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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.

Nickel contents of olivine have been widely used as petrogenetic indicators and as fertility indicators for magmatic sulfide potential of mafic-ultramafic intrusions, on the assumption that olivines crystallized from magmas that had equilibrated with sulfide liquid should be relatively depleted in Ni compared with a sulfide-free baseline. This has given rise to a large accumulation of data that is brought together here, along with data on volcanic olivines, to critically evaluate the effectiveness of the approach. We identify multiple sources of variance in Ni content of olivine at a given Fo content, including variability in mantle melt composition due to depth, water content (and possibly source), subsequent fractional crystallization with and without sulfide, recharge and magma mixing, batch equilibration between olivine and sulfide at variable silicate-sulfide ratio (R), and olivine/liquid ratio; and subsequent equilibration during trapped liquid crystallization in orthocumulates. Baselines for Ni in olivine in relation to Fo content are somewhat lower in orogenic belt settings relative to intrusions in continental large igneous provinces (LIPs). This is probably related to differences in initial parent magma compositions, with plume magmas generally forming deeper and at higher temperatures. No clear, universal discrimination is evident in Ni in olivine between ore-bearing, weakly mineralized, and barren intrusions, even when tectonic setting is taken into account. However, sulfide-related signals can be identified at the intrusion scale in many cases. Low-R factor and low-tenor sulfides are associated with low-Ni olivines in several examples, and these cases stand out clearly. Anomalously high-Ni olivines are a feature of some mineralized intrusions, in part due to trapped liquid reaction effects. However, in some cases, this mechanism cannot account for the magnitude of enrichment. In these cases, enrichment may be due to re-entrainment of “primitive” Ni-rich sulfide by a more evolved Fe-rich magma, driving the olivine to become Ni-enriched due to Fe-Ni exchange reaction between sulfide and olivine during transport. An extreme case of this process may account for ultra-Ni enriched olivine at Kevitsa (Finland), but more subtle signals elsewhere could be positive indicators. A lack of clear mineralized/barren distinction in specific groups of related intrusions, e.g., the deposits of NW China or the Kotalahti Belt in Finland, may well be due to “false negatives” where undiscovered mineralization exists in specific intrusions or in their feeder systems, or may also be due to a multiplicity of confounding factors. Wide variability of both Fo and Ni between related intrusions at regional scale may be a useful regional prospectivity indicator, more than an intrusion-scale discriminant, and is certainly informative as a petrogenetic indicator. In general, the use of Ni-olivine as a fertility tool is more likely to generate false negatives than false positives, but both are possible, and the technique should be used as part of a broader weight-of-evidence approach.

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–

Magmatic Ni-Cu sulfide deposits in orogenic belts have distinct petrological and geochemical features compared with world-class intraplate magmatic deposits. One such feature is the presence of abundant primary hydrous minerals such as phlogopite and amphibole, indicating a H2O-rich parental magma. However, the origin and nature of the fluids have not been established. In the southern Central Asian Orogenic Belt, the Permian Baishiquan and Tianyu mafic–ultramafic intrusions host magmatic Ni-Cu sulfide deposits. Both intrusions are composed of lherzolite, olivine websterite, gabbronorite, gabbro, and diorite. The main ore-host rocks are lherzolite and websterite, with disseminated, net-textured, and massive ores comprising the dominant primary ore types. Low zircon eHf (− 6.9 to 7.9 ‰) and varying δ18O values (5.2 to 6.6 ‰), as well as both arc-type and MOR-type zircon Nb/Yb (0.0013–0.011) and U/Yb (0.33–10.22), identify an altered lower oceanic crust component in the mantle source. A combination of altered lower oceanic crust and upper crust can account for the zircon Hf–O isotopic characteristics. A mixing model further reveals that the Baishiquan and Tianyu magmatic sulfide deposits originated from a depleted mantle source that experienced two stages of subduction metasomatism with a 30% addition of altered oceanic crust in the first stage and 20% in the second. In the second stage, > 10% oceanic sediment with high δ18O must also have been added to result in olivine δ18O values higher than those in mantle. This staged evolution is reflected in both the olivine and zircon signatures with olivine from disseminated and net-textured ores at the Tianyu deposit having high δ18O (4.6 to 6.3 ‰) with a similar range to zircon and high δ7Li isotopic compositions (12.03 to 19.46 ‰). Contamination in the source by oceanic sediment with high δ18O values can account for the olivine δ18O values (4.8 to 5.7 ‰ at Baishiquan) being higher than those in the mantle, while the addition of brine (5% at the Baishiquan deposit) can explain the olivine δ7Li values (20.96 to 31.01 ‰). The results suggest that H2O content, Li content, and δ7Li and δ18O isotopic signatures in olivine and zircon are good indicators of mantle metasomatism and olivine fluid processes in magmatic Ni-Cu sulfide deposits.

Olivine is an important mineral in mafic–ultramafic rocks and records various crustal and mantle processes in basaltic magma. Generally, phosphorus (P) is immobile in olivine and its zoning tends to record magmatic processes. In contrast, lithium (Li) is one of the most mobile elements in olivine and tends to be re-distributed by postcumulus to hydrothermal processes. This study reports coupled Li-P oscillatory and sector zoning in cumulus olivine (Fo > 80 mol%) from magmatic Ni-Cu deposits in northwest China. The close to 1:1 relationship between Li + Na cation and P cation in olivine suggests P substitutes for slowly diffusing Si at the tetrahedral site and Li (Na) substitutes for Mg at the octahedral metal site. The preservation of such coupled Li-P zoning suggests that the charge-balanced–controlled substitution of Li+P5+ for Mg2+Si4+, producing a member of the Li(Fe)PO4 structure, may cause sluggish Li diffusion in olivine. The Li-P zoning is uncorrelated to other elements (Fe, Mg, Cr, Al, Ca, Ti, V, Ni, Zn, Mn, Co, and Sc). The Ca abundances in cumulus olivine are significantly depleted relative to those in volcanic olivine and modeled for olivine using the rhyolite–MELTS program, whereas the Mg, Fe, Mn, Zn, Ni, and Co contents show no signs of depletion. The Cr and Al contents in high Fo olivine are lower than those in volcanic olivine with a similar Fo value. The depletions in Ca, Cr, and Al (both divalent and trivalent cations) have been attributed to post-crystallization re-equilibration processes. We suggest that the selective Ca-Cr depletion in olivine resulted from re-equilibration between olivine and clinopyroxene–orthopyroxene–spinel–melts at the postcumulus stage, whereas the Al content variation in olivine is likely controlled by olivine–spinel (pyroxene) re-equilibration. Olivine fractionation modeling results reveal that Co content in both olivine and sulfides changes slightly during evolution, whereas the olivine Ni/Co ratio decreases dramatically from 30 (at Fo90) to 4 (Fo80). These are consistent with the variation of Ni and Co contents in olivine from sulfide-barren rocks but cannot explain the strong positive Ni-Co correlation observed in olivine from the sulfide-bearing rocks. The considerable increase in the Ni/Co ratio in olivine coexisting with the high Ni tenor sulfide compared with the slight increase of the Ni/Co ratio in olivine coexisting with moderate-low Ni tenor sulfide strongly suggests that the Ni and Co contents and Ni/Co ratio in olivine from the mineralized rocks were the results of olivine–sulfide interaction. The olivine Fe/Zn and Mn/Zn ratios show little difference between sulfide-barren and sulfide-rich rocks, but these ratios decrease considerably with the decreasing Fo values. Overall, the study suggests that elements (Ca, Cr, Al, Mg, Fe, Ni, Co, Zn, etc.) diffuse faster than P have been re-distributed in cumulus olivine by re-equilibration processes, modifying the elemental content and inter-element ratios in olivine. The characteristics of the crystallization, particularly the source recorded in cumulus olivine, may be obscured and overprinted by postcumulus processes.

Various types of igneous suites occurred between 930 Ma and 890 Ma in the North China craton are known to represent a large igneous province (LIP). However, the magma plumbing system of this LIP and its potential consequence to a breakup event are poorly understood. We report morphology, crystal size distribution of plagioclase, and whole-rock and mineral geochemistry profiles of this LIP represented by the two decoupled mafic sill complexes (Niutishan and Pingshan) in the Xuhuai basin. In terms of petrography and whole-rock geochemistry, unlike the lower-level doleritic Niutishan sill, the Pingshan sill is subdivided into an upper and a lower sequence that meets at a Sandwich Horizon but lacks stratification. The significant En reversals present an almost M-shaped profile that differs from a C-shaped profile as previously revealed in the Niutishan sill. Quantitative textural analyses show relatively strong plagioclase orientation in the lower sequence of the Pingshan sill, which is attributed to magma flow. The Pingshan sill is interpreted to have been constructed as multiple magma injections from crustal magma chambers based on the crystal size distribution and the varied crystallization pressure (5.1–7.5 kbar) of clinopyroxene crystals. Similar to the far-field radiating Dashigou dyke swarm (c. 925 Ma), the Niutishan sill is enriched in incompatible elements, which may represent the initiation of the Xuhuai rifting. However, the depleted features of the diamond-bearing Pingshan sill and the other coeval doleritic sills (916–890 Ma) were probably related to the subsequent process switched from continental rifting to lithospheric rupture in the divergent stage of the Wilson cycle. The occurrence of the intrusive rocks evolving from an early radiating dyke swarm to later sill complexes indicates a time-transgressive change from radial to planar patterns, implying that it was the upwelling asthenospheric plume material, instead of plate boundary processes, governed the initial and early evolution of this intracontinental rift.

Sulfide Cu isotope systematic has been used as a metallogenic tracer in various deposits; however, only rarely in magmatic Ni-Cu sulfide deposits. Here we present chalcopyrite δ34S and δ65Cu data for the Kalatongke and Baishiquan Ni-Cu sulfide deposits in the Central Asian Orogenic Belt. The Kalatongke deposit yields δ34S of −3.99‰ to 3.30‰ and δ65Cu of −1.32‰ to 0.07‰, whereas chalcopyrite from the Baishiquan deposit has δ34S values ranging from 1.70‰ to 4.98‰ and δ65Cu from −0.40‰ to 0.59‰. These isotopic ratios show no correlation with intrusion/orebody shape, location of sample in the orebody, lithofacies or type of mineralization. Based on Kalatongke and Baishiquan δ34S data, our multicomponent modeling suggests that, with an increase in the relative crustal component contribution, the measured δ34S values in sulfide ores approach the value of the contaminant. Mass ratios (R′) of silicate magma/(xenomelt + sulfide xenomelt + resitite + crystalline olivine) of 250–800 in the Kalatongke and 10–1000 in the Baishiquan deposit, yield δ34S values of −1.78‰ to 1.74‰ and 1.70‰ to 4.98‰ in these deposits. Contamination by host tuff and shale material with δ34S values of −7.2‰ to 3.3‰ reasonably explains the negative δ34S in the Kalatongke ores. A lack of correlation between the Kalatongke and Baishiquan chalcopyrite δ65Cu values and Cu or S contents (or Cu/Ni ratios) indicates that Cu isotopic fractionation was not controlled by sulfide fractional crystallization, but instead by contamination and the mantle source. Multicomponent modeling shows that an R′ factor between 10 and 1000 can reproduce most δ65Cu signatures in sulfide ores from the Kalatongke and Baishiquan deposits, with the exception of a few negative δ65Cu values. Undetected contamination and heterogeneous mantle resulting from different degrees of partial melting and metasomatism in the mantle source may explain these negative values and the wide range of δ65Cu noted in magmatic sulfide deposits worldwide. The Cu and S isotopes in sulfide from the magmatic Ni-Cu sulfide deposits can be utilized as indicators of crustal contamination and the nature of the mantle source.

Magmatic Ni—Cu deposits that associated with mafic–ultramafic intrusions in convergent settings could form from multiple magma pulses with age difference varying from 1 Ma to >10 Ma years. The Huangshandong deposit in NW China of the southern Central Asian Orogenic Belt was formed in such a setting. The intrusion is composed of four units formed by four magma pluses: a gabbroic sequence (Phase I, crystallized from an evolved magma), a sheet–like ultramafic body (Phase II, crystallized from a relatively primitive magma), a dike–like gabbronorite body (Phase III, crystallized from an evolved magma), and an irregular ultramafic unit (Phase IV, crystallized from a relatively primitive magma). Our zircon SIMS U—Pb dating shows that the Phase I and Phase IV magmas of the Huangshandong deposit were emplaced at 280.3 ± 1.9 Ma and 281.4 ± 2.2 Ma, respectively, indicating that the four magma pulses were intruded over a very short period and cannot be distinguished within the uncertainty of ±2 Ma. Moreover, the zircon crystals in the four units record identical ɛHf (t) values (average of 12.1–13.5) and δ18O values (average of 6.3–6.5‰). However, the intrusive relationships of the four units illustrate that the Huangshandong complex cannot form by in–situ fractionation. Therefore, the indistinguishable Hf—O isotopic values, together with their contemporaneous emplacements, indicate that the four magma pulses could originate from a same staging magma chamber. The overall enrichment of ɛHf (t) value relative to that of the depleted mantle (16) and elevation of δ18O values relative to the mantle value (5.3‰) suggest 15–20% crustal material incorporation. Additionally, the magmas may have been contaminated prior to their arrival at the staging magma chamber, where the magma has subsequently experienced variable olivine fractionations and relatively primitive magma replenishment. For most mafic–ultramafic intrusions which are characterized by long–duration magmatism (>10 Ma) in convergent settings, e.g., intrusions in the Kalatongke area, Tulaergen intrusions, Xiarihamu intrusions, the most important Ni—Cu mineralization are closely related to the last stage magmatism. This finding suggests that the intrusions emplaced at the late stage of subduction and post–collisional period of the orogenic process may have more potential for Ni—Cu mineralization exploration.

The Tulaergen magmatic Ni–Cu deposit is related to mafic‐ultramafic rocks of the Central Asian Orogenic Belt. The ore‐host rocks are lherzolite and websterite and the major ore types are net‐textured and sparsely disseminated ores. The disseminated ores host high‐Fo (82–85) olivine and hornblende with low‐Al contents, high‐rare earth element (REE) abundances and negative Eu anomalies. The net‐textured mineralized lherzolite contains low‐Fo (74–82) olivine and high‐Al hornblende, the latter characterized by low REE concentrations and no Eu anomaly. The contrasting composition of olivine and hornblende suggests two stages of magmatism. In situ analysis of pentlandite, chalcopyrite and pyrrhotite shows that platinum‐group elements contents in sulphides are low. Contrasting Ni, Co, Se, Ag, Cd, and Pb contents in sulphides from net‐textured and in disseminated ores also supports two pulses of magmas, each with a distinct chemical composition. High‐Mg basaltic magma characterized the first stage, followed by a second‐stage less basic magma with a high H2O content. Whole‐rock Sr and Nd isotopic signatures suggest that about 4–6% crustal materials were added to the depleted mantle source. The fractional crystallization of olivine and crustal contamination play important roles in sulphur segregation at Tulaergen based on sulphur content at sulphide saturation modelling. Injection of magma enriched in H2O further enhanced sulphide aggregation and deposit forming. It is proposed that two pulses of magma injections occurred at the Tulaergen deposit, with the products of the first pulse settling at the base, and of the second one with dense mineralization laying at the top of the deposit.

Although there are many mafic–ultramafic intrusions in the western and central regions of Mongolia, Central Asian Orogenic Belt (CAOB), no economic-grade Ni–Cu deposits have yet been discovered. To understand the economic Ni–Cu deposit potential of the intrusions in central Mongolia, the parental magma affinity and sulfide saturation of the Oortsog, Dulaan, and Nomgon Ni–Cu mineralized mafic–ultramafic intrusions are studied. These three intrusions are predominantly gabbroic in composition, while the Oortsog and Dulaan intrusions also contain small proportions of peridotites. The parental magmas of the Oortsog and Dulaan intrusions are tholeiitic, as indicated by their Cr-spinel and clinopyroxene compositions, whereas the parental magma of the Nomgon intrusions is likely calc-alkaline. The compositions of Cr-spinel and clinopyroxene, combined with the presence of significant Nb–Ta depletions, indicate that these rocks were most likely derived from modified mantle sources. Both the Oortsog and Nomgon intrusions form two clusters in terms of their olivine composition, suggesting that multiple magma surges were involved during their emplacement. The relatively low Fo values and Ni contents in olivine from the three intrusions compared to those from Ni–Cu deposits in NW China, as well as those in the Voisey’s Bay deposit in Canada, indicate that the three intrusions were crystallized from relatively evolved magmas. The Cu/Zr ratios of rocks of the Oortsog, Dulaan, and Nomgon intrusions are higher than 1, suggesting that these rocks contain cumulus sulfide. This, coupled with the presence of rounded sulfide inclusions in olivine of the Oortsog and Dulaan intrusions, suggests that sulfide saturation occurred before or during olivine crystallization. The distribution patterns of platinum group elements (PGEs) of the Dulaan and Oortsog intrusions record slight Rh, Pt, and Pd (PPGE) enrichment relative to Os, Ir, and Rh (IPGE). Furthermore, the Ni/Cu ratios of sulfide-bearing rocks from the Oortsog intrusion vary from 1.8 to 3.8, which are consistent with those of the Ni–Cu sulfide deposits in NW China. In contrast, the Ni/Cu ratios of sulfide-bearing rocks from the Nomgon intrusion are extremely low (0.03 to 0.07). This, together with the significant enrichment in PPGE relative to IPGE, suggests that these sulfides of the Nomgon intrusion were segregated from a magma that was extremely enriched in Cu and PPGE but depleted in Ni and IPGE. The characteristics of the chalcophile elements in these intrusions are attributed to the fact that the derivation of the Nomgon magma was significantly different from that of the Dulaan and Oortsog parental magmas. Overall, although the parental magmas of the intrusions in central Mongolia are more evolved than those in NW China, they are comparable in terms of the sizes of their intrusions, constituent minerals, and mineral chemistry. These similarities suggest that the intrusions in central Mongolia have economic Ni–Cu sulfide potential. Furthermore, intrusions similar to the Nomgon intrusion may feature PGE mineralization potential.

The recently discovered Kemozibayi mafic-ultramafic intrusion and its associated magmatic Cu-Ni sulfide deposits are located at the southern margin of the Chinese Altai Mountain, Central Asian Orogenic Belt in north Xinjiang, NW China. The intrusion is composed of olivine websterite, norite, gabbro and diorite. Disseminated and net-textured Ni-Cu sulfide ores are hosted in the center of the gabbro. In this work, new zircon U-Pb ages, Hf-O isotopic and sulfide S isotopic data, and whole rock and mineral chemical analyses are combined in order to elucidate the characteristics of the mantle source, nature of subduction processes, degree of crustal contamination, geodynamic setting of bimodal magmatism in the region, and the metallogenic potential of economic Cu-Ni sulfide deposit at depth. SIMS zircon U-Pb dating of the gabbro yields Permian ages (278.3 ± 1.9 Ma), coeval with the Kalatongke Cu-Ni deposit and with Cu-Ni deposits in the Eastern Tianshan and Beishan areas. Several lines of evidence (positive eHf(t) from + 7.1 to + 13.3, Al2O3, TiO2 and SiO2 contents in clinopyroxene from olivine websterite, high whole rock TiO2 contents) suggest that the primary magma of the Kemozibayi intrusion was a calc-alkaline basaltic magma derived from depleted mantle, and that the degree of partial melting in the magma source was high. The evolution of the Kemozibayi mafic-ultramafic complex was strongly controlled by fractional crystallization and the crystallization sequence was olivine websterite, norite, and then gabbro. This is evidenced by whole rock Fe2O3 contents that are positively correlated with MgO and negatively correlated with Al2O3, CaO and Na2O, similar LREE enrichment and negative Nb, Ta, Hf anomalies in chondrite and primitive mantle-normalized patterns, and a decrease in total REE and trace elements contents and magnetite content from gabbro through to norite and olivine websterite. Varied and low eHf(t) (+ 7.1 to + 13.3) and high δ18O values (+ 6.4‰ to + 7.2‰) in zircon, high La/Ba, and Rb/Y ratios, and low Nb/La ratios in whole rock samples, suggest 5–10% contamination by subduction related fluid and 10–15% contribution from an upper crustal component. The clinopyroxene TiO2 and Alz values (percentage of tetrahedral sites occupied by Al) in the Kemozibayi intrusion show characteristics of rift cumulate rocks, but minor arc cumulate features, indicating that the mantle source might have experienced a lower degree of subduction metasomatism. A high degree of partial melting of the depleted mantle and subducted oceanic sediments with related fluid metasomatism and crustal contamination in the Kemozibayi mafic-ultramafic intrusion are appropriate for the formation of an economic copper and nickel sulfide deposit. Crustal contamination, crustal S addition and early fractionation of olivine and sulfide induced S saturation and the formation of immiscible sulfide in the Kemozibayi intrusion. With no obvious olivine and Ni-rich sulfide co-crystallization, the Cu grade in the present orebody is higher than the Ni grade, and the proportion of mafic rocks is high in the Kemozibayi mafic-ultramafic complex. Cumulatively, these features suggest that the mafic-ultramafic intrusion underwent early olivine and Ni sulfide segregation, and that deeper or extended portions of the present intrusive body may host Ni mineralization.

Cihai and Cinan are Permian magnetite deposits related to mafic-ultramafic intrusions in the Beishan region, Xinjiang, NW China. The Cihai mafic intrusion is dominantly composed of dolerite, gabbro and fine-grained massive magnetite ore, while gabbro, pyrrhotite + pyrite-bearing clinopyroxenite and magnetite ore comprise the major units in Cinan. Clinopyroxene occurs in both deposits as 0.1–2 mm in diameter subhedral to anhedral grains in dolerite, gabbro and clinopyroxenite. High FeO contents (11.7–28.9 wt%), low SiO2 (43.6–54.3 wt%) and Al2O3 contents (0.15–6.08 wt%), and low total REE and trace element contents of clinopyroxene in the Cinan clinopyroxenite imply crystallization early, at high pressure. This clinopyroxene is FeO-rich and Si and Ti-poor, consistent with the clinopyroxene component of large-scale Cu-Ni sulfide deposits in the Eastern Tianshan and Panxi ares, as well as Tarim mafic intrusion and basalt, implying the Cinan mafic intrusion and sulfide is related to tectonic activity in the Tarim LIP. The similar mineral chemistry of clinopyroxene, apatite and magnetite in the Cihai and Cinan gabbros (e.g., depleted LREE, negative Zr, Hf, Nb and Ta anomalies in clinopyroxene, lack of Eu anomaly in apatite and similarity of oxygen fugacity as indicated by V in magnetite), indicate similar parental magmatic characteristics. Mineral compositions suggest a crystallization sequence of clinopyroxenite/with a small amount of sulfide – gabbro – magnetite ore in the Cinan deposit, and magnetite ore – gabbro – dolerite in Cihai. The basaltic magma was emplaced at depth, with magnetite segregation (and formation of the Cinan magnetite ores) occurring in relatively low fO2 conditions, after clinopyroxenite and gabbro fractional crystallization. The evolved Fe-rich basaltic magma rapidly rose to intermediate or shallow depths, forming an immiscible Fe-Ti oxide magma as fO2 increased and leaving a Fe-poor residual magma in the chamber. The residual magmas was emplaced at different levels in the crust, forming the Cihai gabbro and dolerite, respectively. Finally, the immiscible Fe-Ti oxide magma was emplaced into the earlier formed dolerite because of late magma pulse uplift, resulting in a distinct boundary between the magnetite ores and dolerite.

The Huangshannan mafic–ultramafic intrusion is a Permian Ni–Cu sulfide-bearing intrusion in the southern margin of the Central Asian Orogenic Belt. The intrusion consists of an ultramafic unit, which is composed of lherzolite and olivine websterite, and a mafic unit, which is composed of olivine gabbronorite, gabbronorite and leuco-gabbronorite. This intrusion was formed by two separate pulses of magma: a more primitive magma for the early ultramafic unit and a more evolved magma for the late mafic unit. U–Pb isotope geochronology of zircon from the mafic unit yields an age of 278 ± 2 Ma. According to its olivine and Cr-rich spinel compositions, the estimated parental magma of lherzolite for the Huangshannan intrusion has 12.4 wt.% MgO, indicating picritic affinity. Fractional crystallization modeling results and the presence of rounded sulfide inclusions in an olivine crystal (Fo 86.7) indicate that sulfide immiscibility was achieved at the beginning of olivine fractionation. Co-magmatic zircon crystals from gabbronorite have a δ18O value close to 6.5‰, which is 1.2‰ higher than the typical mantle value and suggests significant crustal contamination (∼20%). The positive eHf(t) values of co-magmatic zircon (which vary from +9.2 to +15.3) and positive whole rock eNd(t) values (which vary from +4.7 to +7.8) also indicate that the parental magma was derived from a depleted mantle source and contaminated by 5–20% juvenile arc crust and then by ∼5% upper crustal materials. However, modeling results of sulfur content at sulfide saturation reveal that such a large amount of crustal contamination is not sufficient to trigger sulfide saturation in the parental magma, which strongly suggests that external sulfur addition, probably during contamination, has played a critical role in causing sulfide immiscibility. Furthermore, the arc magmatism geochemical signatures of the Huangshannan intrusion, such as significant Nb and Ta depletion relative to La and low Ca contents in olivine, are interpreted as the result of slab-derived fluid modification during previous subduction. We speculate that the contamination of juvenile arc crust may have occurred in the lower crust because of picritic magma underplating and that partial melting in the mantle was triggered by the impingement of a mantle plume or lithosphere delamination in a post-subduction environment.

The Xinyuan intrusion of the Eastern Junggar terrane is one of the mafic–ultramafic intrusions located in the Northern Xinjiang region and is associated with the southern part of the Central Asian Orogenic Belt (CAOB). Based on the secondary ion mass spectrometry (SIMS) zircon U–Pb dating, the intrusion is 326.2 ± 1.1 Ma old. Positive zircon ɛHf(t) values (+12.4 to +15.7) and mantle-like δ18O values (5.0–5.5‰) suggest that the parental magma was derived from a depleted mantle source with a low degree of crustal contamination. Significant negative Nb–Ta anomaly and large iron lithophile element (LILE) enrichment of the Xinyuan intrusion are identical to those of the coeval basalt–andesite rocks in the study area. Temporal, spatial, and geochemical evidence suggest that the Xinyuan intrusion and coeval basalt–andesite rocks are associated with the northward subduction of the Kelameili Ocean. This, together with the ages of alkaline granites and sedimentary record in the Eastern Junggar, suggests tha...

The Poyi magmatic Ni-Cu sulfide deposit is situated in the Beishan fold belt in the northeastern rim of the Tarim craton. Many Permian magmatic Ni-Cu sulfide deposits, such as those in East Tianshan, are present in the adjacent Central Asian orogenic belt to the north. The Poyi deposit is hosted in a small dike-like ultramafic-troctolitic body that was emplaced into a much larger gabbroic intrusion. Our new zircon U-Pb isotope data reveal that these two intrusions formed ~6 Ma apart. The ultramafic-troctolitic intrusion was emplaced at 269.9 ± 1.7 Ma, whereas the gabbroic intrusion was emplaced at 276.1 ± 1.9 Ma. The results show that the Poyi deposit is the youngest among the major magmatic Ni-Cu sulfide deposits (≥0.2 Mt Ni) of Permian ages in the Beishan-Tianshan region. Sulfide mineralization in the Poyi deposit occurs as steeply dipping disseminated sulfide lenses mostly associated with wehrlites in the center of the dike. Olivine from the Poyi ultramafic rocks has Fo content up to 91 mol %, which is similar to the lower limit of mantle olivine and the most primitive within the Permian Beishan-Tianshan nickel belt. Like other magmatic sulfide deposits in this belt, olivine from the Poyi deposit is depleted in Ca (

The Savannah (formerly Sally Malay) Ni-Cu-Co Camp is composed of a group of mineralised intrusions (Savannah and Savannah North) and petrologically similar mafic-ultramafic intrusions without known mineralisation (Sub-chamber D, Dave Hill, and Wilson’s Creek). The results of a wide range of analytical techniques (geochemical, geochronological and geophysical) are integrated to gain a better understanding of the geometry of the Savannah mineralised magmatic intrusions and the timing of events. Magnetic anisotropy results suggest that Savannah and Savannah North have both been affected by similar deformation events, implying near-synchronous intrusion. However, Savannah and Savannah North show evidence of fundamentally different styles of deformation (strong folding at Savannah, as opposed to gentle tilting at Savannah North). This discrepancy can be reconciled with a resolvable variation in age, with Savannah North being the younger by ca. 0.8–2.5 Ma, as well as difference in the geometry and associate rheological properties of the intrusions: the larger more equant Savannah North intrusion may have been more resistant to deformation than the thinner elongated Savannah body. Isotopic and geochemical data on the mafic-ultramafic intrusions of the Savannah Ni-Cu-Co Camp indicate that the entire intrusive suite, with the exception of the early mafic granulite dykes, was derived from a similar parent magma of basaltic composition with likely continental arc affinity. Results of sulfide tenor calculations combined with mineral chemistry and in-situ S isotope data provide insight into ore genetic processes: in both the Savannah and Savannah North intrusions tenors are low, with median values in semi-massive ores of 3.8% Ni and 0.9% Cu in 100% sulfide for Savannah and 2.7% Ni and 1.0% Cu for Savannah North. PGE tenors are similar and extremely low in both deposits, ranging from below 5 ppb to 200 ppb for Pt (median 6 ppb) and from 40 ppb to 480 ppb (median 110) for Pd, with Pd/Ir of 25–160 and Pd/Pt of 3–50 (10th and 90th percentiles). For both Savannah and Savannah North, S isotopic analyses indicate a limited amount of incorporation of crustal S, and the contaminant does not appear to have been the immediately adjacent Tickalara Metamorphics, implying either a deeper crustal contaminant, or a component of subduction-derived crustal S in the mantle source . Finally, olivine records a history of postcumulus re-equilibration with trapped silicate melt and cumulus sulfide liquid, giving rise to distinctive compositional trends. The Savannah Ni-Cu-Co Camp provides further evidence that arc and collisional environments are conducive to the formation of intrusion-hosted orthomagmatic Ni-Cu-Co deposits. The multidisciplinary approach that we describe here allowed us to unravel the petrological, structural, and mineralisation history of a cryptic but prospective region, and provided insights to help evaluate the prospectivity of neighbouring intrusions. This approach can be used in a wide range of settings to resolve critical factors such as S source, timing of intrusion and mineralisation, and structural controls.

The early Permian Kalatongke Cu Ni sulfide deposit in the Central Asian Orogenic Belt (CAOB) is the most important Cu Ni deposit in northern Xinjiang, NW China. It is hosted mainly by mafic intrusions, which is in contrast to deposits in the Eastern Tianshan area of eastern Xinjiang that are hosted mainly by ultramafic intrusions. The controls on sulfide mineralization in the Kalatongke mafic intrusions are poorly constrained relative to the ultramafic intrusions. Here we use amphibole compositions to trace the nature, oxygen fugacity, and water content of the Kalatongke magmas. The results, together with data for other Ni Cu mineralized magmas in Eastern Tianshan, are used to clarify the formation mechanism of sulfide mineralization in mafic intrusions. Amphiboles in the Kalatongke intrusions are divided into three types based on petrographic features: poikilitic amphiboles in olivine norite and norite (Type 1), which formed by reactions between olivine and pyroxene and interstitial residual melt; zoned amphiboles in norite (Type 2), generated by contamination processes; and needle-shaped amphiboles in diorite (Type 3), which indicate rapid cooling during the early stage of magma evolution. Modeled results show that the melts in equilibrium with amphiboles and clinopyroxenes exhibit enrichment in Th, U, and light rare earth elements (LREE) over heavy REE (HREE). Combined with amphibole and clinopyroxene chemistry, this indicates that the parental magma of the Kalatongke intrusions was strongly contaminated by continental crust during ascent. The oxygen fugacity of the magma during fractionation was evaluated using amphibole chemistry and olivine–sulfide equilibration. The oxygen fugacity of the magmas varied during their evolution, with the Kalatongke deposit magma showing relatively little variation compared with the deposits related to ultramafic intrusions in Eastern Tianshan. The oxygen fugacity of ore-forming magma thus varied significantly during the early stages of magma emplacement. Moreover, the calculated water content of melts in equilibrium with Kalatongke amphibole and clinopyroxenes averages 4.37 wt% in. These lines of evidence indicate that a highly hydrous and relatively oxidized magma favors the formation of sulfide deposits in mafic intrusions. It is inferred that sulfide saturation was delayed to the onset of mafic magma crystallization, rather than trapped in the early crystallized olivine cumulate within the staging magma chamber.

Oxygen fugacity is a key parameter in controlling the petrogenesis of mafic-ultramafic rocks and their associated sulfide mineralization, especially in convergent settings. This study uses new and previously published experimental data on olivine-sulfide pairs to reparameterize an expression for oxygen barometry using the distribution coefficient K D FeNi for Fe-Ni exchange between olivine and sulfide. We derive a new expression, ΔQFM = (9.775 + 0.416 ∙ C Ni − K D FeNi)/4.308, where ΔQFM denotes divergence from the fayalite–magnetite–quartz buffer. The revised oxygen barometry has been applied to the Permian magmatic Ni–Cu deposits in the Central Asian Orogenic Belt, NW China. The Ni–Cu deposits in the East Tianshan—North Tianshan, Central Tianshan, and Beishan—are considered as a single mineral system, whereas the spatially separated deposits in the East Junggar are considered as a separate system. The deposit of the East Tianshan group exhibits a large range of oxygen fugacity (QFM − 2 to ~QFM + 1) and Ni tenor (metal concentration in pure sulfide, ~ 5 to 16 wt%). The Poyi and Huangshannan deposits contain high-Ni tenor sulfides, varying from 12 to 16 wt%. The relatively high Fo values (> 85 mol%) and Ni contents (> 2000 ppm) in olivine of these deposits indicate that the high-Ni tenor sulfides were segregated from less differentiated high-Ni magmas that also had relatively high oxygen fugacity (~QFM + 1). The remaining Ni–Cu deposits in the East Tianshan—the Huangshandong, Huangshanxi, Hulu, Tulaergen, Tudun, and Xiangshanzhong deposits—have intermediate Ni tenors (5–8 wt%). These sulfides correspond to intermediate Fo values (80–84 mol%) and Ni contents (700–1400 ppm) in the coexisting olivine, illustrating that they were segregated from magmas with lower Ni contents thought to be the result of a large amount (15–20%) of olivine fractionation at depth. These magmas are more reduced (− 2

The Permian Huangshanxi mafic-ultramafic intrusion hosts one of the two largest magmatic sulfide deposits in the Eastern Tianshan which is situated in the southern margin of the Central Asian Orogenic Belt. In this paper we use mineral compositions and whole-rock geochemical data to decipher the genetic relationship between magma evolution and sulfide mineralization. The Huangshanxi intrusion consists of three separate intrusive units. Important sulfide mineralization occurs in the base of the last intrusive unit, an elongated, layered ultramafic body composed of lherzolite at the bottom, olivine websterite in the middle and websterite at the top. Based on olivine-liquid equilibria and mass balance, the MgO and FeO contents in the parental magma for a lherzolite sample are estimated to be 8.71 and 8.36 wt.%, respectively. The Huangshanxi mafic-ultramafic intrusive rocks and the estimated “trapped liquids” for several olivine-orthopyroxene cumulate rocks all show light rare earth element enrichments relative to heavy rare earth elements and significant Nb depletions relative to Th and La, which are similar to the characteristics of coeval basalts in the region. The arc-like geochemical features are attributed to pre-Permian mantle metasomatism by slab-derived fluids. Partial melting of the previously-modified mantle is thought to have resulted from heating by upwelling asthenosphere associated with post-subduction lithosphere delamination or by mantle plume activity. The relationship between the Fo and Ni contents of olivine crystals from the Huangshanxi sulfide-poor ultramafic rocks ( in-situ differentiation stage during which the sulfide droplets and olivine crystals settled to form the sulfide-olivine cumulate zones at the base of the Huangshanxi magmatic system.

The Huangshandong Ni–Cu deposit is the largest magmatic sulfide deposit discovered to date in the Central Asian Orogenic Belt in northern Xinjiang, western China. The host intrusion is a 274-Ma composite mafic–ultramafic intrusion consisting of four separate intrusive units: a large layered gabbroic sequence (phase I), a sheet-like ultramafic body (phase II), a dyke-like gabbronorite body (phase III), and an irregular ultramafic unit (phase IV). Important sulfide mineralization is present in the last three intrusive units, predominantly as disseminated and net-textured sulfides (pyrrhotite, pentlandite, and chalcopyrite). The Huangshandong mafic–ultramafic intrusive rocks are characterized by arc-like geochemical signatures such as low Ca content in olivine and negative Nb–Ta anomalies in whole rocks. This, together with a post-subduction setting for the East Tianshan in the Permian, suggests that the source mantle was modified previously by slab-derived fluids in the Carboniferous. The mantle-derived magma was ponded in a staging chamber in the lower part of the newly formed arc crust. The first batch of magma to arrive at Huangshandong was most fractionated and depleted in Ni, crystallizing Fe-rich and Ni-depleted olivine (Fo67

The Permian Hulu intrusion is one of several sulphide-bearing Permian mafic–ultramafic intrusions in the eastern part of the eastern Tianshan located at the southern margin of the Central Asian Orogenic Belt (CAOB) in Xinjiang, NW China. The intrusion is composed of lherzolite, olivine websterite, gabbro, and gabbro-diorite. Disseminated and net-textured Ni-Cu sulphide ores are located at the bottom of the lopolith complex. Negative Zr, Hf, Nb, and Ta anomalies, whole-rock eNd(t) values of +5.7 to +8.8, and variable (Th/Nb)PM values (from 1.06 to 8.13) suggest that the source of the Hulu complexes is depleted mantle metasomatized by subducted slab-derived fluid and/or melt (~5% global subducted sediment and 15% slab fluid) that has experienced approximately 3% lower crustal and 10% upper crustal contamination. The Hulu intrusion is characterized by low PGE abundances i.e. 0.03–1.08 ppb Ir, 0.04–0.69 ppb Ru, 0.02–2.15 ppb Rh, 0.30–48.71 ppb Pt, and 0.21–344 ppb Pd. Our calculations indicate that if the Pd,...