Located in the Eastern Gangdese belt of Tibet, the Jiama skarn orebody is a Cu-polymetallic orebody with significant Pb, Zn, Au, and Ag by-products. The genesis of this orebody is revealed through an analysis of Co, Au, Ag, and Te occurrences. Based on textural and mineralogical relationships, ore formation can be divided into three paragenetic stages. Stage I, the prograde skarn phase, resulted in the formation of andradite, diopside, and wollastonite. This was succeeded by a retrograde period encompassing two sulfide stages-Stage II (Cu-Fe sulfides) and Stage III (Pb-Zn sulfides)-both of which are characterized by the deposition of various sulfides with quartz and calcite. Cobalt was identified in two forms: as the discrete minerals cobaltite (CoAsS) and carrollite ((Ni,Cu)Co2S4), and as an isomorphous substitution enriching sulfides. Tellurium is present within melonite, and Au occurs as native gold. Comparison between ore concentrate powder and ore shows loss of Co and enrichment of Au and Ag during beneficiation. Mantle-derived magma and/or juvenile lower crust involvement was likely during Jiama mineralization based on Co-Te-Au mineralization and other isotope characteristics. Three oreforming fluids were revealed by the mineral assemblages of Co-Te-Au-Ag-Bi. The first ore-forming fluid was accompanied by Co-Cu mineralization and occurred at Delta NNO of 0.4 to 3.9; the second ore-forming fluid was accompanied by Co-Pb-Zn mineralization, while the last phase was dominated by Pb-Zn-Ag-Au-Bi-Te mineralization and occurred at log & fnof;S2 of -12.8 to -8.3 and log & fnof;Te2 of -10.5.

Introduction: Lithium–cesium–tantalum pegmatites are critical sources of rare metals, yet the mechanisms of their formation, especially the role of fluids in elemental and isotopic fractionation, remain debated. Materials and methods: We investigated the Koktokay No. 3 pegmatite dike, the largest rare-element pegmatite in China, using K isotopes and chemical compositions of K-feldspar and muscovite across its concentric zones (I–VIII), combined with petrological modeling. Results: The results show a strong link between fluid exsolution, Li enrichment, and negative δ41K shift, corresponding to abrupt release of fluids and a rapid decline in solid phase abundance. Modeling indicates that low fluid–melt partition coefficients (Dfluid/melt = 0.1 for Li) best reproduce the observed Li enrichment, highlighting fluid exsolution as a key driver of rare-element accumulation. Conclusions: These results provide compelling evidence that late-stage fluid exsolution controls elemental enrichment and modulates K isotopic fractionation, offering new constraints on the petrogenesis of evolved pegmatite systems.

The published early Permian age (281 +/- 2 Ma) of the lherzolite from the Tulaergen No. I mafic-ultramafic intrusion is similar to that of other Ni-Cu sulfide deposits in East Tianshan (southern margin of the Central Asian Orogenic Belt (CAOB)). In contrast, the published formation age of gabbro (300.5 +/- 3.2 Ma) is inconsistent with the age of the regional Ni-Cu sulfide mineralized gabbro. Furthermore, the published Re-Os isochron age of sulfides from the Tulaergen (265.6 +/- 9.2 Ma) disagrees with the zircon U-Pb age. Overall, the crystallization and mineralization ages of the Tulaergen are distinct from those of other magmatic sulfide deposits related to mafic-ultramafic intrusions in the region. Therefore, the question remains as to whether age is the key factor determining mineralization potential, or whether there are other critical factors that can be used to evaluate the ore-forming potential of mafic-ultramafic intrusions in East Tianshan. In this work, a precise SIMS zircon U-Pb age for the ore-bearing gabbro (282.9 +/- 2.4 Ma) is presented, along with an ore sulfide Re-Os age of 278.1 +/- 6.4 Ma, convincingly proving that all magmatic sulfide deposits in East Tianshan are concentrated around a Permian crystallization age. The Tulaergen gabbro epsilon Hf (t = 282.9 Ma) ranges from 9.3 to 15.5, and the delta O-18 values range from 4.9 parts per thousand to 6.3 parts per thousand. Meanwhile, the barren and mineralized gabbro in East Tianshan have distinct zircon epsilon Hf (t) and delta O-18 values, ranging from -3.6 similar to +17.2 and 4.1 parts per thousand to 11.9 parts per thousand, respectively. Depleted mantle-like positive epsilon Hf (t) and O isotopic signatures close to those of the mantle are the common signatures of magmatic sulfide - mineralized mafic-ultramafic rocks. At Tulaergen, amphibole grains show narrow ranges in crystallization temperature, pressure, and water content (1083 degrees C to 11,182 degrees C, 854 MPa to1750 MPa and 2.9 wt% to 4.7 wt%, respectively), consistent with the ranges seen in ore-bearing mafic-ultramafic rocks in East Tianshan. In contrast, barren and Fe-Ti oxide mineralized mafic-ultramafic rocks display a continuous amphibole crystallization trend across a range of temperature, pressure and water content. Large-scale sulfide crystallization and the sudden release of water may be the critical factors that disrupted the continuous crystallization of amphibole in magmatic sulfide deposits. Zircon age and Hf-O isotopes reflect a depleted mantle source and low degree of contamination relate to barren intrusions; concentrated amphibole compositions reveal fractional crystallization of silicate melt and large-scale sulfide segregation. Together, they provide a powerful tool for identifying the mineralization potential of mafic-ultramafic rocks and may enhance exploration strategies at the southern margin of the CAOB.

Recent advances have significantly enhanced our understanding of the magma source, magma evolution, and sulfur saturation mechanisms of the Kalatongke Cu-Ni sulfide deposit in the Central Asian Orogenic Belt. However, limited systematic research has explored the structures that are critical to magma emplacement and sulfide accumulation. In this study, we perform a systematic multiscale analysis of the lithofacies distribution, morphology, and structural relationships between the northern and southern belts of the Kalatongke deposit. We propose that the emplacement and distribution of mafic intrusions and associated sulfide orebodies were controlled by fractures through syn-dextral shear deformation. The geometry of the Y1 and western Y2 intrusions and their mineralization were predominantly controlled by extensional T-fractures resulting from syn-shear deformation, whereas the eastern Y2 and Y3 intrusions were primarily governed by horizontal compressive-slip C-fractures, along with Riedel R and R' fractures. In the northern belt, the Y7 intrusion and its mineralization were influenced by shear between two sets of horizontal fractures trending northeast, which are nearly perpendicular to the main fault orientation of the southern and northern belts. Based on the characteristics of the fractures and the distribution of orebodies across the northern and southern belts, we propose that the Kalatongke deposit was controlled by a negative flower structure, suggesting the presence of deep structural connectivity between the northern and southern belts. Moreover, the distribution pattern of the sulfide orebodies in the Kalatongke deposit was governed primarily by the structures and their associated stress regimes.

The initial silicate melt related to magmatic Ni-Cu deposits located in orogenic settings in China (e.g., East Tianshan orogenic belt, East Kunlun orogenic belt) had a high fO2 that progressively decreased with continued magmatic evolution. It is still unknown if the sulfide melt that separated from the silicate melt inherited this high fO2, or even whether oxygen fugacity in sulfide plays an important role in the mineralization processes. In this work we undertook new in situ Fe, Cu, and Ni isotopic analyses of base metal sulfides from the Xiarihamu magmatic sulfide deposit (East Kunlun orogenic belt), and combined this new data with previously published Fe and Cu isotopic results from orogenic and cratonic magmatic sulfide deposits to assess changes in fO2 in sulfide during sulfide melt evolution, and the role of these processes in metal enrichment. In the Xiarihamu deposit, pentlandite has a Fe/Ni ratio similar to high-temperature pentlandite (Fe4.95Ni4.08S7.96) found in the upper disseminated ores which host high-temperature maucherite inclusions. These findings indicate a high formation temperature for the sulfide in the upper disseminated ores. Atomic % Fe in pyrrhotite suggests that fO2 increased during the transition from disseminated mineralized ultramafic rocks (47.2-50.7), through net-textured + massive mineralized ultramafic rocks (47.1-48.1), to disseminated mineralized gabbros (46.9-47.3). Early crystallized, high temperature sulfides in disseminated ores do not display high oxygen fugacity characteristics (high Fe3+/Sigma Fe), whereas in the silicate melt, fO2 continued to decrease with progressed evolution. Orogenic magmatic sulfide deposits show consistent, uniquely lighter delta 56Fe and delta 65Cu in disseminated ores relative to the same sulfides from massive ores. This cannot be explained by crustal contamination and sulfide melt fractionation based on Fe and Cu isotopes. Uncoupled delta 62Ni (insensitive to fO2 variations) and delta 56Fe, as well as heavy delta 56Fe and Co enrichment in late crystallized pentlandite (low temperature and high Fe3+/Sigma Fe) from the Xiarihamu and Kalatongke deposits (located in different orogenic belts), suggests that an increase in oxygen fugacity and related Fe3+/Sigma Fe ratios exert control on Co mineralization. Iron, Cu and Ni isotopes in sulfide can be used as indicators of Fe3+/Sigma Fe ratios in magmatic sulfide deposits in an orogenic environment, and changes in the Fe3+/Sigma Fe ratio play a critical role in Co enrichment.

When an ascending mantle plume arrives beneath a small craton and encounters ambient orogenic extension, what is likely to happen? We explored this scenario through considering the case of the Tarim mantle plume and the mafic-ultramafic intrusions in the southern Central Asian Orogenic Belt (CAOB). This mantle plume, which arrived beneath the Tarim craton, one of the smaller cratons on Earth, lasted from 300 Ma to 270 Ma with peaks at 290 Ma and 278 Ma. Synchronously, the CAOB was at the late orogenic extension stage with an eastwardpropagating, scissor-like closure of the Paleo-Asian Ocean. Ni-Cu sulfide deposits hosted in mafic-ultramafic intrusions are typically associated with mantle plume events. However, an increasing number of Ni-Cu sulfide deposits are recognized as being emplaced in an associated orogenic setting, such as those associated with the southern CAOB. We observed that the number of mafic-ultramafic intrusions decreases with increasing distance from the Tarim craton (from the Tarim plume), and these intrusions show a 7-8-m.y. time lag in their emplacement ages (295-255 Ma, with peaks at 293 Ma, 282 Ma, and 271 Ma) with respect to the timing of Tarim large igneous province magmatism (300-270 Ma) within the Tarim craton. These unusual geochronological and tectonic links suggest that the plume materials were escaping to the northeast along an extensional belt in the southern CAOB, which is perpendicular to the inferred circular boundary of the plume, resulting in the formation of orogenic-style Ni-Cu sulfide deposits and a continuous magma supply from the deep mantle, prolonging the lifetime of the Tarim plume.

In addition to copper, gold, and molybdenum, porphyry deposits are important reservoirs of critical metals such as rhenium, selenium, tellurium, and platinum group elements (PGEs). However, enrichment of cobalt (Co) has received little attention. Several studies have shown that Co enrichment does occur in porphyry deposits, however, the source(s) of Co and the mechanism(s) responsible for its enrichment in the high-temperature hydrothermal systems that ultimately form Co-rich porphyry deposits, are poorly understood. In order to address this knowledge gap, we investigated the Jinchang porphyry deposit in Northeast China which is one of the most Co-enriched porphyry deposits worldwide. In-situ elemental and Fe-S isotopic analysis, as well as electron backscatter diffraction, have been conducted on two types of pyrite (Py1 and Py2). Py1 exhibits a core-mantlerim structure, with Co enrichment in the core (Avg. 4.5 wt%) and rim (Avg. 7.5 wt%). Py2 displays a distinct core-rim structure, with Co enrichment only in the rim (Avg. 8.4 wt%). The early Co-rich fluid led to the formation of the Co-rich Py1 core. As pyrite continued to grow, Co in the fluid was depleted, leading to the formation of the Co-poor Py1 mantle and Py2 core. The most significant changes in S56Fe values and Co contents were observed between the Py2 core and Py2 rim (S56Fe: X0.94 %o, Co: X10.67 wt%). This significant variation was generated by the re-injection of Co-rich fluids, which led to the coupled dissolution-reprecipitation of pyrite, leading to the formation of the Co-rich Py1 rim and Py2 rim. Each injection of Co-rich fluid not only formed a Corich zone in pyrite, but also precipitated Co-bearing minerals, such as siegenite and cobaltite. The magmatic S34S isotope signature of pyrite and chalcopyrite (1.5-5.3 %o) rules out the possibility that Co originated from a sedimentary source. Due to the low Co content in felsic magmas, the repeated injections of Co-rich mafic magma are the only plausible source for the formation of such Co-rich fluids. Besides other possible causes, the heavy S56Fefluid values derived from mafic magmas suggest the addition of serpentinized oceanic crust slab during subduction, which directly contributed to the formation of mafic magmas. Multiple injections of mafic magma can significantly enhance the Co content in ore-forming fluids, which may be a critical prerequisite for Co enrichment in porphyry deposits worldwide. Early high-temperature and highsalinity fluids create an environment highly favourable to Co enrichment. As temperatures decrease, Co begins to precipitate, and breccia pipes, which experience rapid temperature drops due to fracturing, become favourable areas for Co deposition. The main precipitation stage of Co pre-dates the main stage of porphyry CuAu ore formation, which might be the reason that Co enrichment in porphyry deposits normally goes undetected.

Rare-precious metals (Ni, Co, Cr, and PGEs) are critically important and highly deficient strategic resources for our country since their import dependency rates are as high as 85%similar to 98%. These metals exhibit similar geochemical behaviors and often coexist in mantle-derived basaltic melts. However, mafic-ultramafic intrusions from different tectonic settings show distinct mineralization characteristics and hydrothermal metasomatism-modification further exacerbates their decoupling and re-enrichment. Some major types of global rare-precious metal deposits, such as stratiform reef-type, have not yet been discovered in China. Laterite-type Ni-Co and Proterozoic rift-type Cu-Co deposits are not well developed in China. This review aims to investigate the coexistence, separation, enrichment mechanisms, and localization mechanisms of these elements during magmatic and hydrothermal processes. Based on comprehensive surveys and analysis of existing research progress on Ni, Co, Cr and PGE resources and field investigations of typical deposits, we apply petrological, mineralogical, geochemical and geophysical methods, along with experiments, thermodynamic simulation and global data analysis, to address the following three key aspects: (1) the ore-forming potential for Ni-Co-Cr-PGE under various tectonic backgrounds (such as plume, orogenic belt, rift basin); (2) the separation and enrichment mechanisms of Co-Ni-PGE during magmatic-hydrothermal processes; (3) the coexistence-separation-enrichment mechanisms of Co-Ni during weathering-sedimentary processes. This integrated research aims to understand the endowment and characteristics of China's rare-precious metal resources from the perspective of Earth's evolution and global comparison. It will establish a comprehensive theoretical framework, new metallogenic models, and evaluation criteria for Ni-Co-Cr-PGE ore formation, and then identify new prospective areas and orebelts in China. This research will contribute significantly to the overall goals of the major research program on critical metal metallogeneses in terms of both theoretical advancements and exploration breakthroughs.

The Central Asian Orogenic Belt (CAOB) hosts a number of magmatic Ni-Cu sulfide deposits associated with mafic-ultramafic intrusions. These deep-seated intrusions were exhumed to the surface through orogenic processes, so the history of uplift and exhumation plays a crucial role in their preservation. Understanding this history has significant implications for exploration. We present zircon and apatite (U-Th)/He low-temperature thermochronology data from the Huangshandong, Hulu, and Tulaergen intrusions, located in the Jueluotage of Eastern Tianshan along the southern boundary of the CAOB. These three intrusions show consistent Permian zircon U-Pb ages, and their thermal history reveals two stages of uplift and exhumation. The first stage, a period of rapid uplift from Late Permian to Triassic, has been attributed to the far-field effects of the collision between the Qiangtang and Eurasian continent. Following this, a prolonged period of planation in Tianshan from Jurassic to the present day, marked the second stage, characterized by gradual cooling with cooling rates of 0.56 degrees C/Myr, 0.69 degrees C/Myr, 0.59 degrees C/Myr and exhumation rates of 19.0 f 3.0 m/Myr, 24.0 f 4.0 m/Myr, 20.5 f 3.5 m/Myr for the Huangshandong, Hulu, and Tulaergen intrusions, respectively. These cooling and exhumation rates suggest minor differences in exposure among the three intrusions during this slow cooling stage. However, stratigraphy, morphology, and proportions of ultramafic to mafic indicate that Tulaergen and Hulu may have experienced more extensive erosion. Therefore, the initial rapid cooling stage contributed to the differential exposure of these deep intrusive bodies, while the slower cooling stage favored the preservation of mineral deposits due to the limited exposure. Additionally, the Jueluotage region demonstrates a trend of stronger exhumation in the east than in the west, resulting in the exposure of Cu-Ni deposits at the surface in the eastern part. Therefore, we further hypothesize that regions within orogenic belts that have experienced short-term rapid uplift followed by long-term gradual cooling are favorable for exploring deep-seated mineralized intrusions.

The variations of Ni isotopes have been identified as high as 4‰ in high-temperature magmatic systems, which breaks the traditional view that the larger the large number of elements, the smaller the relative isotopic fractionation. The massive isotopic fractionation generated in high-temperature magmatic system may be caused by the superposition of multiple equilibrium isotope fractionation processes and/or dynamic fractionation and therefore has also been applied to magmatic Ni-Cu sulfide deposits. The current understanding of the Ni isotope fractionation mechanism in high-temperature magmatic processes includes: (1) The Ni isotope composition of basalt cannot represent the mantle value. (2) Partial melting of the mantle and recycling of crustal materials result in limited Ni isotope fractionation, and mantle metasomatism is the main reason for the heterogeneity of Ni isotope in the mantle. (3) The involvement of sulfides in high-temperature magmatic systems is the main controlling factor for the Ni isotope changes, especially for the large Ni isotope fractionation identified in high-temperature magmatic sulfide ore-forming systems, for example, the dissolution, crystallization, segregation and interaction with silicate magma of sulfides. At present, the research and application of Ni isotopes in high-temperature geological processes are still in the development stage, and parameters such as isotopic fractionation coefficients and reduced partition function ratios need to be determined. This requires more accurate simulation calculations and more reasonable high-temperature and high-pressure experiments to solve the problem. Uncovering the isotopic fractionation mechanism during mantle metasomatism is expected to accurately identify the mantle rock type and the detailed metasomatic processes. The combination of Cu and Ni isotopes has great potential in the study of metal enrichment mechanisms and geodynamic environments in magmatic Ni-Cu sulfide deposits.

Copper and iron isotopic signatures in sulfide and silicate minerals are important genetic indicators in magmatic sulfide deposits. Kalatongke is a large‐scale magmatic Cu‐Ni sulfide deposit in the Central Asian Orogenic Belt, and one that experienced multiple stages of magmatism and contamination. It is an ideal deposit in which to study Cu‐Fe isotopic fractionation during multiple stages of magmatism and sulfide mineralization processes. The Kalatongke sulfide orebodies are hosted by three small mafic intrusions in which pyroxene and sulfides (pyrrhotite, pentlandite, and chalcopyrite) are the most common Fe‐rich minerals, and chalcopyrite is the dominant Cu‐rich mineral. Sulfide liquid and silicate melt ▵56FeSul‐Sil (0.03–0.19‰) and ▵65CuCcp‐Sil (−0.78–0.74‰) values are indicative of non‐equilibrium fractionation. Most of the Cu isotope compositions in the sulfide ores at Kalatongke can be modeled as subduction‐ metasomatized, oxidized mantle source‐derived silicate melt (initial δ57Fe = 0.15‰, δ65Cu = −0.07‰) that underwent lower crustal contamination, and then reacted with silicate melt, having an R factor of 100–1,000. Rapid silicate melt and sulfide liquid Fe isotope exchange and re‐equilibration between chalcopyrite and pyrrhotite in the massive ores is reflected in the similarity of their δ56Fe values. Sulfide in disseminated ores shows a range of Fe isotope ratios, influenced by the proportions of monosulfide solid solution (MSS) and intermediate solid solution (ISS) formed. Copper isotopes can be utilized to characterize crustal contamination and silicate melt‐sulfide liquid interaction, while the Fe isotope ratios of sulfide minerals record sulfide liquid segregation and evolution in magmatic sulfide deposits.

The East Qinling pegmatite district is a famous rare-metal production area, and it is the largest pegmatite district hosting abundant rare element (REL)in the Qinling orogenic belt. The Guanpo area, as the most representative and typical pegmatite high. density area in East Qinling, is featured by a large number of pegmatite dykes, high proportion of REL-mineralized pegmatites, multi types of REL mineralization involved in Li, Be, Nb, Ta and Cs, large lithium-mineralized pegmatite dykes, and various REL minerals. From northwest to southeast, this area developed the Huoyangou Sn-Nb-Ta deposit, Nanyangshan, Qiligou-Qiantai and Caijiagou lithium deposits. The internal structures include weakly zoned pegmatites which are homogeneous and layered, and complexly zoned pegmatites. The REL pegmatite dykes belong to spodumene subtype in complex type dominantly, accompanied with lepidolite subtype in complex type and albite-spodumene type. The REL pegmatite magmas are peraluminous with high contents of Si and alkalis, and they are enriched in large ion lithophile elements (Rb, K)and high field strength elements (Nb, Ta, Hf), and poor in Ba and Ti with low Nb/Ta ratios and strong REE tetrad effects. Thus, the REL pegmatite magmas are highly fractionated and evolved. The mineralogical studies show that the Nanyangshan, Qiligou-Qiantai and Caijiagou REL pegmatites have high degrees of evolution compared with tin-bearing pegmatites in Huoyangou deposit. There is a Late Ordovician-Early Silurian pegmatite magma activity in Guanpo area and the main ore forming times are Late Silurian-Early Devonian (424 similar to 408Ma)and Early-Middle Devonian (399 similar to 384Ma). The Guanpo REL pegmatite dykes formed in collision, weakening convergence with crust uplift and post-orogenic extension settings, and mainly concentrate in late orogeny. The tourmaline B isotopes and zircon Hf isotopes indicate that the Guanpo REL pegmatite dykes are derived from Proterozoic crustal materials, mainly metasedimentary rocks. There is no genetic correlation between REL pegmatites and granites exposed in this region, and the REL pegmatite dykes might be products of partial melting of the North Qinling unit. The weakly-zoned Sn-Nb-Ta-mineralized pegmatites in Huoyangou deposit did not experience obvious fractional crystallization after emplacement. The magmas of weakly zoned Li-mineralized pegmatites are enriched in lithium and achieved lithium-saturated melt without obvious fractional crystallization after emplacement and the lithium-bearing minerals continued to deposit in fluid stage. The systems of complexly zoned Li- or Li-Be-Nb-Ta-Cs-mineralized pegmatites began to deposit REL-bearing minerals when REL-saturated melt formed by fractional crystallization after emplacement. With continuous evolution of melt and fluxes therein, REL-rich and fluxed melt formed and different assemblages of REL-bearing minerals occurred. The activities of alkali fluids with or without atmospheric water further complete REL mineralization and redistribution. The formation processes for REL pegmatite magma which involved in the first REL enrichment, and magma-fluid evolution processes which further complete REL enrichment, contribute to formation of the REL pegmatites in Guanpo area. The previous studies on mineralogical, geochemical, wall-rock alteration and regional structures supply the possible REL mineralization indicators for REL prospecting in Guanpo area.

The Bushveld Complex is the largest known layered intrusion in the world and has been extensively studied. However, there remains an absence of systematic investigations of cobalt (Co) and nickel (Ni) distribution at various scales. Elements Co and Ni behave varying degrees of compatibility within chromite, silicates, and sulfides, making them effective proxies for elucidating chemical competition and interaction among these minerals. This study aims to characterize Co and Ni distribution in olivine, pyroxenes, chromite, and whole rocks from different seams of the Bushveld Complex and to reveal their controlling factors. Our results indicate large variations of whole -rock Co and Ni concentrations, with a decreasing sequence of dunites (Co: 156-222 ppm; Ni: 2208-2750 ppm) > harzburgites (Co: 87.8-174 ppm; Ni: 152-2050 ppm) > pyroxenites (Co: 58.7-143 ppm; Ni: 387-1947 ppm) > norites (Co: 16.0-113 ppm; Ni: 153-646 ppm) > anorthosites (Co: 3.20-16.3 ppm; Ni: 19.7-97.2 ppm). In general, olivine has higher Ni contents (717-4496 ppm) and lower Co (105-239 ppm) than chromite (Ni: 524-1948 ppm; Co: 236-563 ppm). Pyroxenes have apparently low Co (orthopyroxene: 39.7-184 ppm; clinopyroxene: 17.2-114 ppm) and Ni contents (orthopyroxene: 224-1195 ppm; clinopyroxene: 177-831 ppm). Chromite in chromitites has lower Co content than that in other rocks. The whole -rock and mineral Co and Ni variations in the stratigraphic profile are closely related with lithology, mineral assemblages and element partition coefficients in minerals. The Co contents in the chromite and pyroxenes vary alternately with the chromitites and rock seams, with lower Co contents in ore samples than that in silicate rocks. Whole rocks and mineral separates in the Merensky Reef exhibit the highest Ni contents (whole -rock: up to 4000 ppm; orthopyroxene: 1035-1195 ppm; clinopyroxene: 730-831 ppm; chromite: 1760-1948 ppm), which are likely attributed to sulfide segregation and diffusion between sulfides and other minerals. In addition, the sulfide segregation may also be a main factor resulting in Co-Ni decoupling in pyroxenes from the Main Zone of the Bushveld Complex.

The Chinese Altai orogenic belt is famous for large numbers of pegmatite dikes, various rare -element (REL) mineralization types and its rich REL resources. In REL pegmatites, columbite-group minerals (CGM) display compositional complexity that can be used to decipher magma evolution and REL metallogenesis. Here, we provide compositional data and internal structures for columbite-group minerals from representative Chinese Altai REL pegmatites, including Koktokay No. 3 (Li-Be-Nb-Ta-Cs-Rb-Hf, early Jurassic), Xiaokalasu (Li-Nb-Ta, late Permian), and Dakalasu (Be-Nb-Ta, middle Triassic), in order to elucidate ore -forming processes and identify possible indicators of REL mineralization to enhance exploration success. The CGM were classi fi ed into fi ve types based on compositional complexity, each of which provides a window into magmatic evolution and crystallization in the pegmatite. In the Koktokay No. 3 pegmatite, CGM evolution in zone I reveals a silicate melt with fl uid at undercooling, while that in zone IV re fl ects a silicate melt followed by complex Ta-rich boundary -layer melt, and that in zone V suggests an evolution from silicate melt, to Ta-rich boundary -layer melt, and fi nally to REL-rich and fl uxed melt accompanied by fl uid activity. In the Xiaokalasu Li -mineralized pegmatite, CGM display a similar evolution trend to that of core -rim CGM in zone V of the Koktokay No. 3 pegmatite. In the Dakalasu pegmatite, CGM and Ti-Nb-Ta phases imply Fe-Mn-Nb-Ta-rich and Ti-Nb-Ta-rich melts, and intergrowths of CGM, Ta/Nb-rich rutile, and microlite result from decomposition of a metastable Ti-Nb-Ta oxide precursor in undercooling conditions. The Nb-Ta and Fe-Mn fractionation and changes in minor/trace element contents in CGM depend on the geochemical features of the elements, chemistry of the pegmatite magma, petrogenetic processes ( e.g. , fractional crystallization, fl uid exsolution, and melt -fl uid - mineral interaction), and buffering of these factors. Fractional crystallization prevailed during melt evolution, producing Ta-rich boundary -layer melt and REL-rich and fl ux -enriched melt. Fluid activity was observed in zones related to magmatic, magmatic - hydrothermal transitional, and hydrothermal stages, leading to CGM chemical redistribution by similar/ low-Ta and high-Sb fl uid replacement and crystallization of stibiotantalite. Fractional crystallization, host -rock assimilation, rapid undercooling, fl uid exsolution, and fl uid activity are important for Be, Li, Nb, and Ta mineralization. Combining the potential indicators [ i.e. , Nb-Ta-oxide phase assemblage, CGM types and evolution, twin -element decoupling (Zr-Hf, Th-U, and Y-REE), trace element content grade, and REE (rare earth element) distribution pattern] could be used to discriminate REL mineralization types and enhance REL exploration success.

The De’erni Cu–Zn-Co deposit is a typical altered ultramafic-hosted volcanogenic massive sulfide deposit comprising four lenticular main orebodies (0.57 Mt Cu, 1.27

In this work, we systematically describe silicate mineral inclusion morphology and genesis in chromite from UG3, MG2 and LG6 chromitite layers of the Eastern Limb of the Bushveld Complex. Rounded to subhedral in-clusions of phlogopite, amphibole and, to a lesser extent, olivine and orthopyroxene, are concentrated at or near the center of chromite grains. The most common occurrences are tabular amphibole forming planar contact with orthopyroxene, phlogopite, and phlogopite surrounding amphibole and olivine. Several features indicate re-equilibration reactions between the host chromite and the inclusions including high Mg# values in orthopyr-oxene inclusions (81.9 to 88.4; average of 85.0), low MgO (5.16 to 8.15 wt%) and high FeO (28.66 to 32.54 wt%) contents in the host chromite, and higher Cr2O3 content in amphibole (0.32 to 3.60 wt%) and phlogopite (0.29 to 2.29 wt%) inclusions relative to cumulus orthopyroxene, amphibole and phlogopite in the silicate rocks. Furthermore, the high H2O (4.16 to 4.45 wt%) and Na2O (0.07 to 6.12 wt%) contents in phlogopite inclusions, low transition element (V, Ni, Co and Zn) contents in the orthopyroxene from chromitite seams, and the devi-ation from mantle 818O values (5.7 to 6.7 %o) in inclusions, indicates alteration by or reaction with, hydrous melt. In addition, the similar orthopyroxene 818O (5.7-6.8 %o) in the MG2 and LG6 hanging wall and footwall, and in amphibole inclusions (818O = 5.9-6.7 %o) from the LG6, MG2 and UG3 chromitite seams, suggest that the hy-drous melt which formed hydrous mineral inclusions in chromite, and in the hanging wall and footwall silicate minerals, had a similar origin. The high 818O values, LG6 olivine inclusions, and the lower H2O and Li contents in Critical Zone (CZ) orthopyroxene from chromitite compared to orthopyroxene from the overlying and underlying rocks, as well as previous experiments and chemical data, all indicated that a pyroxene remelted hydrous alkali-melt was probably the main source of the trapped melt in chromite. Compatible transition metal element (Ni and Co) contents in orthopyroxene from chromitite seams are lower than those in orthopyroxene from mafic rocks, indicating the former intensely reacted with interstitial liquid. Conversely, there is a low but narrow range in H2O content (8.7 ppm to 28.1 ppm) in orthopyroxene from the CZ chromitite relative to orthopyroxene from norite in the overlying and underlying rocks (3.0 ppm to 46.1 ppm), and a lower Li content in orthopyroxene from chromitite (2.4 ppm to 4.2 ppm) relative to the overlying and underlying norite rocks (2.5 ppm to 8.7 ppm). Coupled low H2O-Li contents in the orthopyroxene from chro-mitite seams and reaction with interstitial liquid suggest that chromite selectively captured hydrous silicate melt during grain formation. Capture of hydrous melt related to remelted pyroxene is a likely mechanism of inclusion formation, and was a common phenomenon in chromite from the Eastern Limb of the Bushveld Complex.

中亚造山带内发育大量岩浆型铜镍硫化物矿床,但由于岩体规模较小且产状多变,围岩中碳质层普遍发育,深部浸染状矿体难以准确定位。本文以新疆喀拉通克铜镍硫化物矿床为例,建立了适用于该类型矿床的综合地球物理勘查技术。首先根据岩体与碳质层的地球物理特性,建立了"重力磁法-金属矿地震法-电性源短偏移距瞬变电磁法"技术组合,具体包括:(1)重磁扫面圈定隐伏成矿岩体的地表投影位置;(2)地震勘探圈定岩体的顶底界面和赋存空间;(3)电性源短偏移距瞬变电磁法恢复碳质层的电阻率信息和极化率信息。进而提出通过确定成矿岩体和碳质层的空间关系间接推断矿体赋存空间的新思路:(1)当岩体下方赋存碳质层时,推断岩体的底部或者内部赋存浸染状矿体;(2)当岩体下方未赋存碳质层时,推断岩体的底部或者内部不发育矿体。由此,本文建立了喀拉通克岩浆铜镍矿床含碳质层的成矿模型,并为造山带内其他岩浆型铜镍硫化物矿床的勘探提供了技术方案和探测示范。

Abstract Spinel minerals occur as inclusions in both silicates and sulfides in the Kalatongke magmatic Ni-Cu deposit in NW. China, showing textural and compositional variations. The spinel enclosed in olivine and other silicates (orthopyroxene, clinopyroxene, and hornblende) is predominantly Cr-magnetite with minor Cr-spinel, having wide variations in MgO (0.1–8.0 wt%), Al2O3 (1–25 wt%), Cr2O3 (3–20 wt%), and TiO2 (0.5–6.2 wt%) contents. Such continuous variations suggest that Cr-magnetite in silicates was crystallized from residual melts and experienced extensive reaction with trapped liquid undergoing a typical tholeiitic trend of increasing Fe and Ti concentrations. Crystals of Cr-magnetite enclosed in disseminated sulfides have similar Mg, Al, Cr, Ti, V, Sc, Ga, Mo, Zr, and Nb concentrations to the Cr-magnetite in silicates. Such compositional similarity, which is explained by the simultaneous equilibrium crystallization of Cr-magnetite from the silicate and sulfide melts, shows that the Kalatongke deposit is a typical example of where the same mineral phase is formed from two coexisting immiscible liquids. However, the Cr-magnetite in disseminated sulfide and that in silicates show distinctly different crystal size distribution patterns, illustrating that the chemical equilibrium was attained despite contrasting growth rates. Nevertheless, the Cr-magnetite in disseminated sulfides shows significantly lower Ni, Co, and Zn contents (median value of 845, 22, and 319 ppm) than that in silicates (median value of 1428, 160, and 1039 ppm). This cannot be the result of sulfide fractionation because there is little compositional variation between Cr-magnetite included in pyrrhotite (early crystallized phase) and that immersed in chalcopyrite (late crystallized phase). Such Ni, Co, and Zn depletions, combined with the relatively constrained Fe/Ni, Fe/Co, and Fe/Zn ratios in those Cr-magnetite, are attributed to postcumulus reactions between Cr-magnetite and sulfide melts. The spinel hosted by massive sulfides is magnetite, which has distinctly different compositional variations and crystal size distribution patterns compared with those of the silicate-hosted Cr-magnetite, although the magnetite in massive ore generally has similar contents in some lithophile elements (Zr, Ta, Mo, Sn, Mn) to the silicate-hosted Cr-magnetite. This could be taken as evidence for a mixture of early accumulated sulfide pools with a component of drained sulfide from the cumulates above. This study shows a detailed textural and compositional investigation of spinel is useful to decode the sulfide evolution processes during the formation of magmatic Ni-Cu deposits and highlights that equilibrium crystallization and postcumulus reactions play critical roles in controlling the spinel/magnetite composition.

Here we present an analytical method for Zinc (Zn) isotopic measurements using “standard‐sample bracketing” on a Nu Sapphire multi‐collector inductively coupled plasma‐mass spectrometer. The effects of Zn mass fraction and HNO 3 molarity mismatch between the standard and the sample, as well as the presence of matrix elements have been evaluated. Long‐term reproducibility of better than ±0.03‰ for δ 66 Zn (2 s ) was routinely obtained. Accurate measurements were achieved when C Ni /C Zn < 0.001, C Ti /C Zn < 0.03, C Ba /C Zn < 0.05, C Na /C Zn and C Al /C Zn < 0.5, C Mg /C Zn < 0.1, C Fe /C Zn < 5 and C Cu /C Zn as well as C Cd /C Zn < 10. High‐precision Zn isotopic determination were performed on twenty‐one widely available geological certified reference materials, with an overall range of ~ 0.62‰ (0.15 to 1.07‰), which is nearly twenty times the current analytical precision (0.03), and the results are in agreement with most previously published data within 2 s . Among them, δ 66 Zn JMC 3‐0749L of eleven geological certified reference materials are reported for the first time: 0.22 ± 0.03‰ (dolerite, DR‐N), 0.23 ± 0.02‰ (gabbro, GSR‐10), 0.20 ± 0.04‰ (microgabbro, PM‐S), 0.15 ± 0.02‰ (andesite, GSR‐2), 0.22 ± 0.08‰ (diorite, GSR‐9), 0.19 ± 0.07‰ (syenite, GSR‐7), 0.30 ± 0.06‰ (granite, GSR‐1), 0.25 ± 0.00‰ (rhyolite, GSR‐11), 0.37 ± 0.01‰ (shale, GSR‐5), 0.21 ± 0.03‰ (limestone, GSR‐6) and 0.20 ± 0.03‰ (hornblendite, GSR‐15). The novel Zn isotopic data from these certified reference materials can be used for future interlaboratory comparisons.

The Kalatongke magmatic Ni-Cu deposit features high Ni-Cu grades compared with other Ni-Cu deposits in the Central Asian orogenic belt. The sulfides, mainly hosted by olivine norite and gabbronorite, are characterized by high Cu/Ni ratios. There is wide variety of textural relationships in the mineralized rocks, including globular, sulfide matrix, emulsion, disseminated, net-textured, and semimassive to massive textures. Quantitative textural measurements reveal that more than 65 vol % of the total sulfide volume in disseminated ore (defined as containing 4-10 vol % sulfide) and more than 90 vol % of the total sulfide volume in net-textured ore (typically 16 vol % sulfide) are hosted in few interconnected networks with equivalent sphere diameters (ESDs) larger than 6 mm. This illustrates that sulfide coalescence is a critical process. The remaining sulfide blebs define two groups of log-linear particle size distribution (PSD), i.e., a finer group (ESD of 0.080-<0.529 mm) and a coarser group (ESD of 0.529-4.084 mm). The PSD of the finer group differs slightly among different types of mineralization. The origin of this group of sulfides is attributed to sulfide nucleation simultaneously with crystallization of the olivine-orthopyroxene-plagioclase phases from the ore-forming magma in the current magma chamber. The PSD of the coarser group from net-textured ores is parallel to that from the disseminated ore but has lower intercept values. Modeling results show that aggregation of similar to 40-70% sulfide blebs of different grain size from the disseminated ore into the networks can generate the coarser group sulfide PSD of net-textured ore. In addition, monosulfide solution (MSS, pyrrhotite component)-enriched sulfide globules are commonly located close to sulfide matrix ore breccias and emulsion-textured ores, rimming the net-textured and massive orebodies. These globules are different from the sulfide component that was in equilibrium with the mafic magma, suggesting they were formed by mechanical remobilization of a cumulus MSS-enriched component from a previously segregated and partially crystallized sulfide pool. These observations, combined with the ubiquitous chilled margin xenoliths in the high-grade ores, suggest that the Kalatongke deposit was the result of voluminous magma flow through the current location accompanied by sulfide reworking and percolation. All these textural characteristics could be explained by emplacement within a laterally propagating bladed dike. Moreover, the deformation recorded in the emulsion-textured and massive ores suggests the fault system remains active during magma solidification, driving downward migration of sulfide from the sulfide pool at magmatic temperature to form vein-type massive ore. We suggest that the Kalatongke deposit formed by magma pulses injecting into the current location and that the tectonic movement remains active during the solidification of the intrusion. The syntectonic emplacement model, which may be a common feature in the Central Asian orogenic belt Ni-Cu deposits, indicates that the fault systems beneath the intrusion are of great exploration interest for high-grade ores.