Ni-Cu Sulfide Deposits Research Articles

Late Paleozoic metallogenesis and evolution of the East Tianshan Orogenic Belt (NW China, Central Asia Orogenic Belt)

One of the most largest known and important metallogenic provinces in China is East Tianshan, where seven major types of Late Paleozoic metal deposits have been recognized: (1) porphyry-type Cu-Mo-(Au) ore deposits, (2) volcanic Fe-Cu deposits, (3) orogenic lode gold deposits, (4) magmatic Cu-Ni sulfide deposits, (5) epithermal gold deposits, (6) volcanic hydrothermal Cu deposits, and (7) skarn Cu-Ag deposits. Tectonically, the development of these Late Paleozoic metal mineral deposits was closely associated with the subduction and closure of the ancient Tianshan ocean intervening between the Tarim craton and the Junggar-Kazakhstan block. In the Late Devonian to Early Carboniferous, the northern margin of the Tarim craton existed as a passive-type continental margin, whereas the ancient Tianshan ocean was subducted beneath the southern margin of the Junggar-Kazakhstan block, resulting in the formation of the Dananhu-Tousuquan magmatic arc and associated porphyry-type Cu-Mo-(Au) deposits. In the Middle Carboniferous, the ancient Tianshan ocean began to subduct beneath the northern margin of the Tarim craton, leading to the formation of the Aqishan-Yamansu magmatic arc and associated volcanic Fe-Cu deposits. In the Late Carboniferous, the ancient Tianshan ocean was closed, and a continent-arc collision occurred, leading to the formation of the Tianshan orogen. Following the collision was an extensional event, which was associated with the emplacement of large amounts of ultramafic-mafic complexes and the formation of a number of large- to medium-scale magmatic copper-nickel ore deposits along the Kangger suture zone. In the Early Permian, East Tianshan entered into a post-collision stage, associated with the widespread emplacement of granitoid bodies and eruption of within-plate volcanism, which led to the formation of volcanic hydrothermal copper deposits, skarn-type Cu-Ag deposits, post-orogenic gold deposits, and epithermal gold deposits in East Tianshan.

PGE Geochemical Characteristics of the Huangshanxi Magmatic Ni-Cu Sulfide Deposit, East Tianshan, Xinjiang, and its Significance for the Mineralization

The Huangshanxi sulfide-bearing intrusion, is located in the centre segment of Tudun-Huangshan-Jing`erquan-Tulargen mafic-ultramafic rock belt, the eastern part of the North Tianshan, controlled by the Kangurtag-Huangshan ductile sheer zone, and it is a multiple intrusion which composes of lherzolite, amphibole peridotite, wehrlite, pyroxenite, norite, gabbro, and diorite. The disseminated sulfides and sideronitic sulfides are the mainly ore types, the scale of the ore body is large and the grade is stable relatively. The total concentration of platinum-group elements (PGEs) in rocks and ores is very low, which average value is 0.93ppb and 8.8ppb respectively and it increases with sulfur content increases in ores. The PGE concentration appeared two peaks in the range of 200~300m and 880~980m depth in the drill core, consistent with the content of the sulfides. Rocks and ores samples have similar mantle-normalized PGE patterns which are shown as the PGE flat and slightly fall to the left, and the lower fractionation between IPGE and PPGE. The primitive magma may be the high MgO tholeiitic magma which should be undepleted in PGE and derived from partial melting of a metasomatized mantle source. Compared with continental tholeiite, simulating result reveals that the parental magma is visibly depleted in PGE, possibly duing to the sulfide pre-segregation of initial magma in deep crust. The platinum-group elements geochemical characteristics and petrochemical data show that the crustal contamination and the fractionation of olivine and pyroxene may be the main factors leading to S-saturation and sulfide segregation in deep crust.

Petrogenesis and mineralization of the Hulu Ni-Cu sulphide deposit in Xinjiang, NW China: constraints from Sr-Nd isotopic and PGE compositions

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 εNd(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, Os, Ir, and Cu contents of the primary magma were 2.1 ppb, 0.03 ppb, 0.05 ppb, and 200 ppm, respectively, a variable R-factor between 200 and 1600 with residual magma that had experienced 0.01% early-sulphide segregation can explain the variation in Pd, Os, and Ir contents of sulphide-poor and disseminated sulphide samples of the Hulu deposit. Basaltic magma fractionation and assimilation and/or contamination of sulphur-bearing crustal materials might have triggered sulphur saturation to form Cu-Ni sulphide ores. Tarim basaltic PGE contents cannot be used as the mineralized parent magma for the Hulu intrusion because of the differing evolutionary trends of the Ni/Pd and Cu/Ir values. However, similar Cu/Ni and Pd/Ir values in Tarim basalts and Hulu Cu-Ni sulphide ores, as well as the same early sulphide segregation process, show that certain genetic relationships between them and magma sources are probably similar to each other.

Platinum Group Element Geochemistry of Sulfide-Rich Horizons in the Ural-Alaskan-Type Ultramafic Complex of Duke Island, Southeastern Alaska

The Duke Island Ultramafic Complex in southeastern Alaska is a Ural-Alaskan–type complex that hosts sulfide-rich horizons primarily in the olivine clinopyroxenite unit. Although placer deposits hosting platinum group elements (PGEs) have been found in association with Ural-Alaskan–type complexes in several locations around the world, these ultramafic complexes have traditionally been viewed as sulfide-poor systems and therefore unlikely hosts of economic Ni-Cu sulfide deposits. Sulfide mineralization in the Duke Island Complex consists of massive, net-textured, and disseminated assemblages that formed as a result of the interaction between magma and sulfidic-graphitic country rocks. The sulfide mineralization at Duke Island is characterized by strong depletion in Ir, Os, and Ru (IPGEs), and relative enrichment in Pt, Pd, and Cu. The sulfide-bearing olivine clinopyroxenites formed from a derivative magma produced as a result of the fractional crystallization of olivine and chromite. Although IPGEs may be compatible within olivine and chromite, fractional crystallization of up to 20% cannot explain the observed IPGE depletion. We propose that early crystallization of laurite and Ir alloys accompanied the accumulation of olivine and chromite. R-factor modeling indicates that much of the inter-element variation in the Sulfide mineralization can be attributed to variations in the degree of equilibration between Sulfide and silicate liquids. Mixing between monosulfide solid solution and fractionated Sulfide liquid may also have contributed to the variability. The modeling suggests that the pre-sulfide saturation concentrations of Os, Pt, and Pd in the magmas were approximately 0.03, 2, and 3 ppb, respectively. The concentration of Pd is near that of primitive mantle and the low Pt concentration can be explained by the crystallization of Pt alloy with early-formed dunites and chromitites. This is consistent with models for Pt-rich placers in the Urals that have been derived from chromitites and dunites. The relative enrichments in Pd and Cu are the results of fractional crystallization before Sulfide saturation was achieved. Taken together, the Ni-Cu-PGE elemental characteristics at the Duke Island Complex are similar to those shown by flood basalt-related Sulfide deposits and Cu-rich Sulfide veins studied in different locations around the world.

Major Types and Characteristics of the Late Paleozoic Ore Deposits in the East Tianshan Orogenic Belt, Central Asia

One of the most largest known and important metallogenic provinces in China is East Tianshan, where seven major types of Late Paleozoic metal deposits have been recognized: (1) porphyry-type Cu-Mo-(Au) ore deposit, (2) volcanic Fe-Cu deposit, (3) orogenic lode gold deposit, (4) magmatic Cu-Ni sulfide deposit, (5) epithermal gold deposit, (6) volcanic hydrothermal Cu deposit, and (7) skarn Cu-Ag deposit. Tectonically, the development of these Late Paleozoic metal mineral deposits was closely associated with the subduction and closure of the ancient Tianshan Ocean intervening between the Tarim craton and the Junggar-Kazakhstan block. In the Late Devonian to Early Carboniferous, the northern margin of the Tarim craton existed as a passive-type continental margin, whereas the ancient Tianshan ocean was subducted beneath the southern margin of the Junggar-Kazakhstan block, resulting in the formation of the Dananhu-Tousuquan magmatic arc and associated porphyry-type Cu-Mo-(Au) deposits. In the Middle Carboniferous, the ancient Tianshan ocean began to subduct beneath the northern margin of the Tarim craton, leading to the formation of the Aqishan-Yamansu magmatic arc and associated volcanic Fe-Cu deposits. In the Late Carboniferous, the ancient Tianshan ocean was closed, and a continent-arc collision occurred, leading to the formation of the Tianshan orogen. Following the collision was an extensional event, which was associated with the emplacement of large amounts of ultramafic-mafic complexes and the formation of a number of large- to medium-scale magmatic copper-nickel ore deposits along the Kangger suture zone. In the Early Permian, East Tianshan entered into a post-collosion stage, associated with the widespread emplacement of granitoid bodies and eruption of within-plate volcanism, which led to the formation of volcanic hydrothermal copper deposits, skarn-type Cu-Ag deposits, post-orogenic gold deposits, and epithermal gold deposits in East Tianshan.

Re–Os Isotopic Age of the Hongqiling Cu-Ni Sulfide Deposit in Jilin Province, NE China and its Geological Significance

The major Hongqiling Cu-Ni sulfide deposit in central Jilin Province is located in the eastern part of the Central Asian Orogenic Belt. Rhenium and osmium isotopes in sulfide minerals from the deposit have been used to determine the timing of mineralization and the source of osmium and, by inference, the ore metals. Sulfide ore samples have osmium and rhenium concentrations of 0.28-1.07ppb and 2.39-13.17ppb, respectively. Ten sulfide analyses yield an isochron age of 223 ± 9 Ma, indicating that the Cu-Ni sulfide mineralization formed in the Early Triassic. The initial 187Os/188Os ratio is 0.295 ± 0.019 (MSWD = 1.14). This data indicates that the mineralization was derived mainly from a mantle source with some quantities of crustal components introduced into the rockforming and ore-forming systems during mineralization and magmatic emplacement. Together with the widespread occurrence of late Carboniferous-Permian mafic–ultramafic complexes and associated Permian Cu-Ni deposits in the western part of the Central Asian Orogenic Belt (Northern Xinjiang), we conclude that mantle-crustal interactions were active during the accretion-collisional processes that led to the Cu-Ni mineralization and considerable continental growth in the late Carboniferous-Permian to mid-Triassic.

PGE and Isotope (Hf-Sr-Nd-Pb) Constraints on the Origin of the Huangshandong Magmatic Ni-Cu Sulfide Deposit in the Central Asian Orogenic Belt, Northwestern China

Many magmatic Ni-Cu sulfide deposits have been found to be associated with Permian basaltic magmatism in the Central Asian orogenic belt, Xinjiang, China. The style of basaltic magmatism and the origin of associated Ni-Cu sulfide deposits in the region are highly debated. The Huangshandong mafic-ultramafic intrusion is at the center of the debate mainly because it hosts the largest magmatic Ni-Cu sulfide deposit in the region. In this paper we report integrated petrological and geochemical data for the Huangshandong Ni-Cu sulfide deposit. The host intrusion consists of a massive gabbronorite unit and a layered sequence, which is composed of two to three ultramafic layers overlain by gabbroic rocks with visible modal layering. Important sulfide mineralization in the intrusion is associated with the ultramafic rocks and massive gabbronorite. The ultramafic rocks and massive gabbronorite are characterized by moderate enrichments in light rare earth elements (LREE), pronounced negative Nb-Ta anomalies relative to Th and La, positive eNd (t = 274 Ma) values (6.6−8.3), low initial 87 Sr/ 86 Sr ratios (0.7031−0.7038), low initial 206 Pb/ 204 Pb ratios (17.7−18), and positive eHf values of zircon (14−17). These data are consistent with mixing between a depleted mantle-derived magma and a granitic melt formed by partial melting of a juvenile arc crust as a result of mafic magma underplating. Olivine crystals enclosed in large clinopyroxene and plagioclase crystals from the ultramafic rocks have Fo contents up to 83 mol %. The contents of Ni in the olivine crystals decrease rapidly with Fo contents, indicating sulfide segregation from magma during olivine crystallization. Numerical modeling using bulk sulfide compositions and constraints from olivine-liquid relationships reveals that the parental magma of the intrusion was significantly depleted in PGE and contained <7 wt % MgO. Depletion of PGE in the magma can be explained by previous sulfide segregation possibly due to magma mixing in a staging chamber. Fractional crystallization and addition of external sulfides from juvenile arc crust appear to have played a critical role in triggering the second event of sulfide segregation to form the deposit. We believe that the Huangshandong sulfide ore-bearing intrusion formed by basaltic magmatism related to postsubduction delamination and asthenosphere upwelling instead of a deep-seated mantle plume.

The Erbutu Ni-Cu Deposit in the Central Asian Orogenic Belt: A Permian Magmatic Sulfide Deposit Related to Boninitic Magmatism in An Arc Setting

The Erbutu Ni-Cu sulfide deposit is hosted in a small ultramafic intrusion located at the southern margin of the Central Asian orogenic belt, Inner Mongolia. This deposit is the first case of a magmatic sulfide deposit related to boninitic magmatism in an arc setting. The host intrusion is composed of orthopyroxenite and olivine orthopyroxenite. More than three quarters of the intrusion contains economic, disseminated sulfide mineralization. SHRIMP U-Pb dating of zircons from the intrusion gives a crystallization age of 294.2 ± 2.7 Ma, similar to the age of the Permian Tarim plume in northwest China. Olivine orthopyroxenite is characterized by olivine crystals with relatively high Fo contents (85–88 mol %) and extremely low Ca contents (<250 ppm). Coexisting orthopyroxene crystals have clinoenstatite composition with enstatite from 86 to 88 mol %. Whole-rock data show characteristic enrichments of light REE relative to heavy REE, pronounced negative Nb-Ta anomalies, and moderately positive Hf anomaly. The δ 34S values of sulfide separates are 4 to 5‰, significantly higher than the typical mantle value (0 ± 2‰). The ɛ Hf values of zircons are from −4 to −9. These data indicate that the parental magma was a boninite. Crustal contamination was involved during magma evolution and ore formation.

Characteristics of a Newly Discovered Ni-Cu Sulfide Deposit Hosted in the Poyi Ultramafic Intrusion, Tarim Craton, NW China

The Poyi ultramafic intrusion is part of the 278 Ma Pobei mafic-ultramafic complex located in the northeastern margin of the Tarim craton. Significant Ni-Cu sulfide mineralization associated with ultramafic rocks has been discovered through an ongoing state-funded drilling campaign. The Poyi intrusion is a pipe-like body with a surface exposure measuring 1 × 3 km and a downward extension >1,600 m. It is composed of dunite, lherzolite, and olivine websterite. Minor plagioclase is ubiquitous in the ultramafic rocks. Sulfide mineralization occurs as concordant layers or zones of disseminated sulfides with thicknesses varying from 10 to 80 m within the steeply dipping layers of lherzolite. Olivine in dunite and lherzolite contains forsterite and Ni up to 89 mol % and 3,000 ppm, respectively. Olivine in olivine websterite has slightly lower forsterite content (86 mol %) and significantly lower Ni content (1,100 ppm). The rapid decrease in olivine Ni contents from lherzolite to olivine websterite indicates cotectic sulfide segregation during olivine crystallization. The Poyi ultramafic rocks are characterized by nearly flat REE patterns, negative Nb anomalies, arc-like Th/Yb and Nb/Yb ratios, positive ɛ Nd values (4.7–6.6) and low initial 87 Sr/ 86 Sr ratios (0.7037–0.7066). The arc-like trace element ratios coupled with positive ɛ Nd values for the Poyi ultramafic rocks indicate the involvement of a subduction-modified lithospheric mantle or a granitic melt derived from a juvenile arc crust. The contents of PGE in the Poyi sulfide separates are significantly higher than in sulfide-poor rocks, indicating that immiscible sulfide liquids were the primary collectors of PGE in the intrusion. Sulfide-poor samples from the Poyi intrusion have low γ Os values (10–18). In contrast, sulfide separates from mineralized lherzolites have distinctly higher γ Os values (54–154). It is perplexing that the sulfide separates have mantle-like δ 34 S values (−0.3 to −2‰). Based on the contrasting γ Os values between sulfide-poor rocks and sulfide separates, we suggest that external sulfur played a role in triggering sulfide saturation in the Poyi magma.

The Limoeiro Deposit: Ni-Cu-PGE Sulfide Mineralization Hosted Within an Ultramafic Tubular Magma Conduit in the Borborema Province, Northeastern Brazil

The Limoeiro deposit, located in a high-grade mobile belt of the Brasiliano orogenic cycle (650–500 Ma), represents one of the few magmatic Ni-Cu(-PGE) sulfide discoveries in recent years. The deposit is hosted by an ultramafic chonolith consisting in a partly deformed and metamorphosed tube-like body affected by brittle faults within high-grade gneiss and schist. The absolute age of the ultramafic intrusion that hosts the Limoeiro deposit is not yet known, but regional geologic constraints suggest that both intrusion and host rocks belong to a terrane older than the orogenic cycle. Peak metamorphic parageneses of the ultramafic intrusion and country rocks indicate granulite facies of metamorphism, interpreted as the result of the Neoproterozoic Brasiliano orogenic cycle. The Limoeiro deposit is the first significant discovery of Ni-Cu sulfide in the Borborema province, opening a new window for exploration in this large orogenic belt. Despite the high-grade metamorphism and the tectonic deformation, the primary magmatic structure of the intrusion hosting the Limoeiro deposit is remarkably well preserved. This intrusion forms a tube-like conduit (chonolith) with cross sections a few hundreds of meters in diameter and with a considerable length of more than 4 km. The conduit consists of two distinct sequences of ultramafic rocks, denominated Upper and Lower sequences, each one consisting of a core of harzburgite enveloped by orthopyroxenite, with an irregular and discontinuous outer shell of amphibolite. These ultramafic sequences, characterized by similar composition and structure, have distinctively different S contents resulting from the presence of disseminated Ni-Cu sulfide mineralization only in the Upper sequence. The magmatic system of the Limoeiro deposit is interpreted to result from the input of two major pulses of magma with similar composition, but sulfide saturation and segregation is restricted to the second magma pulse (Upper sequence). Nickel-Cu(-PGE) sulfide mineralization is broadly concordant with the Upper sequence and different orebodies resulted from tectonic slicing of the originally continuous tube-like structure. The bulk of the mineralization in all orebodies consists of thick (up to 150 m) and elongated (up to 1 km) masses of rock containing disseminated sulfides broadly concordant with the chonolithic structure. Thin layers of massive ore occur in the lower portions of some of the orebodies, and represent about 3 vol % of the Limoeiro deposit. The intrusion hosting the Limoeiro deposit is probably the best preserved chonolith that has been overprinted by granulite facies metamorphism within an orogenic terrane. This study indicates that reconstruction of small magma conduits, an important tool for exploration for Ni-Cu sulfide deposits, may be successfully achieved within high-grade orogenic terranes.

The Role of Paragneiss Assimilation in the Origin of the Voisey's Bay Ni-Cu Sulfide Deposit, Labrador: Multiple S and Fe Isotope Evidence

Isotopic and geochemical studies conducted on the Voisey's Bay deposit, Labrador, Canada, suggest crustal contamination of the primary magma as a trigger for sulfur saturation and formation of the deposit. The use of multiple S isotopes has allowed for the identification of a bacterial sulfate reduction biosignature in the Tasiuyak gneiss in the footwall to the Voisey's Bay deposit. This putative biosignature is preserved in the deposit even at high silicate magma/sulfide melt ratios (R-factor) and links the S present in the Voisey's Bay deposit to the Tasiuyak gneiss. Iron isotopes in the Voisey's Bay deposit have been reset to magmatic values at R-factors > ≈100, but S isotope data can be used to model higher R-factors. A contamination model results in calculated R-factors of 433 ± 177. The multiple S isotope data are a new proxy to directly link S from the deposit to crustal S sources even in deposits with high R-factors where the equilibration with large amounts of silicate magma can make interpreting a link between the deposit and the sulfur source difficult

Platinum-group elements-bearing pyrite from the Aguablanca Ni-Cu sulphide deposit (SW Spain): a LA-ICP-MS study

Despite the fact that pyrite is a relatively common phase in Ni-Cu-Platinum-Group Elements (PGE) magmatic sulphide deposits, it has been neglected in the studies on PGE distribution in favour of pyrrhotite, pentlandite and chalcopyrite. An example of this is the Aguablanca deposit, where although pyrite is an important phase in the semi-massive ore and an early study has revealed that it hosts traces of PGE, the presence and origin of PGE into the pyrite has not been investigated in detail. With this in mind, we have measured by laser ablation ICP-MS the content of these and other chalcophile elements (Au, Ag, Co, Ni, Cu, Se, Sb, As, Bi and Te) in pyrite exhibiting different textures. The results show that 1) large idiomorphic pyrite is compositionallyzoned with Os-Ir-Ru-Rh-As-rich layers and Se-Co-rich layers; 2) some idiomorphic pyrites contain unusually high PGE contents (up to 32 ppm Rh and 9 ppm Pt); 3) ribbon-like and small-grained pyrites host IPGE (i.e., Iridium-group PGE, Os, Ir, Ru and Rh) in similar contents (100-200 ppb each) to the host pyrrhotite; and 4) pyrites replacing to plagioclase are depleted in most metals (i.e., PGE, Co, Ni and Ag). Overall, the different textural types of pyrite have similar abundances in Pd, Au, Se, Bi, Te, Sb and As. Mineralogical and compositional data suggests that pyrite is the result of the activity of late magmatic/hydrothermal fluids that triggered the partial replacement of pyrrhotite and plagioclase by pyrite, probably due to an increase in the sulphur fugacity during cooling. During this episode, pyrites inherited the IPGE content of mineral to that was replaced, whereas other elements such as Pd, Au and semi-metals were likely partially introduced into pyrite via altering fluids. These results highlight that pyrite can host appreciable amounts of PGE and therefore it should not be overlooked as a potential carrier of these metals in Ni-Cu-(PGE) sulphide deposits.

Maggie Hays Ni Deposit: Part 2. Nickel Mineralization and the Spatial Distribution of PGE Ore-Forming Signatures in the Maggie Hays Ni System, Lake Johnston Greenstone Belt, Western Australia

The Maggie Hays Ni-Cu sulfide deposit, located in the ~2.9 Ga Lake Johnston greenstone belt of Western Australia, is hosted in a peridotitic to dunitic subvolcanic feeder that cuts felsic volcanic rocks and sedimentary units. Ore formation at Maggie Hays is attributed to assimilation of a sulfide-rich metasedimentary unit located above the subvolcanic feeder, which induced sulfide saturation within the feeder magmas. Massive and disseminated sulfides display chalcophile element fractionation trends indicative of in situ sulfide crystallization. Sulfide saturation and ore formation within the system generated enriched and depleted chalcophile elements ore-forming signatures in the silicate magmas. These ore-forming signatures are quantified as deviations from calculated background abundances and are spatially constrained to known mineralization within the system using a three-dimensional deposit model. Platinum group element (PGE) depletion and enrichment signatures occur approximately 300 m upstream from mineralization at the intersection of the feeder conduit and sulfide-rich sedimentary unit, interpreted to mark the point of sulfide saturation within the system. The magnitude of PGE enrichment increases with proximity to mineralization. PGE depletion signatures exhibit a more complex pattern, attributed to mixing between sulfide liquid, depleted silicate magma, and undepleted recharging magma. The study of the Maggie Hays mineralization and its host sequence demonstrates that enrichment and depletion of the highly chalcophile PGEs, relative to abundances expected in sulfide-undersaturated mantle-derived magmas, is a powerful exploration tool. Constraining the spatial distribution of enrichment and depletion signatures in the context of a robust volcanic, stratigraphic, magmatic, and metallogenic model allows for quantification of the size of Ni sulfide-forming systems and targeting of Fe-Ni-Cu mineralization in komatiite-bearing sequences.

Discussion on the interrelationship among Cu-Ni sulfide deposits, mafic volcanic rocks and intrusive rocks in the Sipu region, northern Guangxi, China

The Sipu region of North Guangxi is located in the southwest of the “Jiangnan Ancient Land”, where there are developed the oldest stratum in southern China, the Proterozoic Sipu Group, and there are also largely exposed mafic intrusive rocks, mafic volcanic rocks and copper-nickel sulfide deposits. Both mafic intrusive rocks and volcanic rocks are rich in MgO (6.52%–26.39%), but poor in K2O (0.05%–1.00%) and TiO2 (0.33%–0.89%). They are also rich in trace elements such as Rb and Ba while poor in Ta, Nb and the like. Both of them have medium contents of rare-earth elements, 30.26×10−6–126.71×10−6, in which LREEs are slightly rich with ΣLREE/ΣHREE of 1.35–2.46, δEu 0.79–1.33, displaying weak or no δEu anomaly, with the same geochemical features. The right-inclined distribution patterns and the features show that magma would be formed at the comagmatic undiagenetic stage. All studies show that mafic intrusive rocks and volcanic rocks are the products of the same source region evolving in different stages and times. The copper-nickel sulfide deposits are characterized by liquation, crystallization and fractionation of mafic rocks, and have some interrelations with mafic intrusive rocks and volcanic rocks with respect to magmatic genesis.

Ore Genesis of the Kalatongke Cu–Ni Sulfide Deposits, Western China: Constraints from Volatile Chemical and Carbon Isotopic Compositions

Abstract:The Kalatongke Cu–Ni sulfide deposits located in the East Junggar terrane, northern Xinjiang, western China are the largest magmatic sulfide deposits in the Central Asian Orogenic Belt (CAOB). The chemical and carbon isotopic compositions of the volatiles trapped in olivine, pyroxene and sulfide mineral separates were analyzed by vacuum stepwise‐heating mass spectrometry. The results show that the released volatiles are concentrated at three temperature intervals of 200–400°C, 400–900°C and 900–1200°C. The released volatiles from silicate mineral separates at 400–900°C and 900–1200°C have similar chemical and carbon isotopic compositions, which are mainly composed of H2O (av. ∼92 mol%) with minor H2, CO2, H2S and SO2, and they are likely associated with the ore‐forming magmatic volatiles. Light δ13CCO2 values (from –20.86‰ to –12.85‰) of pyroxene indicate crustal contamination occurred prior to or synchronous with pyroxene crystallization of mantle‐derived ore‐forming magma. The elevated contents of H2 and H2O in the olivine and pyroxene suggest a deep mantle‐originated ore‐forming volatile mixed with aqueous volatiles from recycled subducted slab. High contents of CO2 in the ore‐forming magma volatiles led to an increase in oxygen fugacity, and thereby reduced the solubility of sulfur in the magma, then triggered sulfur saturation followed by sulfide melt segregation; CO2 contents correlated with Cu contents in the whole rocks suggest that a supercritical state of CO2 in the ore‐forming magma system under high temperature and pressure conditions might play a key role in the assemblage of huge Cu and Ni elements. The volatiles released from constituent minerals of intrusion 1* have more CO2 and SO2 oxidized gases, higher CO2/CH4 and SO2/H2S ratios and lighter δ13CCO2 than those of intrusions 2# and 3#. This combination suggests that the higher oxidation state of the volatiles in intrusion 1# than intrusions 2# and 3#, which could be one of key ore‐forming factors for large amounts of ores and high contents of Cu and Ni in intrusion 1#. The volatiles released at 200–400°C are dominated by H2O with minor CO2, N2+CO and SO2, with δ13CCO2, values (–25.66‰ to –22.98‰) within the crustal ranges, and are considered to be related to secondary tectonic– hydrothermal activities.

Origin of PGE-Poor and Cu-Rich Magmatic Sulfides from the Kalatongke Deposit, Xinjiang, Northwest China

The Kalatongke Cu-Ni sulfide deposit in the Paleozoic Altay orogenic belt, NW China, is hosted in a Per mian mafic intrusion consisting of norite, troctolite, gabbro, and diorite. Disseminated Ni-Cu, massive Ni-Cu, and massive Cu-rich sulfide ores are mainly hosted in norite and gabbro. Some massive Ni-Cu ores also occur in the Carboniferous sedimentary rocks. The geologic and compositional relationships between various sulfide ores and the rocks of Kalatongke offer a new interpretation of the sequence of emplacement of the magmas, which underpins an understanding of the compositions of the ores and the formation of the Kalatongke deposit. Olivine grains from disseminated Ni-Cu ores have Fo values ranging from 71.6 to 78.0 mol % and Ni con tents from 1,000 to 2,200 ppm. Typically, Ni decreases from the cores to the rims from 2,000 to 1,000 ppm at constant Fo content, indicating the reaction of early-formed olivine with later-segregated sulfide melt. Cr spinels at Kalatongke are highly enriched in Fe 3+ and Fe 2+ , with relatively low Cr, Al, and Ti, reflecting reac tion with evolved trapped intercumulus melt. Norites are depleted in Nb, Ta, Zr, Hf, and Th and enriched in Sr and Ba, whereas disseminated Ni-Cu sul fide ores have considerable depletion of Rb and enrichment of Sr and Ba and lack depletion of Nb, Ta, Zr, and Hf, indicating their different origins. Disseminated Ni-Cu sulfide ores have bulk compositions with variable Cu and Ni contents which are much lower than those of massive Cu-rich and Ni-Cu ores, but disseminated and massive Ni-Cu ores have similar PGE contents with relatively low Pd/Ir ratios. Massive Cu-rich ores have much higher Pd and Pt with very high Pd/Ir ratios. The Kalatongke Cu-Ni sulfide deposit appears to have formed from two different pulses of PGE-poor and Cu-rich basaltic magmas that underwent different degrees of assimilation and fractional crystallization. The first magma pulse gained sulfide saturation because of minor crustal contamination and fractionated a small amount of sulfide (<0.03%); the evolved melt then intruded and assimilated crustal materials to attain sulfide saturation again. Sulfide liquid segregated from the magma to form the massive sulfide melts and residual magma formed the noritic rocks in the shallow magma chamber. The segregated massive sulfide melts then un derwent further fractionation to form massive Ni-Cu and massive Cu-rich ores. The second pulse of magma after removal of sulfides (<0.02%) experienced more crustal contamination and re attained S saturation. This new S-saturated and phenocryst-laden magma intruded the earlier formed massive sulfide ores and norites and formed the disseminated sulfide ores.

Magmatic Ni-Cu-(PGE) deposits in magma plumbing systems: Features, formation and exploration

The three most crucial factors for the formation of large and super-large magmatic sulfide deposits are: (1) a large volume of mantle-derived mafic-ultramafic magmas that participated in the formation of the deposits; (2) fractional crystallization and crustal contamination, particularly the input of sulfur from crustal rocks, resulting in sulfide immiscibility and segregation; and (3) the timing of sulfide concentration in the intrusion. The super-large magmatic Ni-Cu sulfide deposits around the world have been found in small mafic-ultramafic intrusions, except for the Sudbury deposit. Studies in the past decade indicated that the intrusions hosting large and super-large magmatic sulfide deposits occur in magma conduits, such as those in China, including Jinchuan (Gansu), Yangliuping (Sichuan), Kalatongke (Xinjiang), and Hongqiling (Jilin). Magma conduits as open magma systems provide a perfect environment for extensive concentration of immiscible sulfide melts, which have been found to occur along deep regional faults. The origin of many mantle-derived magmas is closely associated with mantle plumes, intracontinental rifts, or post-collisional extension. Although it has been confirmed that sulfide immiscibility results from crustal contamination, grades of sulfide ores are also related to the nature of the parental magmas, the ratio between silicate magma and immiscible sulfide melt, the reaction between the sulfide melts and newly injected silicate magmas, and fractionation of the sulfide melt. The field relationships of the ore-bearing intrusion and the sulfide ore body are controlled by the geological features of the wall rocks. In this paper, we attempt to demonstrate the general characteristics, formation mechanism, tectonic settings, and indicators of magmatic sulfide deposits occurring in magmatic conduits which would provide guidelines for further exploration.

Problems of PGE metallogenesis related to mafic–ultramafic complexes in North Xinjiang, China

Platinum group element (PGE) mineralization is mostly related to mafic–ultramafic complexes of the dominant magmatic deposit type. Mineralization of this type mainly relies on two conditions: the abundance of PGE in magma, and the presence of mechanisms favorable to PGE enrichment and separation from sulfur-saturated magma during magmatic evolution. Mafic–ultramafic complexes are widely developed in North Xinjiang, including (1) the large-scale copper-nickel deposits of Kelatongke, Huangshan, Huangshan East, and Tulargen, (2) numerous small to medium-sized copper-nickel deposits such as Xiangshan, Tudun, Hulu, Baishiquan, and (3) the Xiangshan West and Weiya medium-sized V–Ti magnetite deposits. However, mafic–ultramafic complexes in North Xinjiang rarely form PGE deposits. Therefore, questions about PGE metallogenesis in North Xinjiang are discussed in this paper from the standpoint of the ore-forming mechanism of PGE deposits and the characteristics of the North Xinjiang magma sources. The rock types of the post-collisional mafic–ultramafic complexes in North Xinjiang are of a ferrous rock series formed by fractional crystallization, a rock type generally favorable for hosting PGE. For the Cu-Ni sulfide deposits of North Xingjiang, the assimilation of crustal material causes sulfide liquation during processes of magmatic evolution and mineralization. This can be shown petrogeochemically, including the characteristics of Sr, Nd, Pb, O, Os, and S isotopes, which indicate a magmatic ore-forming mechanism for the Xingjiang PGE deposits. The principal reason for weak PGE mineralization in North Xinjiang may be ascribed to a widely-developed depleted mantle source (with positive ɛ Nd values) that underlies it. The North Xinjiang lithosphere is not of typical Precambrian cratonal type, but has more affinities with modified oceanic lithosphere or immature continental lithosphere that would constitute PGE-poor original magma sources unfavorable to PGE mineralization.

News and Notes: Report on Training in “Advances in Chromitite, Ni-Cu Sulphide and PGE Deposits in Ultramafic and Mafic Igneous Rocks with Special Reference to the Nuggihalli Schist Belt (NSB) and Extension Areas, Karnataka, India

News and Notes: Report on Training in “Advances in Chromitite, Ni-Cu Sulphide and PGE Deposits in Ultramafic and Mafic Igneous Rocks with Special Reference to the Nuggihalli Schist Belt (NSB) and Extension Areas, Karnataka, India

Geochemistry of Ore‐bearing Lamprophyre from the Cu‐Ni Deposit in Dhi Samir, Yemen

Abstract:Magmatic Cu‐Ni sulfide deposits are generally associated with mafic‐ultramafic rocks and it has not been reported that lamprophyre is one of the surrounding rocks of Cu‐Ni sulfide deposits. The Dhi Samir deposit in Yemen, however, is a rare example of Cu‐Ni deposits which are hosted in lamprophyre dikes. In this paper, comprehensive research is made on petrology, petrochemistry and isotope geochemistry for Cu‐Ni‐bearing rocks in the Dhi Samir area and the results show that dark rocks related to Cu‐Ni orebodies are sodium‐weak potassium and belong to calc‐alkaline series lamprophyre, especially camptonite, characterized by enriched alkali, iron and titanium. In these rocks large‐ion‐lithophile elements are obviously concentrated, while high field strength elements slightly depleted, showing clear negative anomalies of Ta and Nb, and weak deficiency of Ti. The ΣREE is very high (225.67–290.05 ppm) and the REE partition curves are flat and right‐inclined, featuring a LREE‐enriched pattern with low negative Eu anomalies. Study of magmatic source areas indicates that the rocks have low (87Sr/86Sr) and high εNd(t), and the magmas were probably derived from the enriched mantle I (EM‐I) end‐member. Based on the LA‐ICPMS on zircon U‐Pb isotope dating, the lamprophyre in the Dhi Samir mining area has an age of 602±2.6 Ma, indicating that the rock was formed in the late Proterozoic and in an intraplate setting due to magmatism of an extensional environment in the post‐Pan‐Africa orogeny.