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Canadian Mineralogist
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ISSN (Print) 0008-4476 - ISSN (Online) 1499-1276
Published by GeoScienceWorld

[17 journals]

The origin of gem spodumene in the Hamadan Pegmatite, Alvand Plutonic
Complex, western Iran
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  Authors: Sheikhi Gheshlaghi R; Ghorbani M, Sepahi A, et al.
  Abstract: ABSTRACTPegmatite bodies with a simple mineral composition are widespread within the Sanandaj-Sirjan Zone (SaSiZ), Zagros Orogen, Iran; however, gem-bearing pegmatite bodies are rare. There is a pegmatitic vein within the Hamadan garnet (± andalusite ± staurolite) schist adjacent to the Alvand Plutonic Complex (APC), south of Hamedan city (western Iran), in which large crystals of gem spodumene occur together with quartz, amazonite, beryl, tourmaline, and apatite. This spodumene-bearing pegmatite consists of four major zones with slightly different mineral compositions from the border to the core. The wall zone of quartz-rich granitoid and the intermediate zone of alkali granite have trondhjemitic compositions near the quartzolitic gem-bearing core zone. All parts of the vein are peraluminous in composition and exhibit S-type affinity. Two types of spodumene which have been distinguished in the core zone are colorless to very pale yellow and pink, transparent with vitreous luster and inclusion-free (eye clean) under 10× magnification. The different color in these minerals can be attributed to the slightly different chemical compositions, particularly lower Fe/Mn ratios in the pink material. The δ7Li values of the spodumene (+5.58 to +6.57‰) are indicative of the incorporation of middle continental crustal components in their genesis. Change in the mineral assemblage from tourmaline-bearing in the intermediate zone to spodumene + tourmaline in the core zone of the spodumene-bearing pegmatite is consistent with increasing lithium content from the wall zone to the core. Petrographic, geochemical, and isotopic data indicate that partial melting of middle-crustal Al-rich metapelitic source was followed by fractional crystallization to generate these rocks. In this concern, the required Li for the crystallization of spodumene was probably supplied by the breakdown of staurolite of the Hamadan schist and/or subsequent fractional crystallization of the parent magma. The results also demonstrate that the regional tectonic regime exerts a primary control on the occurrence and emplacement of the miarolitic pegmatite in the upper crust and the formation of gem spodumene during late-stage magmatic activities.
  PubDate: Tue, 29 Mar 2022 00:00:00 GMT
Macro- to nanoscale mineral relationships in surficial
cobalt-arsenic-bearing mine tailings of the Cobalt Mining Camp,
Northeastern Ontario, Canada
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  Authors: Courchesne B; Schindler M, Lussier AJ, et al.
  Abstract: ABSTRACTArsenates, which correspond to the majority of known arsenic (As)-bearing minerals, control the mobilization of As in contaminated soils, sediments, and fluvial environments as well as in tailings and mine waste piles. Additionally, arsenate-bearing Fe-(hydr)oxides are of particular significance for the control of As mobility, as they are among the most thermodynamically stable minerals under near-neutral to alkaline pH conditions. However, in the surficial (upper 30 cm) alkaline mine tailings at the Cobalt Mining Camp in Northeastern Ontario, Canada, these phases only occur in trace amounts. This study attempts to understand this unusual mineralogical feature through an investigation of the relationships between nano- and macroscale mineralogical and geochemical features at two tailings sites (A and B) at the Cobalt Mining Camp. Sixty samples from two depth profiles (0–30 cm; i.e., one sample per centimeter) were collected at the two sites, analyzed for their major and minor chemical elements, and characterized for their mineralogical composition at the nano- to centimeter scale. The tailings material at both sites is predominantly composed of minerals of the amphibole, chlorite, and feldspar groups, as well as carbonates (calcite and dolomite). Minor phases are Co-Fe-Ni-Zn-sulfarsenides and -arsenates. The tailings material at site B contains, on average, higher concentrations of As, Co, Sb, and Zn and lower concentrations of Fe than the material at site A. Secondary (scanning electron microscope) and transmission electron microscopy studies indicate that the alteration of primary sulfarsenides to secondary arsenates may proceed in the following sequence: (1) the formation of Fe-hydroxide and -arsenate mineral surface coatings on sulfarsenides; (2) the downward mobilization of Co-Ni-Zn-arsenate and (FeOHCO3)aq species; (3) replacement of earlier-formed scorodite by Co-Ni-Zn-arsenates; (4) the precipitation of Co-Ni-Zn-arsenates on the surfaces of silicates; and (5) neoformation of Fe-rich hydroxy-interlayered minerals at greater depth, partly replacing earlier-formed Co-Ni-Zn-arsenates. These processes result in layers enriched in As, Co, Sb, and Zn (increase in Co#) and enriched and depleted in Fe (increase and decrease in Fe#) in tailings material at both sites. The TEM studies further indicate that Co-Ni-Zn-arsenates precipitate initially as nanoparticles on the surface of scorodite and detrital silicates and subsequently coarsen through Oswald ripening. The mineralogical-geochemical features depicted in this study provide a better understanding of the geochemical behavior of Co, Fe, and As in alkaline tailings and may assist in the interpretation of mineral-microbial community associations and the development of effective bioleaching strategies for the strategic element cobalt.
  PubDate: Tue, 29 Mar 2022 00:00:00 GMT
A proposed new mineralogical classification system for granitic pegmatites
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  Authors: Wise MA; Müller A, Simmons WB.
  Abstract: 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.
  PubDate: Tue, 29 Mar 2022 00:00:00 GMT
Petrographic and geochemical characteristics associated with felsic
xenolith assimilation in kimberlite
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  Authors: Niyazova S; Kopylova M, Gaudet M, et al.
  Abstract: ABSTRACTAssimilation 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.
  PubDate: Fri, 04 Mar 2022 00:00:00 GMT
Bonding between the decavanadate polyanion and the interstitial complex in
pascoite-family minerals
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  Authors: Hawthorne FC; Hughes JM, Cooper MA, et al.
  Abstract: ABSTRACTThe decavanadate isopolyanion, [V10O28]6–, is a constituent of pascoite-family vanadate minerals and synthetic materials, and both protonated, [HxV10O28](6–x)–, and mixed-valence, [V4+xV5+10–x)O28](6+x)–, varieties have been described. Here we analyze the interaction between the interstitial complex and the decavanadate structural unit using the principle of correspondence of Lewis acidity-basicity. The Lewis base strengths of the decavanadate polyanions vary from 0.054 to 0.154 vu and [V10O28] structures can form from the simple cations Cs+, Rb+, K+, Tl+, and Na+; simple cations with higher Lewis acidities are too acid to form structures. Cations may bond to transformer (H2O) groups to form polyatomic cations that have lower Lewis acidities than the corresponding simple cation. The occurrence of the polyatomic cation {(V5+O2)Al10(OH)20(H2O)18}11+ in caseyite shows the potential for decavanadate phases to incorporate large heteropolycations into their structures. In turn, this suggests that the [V10O28] polyanions may be used to induce co-crystallization of large aqueous polyatomic cations, thus facilitating their structural characterization. There is an inverse relation between the amount of (H2O) in the interstitial complex and the number of bonds between interstitial simple cations and the O2– ions of the vanadate units, and there is a strong correlation between the unit-cell volume per decavanadate unit and the number of (H2O) groups.
  PubDate: Fri, 04 Mar 2022 00:00:00 GMT
The Mineralogy of Pt-Fe alloys and phase relations in the Pt–Fe
binary system
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  Authors: Cabri LJ; Oberthür T, Schumann D.
  Abstract: ABSTRACTA 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.
  PubDate: Fri, 04 Mar 2022 00:00:00 GMT
Significance of viscous coalescence in migmatites of the Assam-Meghalaya
Gneissic Complex, eastern India
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  Authors: Gogoi B; Chauhan H.
  Abstract: ABSTRACTThe magnetite ocelli preserved in the Chandrapur area of the Assam-Meghalaya Gneissic Complex, eastern India, display viscous coalescence. The viscous coalescence phenomenon generally occurs below a critical capillary number, which is governed by the size of the coalescing droplets. The smaller the size of the coalescing droplets, the greater the possibility that they will exhibit viscous coalescing. From our results we infer that intrusion of younger pegmatitic magma into the much older polyphase deformed quartzofeldspathic gneiss of Chandrapur initiated localized partial melting in the gneissic rocks surrounding the intrusions. This localized partial melting produced small magma pools or leucocratic neosome, which was followed by intermingling between the in situ melt (leucocratic neosome) and external melt (pegmatite), leading to chaotic mixing between the two magmatic phases. Chaotic mixing produced thin veins or filaments of the pegmatitic magma as a result of stretching and folding dynamics. Gradually, the thin filaments underwent capillary instability to produce discrete viscous swirls or ocelli. The ocelli consist of leucocratic minerals like K-feldspar, plagioclase, and quartz, with crystals of magnetite at the center representing magnetite ocelli. The mineralogical assemblage of the ocelli matches that of the pegmatitic rocks. After their formation, some of the smaller magnetite ocelli underwent very gentle collisions due to the effect of capillary and viscous forces. Such collisions produced pairs, clusters, or linear structures that are now preserved in the migmatites of the study area.
  PubDate: Fri, 25 Feb 2022 00:00:00 GMT
Shakhdaraite-(Y), ScYNb 2 O 8 , from the Leskhozovskaya granitic
pegmatite, the valley of the Shakhdara River, southwestern Pamir,
Gorno-Badakhshanskii Autonomous Region, Tajikistan: New mineral
description and crystal structure
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  Authors: Pautov LA; Mirakov MA, Sokolova E, et al.
  Abstract: ABSTRACTShakhdaraite-(Y), ideally ScYNb2O8, is a new mineral from the Leskhozovskaya miarolitic granitic pegmatite at the Shakhdara River, southwestern Pamir (Tajikistan). Shakhdaraite-(Y) occurs mainly as grains from 10 to 150 μm in size in a near-miarolitic pegmatite complex in association with quartz, albite, pyrochlore-microlite, fersmite, and an unnamed Sc-Nb oxide; only one large, single, well-shaped crystal 200 μm long was found in a small cavity with quartz, albite, bertrandite, pyrochlore, and jarosite. Shakhdaraite-(Y) is black to dark-brown, streak is brown. Luster is vitreous semi-metallic. It is brittle with conchoidal fracture. Mohs hardness is 5. VHN100 = 436 kg/mm2. Dcalc. = 5.602 g/cm3. In reflected light, it is light gray and its reflective capacity is moderate to low. Anisotropy is distinct, without color effects. Pleochroism was not observed. Internal reflections are red-brown. Reflectance values were measured in air with SiC as reference material [λ(nm), Rmax, Rmin]: 470, 14.6, 13.9; 546, 14.0, 13.4; 589, 13.9, 13.3; 650, 13.8, 13.1. Electron probe microanalysis (WDS mode, 7 points) gives (wt.%): Nb2O5 50.70; Ta2O5 4.52; TiO2 0.08; WO3 0.79; SnO2 1.54; CaO 1.01; Sc2O3 11.35; MnO 1.38; FeO 0.01; Y2O3 12.00; Ce2O3 0.21; Pr2O3 0.04; Nd2O3 0.27; Sm2O3 0.32; Eu2O3 0.07; Gd2O3 0.86; Tb2O3 0.22; Dy2O3 2.07; Ho2O3 0.29; Er2O3 1.33; Tm2O3 0.35; Yb2O3 2.80; Lu2O3 0.32; PbO 0.24; ThO2 1.90; UO2 3.30, total 97.97. The empirical formula of shakhdaraite-(Y) based on O = 8 apfu (atoms per formula unit) is (Nb1.91Sc0.83Y0.53Ta0.10Mn0.10Ca0.09 Yb0.07U4+0.06Dy0.06Sn0.05Th0.04Er0.03Gd0.02W6+0.02Pb0.01Ce0.01Nd0.01Sm0.01Tb0.01Ho0.01Tm0.01Lu0.01Ti0.01)Σ4.00O8, Z = 2. The simplified formula is Sc(Y,Yb)Nb2O8, where Yb is the dominant lanthanoid. Shakhdaraite-(Y) is monoclinic, space group P2/c, a 9.930(2), b 5.6625(11), c 5.2108(10) Å, β 92.38(3)°, V 292.7(5) Å3, Z = 2. The crystal structure was solved by direct methods [R1 = 0.0269, 878 unique reflections (F > 4σF)]. There are three cation M sites: [6]M(1) = Nb2apfu, [6]M(2) = Sc apfu, and [8]M(3) = Y apfu, ideally M = ScYNb2apfu. The M(1) and M(2) octahedra each form a brookite chain along c. The Y-dominant [8]M(3A) polyhedra form a brookite-like kinked chain, and each M(3A) polyhedron of one brookite-like chain shares two edges with the two M(3A) polyhedra from the adjacent brookite-like chain, thus forming a [Y2O8]10– layer. In the structure of shakhdaraite-(Y), M(1A) and M(2) brookite chains and a layer of [8]-coordinated M(3A) polyhedra alternate along a. Shakhdaraite-(Y) is isostructural with samarskite-(Y), ideally YFe3+Nb2O8. Shakhdaraite-(Y) [Russian Cyrillic: шахдараит-(Y)] is named after its type locality: the valley of the Shakhdara River in the southwest of the Pamir Mountains.
  PubDate: Fri, 25 Feb 2022 00:00:00 GMT
The redefinition of gunterite, Na 4 Ca[V 10 O 28 ]·20H 2 O
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  Authors: Kampf AR; Cooper MA, Hawthorne FC, et al.
  Abstract: ABSTRACTGunterite was originally assigned the ideal formula Na4[H2V10O28]·22H2O. More detailed bond-valence analysis brought into question the presence of a protonated decavanadate anion, which led to the reexamination of the mineral. Infrared spectroscopy confirmed the absence of NH4. Reinterpretation of the original crystal structure data and new electron-probe microanalyses support the redefinition of gunterite as having the ideal formula Na4Ca[V10O28]·20H2O. This redefinition has been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association.
  PubDate: Thu, 24 Feb 2022 00:00:00 GMT
A proposed new mineralogical classification system for granitic pegmatites
– Part I: History and the need for a new classification
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  Authors: Müller A; Simmons W, Beurlen H, et al.
  Abstract: ABSTRACTThis study represents the precursor and complementary study for the new classification of granitic pegmatites by Wise et al. (this issue) and provides a detailed analysis of existing classifications of granitic pegmatites in terms of applied classification criteria and applicability. The analyses revealed that a new classification scheme for granitic pegmatites is required. In the second part measurable, inferred, and presumed classification criteria applicable for the classification of pegmatites are listed and discussed, including how they should be utilized in future classification schemes. This study records the process of how the new classification scheme for pegmatites was developed.
  PubDate: Thu, 06 Dec 2018 00:00:00 GMT