The Canadian Mineralogist最新文献

{"title":"Significance of Viscous Coalescence in Migmatites of the Assam-Meghalaya Gneissic Complex, Eastern India","authors":"Bibhuti Gogoi, H. Chauhan","doi":"10.3749/canmin.2000042","DOIUrl":"https://doi.org/10.3749/canmin.2000042","url":null,"abstract":"\u0000 The 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.","PeriodicalId":134244,"journal":{"name":"The Canadian Mineralogist","volume":"6 5","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-02-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"113943041","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Shakhdaraite-(Y), ScYNb2O8, from the Leskhozovskaya Granitic Pegmatite, the Valley of the Shakhdara River, Southwestern Pamir, Gorno-Badakhshanskii Autonomous Region, Tajikistan: New Mineral Description and Crystal Structure","authors":"L. Pautov, M. A. Mirakov, E. Sokolova, Maxwell C. Day, F. Hawthorne, Manuchekhr A. Schodibekov, V. Y. Karpenko, Saimudasir Makhmadsharif, A. R. Faiziev","doi":"10.3749/canmin.2000122","DOIUrl":"https://doi.org/10.3749/canmin.2000122","url":null,"abstract":"\u0000 Shakhdaraite-(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.","PeriodicalId":134244,"journal":{"name":"The Canadian Mineralogist","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-02-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132777929","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Fluid Inclusion and Titanite U-Pb Age Constraints on the Yuanjiang Ruby Mineralization in the Ailao Shan-Red River Metamorphic Belt, Southwest China","authors":"Wenqing Huang, P. Ni, Jungui Zhou, Ting Shui, J. Pan, Mingsen Fan, Yu-Long Yang","doi":"10.3749/canmin.2100009","DOIUrl":"https://doi.org/10.3749/canmin.2100009","url":null,"abstract":"\u0000 The Yuanjiang marble-hosted ruby deposit lies in the central segment of the Ailao Shan metamorphic massif of the Ailao Shan-Red River metamorphic belt. The mineralizing fluid and age were characterized by detailed petrography, Raman spectroscopy, microthermometry, and in situ titanite laser ablation-inductively coupled plasma-mass spectrometry dating. Some fluid inclusions in the corundum show an interesting morphology with a diaspore crystal fully separating the whole inclusion into two smaller inclusions. This morphological feature can be explained by morphological ripening and subsequent reactions between the trapped H2O and the host corundum during the cooling of the inclusion. Fluid inclusions in the ruby belong to the system CO2–H2S–COS–S8–H2S2–CH4–AlO(OH) with various daughter minerals, including diaspore, gibbsite, and native sulfur (S8). The observed seven-component fluid inclusion composition can be explained by two steps: (1) original fluid inclusion capture during deposit formation with compositions including CO2, H2S, COS, CH4, S8, and H2S2, and (2) post-entrapment fluid inclusion modification, such as diaspore and gibbsite. The presence of hydrous minerals in fluid inclusions strongly supports the idea that water was once present in the initial fluids.\u0000 In the Yuanjiang deposit, petrographic evidence shows that titanite formed simultaneously with ruby, and U-Pb dating of titanite allows us to conclude that the ruby mineralization formed at 23.4 ± 0.3 Ma, in other words during the Himalayan orogeny.","PeriodicalId":134244,"journal":{"name":"The Canadian Mineralogist","volume":"27 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-02-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122519938","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Taking Rocks for Granite: An Integrated Geological, Mineralogical, and Textural Study of Curling Stones Used in International Competition","authors":"Derek. D. V. Leung, A. McDonald","doi":"10.3749/canmin.2100052","DOIUrl":"https://doi.org/10.3749/canmin.2100052","url":null,"abstract":"The duopoly of curling stone sources suitable for international competition (Ailsa Craig, Firth of Clyde, Scotland and Trefor, Llŷn Peninsula, North Wales) has led to a long-held paradigm that the rocks from these localities are geologically unique. To evaluate this paradigm, we provide the first comprehensive, detailed analyses of the geological, mineralogical, and textural properties of curling stones, with a focus on three main areas: (1) the collective features of all curling stone lithologies, (2) the differences among the lithologies used for running bands versus striking bands, and (3) the presence of quartz, whose brittleness was previously considered to be undesirable in curling stones. The four curling stone varieties from the two localities (Ailsa Craig Blue Hone, Ailsa Craig Common Green, Blue Trefor, and Red Trefor) were analyzed using petrography, scanning electron microscopy, digital image analysis, powder X-ray diffraction, and normative mineralogy, with the following results: The curling stone varieties that are suitable for international competition can be broadly characterized as fine- to medium-grained, sparsely porphyritic to glomeroporphyritic, weakly to moderately altered, massive to weakly foliated, Phanerozoic granitoids (sensu lato). All four varieties are composed of feldspar (65–80 mod.%, with albite being the dominant component) and quartz (15–25 mod.%), along with mafic and accessory minerals (5–20 mod.%). The Ailsa Craig suite is classified as alkali feldspar quartz syenite, whereas the Trefor suite ranges from quartz monzogabbro (Blue Trefor) to granodiorite-granite (Red Trefor). None are strictly classified as granite.Predominantly equigranular textures are preferred for running bands (Ailsa Craig Blue Hone), whereas seriate to glomeroporphyritic textures are preferred for striking bands (Ailsa Craig Common Green, Blue Trefor, and Red Trefor). These are consistent with observations of used curling stones: pitting adversely affects larger grains in the running band, whereas a wider grain-size distribution correlates with fewer crescent-shaped fractures in the striking band.The appreciable abundance of unstrained, interstitial quartz (15–25 mod.%) in all curling stone samples challenges the longstanding belief of its absence and undesirability in curling stones. The degree of strain in quartz is likely to be a key criterion for selecting prospective curling stone materials.\u0000 In conclusion, none of the examined characteristics of curling stones are unique in comparison to granitoids worldwide.","PeriodicalId":134244,"journal":{"name":"The Canadian Mineralogist","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127702958","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Silica-Rich Garronite-Na From Hirado Island, Nagasaki Prefecture, Japan","authors":"Yutaro Hirahata, S. Kobayashi, H. Nishido","doi":"10.3749/canmin.2000078","DOIUrl":"https://doi.org/10.3749/canmin.2000078","url":null,"abstract":"\u0000 Silica-rich garronite-Na was found together with epistilbite in Miocene basaltic rock from Shiratobana, Hirado Island, Nagasaki Prefecture in Japan for the first time. Garronite-Na occurs as an anhedral crystal that covers the center of a small cavity in altered basaltic rock, whereas the epistilbite covers the inside of the cavity. Electron probe microanalysis of the garronite-Na gives an empirical formula of (Na1.99K0.27)Σ2.26Ca1.61(Fe0.01Al5.31Si10.64)Σ15.96O32·14.3H2O on the basis of O = 32. Its Na/Ca molar ratio varies from 1.00 to 1.53, and its unit-cell parameters (space group I2) calculated from X-ray powder diffraction data are a = 9.983(11) Å, b = 10.089(14) Å, c = 10.070(10) Å, and β = 90.223(3)° with a calculated density of 2.183 g/cm3. Garronite-Na from Hirado Island formed from an alkaline high-silica solution in the later stages of hydrothermal zeolitization associated with volcanic activity.","PeriodicalId":134244,"journal":{"name":"The Canadian Mineralogist","volume":"27 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121035997","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Authigenic Phyllosilicates in Sand Layers from the Mudflats of Saline Lakes in the Northern Great Prairies, Saskatchewan","authors":"J. Bentz, R. C. Peterson","doi":"10.3749/canmin.1900065","DOIUrl":"https://doi.org/10.3749/canmin.1900065","url":null,"abstract":"\u0000 The mudflats of saline lakes are amenable to authigenic clay formation due to the high ionic strength of the solutions driven by evaporative concentration and due to the fluctuating wet/dry cycles. However, the mudflats of saline lakes have received relatively little study given the challenges in sampling unstable sediments coupled with post-depositional alterations that make direct relationships to the climate difficult. In an effort to gain a better understanding of the authigenic phyllosilicates present, the mudflats of 17 sulfate-rich saline lake basins across southern Saskatchewan were sampled. The <2 μm fraction was separated from the sediments and analyzed utilizing X-ray diffraction (XRD), scanning electron microscopy, bulk chemical analysis via digestion and inductively coupled optical emission spectroscopy, and visible and near-infrared reflectance spectroscopy. The mudflat sediments were characterized as highly variable and were classified based on particle size into sediment classes A (clay-rich), B (unsorted till), and C (sand). Despite the high variability in sorting and thickness of the sedimentary layers, the phyllosilicates were distinctive within each class independent of the basin. Phyllosilicates in sediment class A were characterized by well-crystalline dioctahedral (Al) clays similar to the surrounding soils with smectite > illite > kaolinite > chlorite. Phyllosilicates from sediment class B displayed highly variable characteristics ranging between classes A and C. Clays from sediment class C were dominated by illite with decreasing proportions of smectite, kaolinite, and chlorite. The illite in the sand lenses was poorly formed, with broad reflections in the XRD patterns indicative of small crystallite size or high disorder, which is consistent with an authigenic nature. The clays in class C were rich in iron (Fe) and magnesium (Mg) and displayed lath-like morphologies common with authigenic illite forming in sandy porous sediments. The sand lenses of mudflats represent viable targets for finding authigenic clay minerals in detrital-rich sediments to use in understanding past climates on Earth and Mars.","PeriodicalId":134244,"journal":{"name":"The Canadian Mineralogist","volume":"674 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-12-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133322412","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Highly refractory dunite formation at Gibbs Island and Bruce Bank, and its role in the evolution of the circum-Antarctic continent","authors":"N. Akizawa, A. Yamaguchi, K. Tani, A. Ishikawa, Ryo Fujita, S. Choi","doi":"10.3749/canmin.2100030","DOIUrl":"https://doi.org/10.3749/canmin.2100030","url":null,"abstract":"\u0000 The continental margin is of profound importance as it records continental growth by accretion of orogenic magmas and following continental rifting. A high degree of mantle melting due to hydrous fluid input is expected to simultaneously stimulate continental growth and lower the intrinsic density of the mantle than more fertile mantle, which in turn isolates the continental lithosphere from the convective mantle. The mantle peridotites from Gibbs Island (South Shetland Islands) and Bruce Bank in the Drake Passage provide us an insight into the tectonic history in the circum-Antarctic region. To elucidate the continental growth of Antarctica, we present geochemical data of eight dunites from Gibbs Island and one dunite from Bruce Bank, including Re–Os isotope and highly siderophile element compositions.\u0000 The dunites are severely affected by serpentinization as evidenced by antigorite + brucite or lizardite (loss on ignition = LOI ranging from 3 to 34 wt.%) but contain primary euhedral to subhedral chromites with or without spherical inclusions. The chromites rarely form lens-shaped aggregates. A dunite from Gibbs Island contains fresh olivine grains filling a fracture in the chromite with low LOI (3 wt.%), indicating a deserpentinization origin from a precursor serpentinized dunite. The dunites show highly depleted bulk-rock major element compositions (Mg/Si = 1.4–1.6 and Al/Si = 0.004–0.01 for Gibbs Island dunites, Mg/Si = 0.66 and Al/Si = 0.008 for Bruce Bank dunite), overlapping a compositional field defined by forearc peridotites. The positive correlation in Re/Ir–LOI space corroborates Re input during the later serpentinization process. The 187Os/188Os ratios of the dunites range from 0.11907 to 0.14493.\u0000 Phanerozoic Re-depletion (melt depletion) ages of ca. 535–129 Ma are recorded in the Gibbs Island dunites, except for one with a Mesoproterozoic Re-depletion age of ca. 1.2 Ga. Since there exists serpentinization-related perturbation of Re, the ages provide minimum time estimates for melt depletion events. The early Paleozoic melt depletion is inferred to have occurred at a very early stage of Antarctic Peninsula formation in response to plate convergence along the margin of Gondwana, whereas the Mesoproterozoic Re-depletion age reflects convecting mantle heterogeneity unrelated to any nearby crust-forming events. The petrographic characteristics of the chromites and highly depleted nature of the dunites are attributed to melt–peridotite reaction in a subduction zone setting. A feasible interpretation for the dunite formation is that the mantle had experienced two stages of melting with the final stage occurring along the Gondwana continental margin in the subduction zone setting. Resultant highly refractory lithospheric mantle was later displaced and dispersed during the Gondwana breakup. Widespread existence of the dunite may be attributed to multi-stage melt depletion along the continental margin.","PeriodicalId":134244,"journal":{"name":"The Canadian Mineralogist","volume":"46 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129878249","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The chromian spinels of the Lyavaraka ultrabasic complex, Serpentinite Belt, Kola Peninsula, Russia: Patterns of zoning, hypermagnesian compositions, and early oxidation","authors":"A. Barkov, A. A. Nikiforov, V. Korolyuk, L. P. Barkova, R. Martin","doi":"10.3749/canmin.2100019","DOIUrl":"https://doi.org/10.3749/canmin.2100019","url":null,"abstract":"\u0000 The maximum value of Mg# [= 100Mg/(Mg + Fe2+ + Mn)] in chromium-bearing spinel-group minerals (Chr) in the Ultrabasic Core Zone (UCZ) of the Lyavaraka orthopyroxenite – harzburgite – dunite complex of the Serpentinite Belt in the Kola Peninsula is 54.5–67.5. Such highly magnesian compositions of spinel are associated with notable enrichments of ferric iron (Fe3+# 58–63). There are two generations of accessory Chr in the UCZ unit. The first generation occurs as inclusions in olivine that is not unusually magnesian (Mg# 90.3), and the second is closely associated with serpentine. The compositional series of Chr at Lyavaraka attains more aluminous compositions than was observed in nearby intrusive bodies. The anomalously high level of Mg in Chr, also manifest in ilmenite, is mainly a result of the high intrinsic fugacity of oxygen attained locally in the melt. A progressive buildup in H2O and increase in fO2 likely resulted from efficient vesiculation and selective loss of H2 from the Al-undepleted komatiitic magma crystallizing in a shallow setting. The chromian spinel forming in such a modified magma is virtually unzoned in Mn, and a minor quantity of Mn is also present in olivine and orthopyroxene. In contrast, zinc is strongly partitioned in the core of Chr, as it is relatively incompatible in the coexisting olivine and orthopyroxene at that stage. Zinc efficiently partitioned into the H2O-enriched melt, which crystallized as the pegmatitic orthopyroxenite near the contacts at Lyavaraka. A high potential of oxidation appears to be characteristic of all orthopyroxenite – harzburgite – dunite suites of the Serpentinite Belt formed from a primitive melt of komatiitic composition.","PeriodicalId":134244,"journal":{"name":"The Canadian Mineralogist","volume":"23 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121539680","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Oberthürite, Rh3(Ni,Fe)32S32 and torryweiserite, Rh5Ni10S16, two new platinum-group minerals from the Marathon deposit, Coldwell Complex, Ontario, Canada: Descriptions, crystal-chemical considerations, and comments on the geochemistry of rhodium","authors":"A. McDonald, I. Kjarsgaard, L. Cabri, K. C. Ross, D. Ames, L. Bindi, D. Good","doi":"10.3749/canmin.2100014","DOIUrl":"https://doi.org/10.3749/canmin.2100014","url":null,"abstract":"\u0000 Oberthürite, Rh3(Ni,Fe)32S32, and torryweiserite, Rh5Ni10S16, are two new platinum-group minerals discovered in a heavy-mineral concentrate from the Marathon deposit, Coldwell Complex, Ontario, Canada. Oberthürite is cubic, space group , with a 10.066(5) Å, V 1019.9(1) Å3, Z = 1. The six strongest lines of the X-ray powder-diffraction pattern [d in Å (I)(hkl)] are: 3.06(100)(311), 2.929(18)(222), 1.9518(39)(115,333), 1.7921(74)(440), 1.3184(15)(137,355) and 1.0312(30)(448). Associated minerals include: vysotskite, Au-Ag alloy, isoferroplatinum, Ge-bearing keithconnite, majakite, coldwellite, ferhodsite-series minerals (cuprorhodsite–ferhodsite), kotulskite, and mertieite-II, and the base-metal sulfides, chalcopyrite, bornite, millerite, and Rh-bearing pentlandite. Grains of oberthürite are up to 100 × 100 μm and the mineral commonly develops in larger composites with coldwellite, isoferroplatinum, zvyagintsevite, Rh-bearing pentlandite, and torryweiserite. The mineral is creamy brown compared to coldwellite and bornite, white when compared to torryweiserite, and gray when compared chalcopyrite and millerite. No streak or microhardness could be measured. The mineral shows no discernible pleochroism, bireflectance, or anisotropy. The reflectance values (%) in air for the standard COM wavelengths are: 36.2 (470 nm), 39.1 (546 nm), 40.5 (589 nm), and 42.3 (650 nm). The calculated density is 5.195 g/cm3, determined using the empirical formula and the unit-cell parameter from the refined crystal structure. The average result (n = 11) using energy-dispersive spectrometry is: Rh 10.22, Ni 38.83, Fe 16.54, Co 4.12, Cu 0.23 S 32.36, total 100.30 wt.%, which corresponds to (Rh2Ni0.67Fe0.33)Σ3.00(Ni19.30Fe9.09Co2.22Rh1.16Cu0.12)∑31.89S32.11, based on 67 apfu and crystallochemical considerations, or ideally, Rh3Ni32S32. The name is for Dr. Thomas Oberthür, a well-known researcher on alluvial platinum-group minerals, notably those found in deposits related to the Great Dyke (Zimbabwe) and the Bushveld complex (Republic of South Africa).\u0000 Torryweiserite is rhombohedral, space group , with a 7.060(1), c 34.271(7) Å, V 1479.3(1), Z = 3. The six strongest lines of the X-ray powder-diffraction pattern [d in Å (I)(hkl)] are: 3.080(33)(021), 3.029(58)(116,0110), 1.9329(30)(036,1115,1210), 1.7797(100)(220,0216), 1.2512(49)(0416), and 1.0226(35)(060,2416,0232). Associated minerals are the same as for oberthürite. The mineral is slightly bluish compared to oberthürite, gray when compared to chalcopyrite, zvyagintsevite, and keithconnite, and pale creamy brown when compared to bornite and coldwellite. No streak or microhardness could be measured. The mineral shows no discernible pleochroism, bireflectance, or anisotropy. The reflectance values (%) in air for the standard COM wavelengths are: 34.7 (470 nm), 34.4 (546 nm), 33.8 (589 nm), and 33.8 (650 nm). The calculated density is 5.555 g/cm3, determined using the empirical formula and the unit-cell parameters from the ","PeriodicalId":134244,"journal":{"name":"The Canadian Mineralogist","volume":"83 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126194534","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Naldrettite (Pd2Sb): A new find in Brazil and comparison with worldwide occurrences","authors":"G. Garuti, F. Zaccarini","doi":"10.3749/canmin.2000121","DOIUrl":"https://doi.org/10.3749/canmin.2000121","url":null,"abstract":"\u0000 Naldrettite (Pd2Sb) is a PGM discovered in 2005 in Mesamax Northwest deposit, Ungava region, Quebec, Canada. Before and after its approval, PGM with the naldrettite type composition have been reported from a number of localities worldwide. Most frequently, naldrettite has been documented in magmatic Ni–Cu–PGE sulfide deposits, hydrothermal veins in porphyry coppers of the Cu–Au type, and PGE deposits of Alaskan-type zoned intrusions. Naldrettite has been occasionally found in metasomatic Sb–As sulfide ore, metamorphic Ni–oxide ore, and podiform chromitites, although these occurrences have not been fully constrained by solid chemical analyses or paragenetic reconstruction. In this paper we report the first discovery of naldrettite in Brazil. This new finding occurs in a chromitite sample collected in the Luanga Complex, a Neo-archaean layered intrusion in the Carajás Mineral Province. Paragenetic association with alteration assemblages (ferrianchromite, Fe-hydroxides, chlorite) suggests precipitation of naldrettite from metamorphic hydrothermal fluids. The average composition of the Luanga sample (Pd1.76Pt0.24)Σ2.00(Sb0.57As0.43)Σ1.00 shows major substitution of Pt and As. These elements were derived from the breakdown of primary sperrylite, and were incorporated in naldrettite deposited by percolating fluids, at temperature below 350 °C (maximum temperature registered by the crystallization of associated chlorite). An overview of documented occurrences indicates that naldrettite can form in a variety of igneous rocks (ultramafic, mafic, felsic), even involving minimal concentrations of Pd and Sb. Crystallization of naldrettite generally occurs in the post-magmatic stage due to the activity of hydrothermal fluids containing volatile species Sb, As, Bi, Te, and Pd due to its higher mobility compared with the other PGE. A major issue concerns the origin of fluids that can be: (1) “residual”, after the main crystallization of the host magma, (2) “metamorphic”, during regional metamorphism or serpentinization, and (3) “metasomatic”, emanating from an exotic magma intrusion. The combination of two or three of these factors is the most likely process observed in the naldrettite-bearing complexes.","PeriodicalId":134244,"journal":{"name":"The Canadian Mineralogist","volume":"2015 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128260397","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}