Magmatic Ni-Cu Sulfide Deposits Research Articles

Co-Ni distribution and Re-Os isotopic age of the Wuxing complex in the Central Asian orogenic Belt: Implications for sulfide mineralization in Alaskan-type complexes

Alaskan-type mafic–ultramafic complexes have been recognized as potential hosts of magmatic Ni-Cu sulfide deposits. However, the distribution and controlling factors of ore-forming metal elements like Co and Ni within these complexes remain poorly understood. This study offers comprehensive petrological observations and quantifies the Co and Ni contents of silicate minerals and sulfides in the Wuxing complex, the oldest Alaskan-type complex hosting a distinctive PGE-rich Ni-Cu sulfide deposit in the Central Asian Orogenic Belt. The Co-rich minerals, including cobaltite and pentlandite, occur as inclusions or interstitial grains in other mineral phases. Among the sulfide assemblages (pyrrhotite, pentlandite and chalcopyrite), pentlandite exhibits the highest 3.59 ∼ 5.98 wt.% of Co and 28.7 ∼ 32.7 wt.% of Ni contents, with the Co contents being 2 to 10 times higher than those in magmatic Ni-Cu sulfide deposits. Clinopyroxene and hornblende in the Wuxing complex display lower Co and Ni contents compared to those in sulfide-free rocks of typical Alaskan-type complexes. This could be ascribed to the reduction in Co and Ni contents in evolved magmas following sulfide segregation. Additionally, lack of olivine and chromite crystallization would elevate Co and Ni contents in silicate magma and promote the sulfide mineralization in the Wuxing complex. The Re-Os isotopic dating in ore samples at 596 Ma, combined with previously zircon U-Pb ages of 510 ∼ 517 Ma, reveals that long-term magmatism would facilitate mineralization in the Wuxing complex. Our investigations provide a new insight of mineral crystallization for understanding of magmatic Ni-Cu-PGE sulfide mineralization in Alaskan-type complexes.

In situ sulfide saturation induced by geometric changes of magma conduit in the world-class Jinchuan magmatic Ni-Cu sulfide deposit, China

When and how sulfide saturation occurred in the Jinchuan magmatic Ni-Cu sulfide deposit are poorly constrained. To address this issue, we investigated compositional variations and crystallization temperatures of olivine in various ores and rocks in orebody 1 of the Jinchuan deposit. The forsterite (Fo) values and Mn contents in olivine vary respectively from 79.6 to 85.2 and 1270 to 2463 ppm in net-textured ores, 76.7 to 84.2 and 1425 to 2865 ppm in patchy net textured ores, 78.7 to 84.1 and 1440 to 2649 ppm in disseminated ores, and 69.7 to 81.8 and 1495 to 3191 ppm in sulfide-barren lherzolites. The estimated crystallization temperatures of olivine in these ores/rocks range from 803 to 1163 ℃, 871 to 1314 ℃, 821 to 1507 ℃, and 929 to 1652 ℃, respectively. These data revealed two distinct groupings in both olivine Fo-Mn correlations and crystallization temperatures cluster splitting at a Fo of 79.5 and a temperature of 1100 ℃. The wider range of Mn content with a given Fo value higher than 79.5 compared to those with Fo values lower than 79.5 indicates the onset of in situ sulfide saturation at a Fo of 79.5. The termination of sulfide saturation is epitomized by olivine in disseminated ores with a peak Fo content of 84. The abrupt temperature drops from ca. 1400–1500 °C to ca. 800–1100 °C in the parental magma likely occurred when the magma flowed through the westernmost portion of this segment, which resembles a de Laval nozzle. This geometry could have induced rapid cooling and decompression of the magma, consequently promoting degassing through decompression. These reductions in temperature and H2O content of the magma would collectively result in a decrease in the sulfur concentration at sulfide saturation (SCSS), which would exceed any SCSS increase due to decompression. Our findings emphasize the critical role of magma conduit geometry in physicochemical changes of the parental magma for sulfide saturation and subsequent mineralization in the Jinchuan deposit, which may also be applicable to other magmatic deposit worldwide.

Electrical characteristics of ore-forming intrusion No. 2 in the Xiarihamu magmatic Ni-Cu sulfide deposit in East Kunlun Orogenic Belt

The Xiarihamu magmatic Ni-Cu sulfide deposit is situated within the East Kunlun Orogenic Belt and consists of four intrusions. While the estimated Ni resources of intrusion No. 1 exceed 1.2 million tons, the resource potential of other intrusions remains unknown. One significant factor contributing to this knowledge gap is the lack of effective detection and localization methods for concealed intrusions. To address this issue, we conducted an electromagnetic study focusing on intrusion No. 2. Due to the substantial topographic relief in the survey area, the conventional artificial-source electromagnetic method presented limitations in data acquisition. Consequently, we employed the short-offset transient electromagnetic method for data acquisition. A group-network observation mode was utilized to reconstruct the electrical structure of intrusion No. 2 through data inversion. Our results reveal a predominant high-resistivity background within the survey area. Rocks including granite, biotite gneiss, gabbro, and pyroxenite exhibit high resistivities, whereas mineralized ultramafic rocks show lower resistivities due to the presence of sulfides. The detection of concealed conductive bodies serves as a crucial indicator for deep mineral exploration. The distribution characteristics of low-resistivity anomalies indicate that the mafic bodies extend deeper towards the southwest, with mineralized pyroxenites observed beneath the gabbros. The results also suggest a gradual weakening of mineralization from the northeast to the southwest, with conductive mineralized anomalies existing at considerable depths beneath the known exposed intrusion. These findings highlight promising prospecting potential and provide valuable insights into the formation of intrusions within the Xiarihamu deposit, supporting resource exploration in similar deposits.

Machine learning prediction of mafic–ultramafic rock-related Cr-spinel formation environments and its application to the tectonic settings of magmatic sulfide deposits

This study uses the random forest machine learning algorithm to classify and predict Cr-spinel formation environments in mafic–ultramafic rocks. Cr-spinel is an early-crystallized oxide phase in these rocks and exhibits significant compositional variations that provide valuable insights into their formation environments. Traditionally, empirical diagrams have been used to classify the origins of Cr-spinel based on major and trace element compositions; however, overlap exists among spinel from different formation environments. To overcome this limitation, we develop a random forest model using a compiled dataset of Cr-spinel compositions from various tectonic settings, including small intrusions from continental collisional zones, layered intrusions and small intrusions from intra-continental plates (including large igneous provinces and intra-continental rifts), Alaskan-type complexes from oceanic subduction zones, and ophiolites from oceanic spreading centers. The model is trained, validated, and optimized using cross-validation and hyperparameter tuning. The results show high accuracy in predicting the Cr-spinel formation environments, as demonstrated by high precision, recall, and F1 scores. Feature importance analyses reveal that elements, such as Ti, Cr, and Al, play a more significant role in the prediction. Visualization techniques, i.e., the t-distributed stochastic neighbor embedding (TSNE) algorithm, are applied to reduce the dimensionality of the dataset and create decision boundaries for better interpretation. The model is validated using an independent Cr-spinel composition dataset obtained from an area with known geological settings, to confirm the model’s reliability. The model is applied successfully to reveal the heterogeneous sources of the rifting-related Daxueshan magmatic Ni-Cu sulfide deposit in the Baoshan block in the eastern part of the Tethyan orogenic belt. The machine learning algorithm can accurately distinguish different Cr-spinel types using large and diverse datasets to provide valuable insights into geological formation conditions. This approach is a powerful tool for understanding Earth’s geological processes, improving exploration models of magmatic sulfide deposit and reducing mineral exploration costs.

Eclogite in the East Kunlun Orogen, northwestern China: A record of the Neoproterozoic breakup of Rodinia and early Paleozoic continental subduction

An early Paleozoic eclogite belt extends discontinuously for ∼500 km in the East Kunlun Orogen, northwestern China, which provides insight into the evolution of the Proto-Tethys Ocean. However, the nature and age of the eclogite protoliths and subsequent metamorphism are unclear. Here, we report mineral chemical, zircon, and titanite geochronological; whole-rock major and trace elemental; and Sr-Nd isotopic data for eclogites from the Xiarihamu area in the western East Kunlun Orogen. At a minimum, these eclogites underwent peak eclogite-facies metamorphism at 27−28 kbar and 630−650 °C, post-peak decompression, and retrograde amphibolite-facies overprinting. Geochemically, eclogites have characteristics typical of enriched mid-oceanic-ridge basalts and oceanic-island basalts. Inherited magmatic zircon cores yielded a protolith age of 828 Ma, and metamorphic zircons yielded peak and post-peak decompression ages of 443 Ma and 422 Ma, respectively. A titanite U-Pb age of 413 Ma constrains the timing of later amphibolite-facies overprinting. The protoliths of the Xiarihamu eclogites were the products of continental rift-related basaltic magmatism, which was generated during the initial breakup of Rodinia. The protoliths experienced eclogite-facies metamorphism in a continental subduction/collisional setting during the early Paleozoic. The formation of the Xiarihamu eclogites suggests that the Proto-Tethys Ocean had closed by 443 Ma. Given the spatio-temporal relationship between the Xiarihamu magmatic Cu-Ni sulfide deposit and the eclogites studied, the former may have formed in a post-collisional extensional setting. The eclogites and magmatic Cu-Ni sulfide deposit from the Xiarihamu area jointly reveal the evolution of the East Kunlun Orogen from Neoproterozoic supercontinent breakup to early Paleozoic tectonic transitions from collisional convergence to post-collisional extension.

Syn-mineralization hydrous fluid activity in giant Jinchuan magmatic Ni-Cu sulfide deposit in North China Craton

Syn-mineralization hydrous fluid activity in giant Jinchuan magmatic Ni-Cu sulfide deposit in North China Craton

Geophysical technology for exploration of magmatic Ni-Cu sulfide deposits: Case study in Kalatongke deposit

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。

Distribution and controlling factors of nickel and cobalt in the Jinchuan magmatic Cu-Ni sulfide deposit

幔源岩浆形成与演化过程中镍(Ni)、钴(Co)具有相似的地球化学行为。金川岩浆铜镍硫化物矿床以Ni、铜(Cu)为主要矿种,Co为伴生,Ni、Co在金川矿床中的空间分布规律同步变化,然而其Ni/Co比值(36.7)远高于地幔值(18.2)。这表明在金川矿床形成过程中Ni-Co发生了共生分离,但Ni-Co分布特征尚不清楚、其控制因素尚不明确。本文对该矿床中主要矿石矿物的Ni、Co含量及分布进行了系统总结,并与脉石矿物进行对比。结果表明矿石矿物镍黄铁矿是最重要的含Ni、Co矿物相,其Ni、Co含量均远高于磁黄铁矿、黄铜矿及脉石矿物。对于脉石矿物,Ni在橄榄石、磁铁矿、铬铁矿内的含量依次降低,在斜方辉石与单斜辉石中含量最低。Co则在铬铁矿、橄榄石内含量依次降低,在斜方辉石、单斜辉石、磁铁矿中含量最低。在硫化物熔离过程中,Ni在硫化物熔体内相容性更强,更加倾向于进入硫化物熔体,使Ni显著富集于硫化物熔体内,而Co则相对富集于硅酸盐熔体内,由此导致Ni-Co解耦。硫化物冷却结晶过程中,Ni、Co倾向于进入最早结晶的单硫化物固溶体(MSS),并在随后分解作用中集中进入镍黄铁矿内,使镍黄铁矿成为金川矿床中最重要的含Ni-Co矿物相,并使Ni、Co在金川矿床中具有相似的空间分布规律。在硅酸盐熔体结晶分异过程中,Ni在橄榄石中的相容性最强,Co在铬铁矿中相容性最强,因此Ni倾向于进入橄榄石,而Co倾向于进入铬铁矿,由此导致Ni-Co发生解耦。硫化物熔离、橄榄石堆晶均会造成残余熔体Ni亏损程度高于Co,且Ni在斜方辉石与单斜辉石中相容性高于Co将导致残余熔体随冷却结晶Ni/Co比值逐渐降低,因此在粒间硅酸盐矿物结晶过程中Ni、Co倾向于共生。脉石矿物亚固相下与硫化物熔体反应对于Ni-Co共生分离的影响则与结晶作用完全相反。镍黄铁矿和磁黄铁矿出溶于硫化物矿浆结晶早期形成的MSS,在不同岩/矿石类型内Ni、Co含量同步变化,表明镍黄铁矿和磁黄铁矿成分可以用来指示岩浆铜镍硫化物矿床成矿过程中硫化物熔体成分的演变。

Timing and spatial variation of deformation along the Kanggur-Huangshan shear zone in the Chinese Tianshan: Implications for regional differential uplift and mineralization

The Chinese Tianshan experienced large-scale transcurrent tectonics, synkinematic emplacement of ultramafic to felsic intrusions, and the formation of various mineral deposits during late Paleozoic accretionary orogenesis. The relationships among the spatial variation of deformation, the distribution of Permian orogenic Au and magmatic Ni-Cu sulfide deposits, and the kinematic evolution of crustal-scale shear zones, however, remain ambiguous. To address these ambiguities, the spatial variation in the degree of deformation in the Kanggur-Huangshan shear zone in the Chinese Tianshan was characterized using detailed structural measurements and zircon U-Pb and muscovite 40Ar/39Ar age data. The new structural data indicate that a prominent spatial variation exists in the style of deformation throughout the Kanggur-Huangshan shear zone; intense ductile deformation structures are dominant in the east, while brittle structures become progressively more dominant toward to the west. Zircon U-Pb and muscovite 40Ar/39Ar age data for syn- and postkinematic intrusions along the Kanggur-Huangshan shear zone indicate that dextral strike-slip shearing occurred between 279 Ma and 249 Ma. The spatial variation in the degree of deformation and exhumation along the Kanggur-Huangshan shear zone was potentially caused by regional differential uplift induced by the collision of the Tianshan and Beishan regions; this was likely responsible for the predominant occurrence of magmatic Ni-Cu sulfide deposits in the eastern portion of the Kanggur-Huangshan shear zone and orogenic Au deposits in the western portion. The identified spatio-temporal relationship between deformation and distribution of orogenic Au and magmatic Ni-Cu sulfide deposits is crucial to the future success of mineral exploration in the Central Asian orogenic belt.

Magnetite geochemistry and iron isotope signature of disseminated and massive mineralization in the Kalatongke magmatic Cu[sbnd]Ni sulfide deposit, northwest China

Magnetite is a common accessory mineral and an indicator to magma evolution and sulfide fractional crystallization in magmatic NiCu sulfide deposits. The Kalatongke magmatic sulfide deposit at the southern margin of the Central Asian Orogenic Belt is composed of 11 mafic intrusions. The sulfide orebodies (Y1, Y1 deep, and Y2) are hosted by three small mafic intrusions, and magnetite is common in all mineralized samples. Based on ilmenite exsolution texture, composition, and type of mineralization, three types of magnetite are identified, (1) primary Fe-rich magma-related magnetite (type 1), (2) sulfide liquid-related magnetite (type 2), and (3) hydrothermal magnetite (type 3). We speculate that Fe isotope equilibrium fractionation between early or co-crystallized light 54Fe-enriched sulfide and magnetite may account for the ultra-high magnetite δ56Fe value (0.70‰ to 1.35 ‰) in the magmatic magnetite (types 1 and 2). Enriched compatible elements in type 1 magnetite (TiO2 = 1.52 wt% to 7.89 wt%, V = 775 ppm to 2420 ppm, Cr = 2697 ppm to 14,658 ppm, and Ni contents = 478 ppm to 1256 ppm), reflect the characteristics of primary Fe-rich magmatic magnetite crystallized at relatively high temperature and low oxygen fugacity. Type 2 magnetite in massive ores has Ni (762 ppm to 1769 ppm) and δ56Fe (0.89 ‰ to 1.10 ‰) values similar to type 1 magnetite, but significantly lower TiO2, V and Cr contents (TiO2 = 0.07 to 3.72 wt%, V = 61 to 2314 ppm, Cr = 5 to 2937 ppm), indicating co-crystallization with an evolved sulfide liquid across a wide span of temperature and oxygen fugacity. Type 3 magnetite is of hydrothermal fluid origin, with low δ56Fe (0.29 ‰ to 0.41 ‰) and Ni (177 ppm to 377 ppm).Magnetite composition and Fe isotope signatures at the Kalatongke magmatic sulfide deposit can reveal the genesis of magnetite and the evolution of the melt and sulfide. The Y1 orebody was completely crystallized over a short period of time, while the Y1 deep and Y2 east orebodies underwent a protracted evolution during which magnetite co-crystallized from primitive Fe-rich melt, Fe-rich evolved melt and Cu-rich intermediate sulfide solution. Magnetite and sulfide in the Y2 west massive orebody likely formed last. The compatibility of both lithophile and chalcophile elements, combined with Fe isotopes in magnetite, makes magnetite a good indicator of silicate and sulfide melt evolution.

Electromagnetic Characteristics of the Magmatic Ni-Cu Sulfide Deposits in the Orogenic Belt: A Case Study from Kalatongke Deposits in the Central Asian Orogenic Belt

Abstract Geologic and geochemical results from the Ni-Cu deposits of the Central Asian orogenic belt show that carbon from carbonaceous sediments was incorporated in the magma that formed the Ni-Cu deposit. Thus, the presence of an Ni-Cu deposit may be hypothesized at localities where carbonaceous sediments are in contact with mafic intrusions. However, the widely developed carbonaceous layer in the Central Asian orogenic belt has low-resistivity and high-chargeability characteristics similar to those of massive and semimassive orebodies, which makes it difficult to detect Ni-Cu deposits by conventional geophysical methods. To test whether the frequency-domain controlled-source electromagnetic (FDCSEM) method can circumvent this problem, a survey was conducted using horizontal electric fields to map the spatial distribution of rock types around gabbro intrusions containing an Ni-Cu sulfide deposit and barren gabbro intrusions of the Central Asian orogenic belt. The recovered resistivity structure resolved two low-resistivity layers: one was located at an elevation range of 850 to 950 m (the elevation of the surface is about 1,000 m) and widespread along the survey lines, whereas the other was present between 300 and 600 m and was limited to only part of the survey line. These structures are interpreted to represent carbonaceous layers. Gabbro intrusions are present as high-resistivity formations. Based on the drilling results, in the area where the deep carbonaceous layer exists, the Ni-Cu orebodies are associated with gabbro intrusions, whereas where the gabbro intrusions are not associated with a carbonaceous layer, no Ni-Cu orebodies are present. These associations can be detected using FDCSEM with a horizontal electric field and could be used to explore Ni-Cu deposits.

Zircon Th/U ratios suggest a post-collision extensional setting for the Permian Ni-Cu sulfide deposits in the Eastern Tianshan, NW China

Magmatic Ni-Cu sulfide deposits have been discovered in orogenic belts worldwide. However, the optimal period for extensive basaltic magmatism generating Ni-Cu sulfide mineralization during the development of orogenic belts has not been well addressed. Zircon Th/U may be correlated with end-member tectonic stress regimes (continental extension vs. compression) that correlate with distinct magmatic conditions. Here, zircon Th/U ratios from the Permian Huangshan-Jingerquan Ni-Cu metallogenic belt in the Eastern Tianshan are revisited, including magmatic zircons from mafic and felsic rocks and detrital zircons from sedimentary rocks. These zircons are filtered to minimize the effect of amagmatic conditions (e.g., metamorphism, alteration, inclusion and metamictization). After filtration, zircon Th/U ratios in the Huangshan-Jingerquan belt are likely linked to the silica content of the host melt and crystallization temperature under zircon growth with fractionating melts. They display high Th/U ratios (up to 2.5) and δEu values (up to 1.35) during the early Permian. In contrast, the others with low Th/U (most < 1.0) ratios and δEu (<0.8) appear in the pre-Permian except the late Devonian. This indicates that the crust in the region was thickened induced by collision at the end of late Carboniferous and then extended during the early Permian. Conclusively, we suggest that the post-collision extensional setting is the preferred stage for the Permian short-lived (<5 Ma) Ni-Cu sulfide deposits during the development of the Tianshan Orogenic Belt.

Nickel in olivine as an exploration indicator for magmatic Ni-Cu sulfide deposits: A data review and re-evaluation

AbstractNickel 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.

Chromite geochemistry of the Jinchuan Ni-Cu sulfide-bearing ultramafic intrusion (NW China) and its petrogenetic implications

Chromite, as an early-fractionation phase, has good potential to trace the petrogenesis and tectonic setting of mafic-ultramafic cumulate rocks. The Jinchuan ultramafic intrusion in NW China contains one of the world’s largest magmatic Ni-Cu sulfide deposits. Many studies have been carried out on this intrusion, however, the geochemical features of chromite and its related petrogenetic implications are still poorly constrained. In this study, the geochemistry of chromite enclosed in olivine from the Jinchuan intrusion is investigated. The chromite grains have large variations in Fe# (100*Fe3+/(Fe3++Al + Cr) = 1.3–47.0), Cr# (100*Cr/(Cr + Al) = 44.9–92.4), and Mg# (100*Mg/(Mg + Fe2+) = 4.7–25.7). They are depleted in Ni (142–1704 ppm) and Co (214–538 ppm) and enriched in Ti (3507–66298 ppm), accompanied by highly variable contents of Zn (1186–10726 ppm) and Mn (1362–4579 ppm). In the MORB-normalized patterns, chromite grains within the most primitive olivine are characterized by positive anomalies of Ti, V, Zn, and Mn and negative anomalies of Ni, similar to those in the Hawaiian tholeiitic basalts and typical layered intrusions. Variable correlations among the major, minor, and trace elements indicate that all these elements, except for Zn and Mn, may have been governed by multistage magmatic processes with little overprint from postmagmatic hydrothermal alteration. The strong Ni and Co depletions in chromite indicate prior removal of sulfide liquids at depth. The wide range of Ti in chromite may have been caused by the fO2 change during magma fractionation. The variable contents of Zn and Mn, by contrast, may be related to postcumulus processes. Furthermore, the relatively high TiO2 but low Al2O3 contents of the primitive chromite are comparable with those of mantle plume-related cumulate rocks. This feature, coupled with the MORB-normalized patterns in chromite, implies that the Jinchuan intrusion is similar to typical tholeiitic layered intrusions genetically related to a mantle plume.

Oxygen-fugacity evolution of magmatic Ni-Cu sulfide deposits in East Kunlun: Insights from Cr-spinel composition

Abstract In this study, we use Cr-spinel as an efficient indicator to evaluate the oxygen fugacity evolution of the Xiarihamu Ni-Cu deposit and the Shitoukengde non-mineralized intrusion. Oxygen fugacity is calculated using an olivine-spinel oxybarometer, with spinel Fe3+/ΣFe ratios determined by a secondary standard calibration method using an electron microprobe. Cr-spinel Fe3+/ΣFe ratios of the Xiarihamu Ni-Cu deposit vary from 0.32 ± 0.09 to 0.12 ± 0.01, corresponding to magma fO2 values ranging from ΔQFM+2.2 ± 1.0 to ΔQFM-0.6 ± 0.2. By contrast, those of the Shitoukengde mafic-ultramafic intrusion increase from 0.07 ± 0.02 to 0.23 ± 0.04, corresponding to magma fO2 varying from ΔQFM-1.3 ± 0.3 to ΔQFM+1.0 ± 0.5. A positive correlation between fO2 and Cr-spinel Fe3+/ΣFe ratios suggests that the Cr-spinel Fe3+/ΣFe ratios can be used as an indicator for magma fO2. The high fO2 (QFM+2.2) of the harzburgite in the Xiarihamu Ni-Cu deposit suggests that the most primitive magma was characterized by relatively oxidized conditions, and then became reduced during magmatic evolution, causing S saturation and sulfide segregation to form the Xiarihamu Ni-Cu deposit. The evolution trend of the magma fO2 can be reasonably explained by metasomatism in mantle source by subduction-related fluid and addition of external reduced sulfur from country gneisses (1.08–1.14 wt% S) during crustal processes. Conversely, the primitive magma of the Shitoukengde intrusion was reduced and gradually became oxidized (from QFM-1.3 to QFM+1.0) during crystallization. Fractional crystallization of large amounts of Cr-spinel can reasonably explain the increasing magma fO2 during magmatic evolution, which would hamper sulfide precipitation in the Shitoukengde intrusion. We propose that the temporal evolution of oxygen fugacity of the mantle-derived magma can be used as one of the indicators for evaluating metallogenic potential of Ni-Cu sulfide deposits and the reduction processes from mantle source to shallow crust play an important role in the genesis of magmatic Ni-Cu sulfide deposits.

Geology and geochemistry of the Tulaergen conduit-style magmatic Ni-Cu sulfide deposit in the Central Asian Orogenic Belt, northwestern China

Geology and geochemistry of the Tulaergen conduit-style magmatic Ni-Cu sulfide deposit in the Central Asian Orogenic Belt, northwestern China

Addition of H2O at the Baishiquan and Tianyu magmatic Ni-Cu sulfide deposits, southern Central Asian Orogenic Belt, China: evidence from isotopic geochemistry of olivine and zircon

Addition of H2O at the Baishiquan and Tianyu magmatic Ni-Cu sulfide deposits, southern Central Asian Orogenic Belt, China: evidence from isotopic geochemistry of olivine and zircon

The redox conditions and C isotopes of magmatic Ni-Cu sulfide deposits in convergent tectonic settings: The role of reduction process in ore genesis

Reduction process might play a critical role in the genesis of magmatic Ni-Cu sulfide deposits in convergent tectonic settings. To test this hypothesis, we have determined the oxygen fugacities (fO2) and C isotopes of several typical magmatic Ni-Cu sulfide deposits in convergent tectonic settings in western China. Two popular spinel-olivine-orthopyroxene (Spl-Ol-Opx) oxybarometers, one from Wood (1990) and the other from Ballhaus et al. (1991), are evaluated for their accuracy for this type of deposit by comparing the results with those from an independent method, the olivine-sulfide (Ol-Sul) oxybarometer of Barnes et al. (2013). We find that only the results from the Spl-Ol-Opx oxybarometer of Wood (1990) are consistent with those from the independent method. The fO2 of the sulfide-mineralized samples from the selected deposits, estimated using these two methods, are from QFM–0.56 to QFM+1.84 (quartz-fayalite-magnetite buffer). Using the Spl-Ol-Opx oxybarometer of Wood (1990), the estimated fO2 values of the sulfide-unmineralized ultramafic rocks from primitive arc cumulates in the same region, which have higher olivine Fo contents than the sulfide-mineralized rocks, are significantly higher (~QFM+2.42). The decrease of fO2 from the sulfide ore-barren to ore-bearing magmatic systems indicates that reduction process indeed played a critical role in the genesis of the studied magmatic sulfide deposits. The δ13C values of the sulfide-bearing ultramafic rocks are from –16.5 to –37.2‰ (n = 52), which are significantly lower than the primitive arc cumulates (−7.1 to −9.6‰) but similar to those of organic matter in sedimentary rocks worldwide (–15 to –35‰). The isotope data indicate assimilation of organic matter from the country rocks by the parental magmas for the studied magmatic Ni-Cu sulfide deposits, supporting the interpretation that sulfide saturation in the parental magmas were mainly induced by the reduction process associated with the addition of organic matter to the magmas.

Cu-Ni mineralization in Early Permian mafic complexes in the Kalatage area of eastern Tianshan (NW China): Petrogenetic constraints from geochronology, geochemistry, and Hf-Sr-Nd-Os isotopes

The Early Permian was a critical period in the long history of accretion and collision of the southern Altaid orogen. Early Permian mafic-(ultramafic) intrusions and mafic–ultramafic-related sulfide Cu-Ni deposits are common in the eastern Tianshan, but the sulfide Cu-Ni deposits related to the mafic intrusions are still poorly studied, and yet provide key information on the ambient tectonic evolution. In order to help understand their petrogenesis, we report new data on the Early Permian mafic intrusions and related sulfide Cu-Ni deposits in the Dananhu arc of the eastern Tianshan in NW China. The ore-bearing Yueyawan complex is a well-differentiated, zoned mafic intrusion consisting of troctolite, olivine gabbro, layered gabbro, gabbro, and leucogabbro from the bottom upwards. The ore bodies are primarily strata-bound within olivine gabbros and troctolites at the bottom of the complex. The ores are more enriched in Cu than Ni than the more enriched, disseminated, veined and massive equivalents. Gabbros from the mafic complex yield zircon crystallization ages that range from 265 Ma to 273 Ma. The gabbros are tholeiitic and characterized by typical subduction-related geochemical signatures with low TiO2 contents, enrichments in Rb, Ba, U, K, Pb, and Sr, depletion in Nb and Ta, positive Eu and Ti anomalies, high εNd(t) values of +7.44 to +8.06, zircon εHf(t) values of +11.68 to +20.58, and low (87Sr/86Sr)i (0.703322–0.703416). The gabbroic rocks have positive correlations between SiO2 and TiO2, Al2O3, CaO, Nb, and Y, and negative correlations between SiO2 and MgO, Ni, and Co. The (187Os/188Os)i and γOs values of sulfides from the Yueyawan complex that contains Cu-Ni deposits range from 0.266 to 0.372 and 112 to 197, respectively. These geological, petrological, and geochemical characters indicate that the gabbros were mantle-derived, and that fractionation and crustal contamination were essential for the genesis of the magmatic Cu-Ni sulfide deposits. After integrating our data with those of previous investigations, we conclude that the protoliths of the sulfide deposits were probably derived from an asthenospheric garnet-free mantle in a subduction setting in the Early Permian. Oblique ocean-ridge subduction and a resultant slab window plausibly induced asthenospheric upwelling that gave rise to the generation of the mantle-derived melts, which likely moved into strike-slip faults through a slab window in the supra-subduction zone. Strong fractionation, crustal contamination, and multi-stage eruptions led to formation of the Cu-Ni sulfide deposits.

Mineralization age, tectonic setting and ore genesis of the Wuxing Pt–Pd-rich magmatic Cu-Ni sulfide deposit, Northeast China

• Wuxing deposit with age of 516.7 Ma is reported. • Wuxing intrusive rocks experienced independent diagenetic processes. • The Wuxing deposit was formed in a post–collision extensional setting. The Wuxing deposit in Northeast China, tectonically located in the Jiamusi–Khanka Block, is a Pt–Pd-rich Cu-Ni sulfide deposit related to mafic–ultramafic rocks. The zircon U–Pb ages of pyroxenites , gabbros , porphyritic granites , and leucogranits in the mining area are 516.7 ± 2.6, 513.8 ± 2.0, 505.4 ± 2.3 and 499.5 ± 2.9 Ma, respectively, indicating that the diagenesis and metallogenesis of the Wuxing deposit occurred during the Cambrian. The ore-forming complex is cut by quartz diorite porphyritic and plagiogranite porphyry dikes. Zircon U–Pb ages of the quartz diorite porphyrite and plagiogranite porphyry are 206.6 ± 2.1 and 201.6 ± 1.3 Ma, respectively. The U–Pb ages indicate the metallogenic age constraint of 516.7 ± 2.6 Ma for the Wuxing deposit, rather than Cambrian and Triassic magmatic activities. The Hf isotopic composition ε Hf (t) of zircons in the pyroxenites and gabbros are −11.5 to −7.7 and −5.8 to −2.5, with the two–stage model ages (t DM2 ) of 2198–1958 and 1841–1633 Ma, respectively. Geochemically, the mafic–ultramafic complexes are enriched in light rare earth elements (LREE) and large ion lithophile elements (LILE), and depleted in high-field strength elements (HFSE), indicating these rocks originated from the enriched mantle. The porphyritic granites are high-K calc-alkaline rocks (Rittman index δ = 1.92–2.00), and the leucogranites are low-K alkaline rocks ( δ = 4.76–4.86) with ε Hf (t) and t DM2 of −9.2 to +0.8 and 2037–1411 Ma, respectively. The porphyritic granites and leucogranites are characterized by low A/CNK values (0.91–1.05), 10,000 Ga/Al values (1.76–2.36), and Zr saturation temperature (731–823 ℃) similar to those of I-type granites. Along with contemporaneous intrusions, the Wuxing deposit is inferred to have formed in a post-collisional extension environment. Consequently, the origin of the Wuxing deposit is likely related to the evolution of enriched mantle magma during the Cambrian post-collision extensional setting of the Jiamusi–Khanka Block.