ALBERT

Description: There is increasing acceptance of the presence of variable magmatic contributions to the mineralizing fluids in the formation of volcanogenic massive sulfide (VMS) deposits. The world-class Windy Craggy Cu-Co-Au deposit (〉300 MT @ 2.12 wt.% Cu) in northwestern British Columbia is of interest because, unlike most VMS deposits, quarts fluid inclusions from within the deposit range from relatively low to intermediate salinity (most 6-16 wt.% equivalent). In this study we used an excimer (193 nm) laser ablation system interfaced to a quadrupole inductively coupled plasma mass spectrometer to quantify key metals and metalloids that are considered by many to be indicative of magmatic contributions to hydrothermal ore deposits. Although LA-ICP-MS signals from these low-salinity inclusions are highly transient, we were able to quantify Na, Mg, K, Ca, Mn, Fe, Co, Cu, Zn, Sr, Sn, Ba, Ce, Pb and Bi consistently – of the 34 elements that were monitored. Furthermore, Cl, Sb, Cd, Mo, Rb, Br, and As were also measured in a significant number of inclusions. Comparison of the fluid inclusion chemistry with unaltered and altered mafic volcanic and sedimentary rocks and mineralized samples from the deposit indicate that enrichment in the main ore metals (Cu, Zn, Fe, Pb) in the inclusions reflects that of the altered rocks and sulfides. Metals and metalloids that may indicate a magmatic contribution typically show much greater enrichments in the fluid inclusions much greater over the host rocks at the same Cu concentration; in particular Bi, Sn and Sb are significantly elevated when compared to the host rock samples. These data are consistent with the ore-forming fluids at Windy Craggy having a strong magmatic contribution.

Description: The accurate characterization of mafic and ultramafic rocks is a challenging but necessary task given the spatial and genetic relationship of mineralization with specific lithologies (e.g. komatiite hosted nickel-sulfides preferentially associated with cumulate-rich ultramafic rocks). Rock classification is further complicated as most mafic and ultramafic rocks have undergone varying degrees of alteration. The accuracy and reproducibility of characterization can be significantly improved by using portable energy dispersive X-ray Fluorescence (pXRF) chemical data with portable Visible and Near-Infrared (pVis-NIR) mineralogical data.A new workflow using pXRF and pVis-NIR is presented and used to reliably characterize mafic and ultramafic rocks from the Yilgarn Craton, Western Australia. The workflow involves 6 steps: Mitigate and identify compound processing and closure issues. For example, we used a pXRF with helium flush to reliably and rapidly measure light elements and mitigate closure, i.e. problems related to data failing to sum to 100%.Identify and exclude geochemically heterogeneous samples. Heterogeneity may be unrelated to alteration and caused by veining or small-scale structure interleaving of different rock types. Geochemical heterogeneity was evaluated using skewness and kurtosis of SiO2 data.Relate rocks from similar magmatic, weathering and alteration events. This was achieved by interpreting data grouping of Vis-NIR ferric and ferrous iron data via a 852 nm/982 nm reflectance v. 651 nm/982 nm reflectance plot and the Ferrous Abundance Index. Unrepresentative data were omitted.Correct XRF iron data, and characterize lithology and alteration. Values ascribed to regions in the TAS (Total Alkali Silica) diagram were used to approximate FeO and Fe2O3. Subsequently, geochemical indices (e.g. Mg#) were used to characterize the alteration box plot.Characterize fractionation in detail. Fractionation variation diagrams were used to interpret fractionation, e.g. MgO v. Al2O3, Ca/Al v. Al2O3, Ni/Cr v. Ni/Ti, and MgO v. Cr.Identify and quantify talc alteration and serpentinization. This included the use of a new alteration plot (Mg# v. 1410 nmRAD/Albedo) to estimate serpentinization and identify relationships between serpentine, carbonate, chlorite and talc abundances. The results and observations contained in this contribution have important implications for progressive technologies such as core logging platforms that are equipped with pXRF and pVis-NIR instruments.

Description: The Rock Canyon Creek carbonate-hosted REE-F-Ba deposit has tectonic, stratigraphic, and structural similarities with Mississippi Valley-type and sparry magnesite deposits in the southeast Rocky Mountains. The main REE-fluorite zone is a steeply dipping body, extending 1100 m along strike, 50 m wide, and 100 m deep. It spatially coincides with pre-existing crackle breccias in carbonate rocks, and consists of dolomite, fluorite, barite, pyrite, quartz, K-feldspar, calcite, porous apatite, REE-fluorocarbonates, and REE-phosphates. The main fluorocarbonates are bastnaesite, parisite, and synchysite. Monazite, crandallite group minerals, and apatite are the main phosphates. Fluorite content varies from less than 1 to 13.5% (by weight) and ∑REE+Y concentrations vary from trace to 1.95% (by weight). The mineralized zone is heterogeneous on the deposit scale, as indicated by three-dimensional geochemical modeling combined with a geochemical assessment based on 89 mineralized samples and detailed downhole mineral and geochemical profiles of a key borehole. Chemical heterogeneity and key elemental co-variations are explained by strong mineralogical control and have implications for the design of exploration and development programs for this type of deposit. The chondrite-normalized REE pattern of samples from the mineralized zone shows enrichment in LREE, similar to typical carbonatite-related mineralization; however, no carbonatite is exposed nearby.

Description: The geochemistry of rare earth elements (REEs) was studied in rock samples from host formations, ore samples from two mineral deposits (the Hetaoping Cu-Pb-Zn mine: HTP and the Heiyanao Fe-Cu-Pb-Zn mine: HYA) and the overlying or nearby soils to better understand REE concentrations, distributions and behaviour during weathering from different parent materials at the regional scale, Baoshan area, Yunnan Province, Southwest China. The mudstone and sandstone formations have highest total REE (ΣREE) contents. Chondrite-normalized diagrams for rocks and ores show significant light REEs (LREEs) enrichments and Eu depletion (except for ores in HYA). Cerium displays an obvious negative anomaly in carbonate rocks (Є-3-R, C-R, D-R, T-1-R, and T-2-R). Soils overlying carbonate rock formations (T-1-S, C-S, and Є-3-S) have the highest ΣREE contents, while soils overlying basalts have the lowest ΣREE contents. Soils show enrichments in LREEs with negative Eu anomalies and slight Ce anomalies in the studied soils. Soils with high ∑LREE/∑heavy REE (HREE) values may result from the preferential absorption of LREEs by organic matter. Negative Eu anomalies in soils occur for parent materials in the study area lacking feldspar, especially soils developed from carbonates. Compared to the parent materials, most soils show REE enrichment because alkali metals are removed and REEs are concentrated by low mobility in surficial processes and positive Ce anomalies because of weathering dissolution of other trivalent REEs with ionic radii similar to that of Ca2+.Supplementary material:https://doi.org/10.6084/m9.figshare.c.5303140

Description: The paper presents results of investigations of the chemical composition of iron sulphides contained in dust from the pyrometallurgical production process of zinc and lead. The main mineral components of these dusts are sphalerite, galena, iron sulphide – pyrite, zincite, anglesite and probably kirchsteinite. The tests performed have demonstrated that the chemical composition of iron sulphide grains was not close to stoichiometric, the grains were non-uniform in terms of phase composition, and they always included admixtures in the form of inclusions of other sulphides, i.e. zinc sulphide and lead sulphide, and accompanying elements (Ca, Mn, Se, As, Ag, Cu, Cd).

Description: This paper describes the discovery of porphyry Cu-Au ore bodies (No. 2 and No. 3) in Xiongcun, Tibet, China, through the investigation of stream sediments, soils and rocks. The study area (Xiongcun), located in the city of Xigaze, has a complex topography due to its complicated geological background. The Xiongcun No. 1 ore body will soon be mined, and it has been 15 years since its discovery. However, recent research on stream sediments, soils and rocks around the No. 1 ore body has revealed notable Cu anomalies on the periphery. With the successful application of exploratory geochemistry data in the anomaly locations, the No. 2 and No. 3 ore bodies have been revealed. The ore reserves of the No. 2 and No. 3 ore bodies are estimated to reach 1.64 million tons of Cu, more than 80 tons of Au and 200 tons of Ag. We expect that our findings will not only enhance the understanding of the reanalysis of anomalies surrounding the discovered deposits but also contribute to the evaluation of the ore-prospecting potential of this plateau region.

Description: The present study was conducted to determine different geochemical anomalies of rare earth elements (REEs) using a combined approach of stepwise factor analysis (SFA), sequential Gaussian simulation (SGS) ,and concentration-area (C-A) fractal modeling based on surface lithogeochemical samples obtained from the Esfordi phosphate mine (Central Iran). The Esfordi mine is one of the important mines in Bafq metallogenic zone due to average and maximum grade of 0.5 and 1.7%, respectively for REEs. According to SFA operation in two steps, the REEs were placed in the first factor of the second stage (F1-2). Then, the SGS method and C-A fractal modeling were performed on F1-2 factor scores for classification of anomalies. Log-ratio matrix was used to evaluate the correlation of these results with anomalous lithogeochemical samples, as well as to determine the relationship of anomalies with rock types and mineralized units and finally, to validate the results of SGS-fractal modeling. The results confirmed an appropriate correlation between F1-2 anomalies and high-concentration in further rock samples. The main anomalies were found to have good correlation with apatite-iron unit and in general with other apatite-bearing units based on overall accuracy values. The apatite-bearing units with high values of REEs were located in northern and central parts of the mine. The results of combined approach of SFA, SGS, and C-A fractal modeling showed that this hybrid approach can be useful in determining anomalies with proper accuracy.

Description: Characterization of metamorphic rocks to evaluate waste material acid rock drainage potential is particularly challenging as commonly used laboratory methods can result in significant under-prediction of ARD potential. Static tests were conducted for over 300 samples from the Touro copper project and indicate that carbon-based methods frequently overestimate acid neutralization potential due to the presence of both graphite and manganese-iron carbonates. The Modified Sobek method more accurately accounts for the buffering capacity of carbonates and does not account for graphite, although aluminosilicate dissolution kinetics need to be evaluated in the context of sulfide oxidation rates. Historic sulfur assays for the project relied on methods insufficient to fully digest metamorphosed sulfides and required correction. The more aggressive Leco sulfur method provides accurate sulfur estimates and has been adopted for the project going forward.Static test metrics such as the Net Neutralization Potential or Neutralization Potential Ratio, therefore, can give misleading results when incorrect characterization methods are employed. Such metrics should be considered as screening level, used with caution, and complemented with careful field and laboratory kinetic tests. Preliminary humidity cell testing of five Touro samples suggests that terminal pH values for cells that have become acidic closely match predicted NAG pH values. The NAG pH test avoids some of the challenges associated with sulfur and carbon predictions in metamorphic rocks as it directly buffers sulfide oxidation acidity with available material neutralization potential. As such, NAG pH has been adopted as the accepted project metric for segregating acid-generating from non-acid-generating waste.Thematic collection: This article is part of the Hydrochemistry related to exploration and environmental issues collection available at: https://www.lyellcollection.org/cc/hydrochemistry-related-to-exploration-and-environmental-issuesSupplementary material:https://doi.org/10.6084/m9.figshare.c.5389948

Description: In recent years, an increase in the input of lanthanides (Ln), an important group of heavy metals (HMs), has been observed in the environment throughout the world (in particular soil). Anthropogenic Ln sources are mainly connected to phosphogypsum, Ln-bearing microfertilizer and micronutrients, and mine waste. Therefore, assessment of the hazards associated with the presence of Ln in the soil is an urgent issue. Hazardousness, depending strongly upon the buffer capacity of a specified soil, is determined by the organic matter content, the pH value and other soil properties. For a standard soil (containing 10% organic matter and 25% clay), the discrepancy of the hazardousness of HMs can be estimated based on the maximum permissible concentration (MPC) values proposed by ecologists in the Netherlands. Low levels of Ln contamination in the soil are found, making it possible to classify them in the group of moderately and weakly acting pollutants. The MPC value proposed for cerium (Ce) in the standard soil is 44 mg kg−1. Approximate MPC values for several other lanthanides (Ln, Pr, Nd, Sm, Gd and Dy) in soils were proposed based on MPC values for freshwater sediments in the Netherlands. According to the MPC value, Ln falls into the group of moderate- and low-hazardous heavy metals.

Description: In the Zeida abandoned mine, pit lake waters exhibit alkaline pH and high conductivity. The concentrations of the total dissolved lead and zinc are very low due to their adsorption on clay minerals and iron oxyhydroxides. Conversely, arsenic concentrations in two lakes (ZL1 and ZA) exceed WHO water quality guidelines. The As content is relatively high in ZL1 and exists mainly as As(V). In ZA, As(III) occurs in low concentration compared to the total dissolved arsenic, while dimethylarsenic acid (H2AsO2(CH3)2, DMA) prevails. This means that arsenic was methylated by organic matter produced by micro-organisms such as chlorella. The sequential extraction of floor sediments in the two lakes shows that the bioavailable arsenic contents change between them. In ZA, the sediments show high concentrations of lead and arsenic compared to the ZL1 sediment since it is surrounded by mining waste tailings, which are rich in these elements. An arsenic leaching test of ZA sediment shows that bioavailable arsenic is distributed in equal proportion between clay/carbonates, sulfide-organic matter and iron oxide phases, while in ZL1, most of the arsenic is linked to hydrous iron oxides.Supplementary material: Information on quality control/quality insurance for the used analytical techniques, and additional figures 9–13 are available at https://doi.org/10.6084/m9.figshare.c.5545316Thematic collection: This article is part of the Hydrochemistry related to exploration and environmental issues collection available at: https://www.lyellcollection.org/cc/hydrochemistry-related-to-exploration-and-environmental-issues

Description: Mobile radiogenic lead isotopes (206Pb, 207Pb, 208Pb and 210Pb) represent products of radioactive decay of their parental uranium and thorium isotopes (238U, 235U, 232Th), and are considered potential geochemical pathfinders of buried sandstone-type uranium deposits. Soil samples collected along a geochemical traverse intersecting buried uranium roll front mineralization at the REB deposit in the Great Divide Basin, Wyoming, USA were studied. Mineralization of this deposit is hosted in weakly lithified arkosic sands, at a depth of 120–200 m, without a strong surficial expression of its presence at depth, which makes discovery of this deposit type difficult, slow and expensive. All soil samples have been analysed for ratios of the mobile long-lived Pb isotopes and their parental U and Th isotopes, determined from partial leach products obtained using a weak acid leaching technique. The samples were also analysed for trace elements, assayed both in the partial leach products and using conventional whole-soil sample assays. Ratios of the mobile radiogenic Pb isotopes to their parental U and Th isotopes (206Pb/238U, 207Pb/235U and 208Pb/232Th) determined in the partial leach products exhibit anomalous contents in the soil samples collected above the uranium rolls. The anomalous values are several times greater than background values, to lateral distances of 350–400 m outside of the roll fronts. Notably, conventional whole-soil assays have failed to detect the anomalies that were detected using mobile Pb isotopes.Supplementary material: Minor and trace elements assays of the geochemical samples are available at https://doi.org/10.6084/m9.figshare.c.5610980

Description: This study determines the properties of hot spring waters and associated rocks, calculates reservoir temperatures and depths in the Mongolian Altai region, and constructs a conceptual model for geothermal water based on these results. The hot springs consist of HCO3–Na, SO4–Na, and HCO3–SO4–Na mixed waters. They exhibit alkaline pH levels and temperatures in the range 21.3–35°C. X-ray diffraction analyses of outcrop rocks reveal silicate and carbonate-type minerals such as quartz, albite, orthoclase, dolomite, mica and actinolite, while correlation analysis indicates that the chemical composition of the hot spring water is directly related to rock mineral composition, where dissolution of albite, orthoclase and dolomite minerals has played an important role. Reservoir water circulation depths are 2615–3410 m according to quartz and chalcedony geothermometry. The results indicate that the spring water in the Mongolian Altai region comprises a low mineral content with alkaline pH levels and that the reservoir temperature can reach up to 106°C. We also propose a conceptual model for geothermal water in the Chikhertei hot spring. The geothermal water in the Mongolian Altai region has the potential for use in heating systems.Thematic collection: This article is part of the Hydrochemistry related to exploration and environmental issues collection available at: https://www.lyellcollection.org/cc/hydrochemistry-related-to-exploration-and-environmental-issues

Description: Uranium (U) ion contamination in aquatic systems has received considerable attention worldwide. In this paper, an adsorption material was synthesized with a Fe/Ca-based phosphate (CFB-PM) by a sol–gel method. The effect of pH, reaction time and initial concentration of U ions on its capacity to remove U ions from aqueous solution was investigated via static batch experiments. Comparative studies of U ion removal by CFB-PM with four sorbents, namely: nano zero-valent iron (nZVI), hydroxyapatite (HAP), hydroxyapatite-loaded nano zero-valent iron (HAP@nZVI) and high basicity steel slag-loaded hydroxyapatite (HBSS@HAP), were performed. Results showed that U ion adsorption capacity of CFB-PM was better than that of all four. The adsorption capacity showed a decreasing order as: CFB-PM (643.34 mg g–1) 〉 HAP (549.86  mg g–1) 〉 HBSS@HAP (321.82  mg g–1) 〉 HAP@nZVI (153.62  mg g–1) 〉 nZVI (102.65  mg g–1). Scanning electron microscopy energy-dispersive spectrometry examination suggested that the adsorbed U ions were mainly in the form of spheres, sheets or petals on the surfaces of CFB-PM. X-ray diffraction revealed several U-bearing mineral phases (i.e. Ca(UO2)2(PO4)2·3H2O, HPUO6·4H2O and (UO2)3PO4·4H2O). The U ion adsorption behaviours were further explored by Fourier transform IR spectroscopy. The U ion adsorption process of CFB-PM could be well described by a quasi-second-order adsorption kinetics model and the Langmuir adsorption isotherm model. The separation coefficient (RL) was close to zero, indicating that U ion adsorption was dominated by single-layer chemisorption. The findings reported in this study have implications for applying the synthesized material for remediation of U ion-contaminated groundwater.

Description: Rare-earth elements (REEs) in soils are influenced by pedogenic processes and anthropogenic activities. To interpret the fractionation and migration of REEs during weathering in (sub-)tropical regions, the distribution, fractionation patterns and environmental effects of REEs in laterites were investigated in this study. Soil samples from two laterite profiles (labelled S1 and S2) were collected and the concentrations of REEs were measured with an inductively coupled plasma mass spectrometer. The results suggest that the ΣREEs of S2 (119 ± 10 mg kg–1 to 209 ± 10  mg kg–1) have a higher concentration and a wider variation than those of S1 (114 ± 5  mg kg–1 to 154 ± 8  mg kg–1). The REEs in both laterite profiles are enriched in the order HREEs 〉 LREEs 〉 MREEs. The distribution patterns of laterite profiles show evidence of inheritance from parent granites. The laterites preferentially incorporated HREEs, and secondary Fe2O3 and clay minerals were likely to affect the fractionation of REEs in laterites. The enrichment factor of REEs varied from 11.1 to 18.9 for S1 and 10.0 to 27.6 for S1, indicating potential pollution by REEs. The accumulation of REEs in laterites by mining activity should be a concern of government environmental agencies. Supplementary material: Table S1, Reference values of REEs and Fe2O3 in standard materials (GSS-18 and GSS-20); Table S2, Measurement parameters of ICP-MS; Table S3, Concentrations of REEs and Fe2O3 in laterite profiles from Yunnan province, SW China; Table S4, The enrichment factor for the laterite profiles from Yunnan province, SW China are available at https://doi.org/10.6084/m9.figshare.c.5609234

Description: The Cripple Creek alkaline igneous rock-related low-sulfidation epithermal gold telluride deposit, Colorado, is hosted in the 10 km wide Oligocene alkaline volcanic Cripple Creek diatreme in Proterozoic rocks. Gold occurs as native Au, Au-tellurides, and in the structure of arsenian pyrite, in potassically altered high-grade veins, and as disseminations in the host rocks.Correlation coefficients, principal component analysis, hierarchical cluster analysis, and random forests were used to analyze major and trace element compositions of 995 rock samples primarily from low-grade gold mineralization in drill core from three currently operating pits (Wild Horse Extension (WHEX), Globe Hill, and Schist Island) in the northwestern part of the Cripple Creek diatreme. These methods suggest that Ag, As, Bi, Te, and W are the best pathfinders to Au mineralization in low-grade disseminated ore. Although Mo correlates with gold in other studies and is spatially related to gold veins, molybdenite post-dated the formation of gold and is likely related to a late-stage porphyry overprint. These elements, in conjunction with mineralogical studies, indicate that tellurides, fluorite, quartz, carbonates, roscoelite, tennantite-tetrahedrite, pyrite, sphalerite, muscovite, monazite, bastnäsite, and hübnerite serve as exploration guides to ore.

Description: Paleogene sediments, especially the third member of the Dongying Formation (Ed3) and the first and third members of the Shahejie Formation (Es1 and Es3), have been regarded as the most important source rocks in the Nanpu Sag. Organic and inorganic analyses, including Rock-Eval pyrolysis, gas chromatography-mass spectrometry, and element geochemistry, in 91 mudstone samples were used to reconstruct the paleoenvironmental conditions, such as paleoclimate, paleo-salinity, and paleo-redox condition, and to recognize the origin of organic matter. The results show that Es3 has a higher TOC content than Es1 and Ed3. Hydrocarbon genetic potential (S1+S2) of the samples indicate fair to good hydrocarbon potential. The kerogen type of Ed3 and Es1 source rocks are Type II1-II2, while Es3 source rocks are dominated by Type II2-III kerogens. Biomarkers and inorganic geochemical indicatives of source rocks, such as Pr/Ph, V/(V+Ni) and Cu/Zn, indicate a lacustrine environment with fresh to brackish water under suboxic to anoxic conditions during deposition. Ed3 source rocks are characterized by low G/C30H (Gamacerane/C30Hopane) (0.1), TT/C30H and S/H, low Pr/Ph and C24TeT/C23TT, typical of a mixed input of algae and terrestrial higher plants, with algalic dominance. Ed3, Es1, and Es3 source rocks were mostly deposited in semi-arid to humid-warm climate conditions, with an average temperature higher than 15℃. This study suggests that suitable temperatures, a fresh to brackish lacustrine environment, and suboxic to anoxic conditions could result in a high organic matter concentration and preservation, thus providing prerequisites for the formation of high-quality source rocks.

Description: In this study we apply multivariate statistical and predictive classification methods to interpret geochemical data from 8545 stream-sediment samples collected in southern British Columbia, Canada. Data for 35 elements were corrected for laboratory bias and adjusted for values reported below the lower limit of detection. Each sample site was attributed with the closest British Columbia MINFILE occurrence within 2.5 km. MINFILE occurrences were grouped into “GroupModels” based on similarities between the British Columbia Geological Survey mineral deposit models and geochemical signatures. These data were used to create a training data set of 474 observations, including 100 samples not attributed with a MINFILE occurrence. The training set was used to generate predictions for the mineral deposit models from which posterior probabilities were estimated for the remaining 8071 samples. The data underwent a centred logratio transformation and then characterization using either principal component analysis (PCA) or t-distributed stochastic neighbour embedding using 9 dimensions (t-SNE) prior to classification by random forests. The posterior probabilities generated from the t-SNE metric provide a slightly higher level of prediction accuracy compared to the posterior probabilities obtained using the PCA metric. The results are comparable to those obtained using a conventional catchment analysis approach and expert-driven model. The approach presented here provides a repeatable, consistent and defensible methodology for the identification of prospective mineralized terrains and mineral systems.

Description: Light element data are required for robust and accurate lithogeochemical interpretations and are important components in the study of hydrothermal alteration and mineralization processes. In this contribution we review the latest available portable energy dispersive X-Ray Fluorescence (pXRF) technologies exclusively in the context of light element analysis, with focus on the acquisition of data for Na, Mg, Al and Si. We discuss pXRF hardware design limitations, quantify variables that attenuate X-ray energies through numerical modelling, including common pXRF configurations, and empirically investigate modern pXRF technologies used to mitigate X-ray attenuation and improve light element analysis.The void between the sample and detector is a key issue regarding the success of pXRF light element analysis. Dry-air (normal conditions), vacuum purge and helium flush systems are evaluated. Modelled data that use a nominal sample-detector void of 10 mm show that using helium in lieu of air improves X-ray transmission effectiveness from ≈2% to ≈99% for Na and ≈10% to ≈100% for Mg. Modelled detector window data show that using a graphene detector window in lieu of a traditional beryllium detector window improves X-ray transmission effectiveness for Na from ≈38% to ≈64% and ≈57% to ≈77% for Mg. Progressive X-ray transmission effectiveness equates to ≈63% Na and ≈76% Mg when using a helium-graphene pXRF configuration v. ≈1% for Na and ≈6% Mg when using a traditional in-air beryllium pXRF arrangement (i.e. without sample or X-ray entrance window media).Empirically determined improvements of the resolved signal are more modest than those of modelled X-ray transmission effectiveness data. Instrument noise, spectral overlaps and random counting errors are unavoidable and inherent with the limitations of modern detector technologies. However, the employment of helium with graphene detector window technology allows very precise data to be obtained at significantly shorter scan times (i.e. 20 s, instead of the traditional 60–180 s, i.e. 3–9 times faster): a scan time of 20 s can achieve a precision of ≈18% @ ≈0.4% Na and ≈8% @ ≈0.3% Mg for elemental interference-free samples. Precision will improve with increasing analyte concentration.

Description: The Patterson Lake corridor is situated along the southwest margin of the Athabasca Basin and contains several basement-hosted uranium deposits and prospects. Drill core investigations during this study have determined that granite, granodiorite, mafic and alkali intrusive basement rocks are entrained in a deep-seated northeast-striking subvertical heterogeneous high-strain zone defined by anastomosing ductile to semi-brittle shears and brittle faults. The earliest phases of ductile deformation (D1/2), linked with Taltson (1.94–1.92 Ga) orogenesis, involved interference between early fold sets (F1/2) and development of an associated ductile transposition foliation (S1/2). During subsequent Snowbird (ca. 1.91–1.90 Ga) tectonism, this composite foliation was re-folded (D3) by northeast-trending buckle-style folds (F3), including a regional fold centered on the Clearwater aeromagnetic high. In continuum with D3, a network of dextral-reverse chloritic-graphitic shears, with C-S geometry, formed initially (D4a) and progressed to more discrete, spaced semi-brittle structures (D4b; ca. 1.900–1.819 Ga). Basin development (D5a;

Description: The Patterson Lake corridor in the Athabasca Basin region of Saskatchewan, Canada hosts a large-scale uranium system with two major deposits already delineated. The corridor developed in crystalline rocks of the southwest Rae Province, which host all of the known uranium endowment. Orthogneisses along with voluminous pegmatites are the hosts of the uranium mineralization. These rocks, however, underwent significant open-system metasomatic – hydrothermal modification. Principal amongst these alterations is early and pervasive quartz flooding of the host rocks that resulted in the development of widespread secondary quartzites and associated rock types. These secondary quartzites and their altered host rocks suffered ductile deformation, typically focussed at silicification fronts. Late carbonatite dykes exploited the associated shear zones. Semi-brittle deformation zones nucleated near the previously developed ductile high-strain zones. Graphite and associated iron-sulphides precipitated in a semi-brittle structural regime. These graphitized zones provided the necessary structural architecture to focus the uranium system, which developed may be hundreds of millions of years younger developing at ∼1.425 Ga.Host rocks of the Patterson Lake corridor prove that metasedimentary rocks are not a requirement for development of giant Proterozoic unconformity uranium deposits. Crustal-scale fault zones with access to the mantle (i.e. carbonatites) should be considered a key parameter in the exploration model for Proterozoic unconformity uranium deposits. Given the similarity of the mineral assemblages in the crystalline basement rocks of the main exploration corridor to eastern Athabasca Basin region, it is likely that a similar, cryptic geological boundary focussed the giant uranium system in that region.Thematic collection: This article is part of the Uranium Fluid Pathways collection available at: https://www.lyellcollection.org/cc/uranium-fluid-pathways

Description: The field-portable X-ray fluorescence (FPXRF) spectrometer has evolved significantly in the last decade and became one of the most innovative tools for field geologists. Portability and ease of use of FPXRF systems have opened up new and unique applications for even novice technicians. Application of FPXRF in precious metals exploration and mining appears to be challenging due to their low concentrations (lower than detection limit by FPXRF) in nature and even in most ore deposits. This case study shows the success of FPXRF in identifying anomalous zones of platinum group elements (PGE) and Au (target elements) using pathfinder elements in the Pilanesberg PGE deposit, Bushveld Complex, South Africa. Sixty-three core samples were analyzed using both FPXRF and laboratory methods. In these samples, Pt 〈 8ppm, Pd

Description: The Tazareh mine in the eastern Alborz coalfield is one of the most important coal-producing areas in Iran and contains medium volatile (19.1–31.5%), low sulfur (0.015–0.491%) and variable ash yield (3–31.5%) bituminous coal. In this research, a total of 21 samples were collected from the Tazareh coal layers, footwall and hanging wall. The concentrations of rare earth elements (REEs) and other elements were determined by inductively coupled-plasma mass spectrometry (ICP-MS) and inductively coupled plasma-optical emission spectrometry (ICP-OES). Additionally, traditional features of coal and host rocks were studied by X-ray diffraction (XRD) and petrographic methods. The concentration coefficient (CC) of Tazareh coal samples show that Sc (CC = 2.71), Be (CC = 2.68) and Ni (CC = 2.30) are slightly enriched, Li, Cr, Pb, Sb, V, Cs, As, Co, Cu, Nb, Y, Rb, Tl, REE, Zr, Zn, Ta and Th (0.5 

Description: We study the contents of elements and group composition in natural organic matter (NOM) that interacts with acid mine drainage (АMD) and high-sulfide tailings at the Ursk site (Southwestern Siberia, Russia). AMD causes biomass changes in NOM, related changes in the composition of fractions, and hydrolysis of hydrolyzable compounds; it increases the water-soluble fraction and maintains depolymerization of humic acids to fulvic acids, but exerts no effect on substances soluble in organics (bitumen) and on poorly hydrolyzable compounds. Accumulation of inorganic elements and precipitation of minerals obscure the true fraction composition of NOM: the superposed mineral component contributes significantly to the water-soluble, humic acid, hydrolyzable, and non-hydrolyzable fractions, and may reach 26.4 % per total of all fractions. Rock-forming and potentially toxic elements partition among NOM fractions and predominate in the water-soluble fraction. The contents of Au and Ag are the highest in the fractions of humic acids and hydrolyzable compounds but are lower in the non-hydrolyzable residue. The obtained data have implications for possible migration of potentially toxic elements and noble metals and thus for remediation of polluted areas. The observed fractionation of Ag and Au in NOM helps understand the mechanisms of their distribution in organic-bearing environments, such as peatlands or coal basins.

Description: 〈span〉〈div〉Abstract〈/div〉Recently, the effectiveness of the use of traditional methods of searching for kimberlite pipes in the Arkhangelsk diamondiferous province (subarctic zone of Russia) has decreased greatly. Thus, new methods of kimberlite exploration need to be developed. This study discusses new patterns of the distribution of natural radioactive isotopes within the Arkhangelsk diamondiferous province (Zolotitskoe kimberlite field), in particular the isotopes of uranium 〈sup〉234〈/sup〉U and 〈sup〉238〈/sup〉U. A variety of isotopic radiogeochemical studies has shown that the kimberlite pipes are characterized by local radioisotope anomalies, on the surface and in exploration drill core. These irregularities are clearly manifested in the formation of non-equilibrium anomalous isotopic composition of uranium in the surrounding rocks and groundwater of the near-contact zone of the pipes. These uranium isotopes can be used to explore for kimberlites in other areas with similar complex landscape-geological and climate conditions of the subarctic zone.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉The 〈10, 〈4, 〈2.5 and 〈1 µm fractions of eight regolith samples have been extracted as aerosols, then analysed for more than 60 elements by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Precision and accuracy rivals that of conventional digestion and ICP-MS analysis for most elements, but the aerosol extraction and ablation approach can be completed within 30 min, avoids compromising the sample by screening, column settling, fusion and/or digestion, and includes data for elements such as Br, Cl, I and Se that are conventionally analysed by individual procedures. Major element chemistry and scanning electron microscope (SEM) imagery show that the aerosol fractions of regolith are dominated by kaolinite, with quartz in aeolian regolith. The aerosol fractions of Si- and Ca-rich regolith have higher trace element concentrations than the coarser fraction (0.45–2 mm), but chalcophile elements are depleted in the aerosols of Fe-rich regolith relative to the coarser fraction. Improvements in in-field analytical technology coupled with aerosol extraction mean that fine and ultrafine fraction chemistry can be used to guide mineral exploration programmes in close to real time.〈strong〉Supplementary material〈/strong〉〈strong〉:〈/strong〉 The results of the laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis of filter papers are available at 〈a href="https://doi.org/10.6084/m9.figshare.c.4562807"〉https://doi.org/10.6084/m9.figshare.c.4562807〈/a〉〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Trace elements in soils might cause contamination and ecological risks to the environment with increasing anthropogenic disturbance. This study investigated the distribution, speciation, risks, and possible sources of 28 target trace elements in soils of the northeastern Qinghai-Tibet Plateau. The average concentrations of trace elements in soils of the study area ranged from 0.25 (Hg) to 697.38 (Cr) mg/kg. The residual fraction was the dominant host of V, Cr, Cu, Sn, Sb, Hg and REEs while Co, Ni, Zn, Mo, Cd and Pb had large proportions in the non-residual fractions. Risk assessment code analysis showed that Cd should be recognized as a priority pollutant in the study area. Correlation analysis indicated that Pb, Cu, Zn, Cd and Sn might originate from the same or similar source. The 〈sup〉206〈/sup〉Pb/〈sup〉207〈/sup〉Pb and 〈sup〉208〈/sup〉Pb/〈sup〉206〈/sup〉Pb ratios of the soils were in the range of 1.166-1.224 and 2.031-2.122, respectively. The anthropogenic Pb contribution proportion was in the range of 0-53.92% for the study area. The anthropogenic Pb contribution was higher in the areas with more intensive anthropogenic activities. Heavy metals and excessive anthropogenic disturbance should be effectively controlled in the northeastern Qinghai-Tibet Plateau to maintain the ecological sustainability and human health of this fragile area.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉There is a pressing need for new exploration tools to target and vector towards mineralization in covered terrains. Groundwater provides a valuable and under-utilized geochemical sampling medium, and represents an important and cost-effective tool to expose covered terrains to systematic exploration. For Au exploration, researchers agree the best hydrogeochemistry pathfinder is dissolved Au itself, with additional potential from other pathfinders (albeit non-unique) such as As, Ag, W and Mo. Despite Au's relatively low solubility, with rigorous field protocols and appropriate analytical methods, explorers can respond to dissolved Au directly with robust parts per trillion (ppt) level analyses.Even with ppt-level analyses, a practical implication of Au's low solubility is that a deposit's dissolved Au signature is generally weaker than seen in other more mobile pathfinders, producing a smaller detectable footprint, which must be considered when designing exploration programs. Using purpose-drilled groundwater sampling bores, explorers can collect groundwater samples at the density required to respond to dissolved Au where existing bore hole coverage is otherwise insufficient. In addition to its use at the regional scale, with even tighter sample density, hydrogeochemistry also shows promise at the project scale, allowing for 3D modelling of pathfinder dispersion.For hydrogeochemistry to be widely adopted for Au exploration, explorers need confidence in ppt-level dissolved Au analyses, and the context to understand their significance. This paper aims to address these topics and provide a straightforward starting point for Au explorers interested in applying hydrogeochemistry by: (i) summarizing examples of regional sampling programs and more focused case studies to illustrate how covered Au deposits create measurable dissolved Au footprints distinguishable from background; and (ii) sharing examples of dissolved Au analyses being integrated into exploration at the regional and project scales.As seen in the results, the distributions of dissolved Au in the regional- and project-scale programs show remarkably similar and easy to interpret high-contrast, low-frequency anomalies against relatively low backgrounds. These are desirable attributes of any geochemical pathfinder. When combined with the benefits of hydrogeochemistry versus other geochemical exploration tools (e.g. groundwater can create larger footprints requiring fewer samples to detect, and groundwater can recharge from depth to reflect deeper mineralization), dissolved Au is a powerful pathfinder ideally suited for Au exploration in covered terrains.While this paper focuses on the use of dissolved Au, additional pathfinders can provide valuable information, including indications of lithological changes, hydrothermal alteration, and different styles of mineralization, as well as opportunities to use secondary pathfinders when sample density or local conditions may not result in detectable dissolved Au signatures.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉The study area is located on the eastern side of the Van Lake near Sugeçer Village, and has anophiolitic complex which contains serpentinised ultramafic rocks that have been hydrothermally altered. Alteration of the serpentinites to listwaenites occurred by silicification and carbonatization and is clearly detected from field observations and petrographical and geochemical analysis. According to mineral compositions listwaenites are grouped as type-I and type-II listwaenites. Type-I listwaenites are dominantly formed by carbonate minerals, rare serpentine, chromite and mariposite minerals type-II listwaenites mainly contain the silicate minerals. Listwaenites are enriched in Au, As, Cu, Ni and Co compared to serpentines. Furthermore, the listwaenites display enrichment in terms of light rare earth elements and depletion for heavy rare earth element content, when normalized to chondrite. The effect of tectonism is widely observed in the study area. Mineral enrichment in the Sugeçer region is associated with mineral transport by hydrothermal fluids under the influence of tectonism.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉The Brazilian Geological Survey (CPRM–Companhia de Pesquisa de Recursos Minerais) has carried out geochemical surveys focused on the region of Carajás, the largest mineral province in Brazil. One of these surveys, covered the area of Canaã dos Carajás where 257 soil samples, including 32 duplicates, were collected from the B horizon within an area of approximately 3,500 km2. The 〈0.177 mm fraction of these samples was sprayed and digested with aqua regia and then analyzed for 53 elements by ICP-AES and ICP-MS. The statistic treatment of the data allowed to elaborate multi-element geochemical maps based on interpolation techniques and establish geochemical background values in soils. Different methods of obtaining geochemical threshold values are presented and compared. The geochemical behavior of 43 elements, including potentially toxic elements, is discussed. Geochemical background values are established using different statistical methods and more relevant results come from the iterative 2σ technique. The influence of geogenic contribution is largely dominant over anthropogenic effects in the studied area. There is no conclusive evidence of contamination related to human activity at the time when the geochemical survey was carried out. This paper provides multi-element geochemical maps and background values in the most prominent Brazilian mining province.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Using Rock Canyon Creek REE-F-Ba deposit as an example, we demonstrate the need for verifying inherited geochemical data. Inherited La, Ce, Nd, and Sm data obtained by pressed pellet XRF, and La and Y data obtained by aqua regia digestion ICP-AES for 300 drill-core samples analysed in 2009 were compared to sample subsets reanalysed using lithium metaborate-tetraborate (LMB) fusion ICP-MS, Na2O2 fusion ICP-MS, and LMB fusion-XRF. We determine that LMB ICP-MS and Na2O2 ICP-MS accurately determined REE concentrations in SY-2 and SY-4, and provided precision within 10%. Fusion-XRF was precise for La and Nd at concentrations exceeding ten times the lower detection limit; however, accuracy was not established because REE concentrations in SY-4 were below the lower detection limit. Analysis of the sample subset revealed substantial discrepancies for Ce concentrations determined by pressed pellet XRF in comparison to other methods due to Ba interference. Samarium, present in lower concentrations than other REE compared, was underestimated by XRF methods relative to ICP-MS methods. This may be due to Sm concentrations approaching the lower detection limits of XRF methods, elemental interference, or inadequate background corrections. Aqua regia dissolution ICP-AES results, reporting for La and Y, are underestimated relative to other methods.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Based on a global compilation of whole-rock geochemical data, Sr/Y and Sr/MnO are identified as effective discriminators between ore-forming and unprospective intrusions in the porphyry Cu setting. Intrusive rocks are classified into three fertility groups: prospective, unprospective, and mixed-signal, which are designed to assist explorers as a discrimination tool, narrowing the exploration search-space in porphyry Cu districts.Portable X-Ray fluorescence (pXRF) data of Sr, Y and MnO were collected on pulp powders and rock slabs from six porphyry Cu (± Mo ± Au) districts. Pre- and post-mineralization intrusions from porphyry Cu districts have lower Sr/Y and Sr/MnO values than syn-mineralization intrusions from the same districts, although absolute values were variable between districts.PXRF data were compared to conventional whole-rock data to determine if pXRF data were appropriate substitutes for conventional whole-rock methods of evaluating the ore-forming potential of intrusive rocks. PXRF data collected on pulp material were found to be more accurate (〈16% of conventional methods) and more precise (〈5% relative standard deviation) than those collected on intact rock slabs (〈37% of conventional methods; 〈24% relative standard deviation). These differences are attributed to the grain size and mineral homogeneity of samples. Despite the low precision of pXRF analyses on individual rock slabs (mean RSD of 24% Sr/Y and 32% Sr/MnO), mean values for each sample plot in the expected fertility field on the Sr/Y and Sr/MnO diagram. Our results demonstrate that 〈span〉in situ〈/span〉 pXRF data collection provides an effective discriminator of Cu fertility, and represents a powerful field exploration tool.〈strong〉Supplementary material:〈/strong〉〈a href="https://doi.org/10.6084/m9.figshare.c.4447769"〉https://doi.org/10.6084/m9.figshare.c.4447769〈/a〉〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉The Longtoushan Au deposit, located in the Qin-Hang Metallogenic Belt, South China, is a breccia-hosted epithermal Au deposit. It is characterized by distinctive occurrence of magmatic-hydrothermal tourmaline-cemented breccias. Tourmaline-group minerals have an extensive range of chemical composition that could reflect their host environments, including some of economic interest. To investigate the potential of tourmaline as a geochemical indicator for ore exploration, B-isotopic and major element compositions of tourmaline from the Longtoushan Au deposit have been determined. Tourmaline mainly occurs as orbicular aggregates, clusters and veinlets in rhyolite porphyries, granite porphyries and in spatially associated hydrothermal breccias (Au-mineralized and Au-barren). Three types of tourmaline (I, II and III) are recognized at Longtoushan, most of which being the alkali-deficient schorl-dravites. The pre-ore Tourmaline I in the rhyolite porphyry is Fe-rich schorl, contrasting with the dravitic ore-stage Tourmaline II in the mineralized breccia and Tourmaline III in the granite porphyry. Locally, Tourmaline II shows concentric zonings which correlate with core-rim chemical variations (higher Fe, Al in the rim than in the core). Tourmalines from Longtoushan are characterized by a dominant MgFe-1 exchange vector and have relatively low Na contents (avg. 0.66 apfu; formula normalized on 15 total cations), indicating they possibly crystallized in reduced fluids of low-salinity. The δ11B values of tourmalines from this study fall in a narrow range of –14.5 to –10.2‰, indicating dominant magmatic-hydrothermal fluids of continent crust origin. The results suggest that tourmaline from Longtoushan may originate from boron-rich vapors fluids unmixed from the felsic magma, which was favorable〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉The need to innovate to advance exploration success is ongoing and, while regional geochemical surveys are common, increasing the data we collect and improving survey results has stagnated. A new adaption of existing methods known as UltraFine+™ extracts the 〈2 µm fraction of soils and sediments, which is then analysed and combined with spectral mineralogy proxies and physicochemical properties to improve targeting for Au and base-metal exploration. We applied the UltraFine+™ workflow to three small orientation site studies in Western Australia, and reprocessed archived regional soil samples from the Geological Survey of Western Australia to test the method. The orientation programme (〈span〉c〈/span〉. 200 samples) involved samples from the Leonora and Sir Samuel 1:250 000 map sheets, an area that hosts known major Au and base-metal deposits. We then applied this approach to the Kingston 1:250 000 map sheet area, analysing a further 300 samples in a region on the Yilgarn Craton margins that is essentially greenfields, as there has been little exploration and the original geochemical survey data were heavily censored due to the abundance of transported regolith dominated by quartz-rich sand. The archived samples were specifically selected soils (sheetwash or sandplain) with a component of Quaternary–Tertiary transported cover. Results at the orientation test sites (Telfer West, Tooting Bec and DeGrussa) were promising. Importantly, the study revealed a marked decrease in censored results for Au (from 63% to 10% below detection limit). Geochemistry and some example indices for mineral exploration and lithology mapping, as well as example maps using the additional spectral mineralogy proxies or particle-size variation, are presented. The application of the 〈2 µm particle-size separation and the UltraFine+™ workflow importantly demonstrate the additional value from (re-)assaying regional soil and sediment samples to generate new targets and improve regional geochemical maps. This is an exercise that can be applied to new greenfields surveys and, when exploration budgets are lean, to archived samples.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Soils are widely used as geochemical sample media. In transported cover, the soils that host the mobile element signature are the smallest size fractions, so we should consider to concentrate the clay size fraction (〈2 µm) as an improved sample medium. Twenty-seven bulk reference soils were collected in the vicinity of known mineral deposits (including background areas) that reflect common soil types of Western Australia. A selection of these soils was used in replicate testing to assess differences in particle size, sample weight, dispersants and how this relates to the Au and Cu geochemistry. Using multiple analysis of variance tests the sub-micron fractions showed that although the 〈0.2 µm fraction was slightly different to the 〈2 µm and 〈0.75 µm fraction, there was not additional value in the extra effort of extracting these sub-micron fractions, and the 〈2 µm fraction was favoured. Ultrasonics and rinsing were not required for Au analysis, and during wet separation no Au is lost in solution and only a small fraction of the overall Cu (0.5%) was lost. Using a dispersant was critical for solid recovery and that Na-hexametaphosphate (technical or laboratory grade) was found to be the most effective reagent. The 〈2 µm size fraction showed no significant differences for assays of Au using 0.1 g, 0.2 g, 0.5 g, 1 g and 4g (p 〈0.05) with a microwave-assisted aqua regia digestion being the best analytical method for Au recovery. In addition to the geochemistry, the spectral reflectance variation was investigated with respect to particle size and weight, and showed more variation in the smaller weight fraction of material and a loss of quartz in the fine materials as expected. The integration of results from this study generated a new workflow called UltraFine+™ This workflow provides 40 elements, spectral mineralogy, particle size distribution, pH, EC and specific surface area, offering more, quality data to improve mineral exploration using soil and regolith samples.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉The pH-dependence and reversibility of radium (Ra) and strontium (Sr) binding onto a modified bauxite refinery residue (MBRR), and the effects of sample aging, were studied in laboratory uptake / leaching experiments. Natural 〈sup〉226〈/sup〉Ra and stable strontium (Sr〈sub〉nat〈/sub〉) were contacted with MBRR in an 8-day loading period (equilibrium pH ≈ 8.5). Following the addition of exchange isotopes 〈sup〉228〈/sup〉Ra and 〈sup〉85〈/sup〉Sr, the samples were then leached in pH-dependent experiments, where the pH was decreased incrementally from 9 to 3 over seven hours. A further suite of samples was aged at 4°, 23°, and 65°C for 6-months after the initial addition of 〈sup〉226〈/sup〉Ra and Sr〈sub〉nat〈/sub〉 and then studied in a similar set of pH-dependent exchange experiments. Relative concentrations of the Ra and Sr isotope pairs (〈sup〉226〈/sup〉Ra/〈sup〉228〈/sup〉Ra and Sr〈sub〉nat〈/sub〉/〈sup〉85〈/sup〉Sr) provided insights into the adsorption strength, incorporation, reversibility and aging effects. The Sr〈sub〉nat〈/sub〉 data showed that the release of bound Sr from aged MBRR samples as the pH decreases is substantially less than the unaged sample, showing that during the aging period, Sr has been incorporated in less accessible phases. It appears that the uptake of 〈sup〉228〈/sup〉Ra by the higher temperature aged samples is somewhat stronger than the unaged samples, however Ra isotope exchange plots for aged and unaged samples are similar. Consequently, the stronger binding of 〈sup〉228〈/sup〉Ra by the higher temperature aged samples is probably driven by translocation to kinetically less favourable surface sites rather than a significant incorporation of radium within the mineral solids during aging.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Mineral exploration under relatively young, exotic cover still presents a major challenge to discovery. Advances and future developments can be categorized in four key areas, 1) understanding metal mobility and mechanisms, 2) rapid geochemical analyses, 3) data access, integration and interoperability, and 4) innovation in laboratory-based methods.Application of “regolith-style” surface mapping in covered terrains outside of conventional lateritic terrains is achieving success in terms of reducing background noise and improving geochemical contrasts. However, process models for anomaly generation are still uncertain and require further research. The interaction between the surface environment, microbes, hydrocarbons and chemistry is receiving greater attention. While significant progress has been achieved in understanding the role of vegetation, interaction with the water table and cycling of metals in the near surface environment in Australia, other regions of the world, for example the till-covered terrains in the northern hemisphere and arid colluvium-covered areas of South America, have seen less progress. In addition to vegetation, the influence of bacteria, fungi and invertebrates is less well studied with respect to metal mobilization in cover. Field portable-XRF has become a standard field technique, though more often used in a camp setting. Apart from tweaking of analytical quality, the instruments have probably reached their peak of analytical development with instrument add-ons, such as cameras, beam-limiters. wireless transmission and GPS as the main differences between instrument suppliers. Their future rests in automated application in unconventional configurations, for example, core-scanning, and better integration of the analytical data with other information such as spectral analyses. Pattern-drilling persists in industry, however, has benefitted from innovative application of field-portable tools along with rock and mineral chemistry to provide near real-time results and assist in a shift toward more flexible and targeted drilling in greenfields settings.Innovation in the laboratory continues to progress. More selective geochemical analysis, imaging of fine particle size fractions and resistate mineral phases and isotope analysis are faster and more accessible than ever before. The application of genomics (and data analysis) as mineral exploration tools is on the horizon. A continuing problem in geoscience: the supply to industry of suitably trained geochemists, persists, although some needs, particularly at junior level, will be met by recent initiatives at various universities at graduate level. Unfortunately, the current economic climate has had a significant impact on R&D and retention of geochemistry skills by industry. Whilst the future is positive, significant investment is required to develop the next generation of geochemical exploration tools and concepts.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉The strata of the Linxi Formation (LXF) occupy an extensive area in eastern Inner Mongolia, NE China, and have close spatial and genetic relationship with some significant Mesozoic Sn-Cu-Pb-Zn-Ag veins and porphyry polymetallic deposits (ore occurrence). The rock types of the LXF mainly include sandstone, siltstone and shale. Major and trace element data (including REE) of rocks from the LXF in Hanmiao area indicate that these rocks have a greywacke protolith, derived from intermediate-acid arc igneous rocks and deposited during intensive tectonic activity. LA-ICP-MS U-Pb dating of detrital zircons from sandstone of the LXF yields ages of 985±10 Ma to 242±2 Ma. The youngest population of ages shows a peak at ca. 258 Ma, suggesting that the major deposition period of the LXF was in the late Permian. These ages, together with the youngest zircon age (ca. 242Ma), suggest that the deposition of the LXF mainly occurred during the late Permian and extended to the early Triassic. According to the results of analysis of 44 sandstone and siltstone samples, ore elements, e.g. W, Sn, Ag and Mo, are significantly enriched in the LXF of the study area. Combined with the fact that more and more polymetallic deposits have been discovered within the LXF strata in the southern Great Xing'an Range (GXR), it can be concluded that the strata of the LXF might be the ore source bed, and there is a large ore-prospecting potential for polymetallic deposits in the LXF of the GXR.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Multi-element geochemical surveys of rocks, soils, stream/lake/floodplain sediments, and regolith are typically carried out at continental, regional and local scales. The chemistry of these materials is defined by their primary mineral assemblages and their subsequent modification by comminution and weathering. Modern geochemical datasets represent a multi-dimensional geochemical space that can be studied using multivariate statistical methods from which patterns reflecting geochemical/geological processes are described (process discovery). These patterns form the basis from which probabilistic predictive maps are created (process validation). Processing geochemical survey data requires a systematic approach to effectively interpret the multi-dimensional data in a meaningful way. Problems that are typically associated with geochemical data include closure, missing values, censoring, merging, levelling different datasets, and adequate spatial sample design. Recent developments in advanced multivariate analytics, geospatial analysis and mapping provide an effective framework to analyze and interpret geochemical datasets. Geochemical and geological processes can often be recognized through the use of data discovery procedures such as the application of principal component analysis. Classification and predictive procedures can be used to confirm lithological variability, alteration, and mineralization. Geochemical survey data of lake/till sediments from Canada and of floodplain sediments from Australia show that predictive maps of bedrock and regolith processes can be generated. Upscaling a multivariate statistics-based prospectivity analysis for arc-related Cu-Au mineralization from a regional survey in the southern Thomson Orogen in Australia to the continental scale, reveals a number of regions with similar (or stronger) multivariate response and hence potentially similar (or higher) mineral potential throughout Australia.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉The strata of the Linxi Formation (LXF) occupy an extensive area of eastern Inner Mongolia, NE China and have close spatial and genetic relationships with important Mesozoic Sn–Cu–Pb–Zn–Ag veins and porphyry polymetallic deposits (ores). The rock types of the LXF include sandstone, siltstone and shale. Major and trace element (including rare earth element) data for rocks from the LXF in the Hanmiao area indicate that these rocks have a greywacke protolith derived from intermediate to acidic arc igneous rocks and were deposited during intensive tectonic activity. Laser ablation inductively coupled plasma mass spectrometry U–Pb dating of detrital zircons from sandstones in the LXF yields ages of 985 ± 10 to 242 ± 2 Ma. The youngest population of ages shows a peak at 〈span〉c.〈/span〉 258 Ma, suggesting that the main period of deposition of the LXF was in the late Permian. These ages, together with the youngest zircon age (〈span〉c.〈/span〉 242 Ma), suggest that the deposition of the LXF mainly occurred during the late Permian and extended to the early Triassic. According to the results of the analysis of 44 sandstone and siltstone samples, ore elements (e.g. W, Sn, Ag and Mo) are significantly enriched in the LXF in this region. Combined with the fact that increasing numbers of polymetallic deposits have been discovered within the LXF strata in the southern Great Xing'an Range, we conclude that the strata of the LXF may be the source bed of the ore and there is potential for ore prospecting in the polymetallic deposits of the LXF in the Great Xing'an Range.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Heavy mineral sands (HMS) are a resource of Ti-minerals, zircon, monazite and the critical elements Hf and REEs. Portable field techniques capable of measuring the geochemical composition, such as portable XRF (pXRF), may assist in identifying and quantifying the multiple minerals present in HMS. In this study, we assess the application of pXRF for the characterisation of garnet-magnetite mineral sands from the Namibian coastline. Forty-six HMS samples from the northern Namibian coast were analysed by pXRF for SiO〈sub〉2〈/sub〉, Ti, Mn, Fe, Zr, Th, Y, V and Hf. The HMS were analysed as powdered and unground samples to test whether minimal sample preparation yields reliable results. Our tests show that pXRF results of unground sands scatter widely due to sample heterogeneity. Powdered samples, however, can be measured precisely and can be corrected with conventional lab analyses. Some spectral interferences specific for this material occur, e.g., Th on Pb and Bi and Hf on Cu. Selectively corrected pXRF data of powdered HMS were compared to XRD Rietveld data to determine proportions of heavy minerals (Ti minerals, Fe oxides, zircon, garnet). Geochemical and mineralogical data correlated well for garnet and moderately for Fe-oxides and Ti-minerals. Additionally, the presence of zircon and monazite is indicated by Zr, Hf and Th concentrations, which demonstrates that pXRF is a useful tool for HMS characterisation.〈strong〉Supplementary material:〈/strong〉 Tables of raw data (Supplement Table S1), statistical parameters (Supplement Table S2) and corrected pXRF values (Supplement Table S3) are available at 〈a href="https://doi.org/10.6084/m9.figshare.c.4536992"〉https://doi.org/10.6084/m9.figshare.c.4536992〈/a〉〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Waste-rock dumps and water quality of pit-lakes formed at abandoned mines of pyrite-rich ore deposits are of considerable environmental concern around the world. The Mathiatis and Sha mines provide typical examples of abandoned mines where Cyprus-type Cu-pyrite ore was exploited. Supergene alteration of the sulphide ore and the mine waste leads to the formation of efflorescence and generation of acid mine drainage (AMD) filling the pit-lakes. Sulphate concentrations range from 4,600 to 4,850 mg/L and from 35,900 to 38,500 mg/L for the Mathiatis and Sha mines, respectively. Concentrations of heavy metals exceed the established regulatory limits in water. A preliminary assessment of the mine waste at the Mathiatis mine indicated that it cannot be characterized as inert material according to European legislation, posing an environmental threat as a source of AMD. The identified Mg, Ca and Fe efflorescence mineral phases retain temporarily trace metals near the mine waste and the pit-lake shore. Neutralisation experiments on the acidic waters of the epilimnion indicated local limestone is not sufficient for full remediation. However, it could be used as a low-cost pretreatment method for AMD. The study expands the international database of AMD affected areas and provides the basis for future remediation efforts.〈strong〉Supplementary material:〈/strong〉〈a href="https://doi.org/10.6084/m9.figshare.c.4383254"〉https://doi.org/10.6084/m9.figshare.c.4383254〈/a〉〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Tailings constitute an important source of potentially toxic metals and metalloids (PTMM) to the environment. Determining PTMM mobilization potential is relevant for estimating their hazard. The release of Pb, Zn, Fe, Cd and As from oxidized and less oxidized tailings situated at the mining town of Zimapán, México, was evaluated by applying various extraction schemes: ‘geoavailable’, the scheme of the Community Bureau of Reference (BCR), and experiments at distinct pH and redox conditions. Total concentrations varied as: Fe (10.6–19.4%), As (8397–107 649 mg/kg), Zn (1325–30 635 mg/kg), Pb (3810–10 000 mg/kg), and Cd (16–1425 mg/kg). Geoavailability (proportion of elements released with a solution simulating rainwater) in oxidized tailings reached 79.1% for Zn, 69% for Cd, 7.3% for Fe, 5.1% for As, 1% for Pb. Cadmium was the most geoavailable element (1%) in less oxidized tailings. BCR fractionation showed different mobilities among elements and samples from each deposit. Less oxidized tailings could become more hazardous with time, mobilizing mainly Zn, Cd and As. Geoavailable As, Fe and Cd surpass irrigation water standards. In spite of its low mobile proportion, the high total As concentrations may produce hazardous levels in soils. The geoavailable procedure constitutes an easy to apply and economic method that may be used to perform a first evaluation of the tailings’ pollution potential to the nearby soils.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Mapping and modelling of the spatial distribution of geochemical anomalies is a key task for geochemical exploration. This case study explores mapping and modelling of Cu and Fe geochemical anomalies combining the Sequential Gaussian Co-simulation (SGCS) method and Local Singularity Analysis (LSA) in the Malatya region, SE Turkey. A total of 652 topsoil samples were collected on a regular grid design from the study area. A cell declustering technique was applied to the raw data. Both geometric and zonal anisotropy exist in the directional variogram of Cu and Fe. SGCS was applied to create maps representing an equally probable spatial distribution of Cu and Fe geochemical anomalies. SGCS results have been validated by a variety of tests including the reproduction of the variograms, histograms, descriptive statistics and contour plots. LSA is based on a sliding window estimation approach applied to the grid data created for SGCS realization. LSA was carried out and mapped via the results of the realization on the same grid layout. Critical anomaly threshold values of the variables were identified using the singularity and quantile plot. Integration of SGCS and LSA results provides quantification of the uncertainty of spatial distribution and determination of Cu and Fe critical thresholds.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉The fundamentals of X-ray physics are well understood, and many workers have commented on the poor performance and poor reproducibility of atomically-light elements by portable X-ray fluorescence (pXRF). However, the physics responsible for this is rarely discussed in the pXRF literature. Furthermore, it is well known that analysing samples through calico (cotton fabric) or paper bags results in lower concentrations reported by the pXRF instrument but, again, the physics of this is seldom discussed. This paper addresses these shortcomings by presenting X-ray transmission modelling and empirical data to show that the effects reported by many workers are entirely consistent with the physics of X-rays passing through matter, and thus that they are entirely predictable.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉At the buried Atlántida deposit (Cu-Au-(Mo)) in the Atacama Desert of Chile, highly saline pockets of fine-grained material 10 cm – 3 m in diameter were identified on the alluvial surface using remote sensing and detailed regolith mapping. The median salinity (NaCl dominant) of the saline pockets is 2.2% compared to background alluvial material with a median salinity of 0.01%. Their distribution along mapped fault structures and the highly saline nature of the material suggest they form as an expression of groundwater forced through fractures to the surface during seismic activity. A targeted geochemical survey, oriented parallel to the orientation of the structures (sample spacing 250 m along structural trend) specifically sampling saline pockets on relatively old surfaces, was performed over the deposit. Deionized water extraction of soluble salts and analysis by ICP-MS revealed strong correlations of increasing salinity and increasing concentrations of porphyry copper pathfinder elements. Elevated responses of Se, Mo, Re, and Te normalized to a groundwater volume proxy are present directly over the Atlántida deposit. This suggests the rate of erosion and sedimentation is slow enough in the Atacama Desert to preserve surficial anomalies as saline pockets, formed by periodic seismically induced surface flooding of groundwater along faults extending to surface. Targeted sampling of saline pockets along structural trends using weak leach geochemistry in terrains dominated by transported cover can serve as a routine exploration method for the potential discovery of buried copper porphyries, and other styles of mineralization in the Atacama Desert of Chile.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Phosphate is a minor but important constituent of iron ores and is especially undesirable in the production of steel, where it is considered a penalty element and is therefore tightly controlled. Iron ore quality must be determined at source, which means that deleterious elements must be accurately determined as an ongoing process. This demands fast, reliable analytical methods for the determination of, amongst others, phosphorus. However, such analysis is severely hampered by the following factors: The standard analytical method employed is X-ray fluorescence (XRF), but the measurements for phosphorus are seriously affected by matrix and inter-element interferences. An alternative technique is inductively coupled plasma with optical emission spectroscopy (ICP-OES), but there are also complications in using ICP-OES. The abundance of phosphorus in rocks is very low, generally under 0.5% wt. ICP-OES is also very insensitive to phosphorus and therefore must use the most sensitive spectral lines for quantification, and, there are serious spectral interferences on these lines by Fe and Cu. This study examines several analytical approaches for the determination of phosphate, using preparation by fusion and analysis by ICP-OES, demonstrating that suitable mathematical procedures and software applications can produce good results for phosphates, comparable to inter-laboratory tests or XRF.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉To investigate copper, arsenic, lead and zinc contamination in the topsoil of the Erdenet copper mining area in Mongolia, soil samples collected from the surrounding area were examined for trace element concentrations, geochemical fractions, and phase distributions. Of the 19 trace elements analyzed, the highest concentrations of Cu (1443–4866 mg kg-1), As (26–52 mg kg-1), and Mo (24–49 mg kg-1) in soils from the mine industrial area exceeded the corresponding values listed in the National Standard of Mongolia. Copper was largely associated with the organic/sulfide fraction, and As, Pb and Zn were associated with the residual fraction. Significantly high enrichment factor (EF) and geoaccumulation index (Igeo) values confirmed that Cu and As in the soil from the mine industrial area are at serious levels and their sources may be related to anthropogenic activities such as mining.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Geochemical characterization of metal-bearing sulfate salts from underground mine complexes in Nevada, U.S.A. illustrates a variety of compositional and paragenetic trends. The most common metal species observed were Fe, Al, and Mg; and Al-bearing salts were the most commonly observed minerals. Mineralogical investigation shows that salts have variable grain sizes, are inter-grown, and display relationships that differ from those observed at many sites with similar minerals. Determinations for samples collected from one area show the presence of both paragenetically-early and -late minerals. These complex relationships may be the result of multiple generations of mineral growth. Simple dissolution testing indicates the propensity for each of the six distinct mineral phases observed to rapidly produce acidic solutions. Speciation and mineral equilibrium calculations using two different thermodynamic databases (Pitzer and Minteq.v4) show that different solution properties and mineral solubilities would be predicted depending on the database used. Additionally, some speciation results display unreasonable charge imbalances that would need to be rectified for the results to be utilized in predictive modeling. These results highlight the importance of considering various modeling codes and databases when simulating the environmental impact of concentrated solutions resulting from the oxidation of sulfides and formation of secondary minerals.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Molar element ratio analysis of element concentrations consists of four basic tools that provide substantial insight into the lithogeochemistry (and mineralogy) of rocks under examination. These tools consist of: (i) conserved element ratio analysis, (ii) Pearce element ratio analysis, (iii) general element ratio analysis, and (iv) lithogeochemical mineral mode analysis. Conserved element ratio analysis is useful in creating a chemostratigraphic model for the host rocks to mineral deposits, whereas Pearce element ratio analysis and general element ratio analysis are primarily used to identify mineralogical and metasomatic controls on rock compositions, and to investigate and quantify the extent of the material transfers that formed the host rocks and mineralization. Lithogeochemical mineral mode analysis converts element concentrations into mineral concentrations using a matrix-based change-of-basis operation, allowing lithogeochemical data to be interpreted in terms of mineral modes. It can be used to provide proper names to rocks, an important activity for an exploration geologist because of the implications that rock names have on genetic processes and mineral deposit models.This paper provides a review of the theoretical foundations of each of these four tools, and then illustrates how these techniques have been used in a variety of exploration applications to assist in the search for, evaluation and planning of, and the mining of mineral deposits. Examples include the evaluation of total digestion lithogeochemical datasets from mineral deposits hosted by igneous and sedimentary rocks and formed by hydrothermal and igneous processes. In addition, this paper illustrates a more recent geometallurgical application of these methods, whereby the mineral proportions determined by lithogeochemical mineral mode analysis are used to predict rock properties and obtain the ore body knowledge critical for resource evaluation, mine planning, mining, and mine remediation.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉The need to innovate to advance exploration success is ongoing and while regional geochemical surveys are common, increasing the data we collect and improving survey design has stagnated. A new adaption of existing methods known as UltraFine+™ extracts the 〈2 µm fraction of soils and sediments, which is then analysed and combined with spectral mineralogy proxies and physico-chemical properties to improve targeting for Au and base metal exploration. We applied the UltraFine+™ workflow to three small orientation site studies in Western Australia, and reprocessed archived regional soil samples from the Geological Survey of Western Australia to test the method. The orientation program (∼200 samples) involved samples from the Leonora and Sir Samuel 1:250,000 map sheets, an area that hosts known major Au and base metal deposits. We then applied this approach to the Kingston 1:250, 000 map sheet area, analysing a further 300 samples in a region on the Yilgarn Craton margins that is essentially greenfields, as there has been little exploration and the original geochemical survey data was heavily censored due to the abundance of transported regolith dominated by quartz-rich sand. The archived samples were specifically selected soils (sheetwash or sand plain) with a component of Quaternary/Tertiary transported cover. Results at the orientation test sites (Telfer West, Tooting Bec and DeGrussa) were promising. Importantly, the study revealed a marked decrease in censored results for Au (from 63% to 10% below detection limit). Geochemistry and some example indices for mineral exploration and lithology mapping, as well as example maps using the additional spectral mineralogy proxies or particle size variation are presented. The application of the 〈2 µm particle size separation and the UltraFine+™ workflow importantly demonstrates the additional value from (re-)assaying regional soil and sediment samples to generate new targets and improve regional geochemical maps. This is an exercise that can be applied to new greenfields surveys, and when exploration budgets are lean, applied to archived samples.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉The paper presents data on two cores from the dispersion train of gold-bearing sulfide tailings in the Novo-Ursk deposit (Kemerovo region, Russia) where organic-bearing mud and natural organic matter are interbedded with cyanide tailings and acid mine drainage (AMD). The study focuses on speciation of Au, Ag and potentially toxic elements (PTE), including Fe, Cu, Zn, As, Se, and Pb according to selective sequential extractions. Since large contents of elements are found in water solution and bound to Fe(III) compounds, sulfides, and/or organic matter in both cores, the organic material behaves as a natural biogeochemical barrier for potentially toxic elements and precious metals released from AMD. The interaction with organic matter results in biogeochemical sorption and immobilization of elements and is favorable for secondary enrichment in gold and silver. It leads to immobilization of elements which further form new mineral phases or become partitioned between existing phases. On the other hand, very high concentrations of water-soluble and oxidizable species of PTE and Au, which are unstable in surface conditions and may become remobilized when the environment changes, make the organic material less workable and even potentially hazardous. Thus, both positive (secondary enrichment) and negative (pollution) effects should be taken into account in the planning and design of systems for purification, disposal of cyanide tailings, and recovery of useful components from tailings using natural organic matter as a geochemical barrier.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉There is a pressing need for new exploration tools to target and vector towards mineralization in covered terrains. Groundwater provides a valuable and under-utilized geochemical sampling medium, and represents an important and cost-effective tool to expose covered terrains to systematic exploration. For Au exploration, researchers agree the best hydrogeochemistry pathfinder is dissolved Au itself, with additional potential from other pathfinders (albeit non-unique) such as As, Ag, W and Mo. Despite Au's relatively low solubility, with rigorous field protocols and appropriate analytical methods, explorers can respond to dissolved Au directly with robust parts per trillion (ppt)-level analyses.Even with ppt-level analyses, a practical implication of Au's low solubility is that a deposit's dissolved Au signature is generally weaker than seen in other more mobile pathfinders, producing a smaller detectable footprint, which must be considered when designing exploration programmes. Using purpose-drilled groundwater sampling bores, explorers can collect groundwater samples at the density required to respond to dissolved Au where existing borehole coverage is otherwise insufficient. In addition to its use at the regional scale, with even tighter sample density, hydrogeochemistry also shows promise at the project scale, allowing the 3D modelling of pathfinder dispersion.For hydrogeochemistry to be widely adopted for Au exploration, explorers need confidence in ppt-level dissolved Au analyses, and the context to understand their significance. This paper aims to address these topics and provide a straightforward starting point for Au explorers interested in applying hydrogeochemistry by: (i) summarizing examples of regional sampling programmes and more focused case studies to illustrate how covered Au deposits create measurable dissolved Au footprints distinguishable from background; and (ii) sharing examples of dissolved Au analyses that are being integrated into exploration at the regional and project scales.As seen in the results, the distributions of dissolved Au in the regional- and project-scale programmes show remarkably similar and easy to interpret high-contrast, low-frequency anomalies against relatively low backgrounds. These are desirable attributes of any geochemical pathfinder. When combined with the benefits of hydrogeochemistry v. other geochemical exploration tools (e.g. groundwater can create larger footprints requiring fewer samples to detect, and groundwater can recharge from depth to reflect deeper mineralization), dissolved Au is a powerful pathfinder ideally suited for Au exploration in covered terrains.While this paper focuses on the use of dissolved Au, additional pathfinders can provide valuable information, including indications of lithological changes, hydrothermal alteration and different styles of mineralization, as well as opportunities to use secondary pathfinders when sample density or local conditions may not result in detectable dissolved Au signatures.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Biogeochemical orientation surveys were undertaken at low sulphidation epithermal Au-Ag occurrences in the Hauraki Goldfield – Coromandel Volcanic Zone (CVZ) and Taupo Volcanic Zone (TVZ), and at the Waiotapu active geothermal area in the TVZ. Several plant species were sampled including the foliage of tree ferns and tea trees. The ferns - silver fern (‘ponga’), rough tree fern (‘wheki’) and black tree fern (‘mamaku’) - were the most ubiquitous and were easiest to sample, although tea tree was the dominant genus at Waiotapu.At the Waiotapu geothermal area, significantly higher concentrations of Ag, Au, Sb, As, Cs and Rb were present in samples close to Champagne Pool than elsewhere confirming its location as the main outflow source of Au, Ag and their pathfinder elements.The fern survey areas at Luck at Last mine, Pine Sinter and Ohui in the CVZ each exhibited biogeochemical anomalies which successfully highlighted most known quartz veins and provided additional anomalies for further investigation.At Goldmine Hill, Puhipuhi (TVZ), rough tree fern is the most common species. Although this species absorbs lower concentrations of many elements than the silver fern, the spatial distribution of elements is of greater significance than absolute concentrations. Highest Au, Ag, As and Al concentrations occurred in samples from a ridge extending west-north-westward from Goldmine Hill. Antimony and Bi were at anomalous levels in an area peripheral to the precious metal anomalies, indicating potential zonation of elements distal from the Au and Ag.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉The 〈 10 μm, 〈 4 μm, 〈 2.5 μmm and 〈 1 μm fractions of eight regolith samples have been extracted as aerosols, then analysed for 〉 60 elements by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Precision and accuracy rivals that of conventional digestion and ICP-MS analysis for most elements, but the aerosol extraction and ablation approach can be completed within 30 minutes, avoids compromising the sample by screening, column settling, fusion and/or digestion, and includes data for elements such as Br, Cl, I and Se that are conventionally analysed by individual procedures. Major element chemistry and scanning electron microscope (SEM) imagery show the aerosol fractions of regolith are dominated by kaolinite, with quartz in eolian regolith. The aerosol fractions of Si- and Ca-rich regolith have higher trace element concentrations than the coarser fraction (0.45 – 2 mm), but chalcophile elements are depleted in the aerosols of Fe-rich regolith relative to the coarser fraction. Improvements in in-field analytical technology coupled with aerosol extraction mean that fine and ultrafine fraction chemistry can be used to guide mineral exploration programs in close to real time.〈strong〉Supplementary material:〈/strong〉〈a href="https://doi.org/10.6084/m9.figshare.c.4562807"〉https://doi.org/10.6084/m9.figshare.c.4562807〈/a〉〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉This paper describes saline pockets (10 cm – 3 m in diameter) of fine-grained material distributed on alluvial surfaces. These saline pockets are localized along structural trends at the Atlántida buried porphyry-skarn Cu-Au-(Mo) deposit in the Atacama Region of Chile. The distribution and highly saline nature of the material suggests formation by the pooling and evaporation of groundwater forced through fractures to the surface during seismic activity. These saline pockets are a surface expression of the hydrological effects of seismic activity along faults. Saline pockets with similar distribution and characteristics were also identified at three additional alluvium-covered areas, all located in the Antofagasta Region of Chile. Identification and mapping of these saline pockets relies on the ability to identify the continuation of structures through overlying gravels. Regolith mapping using high-resolution drone imagery and digital elevation modelling identified geomorphic markers of faulting which aided in the mapping of the distribution of saline pockets. Saline pockets provide a unique opportunity to sample the direct expression of transported groundwater reaching the surface from depth and provide a prime target medium for mineral exploration through transported gravels.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Robust principal component analysis (PCA) has been proved to be an efficient multivariate statistical method for extraction of a multivariate structure of geochemical data containing outlier values. Furthermore, because of compositional characteristics of geochemical data, logratio transformation approaches also have to be implemented to transform the data from the simplex space into a real space. In order to model the extracted principal component of transformed data, we have used the sequential gaussian simulation (SGS) approach to overcome the drawbacks associated with traditional kriging method, e.g., bias conditionally relevant to underestimation and overestimation, smoothing effect and so on.The results of implementing a robust PCA on both untransformed and logratio transformed data, which have been acquired from an orogenic gold deposit, indicate that the robust PCA analysis of untransformed data is not capable of certifying element association of gold occurrences. However, in robust PCA analysis of transformed data, both varieties of gold mineralization, associated with pyrite mineral and quartz veins, have been revealed. The first variety of gold occurrence is detected in an integrated PC, obtained from PC1, PC2 and PC3, that are associated with Pb, As, Hg, Mo, S and Sb elements in quartz-sulfides veins. The second one, PC4, could be correlated with quartz veins. Furthermore, the results of the geostatistical SGS approach are compatible with the detected anomaly in the Alut gold deposit.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉K-feldspar-quartz vein-type Au deposits, represented by the Hadamengou super-large Au deposit, are widely developed in the Archaean high-grade metamorphic terrane in the western segment of the northern margin of the North China Craton. However, the formation processes of these Au deposits have long been debated, and their genetic relationship with magmatic activity remains unclear. In this study, by examining the geological and geochemical characteristics of the Hadamengou Au deposit and several related intrusions, we find that the Au-(Mo) mineralization system may be related to Indosinian alkaline magmatic activity. The Dongshadegai and Xishadegai intrusions, which are related to the formation of the Hadamengou Au deposit, formed in an Indosinian extensional tectonic environment, and both are characterized by high silica and alkaline contents and strong oxidizing properties, indicating that the parent magmas of these intrusions were capable of dissolving and transporting metallic elements during magma formation and evolution. The Indosinian Hadamengou Au deposit contains minerals such as magnetite and barite, and the H, O, S and Pb isotopic characteristics of this deposit indicate that the ore-forming fluids originated from magmatic-hydrothermal fluids and had oxidizing properties. These observations suggest the presence of an oxidized intrusion-related Au-(Mo) mineralization system in the studied metamorphic terrane.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Exploitation of ore minerals (cinnabar, chalcopyrite, sphalerite) from the old mine in Vallalta (Belluno, NE Italy) has resulted in serious environmental impacts, including the acidification of water, and the contamination of soils and plants. Forty-eight soil samples and four wild plants were examined at four sites in the vicinity of the mine (〈100 m), where mine waste was discharged. After digestion with aqua regia, chemical analyses were carried out on both soils and plants by inductively coupled plasma-optical emission spectroscopy (ICP-OES) for potentially harmful elements (Cr, Cu, Ni, Pb, Zn, Fe, Mn); the mercury concentration was directly ascertained by atomic absorption spectrometry (AAS). The levels of Ni, Cr, Mn and Zn in the soils were generally below the ‘normal’ levels for uncontaminated sites. Conversely, more than 50% of the examined samples presented Cu and Pb concentrations higher than the phytotoxic level (10 mg kg〈sup〉−1〈/sup〉). Iron concentrations exceeded normal values (〈300 mg kg〈sup〉−1〈/sup〉) in 65% of the examined samples. The mercury concentration was high (6–21 mg kg〈sup〉−1〈/sup〉) in all soil samples, mostly above the phytotoxicity limit (10 mg kg〈sup〉−1〈/sup〉). 〈span〉Chaerophyllum hirsutum〈/span〉 presented the highest Hg levels in roots, up to the phytotoxicity level (10 mg kg〈sup〉−1〈/sup〉).Micronutrients Cu, Zn, Fe and Mn showed translocation factors (TFs) of between 0.5 and 1, suggesting that these elements are taken up to a critical concentration and are then arrested in the roots. Iron is less mobile, particularly in 〈span〉C. hirsutum〈/span〉, with the lowest TF of 0.38〈span〉.〈/span〉 The TF for Mn and Hg is 〉1 in 〈span〉S. nemorum〈/span〉 and 〈span〉C. hirsutum〈/span〉; a TF of 〈0.5 in 〈span〉P. braunii〈/span〉, and particularly in 〈span〉T. officinale〈/span〉, suggests that these metals are most likely to be arrested in their roots.Soil contamination is confined to the proximity (〈100 m) of the mine waste. Among the investigated plants, 〈span〉Chaerophyllum〈/span〉 seems to be most suitable for phytoremediation of Hg-contaminated sites.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉In order to investigate copper, arsenic, lead and zinc contamination in topsoil of the Erdenet copper mining area in Mongolia, soil samples collected from the surrounding area were examined for trace element concentrations, geochemical fractions, and phase distributions. Fifteen locations (residential area; mine industrial area; control area; tailings dam) were sampled during all four seasons. Of the 19 trace elements determined, the highest concentrations of Cu (1443–4866 mg kg〈sup〉−1〈/sup〉), As (26–52 mg kg〈sup〉−1〈/sup〉), and Mo (24–49 mg kg〈sup〉−1〈/sup〉) in soils from the mine industrial area exceeded the corresponding values listed in the National Standard of Mongolia. Soil samples were fractionated into five phases: exchangeable, carbonate bound, Fe/Mn oxide bound, organic matter bound, and residual. Copper was largely associated with the organic/sulphide fraction, and As, Pb and Zn were associated mainly with the residual and Fe/Mn oxide fractions. Significantly high enrichment factor (EF) and geoaccumulation index (I〈sub〉geo〈/sub〉) values confirmed that Cu and As in the soil from the mine industrial area reach serious levels and their sources may be related to anthropogenic activities such as mining.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Exploitation of ore minerals (cinnabar, chalcopyrite, sphalerite) from the old mine in Vallalta (Belluno, NE Italy) has resulted in serious environmental impacts, including the acidification of water, and the contamination of soils and plants. Forty-eight soil samples and four wild plants were examined at four sites in the vicinity of the mine (〈100 m), where mine waste was discharged. After digestion with aqua regia, chemical analyses were carried out on both soils and plants by inductively coupled plasma-optical emission spectroscopy (ICP-OES) for potentially harmful elements (Cr, Cu, Ni, Pb, Zn, Fe, Mn); the mercury concentration was directly ascertained by atomic absorption spectrometry (AAS). The levels of Ni, Cr, Mn and Zn in the soils were generally below the ‘normal’ levels for uncontaminated sites. Conversely, more than 50% of the examined samples presented Cu and Pb concentrations higher than the phytotoxic level (10 mg kg〈sup〉−1〈/sup〉). Iron concentrations exceeded normal values (〈300 mg kg〈sup〉−1〈/sup〉) in 65% of the examined samples. The mercury concentration was high (6–21 mg kg〈sup〉−1〈/sup〉) in all soil samples, mostly above the phytotoxicity limit (10 mg kg〈sup〉−1〈/sup〉). 〈span〉Chaerophyllum hirsutum〈/span〉 presented the highest Hg levels in roots, up to the phytotoxicity level (10 mg kg〈sup〉−1〈/sup〉).Micronutrients Cu, Zn, Fe and Mn showed translocation factors (TFs) of between 0.5 and 1, suggesting that these elements are taken up to a critical concentration and are then arrested in the roots. Iron is less mobile, particularly in 〈span〉C. hirsutum〈/span〉, with the lowest TF of 0.38〈span〉.〈/span〉 The TF for Mn and Hg is 〉1 in 〈span〉S. nemorum〈/span〉 and 〈span〉C. hirsutum〈/span〉; a TF of 〈0.5 in 〈span〉P. braunii〈/span〉, and particularly in 〈span〉T. officinale〈/span〉, suggests that these metals are most likely to be arrested in their roots.Soil contamination is confined to the proximity (〈100 m) of the mine waste. Among the investigated plants, 〈span〉Chaerophyllum〈/span〉 seems to be most suitable for phytoremediation of Hg-contaminated sites.〈/span〉

Description: 〈span〉〈strong〉Lead Guest Editor:〈/strong〉 Jaume Bech〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Tailings constitute an important source of potentially toxic metals and metalloids (PTMM) to the environment. Determining PTMM mobilization potential is relevant for estimating their hazard. The release of Pb, Zn, Fe, Cd and As from oxidized and less oxidized tailings situated at the mining town of Zimapán, México, was evaluated by applying various extraction schemes: ‘geoavailable’, the scheme of the Community Bureau of Reference (BCR), and experiments at distinct pH and redox conditions. Total concentrations varied as: Fe (10.6–19.4%), As (8397–107 649 mg/kg), Zn (1325–30 635 mg/kg), Pb (3810–10 000 mg/kg), and Cd (16–1425 mg/kg). Geoavailability (proportion of elements released with a solution simulating rainwater) in oxidized tailings reached 79.1% for Zn, 69% for Cd, 7.3% for Fe, 5.1% for As, 1% for Pb. Cadmium was the most geoavailable element (1%) in less oxidized tailings. BCR fractionation showed different mobilities among elements and samples from each deposit. Less oxidized tailings could become more hazardous with time, mobilizing mainly Zn, Cd and As. Geoavailable As, Fe and Cd surpass irrigation water standards. In spite of its low mobile proportion, the high total As concentrations may produce hazardous levels in soils. The geoavailable procedure constitutes an easy to apply and economic method that may be used to perform a first evaluation of the tailings’ pollution potential to the nearby soils.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Regolith and vegetation (spinifex) chemistry from transects across the Stansmore Fault in the Ngururrpa area of northeastern Western Australia have been used to detect any fault-controlled fluid, and whether the fluid has been in contact with concealed mineralization. On one transect, the fine-fraction of regolith on the fault trace has elevated concentrations of low field strength elements (LFSE), rare earth elements (REE), some chalcophile elements, Zn and Tl. On the second more structurally complex transect, elevated LFSE, REE and Zn concentrations are coincident with the position of one fault and indicate the location of a second. Both fault traces are indicated by spinifex REE, B, Zn, REE and HFSE chemistry, as well as being independently verified by passive seismic data. The wide range in ionic potential of elements on or close to fault traces indicates a high fluid flux, whereas high Zn, Tl, Re, Cd, and B are indicative of sediment-hosted Pb-Zn mineralization. Basin-bounding faults, such as the Stansmore Fault, are spatially related to Mississippi Valley (MVT)-style mineralization elsewhere in the Canning Basin, and rocks hosting sedimentary exhalative (SEDEX)-style mineralization in the adjacent west Arunta Orogen have been reported from the southeastern part of the Ngururrpa area.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉There have been several advances in inductively coupled plasma-mass spectrometer ICP-MS analytical technologies in the last decade. Collision/reaction cell ICP-MS and triple quadrupole ICP-MS techniques can produce lower detection limits for select elements that experience interferences with a standard quadrupole (e.g., Se and As). Triple quadrupole ICP-MS, in particular, can eliminate virtually all polyatomic or isobaric interferences for highly accurate measurements of some element isotopes systematics that are of great interest in mineral exploration, namely Pb/Pb. Laser ablation ICP-MS has become more popular as an effective analytical tool to measure mineral grain trace elements, which could assist in vectoring to mineralization or exploration drill targets. The ablation of a spot on a Li-borate fused glass disk paired with XRF analysis has also gained popularity as an alternative to total whole rock characterization packages that employ several separate digestions and analytical methods. While there have been several advancements in ICP-MS technologies in exploration geochemistry, they have not been widely accepted or implemented. This slow adaptation could be due to the extended recession in the mining industry between 2012 and 2017. It is also possible that standard ICP-MS data (i.e., no collision/reaction cell) is still fit for purpose. This stands in stark contrast to implementation of ICP-MS in the previous decade (1997 to 2007), which was transformational for the industry.Consideration of all elements from large multi-element ICP-MS analytical suites for mineral exploration can be an extremely powerful tool in the exploration toolkit. The discovery of the White Gold district, Yukon is a prime example of how the utilization of soil geochemical data, when plotted spatially, can vector to gold mineralization. The presence of Au+As+Sb soil anomalies were key to delineating mineralization, especially when accompanied by publicly available geological, geographical, and geophysical data. Additionally, elements and element ratios not typically considered in Au exploration including Ni and U were utilized to determine the lithological and structural controls on mineralization. The availability of multi-element ICP-MS data was also useful in the discovery of the Cascadero Copper Taron Cesium deposit. Ore-grade Cs was discovered only because Cs was included in the multi-element ICP-MS exploration geochemistry suite. Before the availability of ICP-MS, it is unlikely that this deposit would have been discovered. 〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉To clarify the mechanism controlling the migration of uranium and typical heavy metals at the sediment-water interface, four sampling cores were collected along the Mianyuan River near a phosphate mining region to investigate their distribution in pore water and sediment along vertical profiles. This study indicated that: (1) the average concentrations of U, Cd, Cu, Pb, Zn, and Ni in the pore water were 2.17, 0.08, 6.28, 1.78, 80.56, and 5.18 μg/L, respectively, some of them being higher than the National Recommended Water Quality Criteria. (2) The enrichment of U, Cu, Pb, Zn, and Ni in the sediment near the urban area clearly indicated that local industries were important pollution sources. (3) The average diffusive fluxes of U, Cd, Cu, Pb, Zn, and Ni of the four profiles were 0.016, 0.007, 0.300, 0.022, 2.925, and -1.328 μg/(m〈sup〉2〈/sup〉·d), indicating that most of metals diffused from the sediment pore water to the overlying water. (4) The IWCTU (Interstitial Water Criteria Toxic Units) values of Pb in the pore water exceeded 1 in most river sections, indicating that the toxicity levels in the sediments presented risk to aquatic organisms.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Using the Rock Canyon Creek carbonate-hosted rare earth element (REE)–F–Ba deposit as an example, we demonstrate the need for verifying inherited geochemical data prior to reinterpretation. Inherited La, Ce, Nd and Sm data obtained by pressed pellet X-ray fluorescence (XRF), and La and Y data obtained by aqua regia digestion inductively coupled plasma atomic emission spectroscopy (ICP-AES) for more than 300 drill-core samples were analysed in 2009 and were subsequently compared to sample subsets re-analysed using lithium metaborate-tetraborate (LMB) fusion ICP mass spectroscopy (ICP-MS), Na〈sub〉2〈/sub〉O〈sub〉2〈/sub〉 fusion ICP-MS, and LMB fusion-XRF. We determine that LMB ICP-MS and Na〈sub〉2〈/sub〉O〈sub〉2〈/sub〉 ICP-MS accurately determined REE concentrations in control reference materials (CRM) SY-2 and SY-4, and provided precision of about 10%. Fusion-XRF was precise for La, Ce and Nd at concentrations greater than ten times the lower detection limit; however, accuracy of this method was not established because REE concentrations in SY-4 were below the lower detection limit. Analysis of the sample subset revealed substantial discrepancies for Ce concentrations determined by pressed pellet XRF in comparison to those determined by other methods due to Ba spectral interference. Samarium, present in lower concentrations than other REE that were determined, was consistently underestimated by XRF methods relative to ICP-MS methods. This may be the result of Sm concentrations approaching the lower detection limits of XRF methods, elemental interference or inadequate background corrections. Aqua regia dissolution results, reporting only for La and Y, are underestimated relative to the other methods. We highlight the importance of selecting the most appropriate analytical method and reference materials for determining the REE content of mineralized rock which may be several orders of magnitude higher than that of typical host rock.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉At the buried Atlántida deposit (Cu–Au–(Mo)) in the Atacama Desert of Chile, highly saline pockets of fine-grained material 10 cm–3 m in diameter were identified on the alluvial surface using remote sensing and detailed regolith mapping. The median salinity (NaCl dominant) of the saline pockets is 2.2% compared to background alluvial material with a median salinity of 0.01%. Their distribution along mapped fault structures and the highly saline nature of the material suggest they form as an expression of groundwater forced through fractures to the surface during seismic activity. A targeted geochemical survey, oriented parallel to the orientation of the structures (sample spacing 250 m along structural trend) specifically sampling saline pockets on relatively old surfaces, was performed over the deposit. Deionized water extraction of soluble salts and analysis by inductively coupled plasma mass spectrometry revealed strong correlations of increasing salinity and increasing concentrations of porphyry copper pathfinder elements. Elevated responses of Se, Mo, Re and Te normalized to a groundwater volume proxy are present directly over the Atlántida deposit. This suggests the rate of erosion and sedimentation is slow enough in the Atacama Desert to preserve surficial anomalies as saline pockets, formed by periodic seismically induced surface flooding of groundwater along faults extending to surface. Targeted sampling of saline pockets along structural trends using weak leach geochemistry in terrains dominated by transported cover can serve as a routine exploration method for the potential discovery of buried copper porphyries and other styles of mineralization in the Atacama Desert of Chile.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Phosphate is a minor but important constituent of iron ores and is especially undesirable in the production of steel where it is considered a penalty element and is therefore tightly controlled. Iron ore quality must be determined at source, which means that deleterious elements must be accurately determined as an ongoing process. This demands fast, reliable analytical methods for the determination of, amongst others, phosphorus. However, such analysis is severely hampered by the following factors: the standard analytical method employed is X-ray fluorescence (XRF), but the measurements for phosphorus are seriously affected by matrix and inter-element interferences. An alternative technique is inductively coupled plasma with optical emission spectroscopy (ICP-OES), but there are also complications in using ICP-OES. The abundance of phosphorus in rocks is very low, generally under 0.5% wt. ICP-OES is also very insensitive to phosphorus and therefore must use the most sensitive spectral lines for quantification, and, there are serious spectral interferences on these lines by Fe and Cu. This study examines several analytical approaches for the determination of phosphate, using preparation by fusion and analysis by ICP-OES, demonstrating that suitable mathematical procedures and software applications can produce good results for phosphates, comparable to inter-laboratory tests or XRF.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Geochemical characterization of metal-bearing sulphate salts from underground mine complexes in Nevada, USA, illustrates a variety of compositional and paragenetic trends. The most common metal species observed were Fe, Al, and Mg; and Al-bearing salts were the most commonly observed minerals. Mineralogical investigation shows that salts have variable grain sizes, are inter-grown, and display relationships that differ from those observed at many sites with similar minerals. Determinations for samples collected from one area show the presence of both paragenetically-early and -late minerals. These complex relationships may be the result of multiple generations of mineral growth. Simple dissolution testing indicates the propensity for each of the six distinct mineral phases observed to rapidly produce acidic solutions. Speciation and mineral equilibrium calculations using two different thermodynamic databases (Pitzer and Minteq.v4) show that different solution properties and mineral solubilities would be predicted depending on the database used. Additionally, some speciation results display unreasonable charge imbalances that would need to be rectified for the results to be utilized in predictive modeling. These results highlight the importance of considering various modeling codes and databases when simulating the environmental impact of concentrated solutions resulting from the oxidation of sulphides and formation of secondary minerals.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉This paper describes saline pockets (10 cm–3 m in diameter) of fine-grained material distributed on alluvial surfaces. These saline pockets are localized along structural trends at the Atlántida buried porphyry-skarn Cu–Au–(Mo) deposit in the Atacama Region of Chile. The distribution and highly saline nature of the material suggest formation by the pooling and evaporation of groundwater forced through fractures to the surface during seismic activity. These saline pockets are a surface expression of the hydrological effects of seismic activity along faults. Saline pockets with similar distribution and characteristics were also identified at three additional alluvium-covered areas, all located in the Antofagasta Region of Chile. Identification and mapping of these saline pockets relies on the ability to identify the continuation of structures through overlying gravels. Regolith mapping using high-resolution drone imagery and digital elevation modelling identified geomorphic markers of faulting which aided mapping the distribution of saline pockets. Saline pockets provide a unique opportunity to sample the direct expression of transported groundwater reaching the surface from depth and provide a prime target medium for mineral exploration through transported gravels.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉The Broken Hammer Cu-Ni-PGE-Au footwall deposit in the North Range of the Sudbury Structure in Canada consists of a shallow surface zone of vein- and vein stockwork-hosted mineralization within Sudbury breccia developed in the quartz monzonite Levack Gneiss Complex. The surface of the deposit consists of a 2-120 cm wide chalcopyrite vein and numerous smaller veins dominated by chalcopyrite-magnetite-millerite with trace gold, platinum group minerals, tellurides, bismuthides, and selenides. The Laurentide Ice Sheet flowed southward across the region depositing a sandy till that contains abundant sperrylite (hundreds of grains), chalcopyrite, pyrite and gold in the heavy mineral fraction down ice of mineralization. Mineral Liberation Analysis of the 〈0.25 mm heavy mineral fraction of metal-rich till identified a broader suite of PGM and sulphides than concentration visual identification methods. The 〈0.063 mm fraction of till displays a strong geochemical signature of the mineralization for Pd, Pt, Au, Cu, and Ag, and to a lesser extent Bi, Te, and Sn, however, geochemical signatures are not detectable as far down-ice as indicator minerals. Till sampling has not been used for exploration in the Sudbury region because of the abundant outcrop and the use of geophysical and prospecting techniques. This study demonstrates that indicator mineral and till geochemical methods are useful exploration tools for the region. The presence of sperrylite and chalcopyrite in oxidized till indicates that even thin (〈1 m) highly weathered till is an effective sample medium here.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Companhia de Pesquisa de Recursos Minerais (CPRM, the Brazilian geological survey) has carried out geochemical surveys focused on the Carajás region, the largest mineral province in Brazil. One of these surveys covered the area of Canaã dos Carajás, where 257 soil samples, including 32 duplicate samples, were collected from the B-horizon of soils within an area of 〈span〉c.〈/span〉 3500 km〈sup〉2〈/sup〉. The 〈0.177 mm fraction of these samples was ground and digested with aqua regia and then analysed for 53 elements by inductively coupled plasma atomic emission spectrometry and inductively coupled plasma mass spectrometry. The statistical treatment of the data allowed the development of multi-element geochemical maps based on interpolation techniques and the establishment of geochemical background values in soils. Different methods of obtaining the geochemical threshold values are presented and compared. The geochemical behaviour of 43 elements, including potentially toxic elements, is discussed. Geochemical background values were established using different statistical methods and the most significant results were obtained from the iterative 2〈span〉σ〈/span〉 technique. The influence of the geogenic contribution in the study area is largely dominant over anthropogenic effects. There is no conclusive evidence of contamination related to human activity at the time when the geochemical survey was carried out. This paper provides multi-element geochemical maps and background values in the most prominent Brazilian mining province.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉The Longtoushan Au deposit, located in the Qin-Hang Metallogenic Belt, South China, is a breccia-hosted epithermal Au deposit. It is characterized by the distinctive occurrence of magmatic-hydrothermal tourmaline-cemented breccia. Tourmaline-group minerals have an extensive range of chemical composition that could reflect their host environments, including some of economic interest. To investigate the potential of tourmaline as a geochemical indicator for ore exploration, chemical and boron isotope compositions of tourmaline from the Longtoushan Au deposit have been determined. Tourmaline mainly occurs as orbicular aggregates, clusters and veinlets in rhyolite porphyries, granite porphyries and in spatially associated hydrothermal breccias (Au-mineralized and Au-barren). Three types of tourmaline (I, II and III) are recognized at Longtoushan, most of which being alkali-deficient schorl-dravites. The pre-ore Tourmaline I in the rhyolite porphyry is Fe-rich schorl, contrasting with the dravitic ore-stage Tourmaline II in the mineralized breccia and Tourmaline III in the granite porphyry. Locally, Tourmaline II shows concentric zoning which correlates with core-rim chemical variations (higher Fe, Al in the rim than in the core). Tourmalines from Longtoushan are characterized by a dominant MgFe〈sub〉-1〈/sub〉 exchange vector and have relatively low Na contents (avg. 0.66 apfu; formula normalized on 15 total cations), indicating they possibly crystallized in reduced fluids of low-salinity. The δ〈sup〉11〈/sup〉B values of tourmalines from this study fall in a narrow range of −14.5 to −10.2‰, indicating dominant magmatic-hydrothermal fluids of continent crust origin. The results suggest that tourmaline from Longtoushan may originate from boron-rich vapor fluids unmixed from felsic magmas. Tourmaline breccia was likely formed by hydraulic fracturing, with open spaces infilled by boron-rich boiling fluids released from the magma. The fluid boiling process during brecciation would be critical for Au-bearing pyrite precipitation, which could compete with coexisting tourmaline for Fe, leaving tourmaline Fe-depleted. We propose that the Fe-poor dravitic tourmaline in the hydrothermal breccia could be used as prospecting guide at the Longtoushan Au deposit.〈strong〉Supplementary material:〈/strong〉 major element and boron isotope composition analyses of tourmaline are available at 〈a href="https://doi.org/10.6084/m9.figshare.c.4468808"〉https://doi.org/10.6084/m9.figshare.c.4468808〈/a〉〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Mapping and modelling of the spatial distribution of geochemical anomalies is a key task for geochemical exploration. This case study explores mapping and modelling of Cu and Fe geochemical anomalies combining the Sequential Gaussian Co-simulation (SGCS) method and Local Singularity Analysis (LSA) in the Malatya region, SE Turkey. A total of 652 topsoil samples were collected on a regular grid design from the study area. A cell declustering technique was applied to the raw data. Both geometric and zonal anisotropy exist in the directional variogram of Cu and Fe. SGCS was applied to create maps representing an equally probable spatial distribution of Cu and Fe geochemical anomalies. SGCS results have been validated by a variety of tests including the reproduction of the variograms, histograms, descriptive statistics and contour plots. LSA is based on a sliding window estimation approach applied to the grid data created for SGCS realization. LSA was carried out and mapped via the results of the realization on the same grid layout. Critical anomaly threshold values of the variables were identified using the singularity and quantile plot. Integration of SGCS and LSA results provides quantification of the uncertainty of spatial distribution and determination of Cu and Fe critical thresholds.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉The fundamentals of X-ray physics are well understood, and many workers have commented on the poor performance and poor reproducibility of atomically-light elements by portable X-ray fluorescence (pXRF). However, the physics responsible for this is rarely discussed in the pXRF literature. Furthermore, it is well known that analysing samples through calico (cotton fabric) or paper bags results in lower concentrations reported by the pXRF instrument but, again, the physics of this is seldom discussed. This paper addresses these shortcomings by presenting X-ray transmission modelling and empirical data to show that the effects reported by many workers are entirely consistent with the physics of X-rays passing through matter, and thus that they are entirely predictable.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Waste-rock dumps and the water quality of pit-lakes formed at abandoned mines of pyrite-rich ore deposits are of considerable environmental concern around the world. The Mathiatis and Sha mines provide typical examples of abandoned mines where Cyprus-type Cu-pyrite ore was exploited. Supergene alteration of the sulphide ore and the mine waste leads to the formation of efflorescence and generation of acid mine drainage filling the pit-lakes. Sulphate concentrations range from 4600 to 4850 mg/l and from 35 900 to 38 500 mg/l for the Mathiatis and Sha mines, respectively. Concentrations of heavy metals exceed the established regulatory limits in water. A preliminary assessment of the mine waste at the Mathiatis mine indicated that it cannot be characterized as inert material according to current European legislation, posing an environmental threat as a source of acid mine drainage (AMD). The identified Mg, Ca and Fe(II)- Fe(III) efflorescence mineral phases retain temporarily trace metals near the mine waste and the open pit-lake shore. Neutralization experiments on the acidic waters of the epilimnion indicated local limestone is not sufficient for full remediation. However, it could be used as a low-cost pretreatment method for AMD. The study expands the international database of AMD affected areas and provides the basis for future remediation efforts.〈strong〉Supplementary material:〈/strong〉 Detection limits and reference material analyses is available at 〈a href="https://doi.org/10.6084/m9.figshare.c.4383254"〉https://doi.org/10.6084/m9.figshare.c.4383254〈/a〉〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉This paper focuses on handheld and top-of-hole techniques which have appeared since 2007 or have undergone major improvements and discusses their benefits, challenges and pitfalls, why use them and what to expect from them. There is an ongoing need to be innovative with the way we undertake mineral exploration. Recent technological advances that have been applied to successful mineral exploration include on-site or portable instruments, on-site laboratory technologies, various core scanners, and technologies for fluid analysis. Portable or field technologies such as pXRF, pXRD, pNIR-SWIR, µRaman, and LIBS, aid in obtaining chemical and mineralogical information. Spectral gamma tools, a well-known technology, recently took advantage of improved ground and airborne (drone) instruments, to complement hyperspectral imagery. At mine and exploration sites, top-of-hole sensing technologies, such as Lab-at-Rig® and various core scanners (both spectral- and XRF-based) become useful tools to analyse meters of core as it is being drilled. Fluid analyses are not as common as analyses of solid materials, but there are advances in such technologies as anodic stripping voltammetry, polarography, and ion exchange electrodes aiming for analysis of commodity or environmentally important elements.Field portable geochemical techniques and on-site technologies now offer instant response and flexibility for most exploration tasks. By providing relevant data within minutes, they allow safer field decisions and focus on the most promising finds, while saving valuable resources in sampling grids or drilling. More efficient laboratory analysis programs are supported by sample screening and homogeneity checking on site. Field analyses are not always as accurate as laboratory ones, but most of the time, can be correlated with them, allowing reliable decisions. The level of confidence in field-made decisions needs to be compared between later and less numerous laboratory analyses, and less precise but more abundant and immediate field analyses. It may be demonstrated that in many cases, the fit–for-purpose nature of the latter allows a better confidence level. Quality compromises associated with field analyses can be reduced by the application of better sample preparation and quality assurance/quality control (QA/QC) procedures. Most of the further development of on-site chemical analysis is expected to be based on its integration with lab methods and on sound QA/QC practice, allowing a precise evaluation of its confidence level and uncertainties. Mineralogical analyses are constrained by our ability to interpret the data in near real-time but offer promising approaches in both surface and drilling exploration campaigns.〈/span〉

Description: The pH-dependence and reversibility of radium (Ra) and strontium (Sr) binding to a modified bauxite refinery residue (MBRR), and the effects of sample ageing, were studied in laboratory uptake/leaching experiments. Natural 226Ra and stable strontium (Srnat) were placed in contact with the MBRR for an 8-day loading period (equilibrium pH c. 8.5). Following the addition of exchange isotopes 228Ra and 85Sr, the samples were then leached in pH-dependent experiments, where the pH was decreased incrementally from 9 to 3 over 7 h. A further suite of samples was aged at 4°, 23° and 65°C for 6 months after the initial addition of 226Ra and Srnat and then studied in a similar set of pH-dependent exchange experiments. The relative concentrations of the Ra and Sr isotope pairs (226Ra/228Ra and Srnat/85Sr) provided insights into the adsorption strength, incorporation, reversibility and ageing effects. The Srnat data showed that the amount of bound Sr released from aged MBRR samples as the pH decreases is substantially lower than the unaged sample, showing that Sr has been incorporated in less accessible phases during the ageing period. It appears that the uptake of 228Ra by the higher-temperature aged samples is somewhat stronger than the unaged samples; however, Ra isotope exchange plots for aged and unaged samples are similar. Consequently, the stronger binding of 228Ra by the higher-temperature aged samples is probably driven by translocation to kinetically less-favourable surface sites rather than a significant incorporation of Ra within the mineral solids during ageing.