ABSTRACTThe increasing demand for high-tech trace elements supports the need for systematic investigations of their primary occurrences. Mineralogy and trace element characteristics of hydrothermal base-metal veins from the Ruhr Basin (Ruhrgebiet) and the Rhenish Massif (Bergisches Land) in Germany were studied by energy-dispersive X-ray fluorescence mapping, laser ablation-ICP-mass spectrometry, and electron microprobe analyses. Quantitative trace element analysis proves elevated concentrations of Ge and Ga in sphalerite from the Ruhrgebiet. In addition to about 6 Mt of sphalerite-dominated ore, a potential of about 10 t of Ge is indicated to be concentrated in the Auguste Victoria and Graf-Moltke base-metal deposits in the Ruhrgebiet. Assessments on physicochemical fluid properties and metal sources using vitrinite reflectance analysis and host rock investigation indicate a genetic link between the Carboniferous carbonaceous rocks (hosting a number of coal seams) and significant trace metal enrichment in the veins. Gallium enrichment, outlining primary growth zones in ore stage 1 sphalerite, is facilitated by the alteration of Al-bearing minerals in adjacent host rocks due to intense fluid/rock interaction. Reduced Ga and very low In concentrations in ore stage 2 may reflect sealed fluid pathways or changes in the fluid properties. The high level of organic matter in the system probably supported enrichment of Ge in the hydrothermal fluids. The constantly high levels of fixation of Ge in sector zoning patterns of the sphalerite during both ore stages indicate a continuous supply. Elevated contents of Sb together with Cu, As, and Pb in sectors of the sphalerite grains point to a local enrichment of nanometer-scale inclusions of sulfosalt-like phases. Sphalerite of both districts and even of the two ore stages in the Ruhrgebiet shows variations in δ34S isotope compositions due to varying sulfur sources. Both the host rock composition and the presence of organic matter contributed to the trace metal enrichment in the Ruhrgebiet base-metal sulfides as compared to the low contents typical of base-metal ore from the Bergisches Land.

ABSTRACTThe Wekusko Lake pegmatite field in central Manitoba, Canada, is known for its multiple pegmatite dike occurrences, most remarkably its Li-rich pegmatites of economic importance. The Li-rich pegmatites from Wekusko Lake are the focus of this study and belong to the Green Bay group of the Wekusko Lake pegmatite field. These dikes were dated at ca. 1.78 Ga and were emplaced early during the D4 brittle–ductile deformational event. The results presented here describe in detail the pegmatite mineralogy, textures, and zonation of the Li-rich dikes of the Green Bay group, with emphasis on white mica chemistry. The aim of this study is to establish the nature and evolution of white micas from the Li-rich pegmatites of the Wekusko Lake pegmatite field in Manitoba. We aim to understand the differentiation mechanisms that allowed the high level of trace element enrichment observed in the white micas of the studied Li-rich pegmatites. Major and trace elements in white micas from a representative and well studied pegmatite dike were analyzed by electron microprobe and LA-ICP-MS. White mica compositions and textural evidence were used to define two different populations that seem to have been affected by magmatic processes (fractional crystallization) and a secondary episode of metasomatism. Fractional crystallization modeling of a granitic melt can explain some of the trace element enrichment, but extreme Cs enrichment cannot be explained via this mechanism. We interpret that many metasomatic white micas crystallized in boundary layers. Their compositions are controlled by the local melt composition, but aqueous fluids likely contributed to the development of the white mica textures. The substitution mechanisms at play depend on the type of trend and on the stage of evolution. Li enrichment without M2+ enrichment in metasomatic white mica grains is observed, and it is postulated that Fe3+ in white mica explains this behavior. The K/Rb ratio decreases in white micas with fractionation, whereas the concentrations of incompatible elements, such as Cs, Rb, Tl, Ta, and Li, increase. At Wekusko Lake, the Nb and Ta contents seem to be controlled in part by the presence of columbite group minerals and in part by crystallization in boundary layers.

ABSTRACT Lauraniite, Cu6Cd2(SO4)2(OH)12·5H2O, is a new mineral from the Laurani Mine, Aroma Province, La Paz Department, Bolivia, where it is found as a secondary mineral associated with serpierite and brochantite, on a matrix consisting of tennantite and chalcocite. Lauraniite occurs as bladed crystals up to 110 μm in length. Crystals are pale blue and transparent, with a vitreous luster and a white streak. Fracture is uneven. Cleavage is perfect on {100}. The calculated density is 3.40 g/cm3 based on the empirical formula. Optically, lauraniite is uniaxial (+) with α = 1.637(3), β = 1.638(3), γ = 1.638(3) (white light), 2V = 20(2)°, and orientation Z ≈ a. The empirical formula, based on data obtained from electron microprobe analysis, is Cu6.13(Cd1.62Zn0.24)(SO4)1.96(OH12.03Cl0.05)12.08·5.08H2O. Lauraniite is monoclinic, P21/c, a = 7.3200(15), b = 25.424(5), c = 11.283(2) Å, β = 91.62(3)°, V = 2099.0(7) Å3, and Z = 4. The crystal structure, determined using single-crystal data obtained using synchrotron radiation, refined to R1 = 0.0468% for 5999 observed reflections with Fo > 4σ(Fo). It is characterized by undulating, brucite-like sheets consisting of seven Cuϕ6 (ϕ: O2–, OH–, H2O) octahedra and two Cd(OH)6(H2O) polyhedra. Sheets are decorated on one side by corner-sharing SO4 tetrahedra. Linkages between adjacent sheets are provided by H-bonds.

ABSTRACT Mengeite, Ba(Mg,Mn2+)Mn3+4(PO4)4(OH)4·4H2O, is a new mineral from the Spring Creek copper mine, near Wilmington, South Australia, Australia, where it occurs as dark orange-red masses to 0.8 mm across in a quartz matrix. The streak is pale salmon pink and the luster is vitreous. Mengeite is non-fluorescent and the Mohs hardness is ∼3. The measured density is 3.40 g/cm3 and the calculated density is 3.43 g/cm3. Mengeite is biaxial (–) with α = 1.757(4), β = 1.776(4), γ = 1.781(4) measured in white light. Electron microprobe analyses results give the empirical formula, based on 24 O apfu: Ba1.09(Mg0.58Mn2+0.26Cu0.10Al0.02Na0.01Ca0.01□0.09)Σ1.07Mn3+3.88(PO4)4.07(OH)3.52·4.13H2O. The idealized formula is Ba(Mg,Mn2+)Mn3+4(PO4)4(OH)4·4H2O. Mengeite is triclinic, space group , with a = 5.4262(11), b = 5.4274(11), c = 16.387(3) Å, α = 87.61(3), β = 98.97(3), γ = 110.56(3)°, V = 446.28(16) Å3, and Z = 1. The crystal structure of mengeite was solved using synchrotron single-crystal X-ray diffraction data and refined to R1 = 0.0453 for 2115 observed reflections with F0 > 4σ(F0). It is based on [(M2(OH)2(AsO4)2] sheets that are linked in the c-direction alternately by [M3(H2O)4O2] octahedra and by BaO10 polyhedra.

ABSTRACT Hydrogen (δ2H) and oxygen (δ18O) stable isotopes are used to trace fluid sources, metals, and contaminants in the environment and Earth's subsurface. Tourmaline-supergroup minerals provide an opportunity to quantify both δ2H and δ18O from the same grain using in situ analytical techniques (e.g., Secondary Ion Mass Spectrometry – SIMS). These minerals occur in a wide variety of geological environments and have a wide range of chemical compositions. However, large differences in chemical composition are problematic during SIMS analysis, as instrumental mass fractionation (IMF) often varies with the chemical composition of the mineral. Therefore, calibration models derived by analyzing tourmalines of different chemical composition must be developed for accurate analysis by SIMS. Hydrogen and oxygen isotope analysis was done on six reference tourmaline samples using a CAMECA 7f SIMS instrument operating at extreme energy filtering. Spot-to-spot repeatability for tourmalines was in the range 4–5‰ and 0.6–1.0‰ for δ2H and δ18O, respectively. There is a strong correlation between IMF and several elements (B, Si, Ca, Fe, and Fe#). Iron content is the most robust predictor of IMF, and we report two calibration curves for the correction of δ2H and δ18O measured by SIMS using reference tourmaline crystals with different Fe contents, ranging from 0.00 to 14.00 wt.% Fe. This is the first calibration curve used to correct for the fractionation of hydrogen isotope ratios in tourmaline as measured by SIMS. Tourmaline-supergroup minerals require a suite of at least three, with a range of Fe content, to ensure accurate and precise H and O analysis by SIMS. Crystallographic orientation effects were not observed for these tourmalines.

ABSTRACT An occurrence of malhmoodite, Fe2+Zr(PO4)2·4H2O, from the Scott's Rose Quartz mine, Custer County, South Dakota, USA, has been identified. It occurs as divergent groups of yellowish, flat-lying platy crystals on football-size masses of altered löllingite with scorodite, parasymplesite, karibibite, schneiderhöhnite, kahlerite, and zircon. An electron probe microanalysis of malhmoodite yielded an empirical formula (based on 12 O apfu) of Fe1.06(Zr1.10Hf0.03)Σ1.13[(P0.93As0.01)Σ0.94O4]2·4H2O. Single-crystal X-ray structure analysis shows that malhmoodite is the Fe-analogue of zigrasite, MgZr(PO4)2·4H2O. Malhmoodite is triclinic with space group P and unit-cell parameters a = 5.31200(10), b = 9.3419(3), c = 9.7062(3) Å, α = 97.6111(13), β = 91.9796(11), γ = 90.3628(12)°, V = 477.10(2) Å3, Z = 2, in contrast to the previously reported monoclinic symmetry with space group P21/c and unit-cell parameters a = 9.12(2), b = 5.42(1), c = 19.17(2) Å, β = 94.8(1)°, V = 944.26 Å3, Z = 4. The crystal structure of malhmoodite is characterized by sheets composed of ZrO6 octahedra sharing all vertices with PO4 tetrahedra. These sheets are parallel to (001) and are joined together by the FeO2(H2O)4 octahedra. The structure determination of malhmoodite, along with that of zigrasite, warrants a re-investigation of synthetic compounds M2+Zr(PO4)2·4H2O (M = Mn, Ni, Co, Cu, or Zn) that have been assumed previously to be monoclinic.

ABSTRACTThe current classification of granitic pegmatites, originally introduced by Černý (1991a), has been the accepted system for grouping pegmatites of diverse mineralogy and chemistry for nearly three decades. Despite its general acceptance, several issues have been highlighted (Müller et al. 2022) which have imposed some limitations on its use and therefore necessitated the need to reevaluate its methodology. A new classification for granitic pegmatites is proposed in an attempt to be more inclusive of pegmatite types omitted in previous classification schemes. The new approach utilizes a more comprehensive suite of accessory minerals and defines three pegmatite groups which are genetically related to granite plutons and the anatexis of metaigneous and metasedimentary protoliths. Pegmatites belonging to Groups 1 and 2 are generated from the residual melts of S-, A-, and I-type granite magmatism (RGM) as well as being direct products of anatexis (DPA), whereas Group 3 pegmatites are only derived by anatexis.

ABSTRACT Assimilation of country rock xenoliths by the host kimberlite can result in the development of concentric reaction zones within the xenoliths and a reaction halo in the surrounding contaminated kimberlite. Petrographic and geochemical changes across the reaction zones in the xenoliths and the host kimberlite were studied using samples with different kimberlite textures and contrasting xenolith abundances from the Renard 65 kimberlite pipe. The pipe, infilled by Kimberley-type pyroclastic (KPK) and hypabyssal kimberlite (HK) and kimberlite with transitional textures, was emplaced into granitoid and gneisses of the Superior Craton. Using samples of zoned, medium-sized xenoliths of both types, mineralogical and geochemical data were collected across xenolith-to-kimberlite profiles and contrasted with those of fresh unreacted country rock and hypabyssal kimberlite. The original mineralogy of the unreacted xenoliths (potassium feldspar-plagioclase-quartz-biotite in granitoid and plagioclase-quartz-biotite-orthopyroxene in gneiss) is replaced by prehnite, pectolite, and diopside. In the kimberlite halo, olivine is completely serpentinized and diopside and late phlogopite crystallized in the groundmass. The xenoliths show the progressive degrees of reaction, textural modification, and mineral replacement in the sequence of kimberlite units KPK — transitional KPK — transitional HK. The higher degree of reaction observed in the HK-hosted xenoliths as compared to the KPK-hosted xenoliths in this study and elsewhere may partly relate to higher temperatures in xenoliths included in an HK melt. The correlation between the degree of reaction and the kimberlite textures suggests that the reactions are specific to and occur within each emplaced batch of magma and cannot result from external post-emplacement processes that should obliterate the textural differences across the kimberlite units. Xenolith assimilation may have started in the melt, as suggested by the textures in the xenoliths and the surrounding halos and proceeded in the subsolidus. Elevated CaO at the kimberlite-xenolith contact appears to be an important factor in producing the concentric mineralogical zoning in assimilated xenoliths.

ABSTRACT A revised Pt–Fe phase diagram is proposed to replace those used in the materials science literature (e.g., Okamoto 2004), and to improve the one of Cabri & Feather (1975) by adding high-temperature phase equilibria data published in the mineralogical literature. The projected solid-solution fields at room temperature in the pure Pt–Fe system lie at the following approximate compositions: for γ(Pt,Fe) from Pt to Pt0.78Fe0.22, for Pt3Fe from Pt3.04Fe0.96 to Pt2.64Fe1.36, for PtFe from Pt1.16Fe0.84 to Pt0.67Fe0.33, and for PtFe3 from Pt1.26Fe2.94 to Pt0.68Fe3.32. The phase relations and phase boundaries are discussed and evaluated for Pt-Fe alloys occurring in pristine intrusive rocks and ores as well as in eluvial and placer deposits derived from the former by physical and chemical weathering over long periods of geologic time. In spite of the variable concentrations of minor and trace elements, the natural Pt-Fe alloy minerals correlate well with phase relations in the pure Pt–Fe binary system.

ABSTRACT The wide-reef facies of the Merensky Reef in the eastern part of the western lobe of the Bushveld Complex was sampled in order to better resolve otherwise spatially constrained variation in highly siderophile elements across this geological unit. The platinum group element mineralogy and whole-rock highly siderophile element concentrations were measured across two vertical sections in close proximity. In one section, the Merensky Reef unit was bound by top and bottom platinum group elements-enriched horizons (reefs) with a well-developed pegmatoidal phase in the top third of the intrareef pyroxenite, but with neither a top nor a bottom chromitite present. The other drill core section featured a thin (<1 cm thick) chromitite layer associated with the highest platinum group element concentrations of any rock in this study as the bottom reef, but with a chromitite-absent top reef, and very poor development of the pegmatoid. Primitive mantle-normalized profiles of the main lithological units show relatively flat, primitive mantle-like highly siderophile element abundances (Cr, V, Co, Ni, platinum group elements, Au and Cu) in the Merensky pyroxenite, with modest depletion in Ir-affiliated platinum group elements. The platinum group element-rich top and bottom reefs, and the pegmatoidal upper pyroxenites, display characteristic enrichment in the Pt-affiliated platinum group elements and undepleted Ir-affiliated platinum group elements. The leuconoritic hanging wall and footwall rocks show comparable highly siderophile element profiles, distinguished from one another by relative depletion in the Pt-affiliated platinum group elements of the footwall samples. The vertical variation in highly siderophile element abundances through both sections is characterized by low platinum group element abundances through the lower reef pyroxenite, with platinum group element, Au, and Cu ± Ni concentrations increasing through the upper pegmatoidal pyroxenite, and main enrichment peaks at the top and bottom reefs. Significant localized (centimeter-scale) zones of chalcophile metal depletion are present immediately above the top reef and below the bottom reef. In addition, a wider zone of Pt-affiliated platinum group elements (with Pd more depleted than Pt)-depletion was identified within the pegmatoidal pyroxenite around one meter below the top reef. The platinum group element mineralogy of the bottom reef consists mainly of platinum group element sulfides, with minor arsenides and antimonides. In contrast, the platinum group element mineralogy of the top reef, and the small amount of data from the intrareef pyroxenite, mainly consist of Pt-affiliated platinum group elements-Bi-tellurides. The Pt-sulfides are mainly equant, relatively coarse crystals (many grains between 50 to 100 μm2 area), contrasting with the Pt-affiliated platinum group elements-Sb-As and -Bi-Te minerals that tend be high aspect-ratio grains, occurring in veinlets or as rims on earlier-forming platinum group element phases. These Te-As-Bi-Sb compounds are closely associated with chlorite, actinolite, quartz, and chalcopyrite, consistent with secondary deposition at lower temperatures and association with aqueous fluids. A model is proposed involving the emplacement of the Merensky unit as a magma pulse into at least semi-crystallized host rock, followed by aqueous fluid saturation and local migration, combined with concentration of late magmatic fluids around the top and bottom contacts of the magma pulse. Late remobilization of Pt-affiliated platinum group elements from the zones immediately (centimeter-scale) above the top reef, and from the underlying meter or two of pyroxenite, and from the centimeters underlying the bottom reef, have added additional platinum group elements to the reefs as late platinum group elements-Te-As-Bi-Sb minerals, independent of whether or not chromite is present in the reef initially.