ALBERT

Description: A gold-bearing ore from the San Salvador vein, Capillitas mine, Argentina, was exposed to an enriched, iron- and sulfur-oxidizing bacterial consortium for two months in an experimental system that represented an oxidized, acid-leached weathering environment. Within this laboratory model, the dissolution of metal sulfide minerals by the bacterial consortium liberated gold grains that floated on water. Surficial crevices on grains contained detrital material associated with μ m-scale, gold-rich bacteriomorphic structures interpreted to be relics of gold dissolution. The presence of nanophase gold particles, i.e., colloids and octahedral platelets, was attributed to gold reprecipitation. These secondary gold structures suggest that gold dissolution/reprecipitation, i.e., cycling, was occurring concurrently with the bacterially catalyzed dissolution of metal sulfides. The flake-like morphology and small size of gold grains, i.e., high surface area to volume ratio increased by μ m-scale surface dissolution textures, would have enhanced their propensity to float. The liberation of buoyant gold grains and secondary gold particles could contribute to rapid gold mobility and dispersion in natural environments.

Description: An assemblage of bismuth-rich, tellurium-bearing minerals in the El Quemado pegmatite, Salta, Argentina, represents late-stage mineralization in a spodumene-subtype, rare-element class granitic pegmatite. The minerals occur in an irregular, volumetrically minor core-margin association, dominated by fine-grained muscovite and quartz, with accessory U-rich fluornatromicrolite, zircon, bismuth, bismuthinite, emplectite, hodrusite, and the sulfotellurides joséite-A, joséite-B, tetradymite and ingodite. Early bismuth is replaced by abundant bismuthinite, which also locally contains symplectitic intergrowths of emplectite (Cu 1.02 Bi 0.98 S 2.00 ). A single euhedral crystal of hodrusite [(Cu 4.04 Fe 0.12 Ag 0.03 ) 4.19 (Bi 5.87 Pb 0.02 ) 5.89 S 10.92 ] has Pb-bearing tips that contain 3.62 to 4.39 wt.% Pb (0.33 to 0.40 apfu respectively). Joséite-A (Bi 4.04 Te 0.95 S 2.01 ) forms an intergrowth with ingodite, enclosed in emplectite. Joséite-B (Cu 0.02 Bi 4.01 Te 1.93 S 1.04 ) is intergrown with joséite-A and with bismuthinite in emplectite. Tetradymite [(Bi 2.00 Cu 0.02 ) 2.02 Te 1.95 S 1.03 ] is included in emplectite and bismuthinite. Ingodite is usually enclosed in bismuthinite as very small grains with a composition Bi 1.98 Te 1.00 S 1.02 . Late-stage or supergene alteration of this association generated fairly abundant bismutite and rare bismite. On the basis of experimental data, the equilibrium association of bismuth, bismuthinite, emplectite and hodrusite, typical of hydrothermal ore deposits but uncommon in granitic pegmatites, is restricted to relatively low temperatures and a pressure in the range 2–3 kbar.

Description: The complex association of secondary phosphates from the Li-bearing, rare-element San Elías pegmatite in the Eastern Pampean ranges of Argentina shows widespread albite-hosted dendritic montebrasite in its northern part and lepidolite in the south. This dendritic montebrasite survived low-temperature processes virtually intact, but subrectangular blocks of montebrasite along the margins of quartz core were extensively modified in three stages: (i) two generations of secondary montebrasite intimately intergrown with hydroxylherderite, augelite, and fluorapatite, (acid hydrous fluids, locally channeled, at ~450°–420°C, ~2 kbar); (ii) goyazite–crandallite and hydroxylapatite formed after P–T equilibration between the pegmatite and its host rock along the path of metamorphic cooling, which introduced Ca, Sr and minor S from the host rocks into the pegmatite (at about 〈300°C); (iii) at a still lower T, the remainder of the primary montebrasite and all of its alteration products were subject to extensive leaching, removal and dispersal of phosphorus, and introduction of Si, generating pseudomorphs consisting mainly of kaolinite, quartz and minor lithian muscovite, K-feldspar (adularia) , and traces of residual microlite as remnants of previous alteration stages.

Description: The Virorco dumortierite-bearing pegmatite dikes, in Sierra de San Luis, Eastern Pampean Ranges of central Argentina, are a group of thin, steeply dipping dikes one to 10 cm thick with variable lengths (a few dm to 〈2 m). The pegmatites are emplaced in partially uralitized norite and gabbro that belong to a larger mafic-ultramafic intrusive belt. The pegmatite dikes are symmetrically zoned, with quartz, albite, oligoclase, tourmaline-supergroup and dumortierite-group minerals, muscovite and kyanite as the major phases; the accessory and trace minerals include beryl, chrysoberyl, garnet, fluorapatite, columbite-(Mn) to tantalite-(Mn), pollucite, gahnite, zircon, uraninite and thorite. Holmquistite was found in the exocontact assemblage. Primary textures of magmatic origin were partially disrupted by partial replacements by later minerals and incipient to strong deformation. The whole-rock chemical composition of the dikes shows SiO 2 contents normal for rare-element pegmatites, whereas amounts of Al 2 O 3 and B 2 O 3 are very high. The composition features high MgO, FeO, CaO and P 2 O 5 and, for pegmatites, unusually low Na 2 O and K 2 O contents. Amounts of trace elements are remarkably high in the case of Cs (4.3–94.1 ppm), Ta (130–500) and Be (137–261). The normalized REE contents are low (0.1 to 30 times chondrite), highlighted by a strong negative Eu anomaly. Five textural and compositional types of tourmaline-supergroup minerals were identified in the different pegmatitic zones, ranging from dravite-rich compositions to rossmanite, passing through schorl and Mn-rich elbaite. At least four generations of the dumortierite–holtite minerals are texturally and compositionally represented in these dikes: the earliest dumortierite replaces muscovite and tourmaline, locally together with a second generation that grades into As-poor holtite. The third generation is represented by overgrowths or individual crystals of As-poor and As-rich holtite; it is commonly overgrown by the last generation of dumortierite enriched in As. The chemical evolution of dumortierite-group minerals is characterized by an increase of Ta, Nb and minor As, followed by an extensive enrichment in As (+ Sb + Bi) along with gradual decrease in Ta + Nb. The various assemblages and particularly the compositional trends of tourmaline, dumortierite–holtite and columbite reflect superimposed processes. The initial stage comprises the magmatic crystallization of a highly evolved and boron-rich peraluminous melt. The second stage was a prograde medium-pressure metamorphism, with a fluid-phase-related episode of crystallization. The most likely source of the initial melt is an extraction of residual melt from an almost completely crystallized rare-element parental pegmatite.

Description: A bstract Ishiharaite is a new sulfide mineral, (Cu,Ga,Fe,In,Zn)S, discovered at the Nueva Esperanza vein, Capillitas mine (27º20'43'' S, 66º23'17'' W, 3290 m osl) an epithermal ore deposit belonging to the Farallón Negro Mining District, northwestern Argentina. The mineral occurs as subhedral, equidimensional, individual grains (20 to 50 μm in size) included in tennantite. It is a dark gray metallic mineral, opaque and non-fluorescent. Under polarizing-reflected light, it is an isotropic mineral, and its color is burgundy brown with a faint violet hue in air and violet-burgundy in oil. The main reflectance values are (R air ,R oil – /nm): 18.27,6.77 – 470; 20.10,7.91 – 546; 21.74,8.96 – 589; and 23.94,10.44 – 650. Ishiharaite is cubic, space group F 4{macron} 3 m , a 5.368(1) Å, V 154.68(1) Å 3 , Z = 4. The strongest five X-ray powder-diffraction lines [ d in Å (I)( hk l)] are: 3.096 (100) (111); 1.897 (60) (220); 1.620 (40) (311); 2.684 (20) (200); 1.097 (15) (422). Electron-microprobe analyses of the natural grains ( n = 22) give an average composition (wt.%) of: S 30.77, Cu 33.61, Ga 13.31, In 9.48, Zn 5.74, Fe 6.13; the average ( n = 6) chemical composition of the synthetic phase is: S 30.73, Cu 28.05, Ga 15.99, In 11.86, Zn 7.37, Fe 6.13. The empirical formulae of ishiharaite and the synthetic analogue, based on 2 apfu , are: (Cu 0.55 Ga 0.19 Fe 0.13 In 0.08 Zn 0.08 ) 1.03 S 0.97 , and (Cu 0.45 Ga 0.24 Fe 0.11 In 0.11 Zn 0.11 ) 1.02 S 0.98 , respectively. The mineral (IMA No. 2013-119) is named in honor of Dr. Shunso Ishihara (b. 1934), Emeritus Advisor of AIST (Advanced Industrial Science and Technology), Tsukuba, Japan.

Description: The syenite pegmatitic segregation veins (SPSV) of the Early Miocene La Peña alkaline complex (LPC), Mendoza, Argentina, are emplaced in a malignite body. They occur as veins, parallel layers, and small elliptical bodies 1 to 6 cm wide and 0.2 to 1 m in length. The veins with a pegmatitic to micropegmatitic texture have a thin dark border composed of andradite, potassic-hastingsite, and dark micas and a thicker internal zone of poikilitic Ba-Sr-poor K-feldspar (Or 90.3 Ab 8.9 An 0.8 ), nepheline (Ne 74.9 Ks 19.4 Qz 5.7 to Ne 78.7 Ks 20.0 Qz 1.3 ), potassic-hastingsite, dark mica, andradite, scarce clinopyroxene (diopside–hedenbergite), and locally zoned microphenocrysts of Ba-Sr-rich K-feldspar (Or 75.6 Ab 21.7 An 2.7 ). Accessory fluorapatite, titanite, interstitial sodalite, and magnetite and secondary abundant Na- and K-rich zeolites, calcite, chlorite-group minerals, and possibly cancrinite have been identified. The textural and mineralogical characteristics of the SPSV show genetic links with the host malignite that belongs to the potassic alkaline series. The SPSV were formed from a residual syenitic melt (malignite) extracted from a parental tephritic magma. In the residual malignite, the concentration of primary crystals (apatite, clinopyroxene, Ba-Sr-rich K-feldspar, and nepheline) formed a crystal network (mush) with the open spaces occupied by small amounts of residual melt enriched in Al, Na, K, and volatiles and depleted in Ba and Sr. Deformation (by shear movements plus magmatic pressures) produced microfractures and fractures which were occupied by residual interstitial melt. In situ crystallization within these fractures resulted in the formation of the SPSV.

Description: Achalaite is a new mineral of the wodginite group from the La Calandria granitic pegmatite, Cañada del Puerto, Córdoba province, Argentina (31°25'S, 64°55'W). The mineral occurs as polygranular aggregates up to 1.5 cm across, included in albite ± quartz with exsolutions of Ta-rich rutile and intergrown with microlite-group minerals. Achalaite has a black color and streak, metallic luster, H = 51/2, D calc = 6.285 g/cm 3 , and appears to lack cleavage. In reflected light, it is light grey with a slightly violet tint in air, and light grey with an olive tint in oil. Its bireflectance in both air and oil is weak but noticeable. Pleochroism is not observed. With crossed polarizers anisotropy in air is weak, particularly noticeable along grain boundaries; in oil, it is medium with light to intermediate olive grey tint. Internal reflections have not been observed either in air or oil. Data on minimum and maximum reflectances for the COM wavelengths are [ (nm): R air , R oil (%)]: 470: 16.89, 17.72 and 5.26, 5.76; 546: 16.49, 17.26 and 4.98, 5.32; 589: 16.34, 17.04 and 4.97, 5.26; 650: 16.23, 16.94 and 4.86, 5.19. Achalaite, indexed by analogy with wodginite, is monoclinic, space group C 2/ c , Z = 4. Refined unit-cell dimensions are a 9.422(4) Å, b 11.427(3) Å, c 5.120(1) Å, β 90.12° (4), V 551.2(3) Å 3 . The strongest five lines in the X-ray powder diffraction pattern are as follows ( d [Å], I %, hkl ): 3.630, 40, 220; 2.964, 100, , 221; 2.493, 40, 041; 1.735, 40, ; 1.711, 50, , 441. Eight electron microprobe analyses (WDS) gave the following mean composition: WO 3 2.41, Nb 2 O 5 30.18, Ta 2 O 5 37.56, TiO 2 6.90, ZrO 2 0.88, SnO 2 3.82, Fe 2 O 3 4.35, FeO 7.54, MnO 5.14, CaO 0.02, UO 2 0.38, total 99.18 wt.%. The average empirical formula is: (Fe 2+ 2.211 Mn 1.524 Fe 3+ 0.226 U 0.030 Ca 0.009 ) 4.000 (Ti 1.819 Fe 3+ 0.920 Ta 0.579 Sn 0.533 Zr 0.150 ) 4.000 (Nb 4.781 Ta 3.000 W 0.219 ) 8.000 O 32 , ideally Fe 2+ TiNb 2 O 8 . Achalaite is the first member of the wodginite group with Nb dominant over Ta; it is genetically considered a post-magmatic phase. The name of achalaite (CNMNC – IMA 2013-103) derives from the Achala granite batholith, located in Córdoba, Argentina.

Description: The assemblage of Nb-Ta-Ti-Sn oxide minerals in some zoned Devonian granitic pegmatites at the La Calandria mine, Cañada del Puerto, shows complex intergrowths of achalaite, ferrotitanowodginite, Ta-rich rutile, columbite-(Mn), ixiolite, and fluorcalciomicrolite. The chemical composition of these phases is variable, but in general the minerals show slight predominance of Nb over Ta and a clearly defined predominance of Fe over Mn, with minor participation of Ti, Sn, and W. The minerals in this assemblage are not in equilibrium and represent magmatic and subsolidus phases that are distinguished texturally and chemically. The primary magmatic stage of mineralization possibly crystallized ixiolite + Ta-rich rutile I in the outer zones of the pegmatite and, less commonly, local columbite-(Mn) in the inner part. Subsolidus unmixing of ixiolite produced achalaite and ferrotitanowodginite I + Ta-rich rutile II. Contemporaneously, Ta-rich rutile I locally exsolved ferrotitanowodginite/achalaite II + cassiterite. A localized Ca-F-rich hydrothermal overprinting event transformed Ta-rich rutile I to Ta-rich rutile III + ferrotitanowodginite/achalaite II + fluorcalciomicrolite. Furthermore, the hydrothermal overprint produced peripheral transformation of columbite-(Mn) to possibly achalaite III and widespread distribution of fluorcalciomicrolite throughout the assemblage.