Abstract Tetrahedrite-(Ni) (IMA2021-031), ideally Cu6(Cu4Ni2)Sb4S13, is the first natural Ni-member of tetrahedrite group mineral found in Luobusa chromite deposit, Tibet, China. The new species occurs as anhedral grains 2 to 20 μm in size, associated with gersdorffite, vaesite, and chalcostibite, which are disseminated in a matrix of dolomite, magnesite, quartz, Cr-rich mica, and Cr-bearing clinochlore. Tetrahedrite-(Ni) is black in color with a reddish-black streak and metallic luster. It is brittle with uneven fractures and has a calculated density of 5.073 g·cm–3. The mean values of 9 electron microprobe analyses (wt%) are Cu 39.83, Ni 5.67, Fe 1.45, Sb 21.69, As 5.45, S 25.39, total 99.48, and the empirical formula calculated on the basis of cation = 16 apfu is M(2)Cu6.00M(1)[Cu4.03(Ni1.55Fe0.42)Σ1.97]Σ6.00X(3)(Sb2.85As1.16)Σ4.01S12.67. Tetrahedrite-(Ni) is cubic, with space group I43m, a = 10.3478(4) Å, V = 1108.00(14) Å3, and Z = 2. Its crystal structure has been solved by X-ray single-crystal diffraction on the basis of 188 independent reflections, with a final R1 = 0.0327. Tetrahedrite-(Ni) is isostructural with tetrahedrite group minerals. It represents the first natural tetrahedrite-group mineral with a Ni-dominated charge-compensating constituent. Tetrahedrite-(Ni) may be the product of late-serpentinization at moderately high-temperature conditions around 350 °C. In this case, tetrahedrite-(Ni) and its mineral paragenesis record an entire geological process of nickel enrichment, migration, activation, precipitation, and alteration from deep mantle to shallow crust.
Abstract The mineral zircon has a robust crystal structure, preserving a wealth of geological information through deep time. Traditionally, trace elements in magmatic and hydrothermal zircon have been employed to distinguish between different primary igneous or metallogenic growth fluids. However, classical approaches based on mineral geochemistry are not only time consuming but often ambiguous due to apparent compositional overlap for different growth environments. Here, we report a compilation of 11 004 zircon trace element measurements from 280 published articles, 7173 from crystals in igneous rocks, and 3831 from ore deposits. Geochemical variables include Hf, Th, U, Y, Ti, Nb, Ta, and the REEs. Igneous rock types include kimberlite, carbonatite, gabbro, basalt, andesite, diorite, granodiorite, dacite, granite, rhyolite, and pegmatite. Ore types include porphyry Cu-Au-Mo, skarn-type polymetallic, intrusion-related Au, skarn-type Fe-Cu, and Nb-Ta deposits. We develop Decision Tree, XGBoost, and Random Forest algorithms with this zircon geochemical information to predict lithology or deposit type. The F1-score indicates that the Random Forest algorithm has the best predictive performance for the classification of both lithology and deposit type. The eight most important zircon elements from the igneous rock (Hf, Nb, Ta, Th, U, Eu, Ti, Lu) and ore deposit (Y, Eu, Hf, U, Ce, Ti, Th, Lu) classification models, yielded reliable F1-scores of 0.919 and 0.891, respectively. We present a web page portal (http://60.205.170.161:8001/) for the classifier and employ it to a case study of Archean igneous rocks in Western Australia and ore deposits in Southwest China. The machine learning classifier successfully determines the known primary lithology of the samples, demonstrating significant promise as a classification tool where host rock and ore deposit types are unknown.
The Pingmiao W (Cu) deposit is located in the central part of the newly-discovered giant Dahutang ore-concentrated district, South China. Field relationships and mineral assemblages confirm that the W (Cu) mineralization in the Pingmiao deposit is genetically related to multiphase late Mesozoic granites, which include the porphyritic two-mica granite, biotite granite porphyry, fine-grained muscovite granite, and Li-mica albite granite. Zircon U–Pb dating shows that these granites emplaced at ca. 146–143 Ma, which are coeval with the W–Cu–Mo-bearing granitoids from other ore deposits in the Dahutang district. The strongly peraluminous (A/CNK > 1.1) feature, negative correlations between Rb and Th and between Rb and P2O5, low Zr + Nb + Ce + Y values (mostly lower than 200), and relatively low Zr saturation temperatures (lower than 800 °C) suggest that these granites are typical S-type granite. These granites show similar Nd isotopes (−8.91 to −4.61), CaO/Na2O (0.2–0.57), and Al2O3/TiO2 (mostly ranging of 50–90) ratios with those W–Cu–Mo-bearing granitoids from other ore deposits in the Dahutang district, suggesting that they derived from partial melting of metapelites in the Shuangqiaoshan Group (or the Proterozoic metamorphic basement geochemically similar to the Shuangqiaoshan Group), with involving of minor mafic–ultramafic volcanic rocks. Geochemical fractionation trends recorded by whole-rocks and micas permit to distinguish the evolutionary trend from the porphyritic two-mica granite and biotite granite porphyry to the fine-grained muscovite granite and Li-mica albite granite. The apparent rare earth element tetrad effect, high Li and F contents, low K/Rb, Zr/Hf, and Nb/Ta ratios, as well as the zoned features of micas suggest that the melt–fluid interaction occurring during the formation of Li-mica albite granite. The Pingmiao granites have reduced redox state, revealed by their low whole-rock Fe2O3/FeO ratios (mostly <0.5), biotite Fe3+/Fe2+ ratios (ranging of 0.02–0.07), zircon Ce4+/Ce3+ ratios (median value of 18.70), and oxygen fugacity (near or below the FMQ buffer). The data in this study indicate that the late Mesozoic granitoids in the Dahutang district are favorable for W, Cu (<1 Mt), and Mo (<0.3 Mt) mineralization. Notably, the more evolved Li-mica albite granite has potential for W, Sn, Nb and Ta mineralization.
Abstract Carbonatite complexes are globally significant sources of rare earth elements (REEs); however, mechanisms governing REE deposition in various tectono-lithologic settings, encompassing host rocks, wall rocks, ore-controlling structures, and metasomatism, remain inadequately understood. The Zhengjialiangzi mining camp, situated within the extensive Muluozhai deposit (containing 0.45 million metric tons [Mt] at 4.0 wt % REE2O3) in the northern segment of the Mianning-Dechang belt, Sichuan (southwestern China), is characterized by a complex vein system that evolved within metamorphosed supracrustal rocks of the Yangxin and Mount Emei Formations. The mineralization is coeval with Oligocene intrusions of carbonatite and nordmarkite at ~27 Ma. The major gangue minerals include fluorite, barite (transitional to celestine), and calcite, with bastnäsite serving as the primary host for REEs in all analyzed orebodies. Several other accessory to minor minerals were identified in the ore veins, including some that had not previously been known to occur in the Muluozhai deposits (e.g., thorite and pyrochlore). The stable isotopic (C-O-Ca) and trace element compositions of calcite, along with whole-rock data, suggest that carbonate material was derived from the mantle and subsequently reequilibrated with the Yangxin marbles. The radiogenic isotope (Sr-Nd-Pb) compositions of vein material remained unaffected by wall-rock contamination and suggest a mantle source influenced by crustal recycling, consistent with other REE deposits hosted by carbonatite and nordmarkite in the region. The combined petrographic and geochemical evidence suggests derivation of Muluozhai mineralization from a carbonatitic source and interaction of carbonatite-derived fluids with wall rocks, xenoliths, and early-crystallizing mineral phases, particularly barite.
Abstract Recent investigations found that hydrothermal activity and sulfide mineralization occurs along the Southwest Indian Ridge (SWIR). The Longqi and Duanqiao hydrothermal fields between 49° E and 53° E of the SWIR are two prospective mineralization areas discovered by Chinese scientists. With the aim to determine the mineralogical and chemical characteristics of sulfide minerals, we have conducted detailed studies for samples from the two areas using an optical microscope, X‐ray diffractometer, scanning electron microscope, and electron microprobe. The mineralization processes in the Longqi area are divided into three main stages: (1) the low‐medium‐temperature stage: colloform pyrite (Py I) + marcasite → euhedral pyrite (Py II), (2) the high‐temperature stage: isocubanite (±exsolved chalcopyrite) + pyrrhotite → coarse‐grained chalcopyrite (Ccp I), and (3) the medium–low‐temperature stage: sphalerite + fine‐grained chalcopyrite inclusions (Ccp II) → aggregates of anhedral pyrite (Py III) ± marcasite → Fe‐oxide (‐hydroxide) + amorphous silica. The mineralization processes in the Duanqiao area are divided into two main stages: (1) the medium–high‐temperature stage: subhedral and euhedral pyrite (Py I′) → coarse‐grained chalcopyrite (Ccp I′) and (2) the medium–low‐temperature stage: sphalerite → fine‐grained chalcopyrite (Ccp II′) + chalcopyrite inclusions (Ccp II′) → silica‐cemented pyrite (Py II′) + marcasite → Fe‐oxide + amorphous silica. We suggest that the fine‐grained chalcopyrite inclusions in sphalerite from Longqi and Duanqiao were formed by co‐precipitation and replacement mechanisms, respectively. Primary sphalerites from both fields are enriched in Fe (avg. 5.84 wt% for the Longqi field vs. avg. 3.69 wt% for the Duanqiao field), Co (avg. 185.56 ppm for the Longqi field vs. 160.53 ppm for the Duanqiao field), and Cd (avg. 1950 ppm for the Longqi field vs. avg. 525.26 ppm for the Duanqiao field). Cu contents in pyrite from the Duanqiao field (Py I′: avg. 849.23 ppm and Py II′: avg. 1191.11 ppm) tend to be higher than those from the Longqi field (Py I: avg. 26.67 ppm, Py II: avg. 445 ppm, and Py III: avg. 179.29 ppm). Chalcopyrite from both fields is enriched in Zn (Ccp I: avg. 3226.67 ppm, Ccp II: avg. 9280 ppm, Ccp I′: avg. 848 ppm, Ccp II′ (inclusions): avg. 1098 ppm, and Ccp II′ (fine‐grained): avg. 1795 ppm). The varying contents of Zn in the different pyrite and chalcopyrite generations may result from the zone refining process. An integrated study of the mineralogy and mineralogical chemistry suggests that the hydrothermal fluids of the Longqi area are likely conditioned with higher temperatures and relatively lower f O2 and f S2 than those of the Duanqiao area, but in contrast to the former, the latter is much affected by the compositions of the surrounding rocks.
Abstract Calcioancylite-(La), ideally (La,Ca) 2 (CO 3 ) 2 (OH,H 2 O) 2 , has been discovered from nepheline syenite of the Gejiu alkaline complex in the Honghe Hani and Yi Autonomous Prefecture, Yunnan Province, China. The mineral occurs as aggregates of subhedral grains, and the size of single crystals varies between 5–20 μm. Calcioancylite-(La) is colourless to pale pinkish grey and has transparent to translucent lustre. It is brittle with a Mohs hardness of 4. The calculated density is 4.324 g/cm 3 . The mineral is biaxial (−), with α =1.662, β = 1.730, γ = 1.771, 2V meas. = 70°(1) and 2V calc. = 73°. Electron microprobe analysis for holotype material yielded an empirical formula of (La 0.58 Ce 0.55 Pr 0.14 Nd 0.10 Ca 0.39 Sr 0.20 K 0.04 ) Σ2.00 (CO 3 ) 2 [(OH) 1.25 F 0.06 ⋅0.69H 2 O] Σ2.00 . Calcioancylite-(La) is orthorhombic, with space group Pmcn , a = 5.0253(3) Å, b = 8.5152(6) Å, c = 7.2717(6) Å, V = 311.17(4) Å 3 and Z = 2. By using single-crystal X-ray diffraction, the crystal structure has been determined and refined to a final R 1 = 0.0652 on the basis of 347 independent reflections ( I > 2σ). The seven strongest powder X-ray diffraction lines [ d in Å ( I ) ( hkl )] are: 2.334 (100) (013), 2.970 (80) (121), 4.334 (75) (110), 3.678 (68) (111), 2.517 (55) (200), 2.647 (47) (031) and 2.077 (44) (221). Calcioancylite-(La) is the La-analogue of calcioancylite-(Ce) and is a new member of ancylite-group minerals. The mineral and its name have been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA2021-090).
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