (bulk and clay-size fractions). Fault zones in the field are characterized by low-porosity deformation bands, typical secondary structures developed in high-porosity sandstones. Laboratory results indicate that in the host rock far from faults, smectite, illite and subordinately kaolinite, are present within the pores of the Rio do Peixe sandstones. Such clay minerals formed after sediment deposition, most likely during shallow diagenetic processes (feldspar dissolution) associated with meteoric water circulation. Surprisingly, within fault zones the same clay minerals are absent or are present in amounts which are significantly lower than those in the undeformed sandstone. This occurs because fault activity obliterates porosity and reduces permeability by cataclasis, thus: (1) destroying the space in which clay minerals can form; and (2) providing a generally impermeable tight fabric in which external meteoric fluid flow is inhibited. We conclude that the development of fault zones in high-porosity arkosic sandstones, contrary to other low-porosity lithologies, inhibits clay mineral authigenesis.

Description: Minerals, Vol. 8, Pages 413: Infra Red Spectroscopy of the Regulated Asbestos Amphiboles Minerals doi: 10.3390/min8090413 Authors: Giancarlo Della Ventura Ruggero Vigliaturo Reto Gieré Simone Pollastri Alessandro F. Gualtieri Gianluca Iezzi Vibrational spectroscopies (Fourier Transform Infra Red, FTIR, and Raman) are exceptionally valuable tools for the identification and crystal–chemical study of fibrous minerals, and asbestos amphiboles in particular. Raman spectroscopy has been widely applied in toxicological studies and thus a large corpus of reference data on regulated species is found in the literature. However, FTIR spectroscopy has been mostly used in crystal–chemical studies and very few data are found on asbestos amphiboles. This paper is intended to fill this gap. We report new FTIR data collected on a suite of well-characterized samples of the five regulated amphibole species: anthophyllite, amosite, and crocidolite, provided by the Union for International Cancer Control (UICC) Organization, and tremolite and actinolite, from two well-known occurrences. The data from these reference samples have been augmented by results from additional specimens to clarify some aspects of their spectroscopic features. We show that the FTIR spectra in both the OH-stretching region and in the lattice modes region can be effective for rapid identification of the asbestos type.

Description: Minerals, Vol. 8, Pages 414: Supergene Uranyl Mineralization of the Rabejac Deposit, Lodève, France Minerals doi: 10.3390/min8090414 Authors: Fabrice Dal Bo Frédéric Hatert Simon Philippo The Rabejac uranium deposit that is located in the Lodève region, France, is the type locality for three uranyl minerals species (fontanite, seelite, and rabejacite). In addition, this deposit shows an extraordinary supergene uranyl mineralization characterized by the presence of many rare secondary uranyl species. In the present study, a mineralogical description as well as new chemical and crystallographic data are reported on (meta)zeunerite, (meta)nováčekite, (meta)uranospinite, heinrichite, nováčekite-I, arsenuranospathite, umohoite, calcurmolite, becquerelite, billietite, and liebigite. The chemical data indicate that the arsenate members of the autunite/meta-autunite group incorporate a significant amount of phosphorus. Moreover, the uranospinite samples usually exhibit high Mg content, thus moving toward the nováčekite end-member composition. The refined unit-cell parameters for all of the investigated mineral species are in agreement with the previous data reported in the literature. Finally, a model describing the alteration of the primary uraninite and the formation of secondary uranyl minerals is proposed in agreement with the observed mineral assemblages.

Description: Minerals, Vol. 8, Pages 412: Intracrystalline Reaction-Induced Cracking in Olivine Evidenced by Hydration and Carbonation Experiments Minerals doi: 10.3390/min8090412 Authors: Romain Lafay German Montes-Hernandez François Renard Pierre Vonlanthen In order to better understand the microtextural changes associated with serpentinization reactions, natural millimeter-sized olivine grains were experimentally reacted with alkaline NaOH and NaHCO3 solutions at a temperature of 200 °C and for durations of 3 to 12 months. During hydration experiments, dissolution and precipitation were intimately correlated in time and space, with reaction products growing in situ, either as layered veins or as nearly continuous surface cover. In contrast, carbonation experiments showed a strong decoupling between both processes leading to essentially delocalized precipitation of the reaction products away from dissolution sites. Textural analyses of the samples using scanning electron microscopy, Raman spectroscopy, and X-ray synchrotron microtomography provided experimental evidence for a cause-and-effect relationship between in situ precipitation and intracrystalline reaction-induced cracking in olivine. Juvenile cracks typically nucleated at the tip of dissolution notches or on diamond-shaped pores filled with reaction products, and propagated through the olivine crystal lattice during the course of the reaction. The occurrence of new cracks at the tip of diamond-shaped pores, but also of tiny subspherical pores lining up along microcracks, indicated that fracturation and porosity networks were mutually driven, making serpentinization an extremely efficient alteration process over time. Alternatively, our data suggested that some form of porosity also developed in absence of fracturation, thus further highlighting the remarkable efficiency and versatility of serpentinization processes.

Description: Minerals, Vol. 8, Pages 411: Chemical Stability and Leaching Behavior of One-Part Geopolymer from Soil and Coal Fly Ash Mixtures Minerals doi: 10.3390/min8090411 Authors: April Anne S. Tigue Roy Alvin J. Malenab Jonathan R. Dungca Derrick Ethelbhert C. Yu Michael Angelo B. Promentilla Aluminosilicate minerals have become an important resource for an emerging sustainable material for construction known as geopolymer. Geopolymer, an alkali-activated material, is becoming an attractive alternative to Portland cement because of its lower carbon footprint and embodied energy. However, the synthesis process requires typically a two-part system for alkali activation wherein the solid geopolymer precursor is mixed with aqueous alkali solutions. These alkali activators are corrosive and may be difficult to handle in the field-scale application. In this study, a one-part geopolymer in which coal fly ash was mixed with solid alkali activators such as sodium hydroxide and sodium silicate to form a powdery cementitious binder was developed. This binder mixed with soil only requires water to form the soil-fly ash (SO-CFA) geopolymer cement, which can be used as stabilized soil for backfill/foundation. This geopolymer product was then evaluated for chemical stability by immersing the material with 5% by weight of sulfuric acid solution for 28 days. Indication suggests that the geopolymer exhibited high resistance against acid attack with an observed increase of unconfined compressive strength even when the immersion time in acidic solution was increased to 56 days. The mineralogical phase, microstructure, and morphology of the material were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), respectively. Results not only confirmed the formation of gypsum due to acid attack but also indicated the dissolution of anorthite and albite that may have caused the microstructure to be composed of sodium aluminosilicate hydrate (N–A–S–H) and calcium (alumino) silicate hydrate (C(–A)–S–H) with poly(ferro-sialate-siloxo) and poly(ferro-sialate-disiloxo) networks. A column leaching test with deionized water was also performed on the soil-fly ash geopolymer to study the leachability of metals in the material. Results showed that arsenic exhibits higher mobility in the geopolymer as compared to that of cadmium, chromium, and lead.

Description: Minerals, Vol. 8, Pages 418: Authigenic Mg-Clay Minerals Formation in Lake Margin Deposits (the Cerro de los Batallones, Madrid Basin, Spain) Minerals doi: 10.3390/min8100418 Authors: Juan Emilio Herranz Manuel Pozo The Madrid Basin contains large and well developed deposits of Mg-clays of Miocene age. These were developed in an environment controlled by a lacustrine saline-alkaline environment with an arid or semi-arid climate, leading to large deposits of Mg-clays. This paper summarizes the study about the formation of Mg-clay minerals in the transition from mudflat lithofacies made-up of Mg-smectite to palustrine lithofacies where sepiolite is predominant. The samples collected in the field were characterized by XRD (X-Ray Diffaction) (bulk sample and clay fraction), examined using SEM (Scanning Electron Microscopy) and analyzed by XRF (X-Ray Fluorescence) and FTIR (Fourier Transform Infrared Spectroscopy). The results suggest that during the formation of these materials dissolution-precipitation, direct precipitation and recrystallization mechanisms intervened. The type of water present (runoff, lake and/or groundwater) is a key factor for the development of the different mineral phases. In the case of the study, the analyzed series goes from mudflat conditions with influence of runoff water to a palustrine environment. During this evolution, the influence of groundwater increases with time. This is reflected in the affinity between the samples analyzed and the presence of certain elements that could serve as indicators of changes between different media.

Description: Minerals, Vol. 8, Pages 416: Rare Earth and Phosphorus Leaching from a Flotation Tailings of Florida Phosphate Rock Minerals doi: 10.3390/min8090416 Authors: Haijun Liang Patrick Zhang Zhen Jin David W. DePaoli Phosphorite, or phosphate rock, is the raw material of phosphoric acid production. It has also been regarded as the most important secondary rare earth element (REE) resource due to low contents of rare earth elements contained in the ore. In Florida, there is about 19 Mt of phosphate rock mined annually. After beneficiation, the phosphate rock concentrate is utilized to produce phosphoric acid via a wet-process in which sulfuric acid is used to digest phosphate. During these processes, REEs and some phosphorus get lost in the byproducts including phosphatic clay, flotation tailings, phosphogypsum (PG), and phosphoric sludge. Recovering REEs and phosphorus from these wastes is beneficial to maximize the utilization of these valuable resources. This study focused on the effects of wet-process operating conditions on REE and phosphorus leaching from a kind of flotation tailing of Florida phosphate rock. The tailings were first beneficiated with a shaking table, and then a series of leaching tests were conducted on the shaking table concentrate. The results indicated that REEs had similar trends of leaching efficiency to those of phosphorus. Under the conditions of 16% phosphoric acid concentration in the initial pulp, a temperature of 75 °C, a stoichiometric ratio of sulfuric acid (H2SO4) to calcium oxide (CaO) of 1.1, and a weight ratio of liquid to solid of 3.5, REE and phosphorus leaching efficiencies reached relatively high values of approximately 61% and 91%, respectively. Analyses indicated that the phosphate ions (PO43−) in the leaching solution tended to combine with REE ions to form REE phosphates which precipitated into PG, but the other large amount of anions such as sulfate ions (SO42−) and fluoride ions (F−) took effect of steric hindrance to prevent PO43− from combining with REE cations. These two opposite effects determined the REE distribution between the leaching solution and PG.

Description: Minerals, Vol. 8, Pages 421: A Study on the Flocculation and Sedimentation of Iron Tailings Slurry Based on the Regulating Behavior of Fe3+ Minerals doi: 10.3390/min8100421 Authors: Tao Yue Xiqing Wu Xiao Chen Tianyu Liu Based on the regulating behavior of Fe3+, flocculation and sedimentation tests of iron tailings slurry flocculated using 2 mg/L anionic polyacrylamide (APAM) were studied, including the tests of Fe3+ dosage, regulating time, and pH. Flocculation–sedimentation tests showed that: a recommended addition of 56 mg/L Fe3+ produced a surprisingly bad flocculation effect; sedimentation ability decreased with the increase of regulating time, however, the regulating ability during the first 1 min was low; Fe3+ displayed a high regulating effect at pH 6–7, and then decreased with the increase of slurry pH. Size analysis demonstrated that the regulating ability of Fe3+ was related to the change of floc size, which increased with the decrease of size. Zeta potential analysis and calculation showed that small concentrations of Fe3+ and certain hydroxyl complex ions (such as Fe(OH)2+ and Fe(OH)2+) adsorbed onto the APAM molecular chains, resulting in a decreased charge density of the APAM molecules, and this electrostatic adsorption was able to make the polymer curl more easily. Fourier Transform Infrared Spectroscopic (FTIR) indicated the APAM on the hematite was slightly degraded into a monomer-like short-chain polymer while adding certain concentration of Fe3+. Scanning Electron Microscope (SEM) imaging showed that the network structure of APAM molecules treated by Fe3+ collapsed, and the APAM adsorption amount on hematite was significantly reduced. Therefore, the effect of Fe3+ on the APAM could be recommended as a new method for desorption and degradation of the APAM contained in the tailings slurry or flocs.

Description: Minerals, Vol. 8, Pages 420: Cerromojonite, CuPbBiSe3, from El Dragόn (Bolivia): A New Member of the Bournonite Group Minerals doi: 10.3390/min8100420 Authors: Hans-Jürgen Förster Luca Bindi Günter Grundmann Chris J. Stanley Cerromojonite, ideally CuPbBiSe3, represents a new selenide from the El Dragόn mine, Department of Potosí, Bolivia. It either occurs as minute grains (up to 30 µm in size) in interstices of hansblockite/quijarroite intergrowths, forming an angular network-like intersertal texture, or as elongated, thin-tabular crystals (up to 200 μm long and 40 μm wide) within lath-shaped or acicular mineral aggregates (interpreted as pseudomorphs) up to 2 mm in length and 200 μm in width. It is non-fluorescent, black, and opaque, with a metallic luster and black streak. It is brittle, with an irregular fracture, and no obvious cleavage and parting. In plane-polarized incident light, cerromojonite is grey to cream-white, and weakly pleochroic, showing no internal reflections. Between crossed polarizers, cerromojonite is weakly anisotropic, with rotation tints in shades of brown and grey. Lamellar twinning on {110} is common. The reflectance values in air for the COM standard wavelengths (R1 and R2) are: 48.8 and 50.3 (470 nm), 48.2 and 51.8 (546 nm), 47.8 and 52.0 (589 nm), and 47.2 and 52.0 (650 nm). Electron-microprobe analyses yielded a mean composition of: Cu 7.91, Ag 2.35, Hg 7.42, Pb 16.39, Fe 0.04, Ni 0.02, Bi 32.61, Se 33.37, total 100.14 wt %. The empirical formula (based on 6 atoms pfu) is (Cu0.89Hg0.11)Σ = 1.00(Pb0.56Ag0.16Hg0.15 Bi0.11Fe0.01)Σ = 0.99Bi1.00Se3.01. The ideal formula is CuPbBiSe3. Cerromojonite is orthorhombic (space group Pn21m), with a = 8.202(1) Å, b = 8.741(1) Å, c = 8.029(1) Å, V = 575.7(1) Å3, Z = 4. Calculated density is 7.035 g·cm−3. The five strongest measured X-ray powder diffraction lines (d in Å (I/I0) (hkl)) are: 3.86 (25) (120), 2.783 (100) (122), 2.727 (55) (212), 2.608 (40) (310), and 1.999 (25) (004). Cerromojonite is a new member of the bournonite group, representing the Se-analogue of součekite, CuPbBi(S,Se)3. It is deposited from strongly oxidizing low-T hydrothermal fluids at a fSe2/fS2 ratio >1, both as primary and secondary phase. The new species has been approved by the IMA-CNMNC (2018-040) and is named for Cerro Mojon, the highest mountain peak closest to the El Dragón mine.

Description: Minerals, Vol. 8, Pages 422: Effect of Acidithiobacillus ferrooxidans on Humic-Acid Passivation Layer on Pyrite Surface Minerals doi: 10.3390/min8100422 Authors: Hongying Yang Wenjie Luo Ying Gao The effect of Acidithiobacillus ferrooxidans on the humic-acid passivation layer on pyrite surfaces was studied by atomic-force microscopy, leaching experiments, and adsorption experiments. Atomic-force-microscopy results showed that humic-acid was adsorbed onto the pyrite surface. The bacteria grew and reproduced on the humic-acid layer. Leaching experiments showed that the humic-acid passivation layer prevented the oxidation of pyrite by Fe3+ under aseptic conditions. Bacteria destroyed the humic-acid layer, promoted pyrite oxidation, and increased the oxidation of pyrite from 1.64% to 67.9%. Bacterial adsorption experiments showed that the humic-acid passivation layer decreased the speed of bacterial adsorption on the pyrite surface but had no effect on the number of bacteria adsorbed on the pyrite surface. The maximum number of bacteria adsorbed by pyrite with and without the humic-acid layer was 4.17 × 1010 cells∙mL−1 and 4.4 × 1010 cells∙mL−1, respectively. Extracellular polymeric stratum layer of bacteria cultured at different concentrations of humic-acid was extracted and analyzed. This layer could destroy the humic-acid layer and promote pyrite oxidation.

Description: Minerals, Vol. 8, Pages 423: Petrogenesis of Heavy Rare Earth Element Enriched Rhyolite: Source and Magmatic Evolution of the Round Top Laccolith, Trans-Pecos, Texas Minerals doi: 10.3390/min8100423 Authors: Brent A. Elliott The Round Top rhyolite located in Trans-Pecos Texas is enriched in Be, F, Li, Nb, Rb, Sn, Th, U, Y, Zr, and rare earth elements (REEs). REE-bearing minerals are mainly ubiquitous nano-scale accessory phases throughout the groundmass, incorporated in synchysite-group minerals, xenotime-(Y), Y- and Ce-rich fluorite, and zircon. The rhyolite is peraluminous, high-silica, alkaline (not peralkaline), with elevated heavy rare earth element concentrations and anonymously negative Eu values. Pervasive spongy groundmass and recrystallization textures are consistent with the elevated and remobilized Zr, Th, and Y + HREE (heavy rare earth element) concentrations and a high field strength element (HFSE) soluble, sub-alkalic, F-rich, magmatic system. REE-bearing minerals are present as late-magmatic, interstitial phases and attributed with closed-system, post-magmatic, hydrothermal alteration. Petrogenetic modeling provides scenarios that explain the geochemical evolution and REE complexing behavior in evolved rhyolite magmas, and determines possible source compositions and evolution. Trace element models suggest a system typical of having extensive magmatic differentiation. The resulting rhyolite magma is indicative of a silica-rich magmatic system enriched in H2O, Li, and/or F that could be considered transitional between pure silicate melt and hydrothermal fluid, where fluorine-ligand complexing was prevalent through late magmatic cooling and crystallization processes. Thorough differentiation and high fluorine activity contributed to the late stage crystallization of REE-bearing minerals in the Round Top rhyolite.

Description: Minerals, Vol. 8, Pages 419: The Synthesis of Secondary Iron Minerals Induced by Quartz Sand during the Bioleaching Process Improves the Dewaterability of Municipal Sewage Sludge Minerals doi: 10.3390/min8100419 Authors: Yingying Ma Heru Wang Yongwei Song Yiqian Wu Zehao Guo This study elucidated the mechanisms during the bioleaching process when optimizing the dewaterability of municipal sludge using quartz sand. The experiment was conducted with a shaking table and a series of controlled trials designed to investigate the influence of quartz sand on sludge dewaterability. Scanning electron microscopy and X-ray diffraction were applied to explore the quartz sand’s action mechanism. Results indicated that quartz sand could improve the sludge bioleaching efficiency. The optimal reaction time was between 24–48 h and 48–72 h with and without 10 g·L−1 of quartz sand, and a minimum sludge specific resistance to filtration was 1.2 × 1012 and 2.4 × 1012 m·kg−1, respectively. Quartz sand could provide nucleating sites for secondary iron minerals and overcome the unfavorable influence of a low Fe3+ supply rate in the initial bioleaching stage (0–24 h). Because it was conducive to accelerating the initial mineral precipitation, quartz sand could improve bioleaching efficiency. The X-ray diffraction spectrum showed that quartz sand induced changes in the synthesis pathway of secondary iron minerals when the concentration of Fe2+ ≥ 4 g·L−1. This then promoted the transformation of schwertmannite into jarosite during the mineralization process, which immobilizes nutrients such as K+ and NH4+ in the form of jarosite. Accordingly, bioleached sludge dewaterability and its utilization value can be improved. These results provide theoretical reference for improving bioleaching techniques in the treatment of municipal sludge.

Description: Minerals, Vol. 8, Pages 417: Optimizing Flotation Circuit Recovery by Effective Stage Arrangements: A Case Study Minerals doi: 10.3390/min8100417 Authors: Vahid Radmehr Sied Ziaedin Shafaei Mohammad Noaparast Hadi Abdollahi Recovery is one of the most important metallurgical parameters in designing and evaluating flotation circuits. The present study used the recovery arrangement for two and three stage circuits to evaluate the effect of stage recovery on the overall circuit recovery and flotation circuit configuration. The results showed that mainly the highest recovery value should be assigned to the rougher stage in order to achieve the maximum overall circuit recovery. Countercurrent rougher-cleaner and rougher-scavenger circuits, in which recycling streams step back one stage at a time, follow a general rule for the assignment of recovery. Finally, a flotation plant containing six flotation banks was examined as a case study. A program for calculating total circuit recovery, for all possible combinations of recovery was developed in MATLAB software. 720 recovery combinations were evaluated. The results showed that optimal recovery allocation in stages could be effective in achieving overall circuit recovery. It was shown that the use of a large number of stages in some of the flotation circuits leads to the loss of equipment and additional costs. The proposed approach can be employed as an effective tool for designing and optimizing various flotation circuits and their operational parameters.

Description: Minerals, Vol. 8, Pages 341: Activation Mechanism of Lead Ions in Perovskite Flotation with Octyl Hydroxamic Acid Collector Minerals doi: 10.3390/min8080341 Authors: Yu Zheng Yating Cui Weiqing Wang The activation mechanism of lead ions (Pb2+) in perovskite flotation with an octyl hydroxamic acid collector was systematically investigated using microflotation experiments, zeta-potential measurements, adsorption tests, Fourier transform infrared (FT-IR) analysis, and X-ray photoelectron spectroscopy (XPS) analysis. The results of microflotation experiments and adsorption tests indicate that the presence of Pb2+ can promote the adsorption of octyl hydroxamic acid (OHA) on the perovskite surface and enhance the flotability of perovskite under weakly acidic conditions. The maximum recovery of 79.62% was obtained at pH 6.5 in the presence of Pb2+, and the maximum recovery of 57.93% was obtained at pH 5.7 without Pb2+. At pHs below 7, lead species are mainly present as Pb2+ and PbOH+ in the solution; besides this, the relative content of titanium increases on the perovskite surface. The adsorption of Pb2+ and PbOH+ on the perovskite surface makes the zeta-potential of perovskite shift positively, and increases the number of activated sites on the perovskite surface. FT-IR and XPS analyses confirm that OHA chemisorbs on the surface of Pb2+-activated perovskite and forms hydrophobic Pb-OHA complexes, which improve the flotability of perovskite.

Description: Minerals, Vol. 8, Pages 340: Dynamic Disorder of Fe3+ Ions in the Crystal Structure of Natural Barioferrite Minerals doi: 10.3390/min8080340 Authors: Arkadiusz Krzątała Taras L. Panikorovskii Irina O. Galuskina Evgeny V. Galuskin A natural barioferrite, BaFe3+12O19, from a larnite–schorlomite–gehlenite vein of paralava within gehlenite hornfels of the Hatrurim Complex at Har Parsa, Negev Desert, Israel, was investigated by Raman spectroscopy, electron probe microanalysis, and single-crystal X-ray analyses acquired over the temperature range of 100–400 K. The crystals are up to 0.3 mm × 0.1 mm in size and form intergrowths with hematite, magnesioferrite, khesinite, and harmunite. The empirical formula of the barioferrite investigated is as follows: (Ba0.85Ca0.12Sr0.03)∑1(Fe3+10.72Al0.46Ti4+0.41Mg0.15Cu2+0.09Ca0.08Zn0.04Mn2+0.03Si0.01)∑11.99O19. The strongest bands in the Raman spectrum are as follows: 712, 682, 617, 515, 406, and 328 cm−1. The structure of natural barioferrite (P63/mmc, a = 5.8901(2) Å, c = 23.1235(6) Å, V = 694.75(4) Å3, Z = 2) is identical with the structure of synthetic barium ferrite and can be described as an interstratification of two fundamental blocks: spinel-like S-modules with a cubic stacking sequence and R-modules that have hexagonal stacking. The displacement ellipsoids of the trigonal bipyramidal site show elongation along the [001] direction during heating. As a function of temperature, the mean apical Fe–O bond lengths increase, whereas the equatorial bond lengths decrease, which indicates dynamic disorder at the Fe2 site.

Description: Minerals, Vol. 8, Pages 339: Thalhammerite, Pd9Ag2Bi2S4, a New Mineral from the Talnakh and Oktyabrsk Deposits, Noril’sk Region, Russia Minerals doi: 10.3390/min8080339 Authors: Anna Vymazalová František Laufek Sergey F. Sluzhenikin Vladimir V. Kozlov Chris J. Stanley Jakub Plášil Federica Zaccarini Giorgio Garuti Ronald Bakker Thalhammerite, Pd9Ag2Bi2S4, is a new sulphide discovered in galena-pyrite-chalcopyrite and millerite-bornite-chalcopyrite vein-disseminated ores from the Komsomolsky mine of the Talnakh and Oktyabrsk deposits, Noril’sk region, Russia. It forms tiny inclusions (from a few μm up to about 40–50 μm) intergrown in galena, chalcopyrite, and also in bornite. Thalhammerite is brittle and has a metallic lustre. In plane-polarized light, thalhammerite is light yellow with weak bireflectance, weak pleochroism, in shades of slightly yellowish brown and weak anisotropy; it exhibits no internal reflections. Reflectance values of thalhammerite in air (R1, R2 in %) are: 41.9/43.0 at 470 nm, 43.9/45.1 at 546 nm, 44.9/46.1 at 589 nm, and 46.3/47.5 at 650 nm. Three spot analyses of thalhammerite give an average composition: Pd 52.61, Bi 22.21, Pb 3.92, Ag 14.37, S 7.69, and Se 0.10, total 100.90 wt %, corresponding to the empirical formula Pd8.46Ag2.28(Bi1.82Pb0.32)Σ2.14(S4.10Se0.02)Σ4.12 based on 17 atoms; the average of five analyses on synthetic thalhammerite is: Pd 55.10, Bi 24.99, Ag 12.75, and S 7.46, total 100.30 wt %, corresponding to Pd8.91Ag2.03Bi2.06S4.00. The density, calculated on the basis of the empirical formula, is 9.72 g/cm3. The mineral is tetragonal, space group I4/mmm, with a 8.0266(2), c 9.1531(2) Å, V 589.70(2) Å3 and Z = 2. The crystal structure was solved and refined from the single-crystal X-ray-diffraction data of synthetic Pd9Ag2Bi2S4. Thalhammerite has no exact structural analogues known in the mineral system; chemically, it is close to coldwellite (Pd3Ag2S) and kravtsovite (PdAg2S). The strongest lines in the X-ray powder diffraction pattern of synthetic thalhammerite [d in Å (I) (hkl)] are: 3.3428(24)(211), 2.8393(46)(220), 2.5685(21)(301), 2.4122(100)(222), 2.3245(61)(123), 2.2873(48)(004), 2.2201(29)(132), 2.0072(40)(400), 1.7481(23)(332), and 1.5085(30)(404). The mineral honours Associate Professor Oskar Thalhammer of the University of Leoben, Austria.

Description: Minerals, Vol. 8, Pages 342: Numerical Modeling of REE Fractionation Patterns in Fluorapatite from the Olympic Dam Deposit (South Australia) Minerals doi: 10.3390/min8080342 Authors: Sasha Krneta Cristiana L. Ciobanu Nigel J. Cook Kathy J. Ehrig Trace element signatures in apatite are used to study hydrothermal processes due to the ability of this mineral to chemically record and preserve the impact of individual hydrothermal events. Interpretation of rare earth element (REE)-signatures in hydrothermal apatite can be complex due to not only evolving fO2, fS2 and fluid composition, but also to variety of different REE-complexes (Cl-, F-, P-, SO4, CO3, oxide, OH− etc.) in hydrothermal fluid, and the significant differences in solubility and stability that these complexes exhibit. This contribution applies numerical modeling to evolving REE-signatures in apatite within the Olympic Dam iron-oxide-copper-gold deposit, South Australia with the aim of constraining fluid evolution. The REE-signatures of three unique types of apatite from hydrothermal assemblages that crystallized under partially constrained conditions have been numerically modeled, and the partitioning coefficients between apatite and fluid calculated in each case. Results of these calculations replicate the measured data well and show a transition from early light rare earth element (LREE)- to later middle rare earth element (MREE)-enriched apatite, which can be achieved by an evolution in the proportions of different REE-complexes. Modeling also efficiently explains the switch from REE-signatures with negative to positive Eu-anomalies. REE transport in hydrothermal fluids at Olympic Dam is attributed to REE–chloride complexes, thus explaining both the LREE-enriched character of the deposit and the relatively LREE-depleted nature of later generations of apatite. REE deposition may, however, have been induced by a weakening of REE–Cl activity and subsequent REE complexation with fluoride species. The conspicuous positive Eu-anomalies displayed by later apatite with are attributed to crystallization from high pH fluids characterized by the presence of Eu3+ species.

Description: Minerals, Vol. 8, Pages 345: Eogenetic Karst Control of Carbonate Reservoirs during a Transient Exposure: A Case Study of the Ordovician Yingshan Formation in the Northern Slope of the Tazhong Uplift, Tarim Basin, China Minerals doi: 10.3390/min8080345 Authors: Yong Dan Liangbiao Lin Bin Liang Qingyu Zhang Yu Yu Jianwen Cao Jingrui Li The Tazhong area of the Tarim Basin contains abundant oil and gas resources in Ordovician carbonate rocks, especially in the karst pores and caves of the Yingshan Formation. Research has indicated that the Yingshan Formation underwent a 7–11 Ma exposure during the middle Caledonian Period, resulting in large-scale karst pores and caves. However, the continental freshwater karst model cannot adequately explain the origin and distribution of karst pores and caves. In order to develop a more accurate karst model to guide petroleum exploration in the region, we analyzed the karst morphology, cave development statistics, and paleokarst environments. Karst reservoir characteristics were analyzed on the basis of the following analysis: (1) Karst morphological analyses based on core description and formation micro-imager (FMI) log analyses. The results showed that alveolar-like and Swiss cheese-like solution pores, spongy dissolution zones, pit cenotes, and small continuous karst caves developed in the Yingshan Formation. (2) The statistical analysis of pore and cave characteristics indicated that most of the karst pores and caves developed within 50 m below the unconformity where the average height of these features ranged from 0.1 to 3.0 m and their widths ranged up to 100 m. These pores and caves were commonly filled with gravel, clay, and calcite. Horizontal well and seismic attribute analysis indicated that these pores and caves were distributed over a large area. In plain view, the karst pore-cave system is comprised of cross-linked anastomosing networks of horizontal cave passages. And (3) Cathode luminescence and electron microprobe analyses suggested that clay filling within karst caves was freshwater related, while calcite filling was of seawater origin. Cements within solution pores showed three phases of luminescence, suggesting an alternating freshwater and seawater environment. Based on these characteristics, the karsts of the Yingshan Formation in the Tazhong area are interpreted to be similar to the eogenetic karsts in the Yucatan Peninsula of modern Mexico. Accordingly, this study indicates that the pore-caves of the Yingshan Formation can be subdivided into three sections. Further, the development and filling of these pore-cave sections are interpreted to have formed by eogenetic mixed-water karstification during three phases of relatively stable sea level in a coastal margin environment.

Description: Minerals, Vol. 8, Pages 349: Role of DTAB and SDS in Bubble-Particle Attachment: AFM Force Measurement, Attachment Behaviour Visualization, and Contact Angle Study Minerals doi: 10.3390/min8080349 Authors: Yaowen Xing Mengdi Xu Ming Li Wei Jin Yijun Cao Xiahui Gui Atomic force microscopy (AFM) and contact angle measurements were used to study the role of dodecyltrimethylammonium bromide (DTAB) and sodium dodecyl sulphate (SDS) in bubble-particle attachment. The results show that the forces between bubbles and the hydrophilic glass particle were always repulsive in the absence of DTAB and SDS. An attractive hydrophobic force was induced when the particles became hydrophobic, and the force was proportional to the water contact-angle. In the presence of DTAB and SDS, the cationic head group of DTAB adsorbed onto the negative hydrophilic glass surface as a monolayer and thus induced a hydrophobic force. However, at a high DTAB concentration, the DTAB molecules began to adsorb as a bilayer, reverting back to a hydrophilic surface. The hydrophobic force disappeared and the water film between the bubble and particle was stabilised under the repulsive double-layer force. The anionic SDS molecules could not adsorb onto the hydrophilic glass surface. The repulsive force always dominated the bubble-particle interaction. In the case of hydrophobic glass, the hydrophobic force decreased, and even disappeared, with the addition of DTAB and SDS. All the findings from the AFM force curves were consistent with the attachment behaviour and contact angle results.

Description: Minerals, Vol. 8, Pages 353: Multiscale Computational Simulation of Amorphous Silicates’ Structural, Dielectric, and Vibrational Spectroscopic Properties Minerals doi: 10.3390/min8080353 Authors: José Ángel Martínez-González Javier Navarro-Ruiz Albert Rimola Silicates are among the most abundant and important inorganic materials, not only in the Earth’s crust, but also in the interstellar medium in the form of micro/nanoparticles or embedded in the matrices of comets, meteorites, and other asteroidal bodies. Although the crystalline phases of silicates are indeed present in nature, amorphous forms are also highly abundant. Here, we report a theoretical investigation of the structural, dielectric, and vibrational properties of the amorphous bulk for forsterite (Mg2SiO4) as a silicate test case by a combined approach of classical molecular dynamics (MD) simulations for structure evolution and periodic quantum mechanical Density Functional Theory (DFT) calculations for electronic structure analysis. Using classical MD based on an empirical partial charge rigid ionic model within a melt-quenching scheme at different temperatures performed with the GULP 4.0 code, amorphous bulk structures for Mg2SiO4 were generated using the crystalline phase as the initial guess. This has been done for bulk structures with three different unit cell sizes, adopting a super-cell approach; that is, 1 × 1 × 2, 2 × 1 × 2, and 2 × 2 × 2. The radial distribution functions indicated a good degree of amorphization of the structures. Periodic B3LYP-geometry optimizations performed with the CRYSTAL14 code on the generated amorphous systems were used to analyze their structure; to calculate their high-frequency dielectric constants (ε∞); and to simulate their IR, Raman, and reflectance spectra, which were compared with the experimental and theoretical crystalline Mg2SiO4. The most significant changes of the physicochemical properties of the amorphous systems compared to the crystalline ones are presented and discussed (e.g., larger deviations in the bond distances and angles, broadening of the IR bands, etc.), which are consistent with their disordered nature. It is also shown that by increasing the unit cell size, the bulk structures present a larger degree of amorphization.

Description: Minerals, Vol. 8, Pages 359: Influence of the Structure and Experimental Surfaces Modifications of 2:1 Clay Minerals on the Adsorption Properties of Methylene Blue Minerals doi: 10.3390/min8080359 Authors: Pardo Cecilia López-Moreno Hernández Pozo Bentabol Franco In this work the adsorption capacities of methylene blue on Mg-smectite and sepiolite and its derived material obtained after acid treatment and/or the addition of Fe at its surfaces are studied. Natural smectite with high Mg-content in its octahedral sheet (Mg-smectite) displays higher adsorption capacity than the sepiolite due to the ability of Mg-smectite to expand the basal spacing to accommodate methylene blue cations between adjacent layers and the inability of sepiolite to adsorb these cations within the structural channels. The acid-activation of Mg-smectite causes a clear decrease in the adsorption capacity attributed to the partial loss of the interlayer positions by the loss of the octahedral sheet and subsequent formation of amorphous silica. Moreover, the adsorption of the Mg-smectite decreases even more when iron oxohydroxides species are incorporated in its interlayer spacing making inaccessible the interlayer active sites for the adsorption of methylene blue cations. On the contrary, the microwave-assisted acid treatment of sepiolite causes a slight increase in the adsorption capacity related with the dispersion of fibers. Nevertheless, contrary to that observed with Mg-smectite, higher increasing of adsorption capacities are obtained after the formation of new adsorption centers due to the incorporation of iron oxohydroxides species at the external surfaces of sepiolite.

Description: Minerals, Vol. 8, Pages 360: Adsorption Structure and Mechanism of Styryl Phosphoric Acid at the Rutile–Water Interface Minerals doi: 10.3390/min8080360 Authors: Wei Xiao Fen Jiao Hongbo Zhao Wenqing Qin Guanzhou Qiu Jun Wang The microstructure and mechanism of styryl phosphoric acid (SPA) adsorbed at the rutile–water interface were investigated through zeta potential measurement, ultraviolet-visible spectrophotometry (UV-Vis), Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The results of the zeta potential measurement illustrate that SPA is mainly electrostatically adsorbed on the rutile surface, and the adsorption process and result can be well fitted by the Stern-Grahame equation. The adsorption is severely affected by pH due to different species of SPA occurring in different pH solutions. The compound of P–O–Ti, with a structure of bidentate binuclear or bidentate mononuclear complexes, is formed after SPA is adsorbed on the rutile surface. SPA can be adsorbed on the rutile surface through the coordination of self-polymerization and bidentate mononuclear, which greatly increases the hydrophobicity of the rutile surface. Based on the above analysis and discussion, we proposed the adsorption model of SPA at the rutile–water interface, which was conducive to the modification and synthesis of a highly efficient flotation collector of the primary rutile ore.

Description: Minerals, Vol. 8, Pages 365: The Prismatic Layer of Pinna: A Showcase of Methodological Problems and Preconceived Hypotheses Minerals doi: 10.3390/min8090365 Authors: Yannicke Dauphin Alain Brunelle Kadda Medjoubi Andrea Somogyi Jean-Pierre Cuif The prismatic layer of Pinna (Mollusca) is one of the most studied models for the understanding of the biomineralization mechanisms, but our knowledge of the organic components of this layer is limited to the proteins of the soluble organic matrices. The interplay of the mineral and organic matrices is studied using scanning electron and atomic force microscopy, infra-red spectrometry, thermogravimetric analyses, aminoacids analyses, thin layer chromatography (TLC), X-ray fluorescence, X-ray Absorption near Edge Structure (XANES) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). Proteins, polysaccharides and lipids are detected within the prisms and their envelopes. The role of the technical choices to study calcareous biominerals is evidenced, showing that a single analysis is not enough to decipher complex biominerals.

Description: Minerals, Vol. 8, Pages 362: Authigenic Clay Minerals from Interface Reactions of Concrete-Clay Engineered Barriers: A New Perspective on Mg-Clays Formation in Alkaline Environments Minerals doi: 10.3390/min8090362 Authors: Jaime Cuevas Ana Isabel Ruiz Raúl Fernández Daniel González-Santamaría María Angulo Almudena Ortega Elena Torres María Jesús Turrero Artificial and singular geochemical environments are created around the engineered barrier systems (EBS) designed to isolate high level nuclear wastes in deep geological repositories. A concrete-bentonite interface takes place within the EBS and it builds a significant chemical gradient (pH), approximately from pH 8 (bentonite) to pH 12 (low alkali concrete), in a few millimetre thickness. This disequilibrium triggers dissolution and precipitation reactions and form a thin altered region. In this area, poorly ordered authigenic clay minerals, mainly hydrated magnesium silicates, are formed adjacent to hydrated calcium silicates and calcite precipitates adhered to the interface with concrete. This paper presents the development of this authigenic mineral layer comparing 6–18 months to 13 years interfaces. Scanning Electron Microscopy with Energy Dispersive X-ray spectroscopy (SEM-EDX) morphological and chemical characterization with the aid of ternary plots, X-ray diffraction (XRD) and infrared (IR) data show the young to old interface evolution from single brucite layers to stevensite-saponite silicates composition. Geochemical calculations indicate that this layer acts as a pH~11 buffer useful to minimize bentonite alteration and to favour the retention of amphoteric metal ions.

Description: Minerals, Vol. 8, Pages 363: Hydrothermal Metasomatism and Gold Mineralization of Porphyritic Granite in the Dongping Deposit, North Hebei, China: Evidence from Zircon Dating Minerals doi: 10.3390/min8090363 Authors: Hao Wei Jiuhua Xu Guorui Zhang Xihui Cheng Haixia Chu Chunjing Bian Zeyang Zhang A porphyritic granite intrusion was recently discovered in the Zhuanzhilian section of the Dongping gold deposit. There is as many as one tonnage of Au in the fractured shear zone within the porphyritic granite intrusion, but no relevant reports concerning the origin and age of the intrusion has been published as yet. In this paper, zircon U-Pb dating is used to study the geochronology of porphyritic granite, in order to find out the evidence of age and the relationship with gold mineralization. There are two groups of zircon 207Pb/235U-206Pb/238U concordant ages of porphyritic granites: The concordant age of 373.0 ± 3.5 Ma, with the weighted mean age of 373.0 ± 6.4 Ma; and the concordant age of 142.02 ± 1.2 Ma with the weighted mean age of 142.06 ± 0.84 Ma. We believe that the first group might represent the age of residual zircon of alkaline complex, while the second group might be related with main gold mineralization. The obtained results of the petrography and electron probe analysis indicate that the porphyritic quartz and porphyritic granite, as well as gold mineralization, might be products of a late replacement of tectonic-hydrothermal fluid, which was rich in Si, Na and K originally and later yielded gold-forming fluids.

Description: Minerals, Vol. 8, Pages 370: Revisiting the Organic Template Model through the Microstructural Study of Shell Development in Pinctadamargaritifera, the Polynesian Pearl Oyster Minerals doi: 10.3390/min8090370 Authors: Cuif Dauphin Luquet Medjoubi Somogyi Perez-Huerta A top-down approach to the mineralized structures and developmental steps that can be separated in the shells of Pinctada margaritifera was carried out. Detailed characterizations show that each of the two major layers usually taken into account (the outer prismatic layer and the inner nacreous layer) is actually the result of a complex process during which the microstructural patterns were progressively established. From its early growing stages in the deeper part of the periostracal grove up to the formation of the most inner nacreous layers, this species provides a demonstrative case study illustrating the leading role of specifically secreted organic structures as determinants of the crystallographic properties of the shell-building units. Gathering data established at various observational scales ranging from morphology to the nanometer level, this study allows for a reexamination of the recent and current biomineralization models.

Description: Minerals, Vol. 8, Pages 369: Effects of Xanthate on Flotation Kinetics of Chalcopyrite and Talc Minerals doi: 10.3390/min8090369 Authors: Limei Bai Jie Liu Yuexin Han Kai Jiang Wenqing Zhao This paper investigated the effects of using or not using potassium butyl xanthate (PBX) as a collector on the flotation kinetics of talc and chalcopyrite. By means of atomic force microscopy (AFM), Fourier-transform infrared spectroscopy (FTIR), a contact angle measuring instrument and particle size analyzer, the underlying causes behind the flotation rate changes of talc and chalcopyrite are analyzed. Experimental results showed that in collectorless flotation, the law of change in the flotation rate constant (k) of the two minerals over time is independent of pH, and k values of chalcopyrite are much smaller than those of talc. In the presence of PBX, the flotation speed of chalcopyrite greatly increases, and the k values of chalcopyrite are far larger than those of talc. This is mainly because the amount of xanthate adsorbed on the surface of chalcopyrite is large and the adsorption is in the form of chemisorption, while the adsorption of xanthate on the talcum surface is in very small amounts and in the form of physical adsorption. Simulation results indicated that the collectorless flotation of chalcopyrite conform to the classical first-order kinetics model and the Kelsall model, whereas that of talc only conform to the latter, which is due to the layered structure of talc. In the presence of the collector, talc flotation conforms to the two model, because talc has a higher floatability and particle morphology has less influence on the flotation rate.

Description: Minerals, Vol. 8, Pages 376: Microwave-Assisted Acid Activation of Clays Composed of 2:1 Clay Minerals: A Comparative Study Minerals doi: 10.3390/min8090376 Authors: Juan Antonio Cecilia Laura Pardo Manuel Pozo Eva Bellido Francisco Franco The effect of the microwave-assisted acid treatment (MAT) on the structure and texture of dioctahedral (montmorillonite) and trioctahedral (saponite) smectites, kerolitic clays and sepiolites were studied by scanning electron microscopy, nitrogen adsorption, X-ray fluorescence, X-ray diffraction and Fourier transform infrared spectroscopy. This study shows that in the smectite group of minerals the effectiveness of MAT is notably influenced by the chemical composition of the octahedral sheet, whereas in kerolitic clays it is influenced by the proportion of the expandable phase in the mixed layer sequence. On the other hand, the reactivity of sepiolites depends on the width of the natural fibres. With these treatments, extremely high specific surface area (SSA) increments are achieved in just 16 min. The SSA increments reach values up to 231 m2/g (%ΔSBET = 80) in sepiolites, 198 m2/g (%ΔSBET = 155) in Mg-smectites, and 161 m2/g (%ΔSBET = 61) in kerolitic clays.

Description: Minerals, Vol. 8, Pages 374: Kriging Interpolation for Evaluating the Mineral Resources of Cobalt-Rich Crusts on Magellan Seamounts Minerals doi: 10.3390/min8090374 Authors: Dewen Du Shijuan Yan Fengli Yang Zhiwei Zhu Qinglei Song Gang Yang The evaluation of mineral resources on seamounts by geostatistics faces two key challenges. First, the conventional distance/orientation- and the simple distance-based variogram functions used are ineffective at expressing the spatial self-correlation and continuity of cobalt-rich crust thicknesses on seamounts. Second, the sampling stations used for a single seamount are generally very sparsely distributed because of the high survey costs, which results in an insufficient number of information points for variogram fitting. Here, we present an alternative geostatistical method that uses distance/gradient- and distance/relative-depth-based variograms to process data collected from several neighboring seamounts, allowing the variogram fitting. The application example reported for the Magellan seamounts demonstrates the suitability of the method for evaluating the mineral resources of cobalt-rich crusts. The method could be effective also for the analysis of surface data obtained from mountain slopes on land (e.g., soil).

Description: Minerals, Vol. 8, Pages 373: Sulfide Formation as a Result of Sulfate Subduction into Silicate Mantle (Experimental Modeling under High P,T-Parameters) Minerals doi: 10.3390/min8090373 Authors: Yuliya Bataleva Yuri Palyanov Yuri Borzdov Ca,Mg-sulfates are subduction-related sources of oxidized S-rich fluid under lithospheric mantle P,T-parameters. Experimental study, aimed at the modeling of scenarios of S-rich fluid generation as a result of desulfation and subsequent sulfide formation, was performed using a multi-anvil high-pressure apparatus. Experiments were carried out in the Fe,Ni-olivine–anhydrite–C and Fe,Ni-olivine–Mg-sulfate–C systems (P = 6.3 GPa, T of 1050 and 1450 °C, t = 23–60 h). At 1050 °C, the interaction in the olivine–anhydrite–C system leads to the formation of olivine + diopside + pyrrhotite assemblage and at 1450 °C leads to the generation of immiscible silicate-oxide and sulfide melts. Desulfation of this system results in the formation of S-rich reduced fluid via the reaction olivine + anhydrite + C → diopside + S0 + CO2. This fluid is found to be a medium for the recrystallization of olivine, extraction of Fe and Ni, and subsequent crystallization of Fe,Ni-sulfides (i.e., olivine sulfidation). At 1450 °C in the Ca-free system, the generation of carbonate-silicate and Fe,Ni-sulfide melts occurs. Formation of the carbonate component of the melt occurs via the reaction Mg-sulfate + C → magnesite + S0. It is experimentally shown that the olivine-sulfate interaction can result in mantle sulfide formation and generation of potential mantle metasomatic agents—S- and CO2-dominated fluids, silicate-oxide melt, or carbonate-silicate melt.

Description: Minerals, Vol. 8, Pages 379: Origin of Platinum Group Minerals (PGM) Inclusions in Chromite Deposits of the Urals Minerals doi: 10.3390/min8090379 Authors: Federica Zaccarini Giorgio Garuti Evgeny Pushkarev Oskar Thalhammer This paper reviews a database of about 1500 published and 1000 unpublished microprobe analyses of platinum-group minerals (PGM) from chromite deposits associated with ophiolites and Alaskan-type complexes of the Urals. Composition, texture, and paragenesis of unaltered PGM enclosed in fresh chromitite of the ophiolites indicate that the PGM formed by a sequence of crystallization events before, during, and probably after primary chromite precipitation. The most important controlling factors are sulfur fugacity and temperature. Laurite and Os–Ir–Ru alloys are pristine liquidus phases crystallized at high temperature and low sulfur fugacity: they were trapped in the chromite as solid particles. Oxygen thermobarometry supports that several chromitites underwent compositional equilibration down to 700 °C involving increase of the Fe3/Fe2 ratio. These chromitites contain a great number of PGM including—besides laurite and alloys—erlichmanite, Ir–Ni–sulfides, and Ir–Ru sulfarsenides formed by increasing sulfur fugacity. Correlation with chromite composition suggests that the latest stage of PGM crystallization might have occurred in the subsolidus. If platinum-group elements (PGE) were still present in solid chromite as dispersed atomic clusters, they could easily convert into discrete PGM inclusions splitting off the chromite during its re-crystallization under slow cooling-rate. The presence of primary PGM inclusions in fresh chromitite of the Alaskan-type complexes is restricted to ore bodies crystallized in equilibrium with the host dunite. The predominance of Pt–Fe alloys over sulfides is a strong indication for low sulfur fugacity, thereby early crystallization of laurite is observed only in one deposit. In most cases, Pt–Fe alloys crystallized and were trapped in chromite between 1300 and 1050 °C. On-cooling equilibration to ~900 °C may produce lamellar unmixing of different Pt–Fe phases and osmium. Precipitation of the Pt–Fe alloys locally is followed by an increase of sulfur fugacity leading to crystallize erlichmanite and Ir–Rh–Ni–Cu sulfides, occurring as epitaxic overgrowth on the alloy. There is evidence that the system moved quickly into the stabilization field of Pt–Fe alloys by an increase of the oxygen fugacity marked by an increase of the magnetite component in the chromite. In summary, the data support that most of the primary PGM inclusions in the chromitites of the Urals formed in situ, as part of the chromite precipitation event. However, in certain ophiolitic chromitites undergoing annealing conditions, there is evidence for subsolidus crystallization of discrete PGM from PGE atomic-clusters occurring in the chromite. This mechanism of formation does not require a true solid solution of PGE in the chromite structure.

Description: Minerals, Vol. 8, Pages 380: Major and Trace Element Geochemistry of Pyrite and Pyrrhotite from Stratiform and Lamellar Orebodies: Implications for the Ore Genesis of the Dongguashan Copper (Gold) Deposit, Eastern China Minerals doi: 10.3390/min8090380 Authors: Zhongfa Liu Yongjun Shao Haodi Zhou Nan Liu Kuanxin Huang Qingquan Liu Jiandong Zhang Cheng Wang The Dongguashan copper (gold) deposit in Anhui Province is one of the largest copper (gold) deposits in the Tongling ore district, which is the most important region in the Middle–Lower Yangtze River Metallogenic Belt, Eastern China. Stratiform and lamellar orebodies are the major deposit types. Pyrite and pyrrhotite from the stratiform deposit type (Py I, Po I) and lamellar deposit type (Py II, Po II) are investigated using Electron-probe Microanalyses (EPMA) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). Py I, Py II, Po I and Po II have high contents of Cu, Co, Au and Se, low contents of As, Pb and Zn, with Co/Ni ratios of 0.50−48.00, 4.00−45.00, 1.55−14.45 and 1.02−1.36, respectively, most of which are greater than 1 and vary widely; these characteristics are consistent with those of pyrite with a magmatic–hydrothermal origin. The higher Au/Ag and Fe/(S + As) ratios of pyrite and crystallization temperatures (286–387 °C) of hexagonal pyrrhotite indicate that the mineralization occurrs in environments with medium- to high-temperatures, high sulfur fugacity and medium-shallow depths. Therefore, we suggest that the Dongguashan copper (gold) deposit is a stratabound skarn-type ore deposit associated with magma intrusion activity during the Yanshanian Period.

Description: Minerals, Vol. 8, Pages 386: Water Adsorption on the β-Dicalcium Silicate Surface from DFT Simulations Minerals doi: 10.3390/min8090386 Authors: Qianqian Wang Hegoi Manzano Iñigo López-Arbeloa Xiaodong Shen β-dicalcium silicate (β-Ca2SiO4 or β-C2S in cement chemistry notation) is one of the most important minerals in cement. An improvement of its hydration rate would be the key point for developing environmentally-friendly cements with lower energy consumption and CO2 emissions. However, there is a lack of fundamental understanding on the water/β-C2S surface interactions. In this work, we aim to evaluate the water adsorption on three β-C2S surfaces at the atomic scale using density functional theory (DFT) calculations. Our results indicate that thermodynamically favorable water adsorption takes place in several surface sites with a broad range of adsorption energies (−0.78 to −1.48 eV) depending on the particular mineral surface and adsorption site. To clarify the key factor governing the adsorption of the electronic properties of water at the surface were analyzed. The partial density of states (DOS), charge analysis, and electron density difference analyses suggest a dual interaction of water with a β-C2S (100) surface including a nucleophilic interaction of the water oxygen lone pair with surface calcium atoms and an electrophilic interaction (hydrogen bond) of one water hydrogen with surface oxygen atoms. Despite the elucidation of the adsorption mechanism, no correlation was found between the electronic structure and the adsorption energies.

Description: Minerals, Vol. 8, Pages 384: Rock Classification Using Multivariate Analysis of Measurement While Drilling Data: Towards a Better Sampling Strategy Minerals doi: 10.3390/min8090384 Authors: Veena S. Vezhapparambu Jo Eidsvik Steinar L. Ellefmo Measurement while drilling (MWD) data are gathered during drilling operations and can provide information about the strength of the rock penetrated by the boreholes. In this paper MWD data from a marble open-pit operation in northern Norway are studied. The rock types are represented by discrete classes, and the data is then modeled by a hidden Markov model (HMM). Results of using different MWD data variables are studied and presented. These results are compared and co-interpreted with optical televiewer (OTV) images, magnetic susceptibility and spectral gamma values collected in the borehole using down-the-hole sensors. A model with penetration rate, rotation pressure and dampening pressure data show a good visual correlation with OTV image for the studied boreholes. The marble class is characterized by medium penetration rate and medium rotation pressure, whereas the intrusions are characterized by low penetration rate and medium to high rotation pressure. The fractured marble is characterized by high penetration rate, high rotation and low dampening pressure. Future research will use the presented results to develop a heterogeneity index, develop an MWD-based 3D-geology model and an improved sampling strategy and investigate how to implement this in the mine planning process and reconciliation.

Description: Minerals, Vol. 8, Pages 385: Carbonaceous Materials in the Fault Zone of the Longmenshan Fault Belt: 1. Signatures within the Deep Wenchuan Earthquake Fault Zone and Their Implications Minerals doi: 10.3390/min8090385 Authors: Li-Wei Kuo Jyh-Rou Huang Jiann-Neng Fang Jialiang Si Haibing Li Sheng-Rong Song Graphitization of carbonaceous materials (CM) has been experimentally demonstrated as potential evidence of seismic slip within a fault gouge. The southern segment of the Longmenshan fault, a CM-rich-gouge fault, accommodated coseismic slip during the 2008 Mw 7.9 Wenchuan earthquake and potentially preserves a record of processes that occurred on the fault during the slip event. Here, we present a multi-technique characterization of CM within the active fault zone of the Longmenshan fault from the Wenchuan earthquake Fault Scientific Drilling-1. By contrast with field observations, graphite is pervasively and only distributed in the gouge zone, while heterogeneously crystallized CM are present in the surrounding breccia. The composite dataset that is presented, which includes the localized graphite layer along the 2008 Wenchuan earthquake principal slip zone, demonstrates that graphite is widely distributed within the active fault zone. The widespread occurrence of graphite, a seismic slip indicator, reveals that surface rupturing events commonly occur along the Longmenshan fault and are characteristic of this tectonically active region.

Description: Minerals, Vol. 8, Pages 387: Halloysite Nanotubes as an Effective and Recyclable Adsorbent for Removal of Low-Concentration Antibiotics Ciprofloxacin Minerals doi: 10.3390/min8090387 Authors: Rongqing Cheng Haipeng Li Zhiliang Liu Chunfang Du In this work, halloysite nanotubes (HNTs) without modification were used as an efficient adsorbent to explore its natural adsorption capability, which showed excellent adsorption ability for low-concentration ciprofloxacin (CIP). The physicochemical properties of HNTs before and after adsorption were investigated by several characterization techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), N2 adsorption–desorption analysis, X-ray diffractometer (XRD), and zeta potential analysis. The influences of temperature, initial CIP concentration, adsorbent dosage, and pH value on CIP adsorption performance were also studied. The kinetics analysis revealed that CIP adsorption on HNTs was a kind of monolayer adsorption process and followed a pseudo-second-order rate equation. The zeta potential result indicated that electrostatic interaction between HNTs and CIP molecules was possibly responsible for the adsorption performance. Moreover, HNTs showed no apparent loss in CIP adsorption capability after five cycles, exhibiting potential applications in wastewater treatment.

Description: Minerals, Vol. 8, Pages 392: Two-Stage SART Process: A Feasible Alternative for Gold Cyanidation Plants with High Zinc and Copper Contents Minerals doi: 10.3390/min8090392 Authors: Humberto Estay Minghai Gim-Krumm Michelle Quilaqueo The SART (sulfidization, acidification, recycling, and thickening) process (SP) has been successfully implemented in gold cyanidation plants to address issues associated with high cyanide-soluble copper content ores. However, this process could produce a relatively low grade precipitate, decreasing the sale price when gold plants have high zinc and copper content in their solutions. A potential option in this case would be the use of a two-stage SART process (TSSP) to produce separate zinc and copper precipitates. The additional equipment involved with this process would increase the capital cost, thereby generating concerns about the optimal range of metal contents that could justify this option. This study presents a methodology to quantify the feasible range of Cu/Zn concentrations that would justify a two-stage SART process. The study is based on a thermodynamic model and a simple economic evaluation. Results show the TSSP is preferred when the Cu/Zn ratio ranges between 0.2 and 1.5 with copper concentration higher than 500 mg/L. The TSSP appears to be a viable option to consider for gold plants having concentrations of copper and zinc higher than 200 mg/L for both metals.

Description: Minerals, Vol. 8, Pages 394: Geology and U-Th-Pb Dating of the Gakara REE Deposit, Burundi Minerals doi: 10.3390/min8090394 Authors: Seconde Ntiharirizwa Philippe Boulvais Marc Poujol Yannick Branquet Cesare Morelli Joël Ntungwanayo Gilbert Midende The Gakara Rare Earth Elements (REE) deposit is one of the world’s highest grade REE deposits, likely linked to a carbonatitic magmatic-hydrothermal activity. It is located near Lake Tanganyika in Burundi, along the western branch of the East African Rift. Field observations suggest that the mineralized veins formed in the upper crust. Previous structures inherited from the Kibaran orogeny may have been reused during the mineralizing event. The paragenetic sequence and the geochronological data show that the Gakara mineralization occurred in successive stages in a continuous hydrothermal history. The primary mineralization in bastnaesite was followed by an alteration stage into monazite. The U-Th-Pb ages obtained on bastnaesite (602 ± 7 Ma) and on monazite (589 ± 8 Ma) belong to the Pan-African cycle. The emplacement of the Gakara REE mineralization most likely took place during a pre-collisional event in the Pan-African belt, probably in an extensional context.

Description: Minerals, Vol. 8, Pages 399: New Occurrence of Rusinovite, Ca10(Si2O7)3Cl2: Composition, Structure and Raman Data of Rusinovite from Shadil-Khokh Volcano, South Ossetia and Bellerberg Volcano, Germany Minerals doi: 10.3390/min8090399 Authors: Dorota Środek Rafał Juroszek Hannes Krüger Biljana Krüger Irina Galuskina Viktor Gazeev Rusinovite, Ca10(Si2O7)3Cl2, was found at two new localities, including Shadil-Khokh volcano, South Ossetia and Bellerberg volcano, Caspar quarry, Germany. At both of these localities, rusinovite occurs in altered carbonate-silicate xenoliths embedded in volcanic rocks. The occurrence of this mineral is connected to specific zones of the xenolith characterized by a defined Ca:Si < 2 ratio. Chemical compositions, as well as the Raman spectra of the investigated rusinovite samples, correspond to the data from the locality of rusinovite holotype—Upper Chegem Caldera, Northern Caucasus, Russia. The most intense bands of the Raman spectra are related to vibrations of (Si2O7) groups. Unit cell parameters of rusinovite from South Ossetia are: a = 3.76330(4) Å, b = 16.9423(3) Å, c = 17.3325(2) Å, V = 1105.10(4) Å3, Z = 2. The performed synchrotron radiation diffraction experiments did not confirm a doubling of c as reported for the synthetic phase, Ca10(Si2O7)3Cl2. However, one-dimensional diffuse scattering parallel to b* has been observed. This can be interpreted with an ordered arrangement of Si2O7 groups creating layers with a doubled a parameter. Consequently, the two different displacements of neighbouring layers allow random stacking faults to occur.

Description: Minerals, Vol. 8, Pages 165: Response Surface Methodology for Optimization of Copper Leaching from Refractory Flotation Tailings Minerals doi: 10.3390/min8040165 Authors: Xu Bai Shuming Wen Jian Liu Yilin Lin Response surface methodology is used to optimize the leaching process for refractory flotation copper tailings. The proportion of the refractory combination oxide copper (chrysocolla) is 64.84%. At present, few studies have examined the leaching of chrysocolla. In this study, we examine the effects of several variables, including the amount of concentrated sulfuric acid, leaching temperature, and leaching time, on leaching efficiency. Using a response surface methodology, we develop a quadratic model relanbting all the above experimental variables with leaching efficiency. The resulting model is highly consistent with experimental data. According to the model, the factor with the greatest influence on leaching efficiency is the amount of concentrated sulfuric acid. According to the model, the optimal leaching conditions are 85 kg/t concentrated sulfuric acid, a leaching temperature of 68.51 °C, and a leaching time of 4.36 h. The actual measured leaching efficiency under these conditions is 85.86%, which is close to the value of 86.79% predicted by the model. We study the leaching processes using scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) surface scan analyses. Both methods allow us to explore the content of the main element and visually observe its distribution, allowing us to develop effective methods for treating low-grade oxide ores.

Description: Minerals, Vol. 8, Pages 170: Breakage Function for HPGR: Mineral and Mechanical Characterization of Tantalum and Tungsten Ores Minerals doi: 10.3390/min8040170 Authors: Hernan Anticoi Eduard Guasch Sarbast Hamid Josep Oliva Pura Alfonso Maite Garcia-Valles Marc Bascompta Lluis Sanmiquel Teresa Escobet Rosa Argelaguet Antoni Escobet Jose Juan de Felipe David Parcerisa Esteban Peña-Pitarch The modelling of high pressure grinding rolls is described by the population balance model, a mass balance which includes several functions that are related to the mineral characteristics, material kinetics and operative conditions of the device. The breakage distribution function is one of these functions and refers to the way in which the daughter particles are generated by the process of comminution. The piston-die press is presented as a methodology to determine the breakage distribution function of two different materials, from the mechanical response point of view: altered granite and a cal-silicate material. The aim is to determine the relation between the operative conditions and the mineral characteristics in order to explain and predict the breakage function parameters. The materials were characterised using XRD and single compression strength tests. The altered granite is a brittle material, which generates more fines under single compression conditions compared to bed compression conditions, mainly due to the mineral composition and the response of the material to the breakage action. The cal-silicate material shows a normal trend in its breakage behaviour. As is expected, the mineralogical characterisation is a useful tool to predict the values of the parameters of the breakage distribution function.

Description: Minerals, Vol. 8, Pages 169: Carbonation-Induced Mineralogical Changes in Coal Mining Waste Blended Cement Pastes and Their Influence on Mechanical and Microporosity Properties Minerals doi: 10.3390/min8040169 Authors: Moisés Frías Raquel Vigil de la Villa Rosario García Olga Rodríguez Lucía Fernández-Carrasco Sagrario Martínez-Ramírez The worldwide pursuit of new eco-efficient pozzolans is ongoing. Kaolinite-based waste is an eco-friendly source of recycled metakaolinite, a highly pozzolanic product. In this study, a blended cement paste containing 20% activated coal waste (ACW) was exposed to a 100% CO2 atmosphere at 65% RH for 7 days. The variations in its phase composition and strength were studied and compared to an OPC control. Both pastes were cured for 28 days prior to the carbonation test. Reaction kinetics were assessed using XRD, SEM/EDX, TG/DTG, FT-IR, Micro-Raman spectroscopy, pore solution pH and the cumulative carbonated fraction. The blended cement carbonated 68% faster than the control. While portlandite carbonation was the main reaction in both cements, decalcification was also observed (more intensely in the 20% ACW paste) in other hydraulic calcium phases (C-S-H gel, monocarboaluminate (C4AcH12), ettringite and tetracalcium aluminate (C4AH13). The end product of this reaction was calcium carbonate, mainly in the form of calcite, although traces of aragonite and amorphous carbonate were also detected. Compressive strength values rose with accelerated carbonation time and pore size reduction in both cement pastes.

Description: Minerals, Vol. 8, Pages 177: Growth Behavior and Size Characterization of Metallic Iron Particles in Coal-Based Reduction of Oolitic Hematite–Coal Composite Briquettes Minerals doi: 10.3390/min8050177 Authors: Yanfeng Li Yuexin Han Yongsheng Sun Peng Gao Yanjun Li Guichen Gong To reveal the growth behavior and size characterization of iron particles in coal-based reduction, we reduced oolitic hematite–coal composite briquettes at various temperatures, durations and ore size fractions. The degree of metallization and microstructure of the reduced briquettes and the characteristic of iron particle size were investigated through chemical composition analysis, scanning electron microscopy, energy dispersive spectroscopy, and Bgrimm process mineralogy analysis. Results showed that iron oxides in the oolitic hematite ore were reduced to metallic iron from outer to inner layers; these oxides gradually grew into quasi-spherical iron particles with random distribution in the gangue. As reduction continued, iron grains agglomerated occurred, and iron particle clusters were formed in the form of quasi-spherical, chained, blocky, and clavate when they were viewed in the cross section. The boundaries among the iron grains of the iron particle cluster continuously faded and disappeared, and an iron particle with increased size and homogeneity was finally produced. The reduction temperature, time, and ore size fraction influenced the reduction of composite briquettes and iron particle size. The degree of metallization increased as reduction temperature was increased, reduction time was extended, or ore size fraction was decreased until the equilibrium of reaction was achieved. Moreover, the iron particle size gradually increased as reduction temperature was increased, reduction time was extended, or ore size fraction was decreased.

Description: Minerals, Vol. 8, Pages 174: Key Factors Affecting Strength Development of Steel Slag-Dredged Soil Mixtures Minerals doi: 10.3390/min8050174 Authors: Kanako Toda Haruna Sato Nilan Weerakoon Tsubasa Otake Satoshi Nishimura Tsutomu Sato Some of the steel slag from ironworks and dredged soils from marine and waterfront engineering work are partially treated as waste. However, a mixture of these two kinds of waste has the potential to be used as construction materials when mixed, due to chemical reactions forming secondary phases. Utilizing waste of such kind as a resource will help to improve sustainability in society by reducing waste and replacing virgin resources such as cement. Recently, it was reported that mixtures of steel slag and dredged soil hardens under specific conditions. The phase compositions of dredged soils and steel slags vary depending on the quantity of each component, which results in unpredictable strength development of mixtures. The effect of the variations in the components of steel slags and dredged soils on strength development of the mixtures is not yet clear, limiting the utilization of both materials. Understanding the hardening mechanisms of the mixtures will enable the prediction of strength development. Focusing on the variations in the components in steel slags and, especially of dredged soils, this study aims to identify the components in both materials that affect the secondary phase formation that are responsible for strength development. We found support for suggestions that calcium silicate hydrate, C-S-H, is one of the secondary phases responsible for the strength development of the mixtures. From a comparison of two kinds of steel slags and various dredged soils, the amount of portlandite in the steel slags and the amount of amorphous silica in the dredged soils are suggested as a couple of the key components of starting materials involved in the C-S-H formation.

Description: Minerals, Vol. 8, Pages 176: Molecular Simulation of Minerals-Asphalt Interfacial Interaction Minerals doi: 10.3390/min8050176 Authors: Daisong Luo Meng Guo Yiqiu Tan The interfacial interaction between asphalt binder and mineral aggregate makes different components have different diffusion behavior. It influences the performance of interface and consequently that of the mix. In this research, the models of four asphalt components (asphaltene, resin, aromatics and saturate) and five minerals were constructed individually, and then the Al2O3-asphalt interface model was constructed by adding the asphalt layer and mineral layer together. The interfacial behavior at molecular scale was simulated by setting boundary conditions, optimizing the structure and canonical ensemble. The mean square displacement (MSD) and diffusion coefficient of particles were selected as indicators to study the diffusion of asphalt components on the surface of Al2O3. The results show that when the temperature was 65 °C, asphalt binder showed more viscosity, the diffusion speed of asphalt components ranked according to their molecular mass, which was saturate > aromatics > resin > asphaltene. At 25 °C and 165 °C, the resin had the fastest diffusion speed, which was nearly twice of asphaltene. The interaction between asphalt components and Al2O3 mineral surface can make the diffusion of asphalt components independent on temperature.

Description: Minerals, Vol. 8, Pages 175: The Hydrothermal Breccia of Berglia-Glassberget, Trøndelag, Norway: Snapshot of a Triassic Earthquake Minerals doi: 10.3390/min8050175 Authors: Axel Müller Morgan Ganerød Michael Wiedenbeck Skule Svendsen Spjelkavik Rune Selbekk The quartz-K-feldspar-cemented breccia of Berglia-Glassberget in the Lierne municipality in central Norway forms an ellipsoid structure 250 m × 500 m in size. The hydrothermal breccia is barren in terms of economic commodities but famous among mineral collectors for being a large and rich site of crystal quartz of various colours and habits. Despite being a famous collector site, the mineralization is rather unique in respect to its geological setting. It occurs within Late Palaeoproterozoic metarhyolites of the Lower Allochthon of the Norwegian Caledonides regionally isolated from any other contemporaneous hydrothermal or magmatic event. In order to understand better the formation of the Berglia-Glassberget breccia, the chemistry, fluid inclusion petrography and age of the breccia cement were determined. Structural features indicate that the Berglia-Glassberget is a fault-related, fluid-assisted, hydraulic breccia which formed by single pulse stress released by a seismic event. 40Ar-39Ar dating of K-feldspar cement revealed a middle Triassic age (240.3 ± 0.4 Ma) for this event. The influx into the fault zone of an aqueous CO2-bearing fluid triggered the sudden fault movement. The high percentage of open space in the breccia fractures with cavities up 3 m × 3 m × 4 m in size, fluid inclusion microthermometry, and trace element chemistry of quartz suggests that the breccia was formed at depths between 4 and 0.5 km (1.1 to 0.1 kbar). The origin of the breccia-cementing, CO2-bearing Na-HCO3-SO4 fluid may have been predominantly of metamorphic origin due to decarbonation reactions (T > 200 °C) of limestones of the underlying Olden Nappe. The decarbonation reactions were initiated by deeply derived, hot fluids channelled to sub-surface levels by a major fault zone, implying that the breccia is situated on a deep-seated structure. Regionally, the Berglia-Glassberget occurs at a supposed triple junction of long-lived fault zones belonging to the Møre-Trøndelag, Lærdal-Gjende and the Kollstraumen fault complexes. These fault systems and the associated Berglia-Glassberget earthquake are the expression of rifting and faulting in northern Europe during the middle/late Triassic.

Description: Minerals, Vol. 8, Pages 180: Fabrication of Si Nanoparticles@Carbon Fibers Composites from Natural Nanoclay as an Advanced Lithium-Ion Battery Flexible Anode Minerals doi: 10.3390/min8050180 Authors: Sainan Liu Qiang Zhang Huaming Yang Dawei Mu Anqiang Pan Shuquan Liang In this paper, a cost-effective strategy for fabricating silicon-carbon composites was designed to further improve the electrochemical performance and commercialization prospects of Si anodes for lithium-ion batteries (LIBs). Silicon-carbon fibers (CFs) were prepared by loading Si nanoparticles (SiNPs) on interconnected carbon fibers via an electrospinning technique (SiNPs@CFs). The Si nanoparticles were obtained by the reduction reaction of natural clay minerals. As a flexible anode for LIBs, the SiNPs@CFs anode demonstrated a reversible capacity of 1238.1 mAh·g−1 and a capacity retention of 77% after 300 cycles (in contrast to the second cycle) at a current density of 0.5 A·g−1. With a higher current density of 5.0 A·g−1, the electrode showed a specific capacity of 528.3 mAh·g−1 after 1000 cycles and exhibited a superior rate capability compared to Si nanoparticles. The excellent electrochemical properties were attributed to the construction of flexible electrodes and the composite comprising carbon fibers, which lessened the volume expansion and improved the conductivity of the system.

Description: Minerals, Vol. 8, Pages 181: PGE–(REE–Ti)-Rich Micrometer-Sized Inclusions, Mineral Associations, Compositional Variations, and a Potential Lode Source of Platinum-Group Minerals in the Sisim Placer Zone, Eastern Sayans, Russia Minerals doi: 10.3390/min8050181 Authors: Andrei Y. Barkov Gennadiy I. Shvedov Robert F. Martin We report the results of a mineralogical investigation of placer samples from the upper reaches of the Sisim watershed, near Krasnoyarsk, in Eastern Sayans, Russia. The placer grains are predominantly Os–Ir–(Ru) alloys (80%) that host various inclusions (i.e., platinum-group elements (PGE)-rich monosulfide, PGE-rich pentlandite, Ni–Fe–(As)-rich laurite, etc.) and subordinate amounts of Pt–Fe alloys. Analytical data (wavelength- and energy-dispersive X-ray spectroscopy) are presented for all the alloy minerals and the suite of micrometer-sized inclusions that they contain, as well as associated grains of chromian spinel. The assemblage was likely derived from chromitite units of the Lysanskiy mafic–ultramafic complex, noted for its Ti–(V) mineralization. In the Os–Ir–(Ru) alloys, the ratio Ru/Ir is ≤1, Ir largely substitutes for Os, and compositional variations indicate the scheme [Ir + Ru] → 2Os. In contrast, in the laurite–erlichmanite series, Ir and Os are strongly and positively correlated, whereas Ir and Ru are negatively correlated; Ru and Os are inversely correlated. These compositions point to the scheme [Os2+ + 2Ir3+ + □] → 4Ru2+ or alternatively, to Os2+ + Ir2+ → 2Ru2+. We deduce a potential sequence of crystallization in the parental rock and address the effects of decreasing temperature and increasing fugacity of sulfur and arsenic on the assemblage. Inclusions of Ti-rich minerals in the alloy grains are consistent with the Lysanskiy setting; the complete spectrum of chromite–magnesiochromite compositions indicates that an important part of that complex was eroded. A localized fluid-dominated micro-environment produced the unique association of laurite with monazite-(Ce), again considered a reflection of the special attributes of the Lysanskiy complex.

Description: Minerals, Vol. 8, Pages 182: Evaluation of Local Matching Methods in Image Analysis for Mineral Grain Tracking in Microscope Images of Rock Sections Minerals doi: 10.3390/min8050182 Authors: Magdalena Habrat Mariusz Młynarczuk Modern geological techniques have resulted in vast and growing databases of digital images and video sequences of rocks, which are available for the use of researchers. The number of database images continues to increase exponentially, creating a need for techniques that will enable the automation of data set management. Desired techniques include query by image, a topic that has been extensively elaborated on in the literature recently. Unfortunately, using such techniques in the geological sciences has been very sporadic and insufficient. This paper presents the evaluation of characteristic local features within rock images for tracking objects on images or video sequences. It also discusses the possibilities for using selected local feature descriptors for content-based image retrieval (CBIR) in the area of geological sciences. The evaluation was performed for the Speeded Up Robust Features (SURF), Binary Robust Invariant Scalable Keypoints (BRISK), Harris–Stephens Algorithm (HSA), Minimum Eigenvalue Algorithm (MEA), and Features from Accelerated Segment Test algorithm (FAST) methods, which are widely known and appreciated in the computer vision field. These methods were analysed for their application to microscopic images of rocks. Five functional cases of geological grain tracking were investigated, based on a selected non-transformed query image, as well as a computer-rotated, acquisitive-rotated, computer-magnified, and an acquisitive-magnified query image. The results demonstrated that these methods can be successfully used for geological applications.

Description: Minerals, Vol. 8, Pages 183: Catalan Imitations of the Ligurian Taches Noires Ware in Barcelona (18th–19th Century): An Example of Technical Knowledge Transfer Minerals doi: 10.3390/min8050183 Authors: Roberta Di Febo Lluís Casas Claudio Capelli Roberto Cabella Oriol Vallcorba The ware called Taches Noires was developed in Albisola (Liguria, NW Italy) during the 18th century. In just a few years, it spread all over the Mediterranean (Italy, France, Spain, Tunisia, and Greece) and also in the New World (Canada, the Caribbean Islands, and Mexico). The success of the Taches Noires ware was so massive that it was soon copied by Spanish and French workshops. A collection of Catalan imitations and Ligurian imports found in Barcelona were analysed and compared to previously existing data from Barcelona productions, as well as reference samples from Albisola. The study proved the presence of both local imitations and original Albisola imports. The analysis showed a homogeneous product of high technical quality for the Albisola pottery. On the contrary, the local imitations presented a greater diversification in the choice and manipulation of the raw materials, probably related to the existence of different workshops engaged in the manufacturing of these products. Nevertheless, for one of the local groups, ceramists adopted a glaze recipe similar to the one used in Albisola, clearly indicating a direct transfer of knowledge, and possibly of potters, from Albisola to Barcelona.

Description: Minerals, Vol. 8, Pages 189: Diamond Exploration Potential of the Northern East European Platform Minerals doi: 10.3390/min8050189 Authors: Elena V. Shchukina Vladimir S. Shchukin In this study, we assess the diamond exploration potential of the northern East European Platform based on aeromagnetic survey results and the morphologic and geochemical analysis of 1513 grains of kimberlite indicator minerals (KIMs), such as purple pyrope garnet, olivine, and Cr-diopside. These minerals were recovered from samples collected from modern river and stream sediments in four areas located in the north-eastern (within the Arkhangelsk Diamondiferous Province) and south-western (hundreds of kilometers outside of the Arkhangelsk Diamondiferous Province) parts of the Arkhangelsk region in the European part of Russia. All the studied areas are located within ancient cratons, including the Kola, Karelian, and Shenkursk cratons. Based on the major element compositions of the KIMs and thermobarometric calculations, this study confirms that the lithospheric mantle beneath the studied areas is suitable for the formation and preservation of diamonds. The high percentage of KIMs with primary magmatic grain surface morphologies is evidence of the presence of local kimberlite sources within all of the studied areas. The significant amount of diamond-associated KIMs indicates that the potential sources are diamondiferous. Hence, the results suggest that the studied areas can be recommended for further diamond prospecting activity with a high probability of discovering new diamondiferous kimberlites.

Description: Minerals, Vol. 8, Pages 194: Trace Element and U–Pb Core Age for Zircons from Western Meiganga Gold Placer, Cameroon: Their Genesis and Archean-Proterozoic Sources Minerals doi: 10.3390/min8050194 Authors: Nguo Sylvestre Kanouo Gabriel Ngueutchoua Arnaud Patrice Kouske Rose Fouateu Yongue Akella Satya Venkatesh Trace element concentrations and U–Pb ages were obtained using Laser Ablation Split Stream Method from the core of 115 zircon grains from the western Meiganga gold placer deposit. The data was used to characterize zircon, to understand the history of crystallization and to locate source rocks within the local and regional geological settings. Zircon trace element geochemistry was used to distinguish between magmatic and metamorphic affinity. The magmatic zircons have characteristics compatible with their probable origin from granitoid, syenite, tonalite, charnockite and mafic to ultramafic rocks. The metamorphic zircons composition is compatible with growth from anatectic melts and by sub-solidus crystallization in equilibrium with garnet. The zircon ages reveal Archean, Paleoproterozoic, Mesoproterozic, and Neoproterozoic events with the principal source could mainly belong to Paleoproterozoic magmatic lineage. Some of the Paleoproterozoic magmatic zircons were probably sourced from two mica granite found within the local geology, whereas the remaining zircons have features indicating source rocks within the Congo Craton. We suggest that the geologic history of these zircons is related to crustal-scale magmatic and/or tectono-metamorphic events, possibly linked to Eburnean and Pan-African orogeny.

Description: Minerals, Vol. 8, Pages 215: Bioleaching of Arsenic-Bearing Copper Ores Minerals doi: 10.3390/min8050215 Authors: José Díaz Jennyfer Serrano Eduardo Leiva World copper (Cu) production has been strongly affected by arsenic (As) content, because As-rich Cu concentrates are not desirable in the metal foundries. When As-rich Cu concentrates are processed by smelting they release As as volatile compounds into the atmosphere and inside furnaces, generating serious risks to human health. In recent years, exports of Cu concentrates are being penalized for the increasingly high As content of the ores, causing economies that depend on the Cu market to be seriously harmed by this impurity. In the last few decades, biohydrometallurgy has begun to replace the traditional Cu sulfide processing, however bioleaching processes for As-bearing Cu ores which contain enargite are still in the development stage. Researchers have not yet made successful progress in enargite bioleaching using typical mesophilic and thermophilic bacteria that oxidize sulfide. New approaches based on direct oxidative/reductive dissolution of As from enargite could result in significant contributions to Cu biohydrometallurgy. Thus, As-rich Cu concentrates could be pre-treated by bioleaching, replacing current technologies like roasting, pressure leaching and alkaline leaching by selective biological arsenite oxidation or arsenate reduction. In this article, we review the As problem in Cu mining, conventional technologies, the biohydrometallurgy approach, and As bioleaching as a treatment alternative.

Description: Minerals, Vol. 8, Pages 214: Metasomatic Replacement of Albite in Nature and Experiments Minerals doi: 10.3390/min8050214 Authors: Kirsten Drüppel Richard Wirth Replacement of albite by sodium-rich, secondary phases is a common phenomenon, observed in different geological settings and commonly attributed to alkaline metasomatism. We investigated growth of nepheline and sodalite on albite in time series experiments between two and 14 days. A total of 42 hydrothermal experiments were performed in cold-seal hydrothermal vessels at a constant pressure of 4 kbar and 200–800 °C in the system SiO2–Al2O3–NaCl–H2O. To allow for fluid flow and material transport, a double-capsule technique was used; hereby, a perforated inner Pt capsule was filled with cleavage fragments of natural albite, whereas the shut outer Au capsule was filled with γ-Al2O3 and the NaCl–H2O solution. Complete overgrowth of albite by sodalite and nepheline occurred after just two days of experiments. At high salinity (≥17 wt % NaCl) sodalite is the stable reaction product over the whole temperature range whereas nepheline occurs at a lower relative bulk salinity than sodalite and is restricted to a high temperature of ≥700 °C. The transformation of albite starts along its grain margins, cracks or twin lamellae. Along the reaction front sodalite crystallizes as small euhedral and highly porous grains forming polycrystalline aggregates. Coarse sodalite dominates in the outermost domains of the reaction zones, suggesting recrystallization. Sodalite may contain fluid inclusions with trapped NaCl-rich brine, demonstrating that the interconnected microporosity provides excellent pathways for fluid-assisted material transport. Highly porous nepheline forms large, euhedral crystals with rectangular outline. Sodalite and nepheline in natural rock samples display only minor porosity but fluid and secondary mineral inclusions, pointing to coarsening of a previously present microporosity. The reaction interface between sodalite and albite in natural rock samples is marked by open channels in transmission electron microscopy. In many of the experiments, a zone of Si–H-rich, amorphous material is developed at the reaction front, which occurs at a temperature of up to of 750 °C as nanometer to 350 µm wide reaction zone around albite. This change in composition corresponds with the abrupt termination of the crystalline feldspar structure. The presence of sodalite as micro- to nanometer-sized, euhedral crystals within the amorphous zone demonstrates, that both the sodalite reaction rim and the amorphous material allow for fluid-assisted material transport between the crystalline albite (release of Si, Al) and the bulk fluid (H2O, Na, Cl). This texture, moreover, suggests that the amorphous phase represents a metastable interstage reaction product, which is progressively replaced by sodalite and nepheline. Remarkably, product sodalite, nepheline, and the amorphous material largely inherit the trace element budget of the respective ancestor albite, indicating that at least part of the trace elements remained fixed during the reaction process. The observed reaction textures in both natural and experimental samples indicate an interfacial dissolution–reprecipitation mechanism. Results of our study bear important implications with respect to mineral replacement in the presence of a fluid phase, especially regarding the interpretation of trace element patterns of the product phases.

Description: Minerals, Vol. 8, Pages 218: Tsygankoite, Mn8Tl8Hg2(Sb21Pb2Tl)Σ24S48, a New Sulfosalt from the Vorontsovskoe Gold Deposit, Northern Urals, Russia Minerals doi: 10.3390/min8050218 Authors: Anatoly Kasatkin Emil Makovicky Jakub Plášil Radek Škoda Atali Agakhanov Vladimir Karpenko Fabrizio Nestola Tsygankoite, ideally Mn8Tl8Hg2(Sb21Pb2Tl)Σ24S48, is a new sulfosalt discovered at the Vorontsovskoe gold deposit, Northern Urals, Russia. It occurs as lath-like elongated crystals up to 0.2 mm embedded in calcite–dolomite–clinochlore matrix. The associated minerals also include aktashite, alabandite, arsenopyrite, barite, cinnabar, fluorapatite, orpiment, pyrite, realgar, routhierite, sphalerite, tilasite, and titanite. The new mineral is non-fluorescent, black, and opaque with a metallic lustre and black streak. It is brittle with an uneven fracture and no obvious parting and cleavage. Its Vickers hardness (VHN10) is 144 kg/mm2 (range 131–167 kg/mm2) and its calculated density is 5.450 g cm. In reflected light, tsygankoite is white; between crossed polars it is dark grey to black. It is strongly anisotropic: rotation tints vary from light grey to dark grey to black. Pleochroism and internal reflections are not observed. The chemical composition of tsygankoite (wt %, electron-microprobe data) is: Mn 6.29, Hg 5.42, Tl 26.05, Pb 5.84, As 3.39, Sb 30.89, S 21.87, total 99.75. The empirical formula, calculated on the basis of 90 atoms pfu, is: Mn8.06Tl8.00Hg1.90(Sb17.87As3.19Pb1.99Tl0.97)Σ24.02S48.03. Tsygankoite is monoclinic, space group C2/m, a = 21.362(4) Å, b = 3.8579(10) Å, c = 27.135(4) Å, β = 106.944(14)°, V = 2139.19(17) Å3 and Z = 1. The five strongest diffraction peaks from X-ray powder pattern (listed as (d,Å(I)(hkl)) are: 3.587(100)(112), 3.353(70)(−114), 3.204(88)(405), 2.841(72)(−513), and 2.786(99)(−514). The crystal structure of tsygankoite was refined from single-crystal X-ray diffraction data to R = 0.0607 and consists of an alternation of two thick layer-like arrays, one based on PbS-archetype and the second on SnS-archetype. Tsygankoite has been approved by the IMA-CNMNC under the number 2017-088. It is named for Mikhail V. Tsyganko, a mineral collector from Severouralsk, Northern Urals, Russia, who collected the samples where the new mineral was discovered.

Description: Minerals, Vol. 8, Pages 220: Automatic Parameter Tuning of Multiple-Point Statistical Simulations for Lateritic Bauxite Deposits Minerals doi: 10.3390/min8050220 Authors: Yasin Dagasan Philippe Renard Julien Straubhaar Oktay Erten Erkan Topal The application of multiple-point statistics (MPS) in the mining industry is not yet widespread and there are very few applications so far. In this paper, we focus on the problem of algorithmic input parameter selection, which is required to perform MPS simulations. The usual approach for selecting the parameters is to conduct a manual sensitivity analysis by testing a set of parameters and evaluating the resulting simulation qualities. However, carrying out such a sensitivity analysis may require significant time and effort. The purpose of this paper is to propose a novel approach to automate the parameter tuning process. The primary criterion used to select the parameters is the reproduction of the conditioning data patterns in the simulated image. The parameters of the MPS algorithm are obtained by iteratively optimising an objective function with simulated annealing. The objective function quantifies the dissimilarity between the pattern statistics of the conditioning data and the simulation image in two steps: the pattern statistics are first obtained using a smooth histogram method; then, the difference between the histograms is evaluated by computing the Jensen–Shanon divergence. The proposed approach is applied for the simulation of the geological interface (footwall contact) within a laterite-type bauxite mine deposit using the Direct Sampling MPS algorithm. The results point out two main advantages: (1) a faster parameter tuning process and (2) more objective determination of the parameters.

Description: Minerals, Vol. 8, Pages 219: Preparation of Mullite-Silica Composites Using Silica-Rich Monophasic Precursor Obtained as a Byproduct of Mineral Carbonation of Blast-Furnace Slag Minerals doi: 10.3390/min8050219 Authors: Kyungsun Song Wonbaek Kim Chang-Yul Suh Jun-Hwan Bang Ji-Whan Ahn Previously, mineral carbonation of blast-furnace slag was carried out to sequestrate CO2 and attain pure CaCO3 crystals. In this process, amorphous silica-alumina nanoparticles were obtained as a byproduct. In this study, the crystallization of these nanoparticles on calcination at various temperatures in air was examined using TGA-DTA, XRD, MAS-NMR spectroscopy, and FT-IR spectroscopy. The precursor nanoparticles (Si:Al = 78:22 mol %) were prepared using the solution extracted from blast-furnace slag (BFS) with acetic acid at room temperature. The XRD analysis showed that the initial amorphous state was retained up to 800 °C, and decomposition to amorphous silica and mullite started after calcination at 950 °C. At temperatures between 1150 °C and 1250 °C, amorphous silica crystalized to cristobalite, which eventually melted to glassy silica at 1500 °C. The mullite crystals initially adopted a metastable tetragonal phase and transformed to a stable, needle-like orthorhombic phase at higher temperatures. 27Al MAS-NMR spectroscopy revealed that octahedrally coordinated Al was favored up to a temperature of 800 °C as a result of the dehydration process and transformed into tetrahedrally coordinated Al at higher temperatures. A microstructural examination revealed that the initially randomly-oriented mullite developed into stable, needle-like grains owing to anisotropic grain growth in the presence of a glass phase at high temperatures. This study suggests that the recycling of BFS can be exploited for the procurement of a mullite-type ceramic material.

Description: Minerals, Vol. 8, Pages 231: Microcrack Evolution and Associated Deformation and Strength Properties of Sandstone Samples Subjected to Various Strain Rates Minerals doi: 10.3390/min8060231 Authors: Chong-Feng Chen Tao Xu Shao-Hua Li The evolution of micro-cracks in rocks under different strain rates is of great importance for a better understanding of the mechanical properties of rocks under complex stress states. In the present study, a series of tests were carried out under various strain rates, ranging from creep tests to intermediate strain rate tests, so as to observe the evolution of micro-cracks in rock and to investigate the influence of the strain rate on the deformation and strength properties of rocks. Thin sections from rock samples at pre- and post-failure were compared and analyzed at the microscale using an optical microscope. The results demonstrate that the main crack propagation in the rock is intergranular at a creep strain rate and transgranular at a higher strain rate. However, intergranular cracks appear mainly around the quartz and most of the punctured grains are quartz. Furthermore, the intergranular and transgranular cracks exhibit large differences in the different loading directions. In addition, uniaxial compressive tests were conducted on the unbroken rock samples in the creep tests. A comparison of the stress–strain curves of the creep tests and the intermediate strain rate tests indicate that Young’s modulus and the peak strength increase with the strain rate. In addition, more deformation energy is released by the generation of the transgranular cracks than the generation of the intergranular cracks. This study illustrates that the conspicuous crack evolution under different strain rates helps to understand the crack development on a microscale, and explains the relationship between the micro- and macro-behaviors of rock before the collapse under different strain rates.

Description: Minerals, Vol. 8, Pages 233: Geophysical Investigation of the Pb–Zn Deposit of Lontzen–Poppelsberg, Belgium Minerals doi: 10.3390/min8060233 Authors: Maxime Evrard Gaël Dumont Thomas Hermans Michel Chouteau Olivier Francis Eric Pirard Frédéric Nguyen The drillhole information from the Lontzen–Poppelsberg site has demonstrated three orebodies and has allowed the estimation of the extension of the lodes, their dip, and the location at the ground surface. The localisation of the lodes makes them excellent targets for further exploration with geophysics. This deposit is classified as a Mississippi Valley Type (MVT) deposit. It consists mainly of Pb–Zn–Fe sulphides that display contrasting values in resistivity, chargeability, density, and magnetic susceptibility, with regards to the sedimentary host rocks. The dipole–dipole direct current (DC) resistivity and induce polarization (IP) profiles have been collected and inverted to successfully delineate the Pb–Zn mineralization and the geological structures. Short-spacing EM34 electromagnetic conductivity data were collected mainly on the top of Poppelsberg East lode and have revealed a conductive body matching with the geologically modelled mineralization. Gravity profiles have been carried out perpendicularly to the lode orientation; they show a strong structural anomaly. High resolution ground magnetic data were collected over the study area, but they showed no anomaly over the ore deposits. The geophysical inversion results are complementary to the model based on drill information, and allow us to refine the delineation of the mineralization. The identification of the geophysical signatures of this deposit permits targeting new possible mineralization in the area.

Description: Minerals, Vol. 8, Pages 232: Integrating the Theory of Sampling into Underground Mine Grade Control Strategies Minerals doi: 10.3390/min8060232 Authors: Simon C. Dominy Hylke J. Glass Louisa O’Connor Chloe K. Lam Saranchimeg Purevgerel Richard C.A. Minnitt Grade control in underground mines aims to deliver quality tonnes to the process plant via the accurate definition of ore and waste. It comprises a decision-making process including data collection and interpretation; local estimation; development and mining supervision; ore and waste destination tracking; and stockpile management. The foundation of any grade control programme is that of high-quality samples collected in a geological context. The requirement for quality samples has long been recognised, where they should be representative and fit-for-purpose. Once a sampling error is introduced, it propagates through all subsequent processes contributing to data uncertainty, which leads to poor decisions and financial loss. Proper application of the Theory of Sampling reduces errors during sample collection, preparation, and assaying. To achieve quality, sampling techniques must minimise delimitation, extraction, and preparation errors. Underground sampling methods include linear (chip and channel), grab (broken rock), and drill-based samples. Grade control staff should be well-trained and motivated, and operating staff should understand the critical need for grade control. Sampling must always be undertaken with a strong focus on safety and alternatives sought if the risk to humans is high. A quality control/quality assurance programme must be implemented, particularly when samples contribute to a reserve estimate. This paper assesses grade control sampling with emphasis on underground gold operations and presents recommendations for optimal practice through the application of the Theory of Sampling.