煎茶岭与金川硫化镍矿床的铂族元素地球化学特征对比及其意义

采用ICP—MS方法分析了煎茶岭和金川硫化镍矿床岩石、矿石的铂族元素含量,煎茶岭岩体蛇纹岩的Cu／Pd比值低于原生地幔岩浆,说明岩浆熔离作用较弱,矿石的Pd／Ir比值较小,指示其多数矿石属于岩浆型,以岩浆成矿作用为主;而金川岩体的平均Cu／Pd比值远大于原生地幔岩浆,表明岩浆熔离作用强,矿石的Pd／Ir比值较大,体现了钯族元素矿化及成矿物质以幔源为主的特征。煎茶岭在成矿过程中有壳源物质的混染,整体上岩石、矿石铂族元素含量较低,这与岩浆熔离作用弱、铂族元素成矿作用不发育等因素有关;金川在成岩成矿过程中也有少量地壳物质的混染,但岩石、矿石铂族元素含量较高,反映了以岩浆深部熔离成矿作用为主的特征。     

金川超大型铜镍硫化物矿床的铂族元素地球化学特征

对金川超大型铜镍岩浆硫化物矿床岩石、矿石的铂族元素地球化学特征研究表明 ,金川岩体的平均Cu/Pd值远大于原生地幔岩浆的Cu/Pd值 ,说明其岩石为因硫化物析离而失去Pd的岩浆所结晶 ;且岩石的PGE具有部分熔融趋势 ,与地幔橄榄岩接近 ,这些均指示存在岩浆熔离作用。该矿床岩石、矿石的PGE球粒陨石标准化分布模式比较对应 ,均可分为两种类型 ,反映了岩浆多次侵入、熔离分异同时成岩成矿的特征。另外 ,PGE S关系分析表明其成岩成矿过程中有少量地壳物质混染。PGE地球化学特征参数还指示了其高镁拉斑玄武质母岩浆的性质。     

Sulfides associated with podiform bodies of chromite at Tsangli,Eretria, Greece

Small bodies of pyrrhotite, chalcopyrite, minor pentlandite, and magnetite occur at the peripheries of podiform bodies of chromite in ultramafic ophiolitic rocks at Tsangli, Eretria, central Greece. Banding of magnetite and sulfide within the bodies is reminiscent of magmatic banding. A magmatic origin has been proposed for similar sulfide masses in the Troodos ophiolite (Panayiotou, 1980). The compositions of the host rocks, chromite, and of the sulfides have been investigated. On average, the sulfide mineralization, recalculated to metal content in 100% sulfide, contains 0.55% Ni, 5.15% Cu, 0.29% Co, 9 ppb Pd, 179 ppb Pt, 16 ppb Rh, 112 ppb Ru, 31 ppb Ir, 58 ppb Os, and 212 ppb Au. These metal contents, particularly the high Cu/(Cu+Ni) ratio of 0.78 and the Pt/(Pd+Pt) ratio of 0.95, are inconsistent with the sulfides having reached equilibrium with their Ni rich host rocks at magmatic temperatures and accordingly it is concluded that they are not of magmatic origin. The average ³⁴S value of the sulfide bodies is +2 while that of a sample of pyrite from country-rock schist is –15.6. These values are inconclusive as to the origin of the sulfur. It is suggested that the sulfides have been precipitated by hydrothermal fluids, possibly those responsible for the serpentinization of the host rocks. The source of the metals may have been the host rocks themselves.     

GEOCHEMICAL CHARACTERISTICS OF PLATINUM GROUP ELEMENTS IN JINCHUAN SUPER-LARGE SULFIDE COPPER-NICKEL DEPOSIT, JINCHANG CITY, GANSU PROVINCE, CHINA

The platinum-group element geochemistry of rocks and ores from Jinchuan super-large copper-nickel sulfide deposit is systemically studied in this paper. The Cu/Pd mean ratio of Jinchuan intrusion is lower than that of original mantle magma, which indicates that these ultrabasic rocks were crystallized from magma that lost Pd in the form of melting segregation of sulfides. The PGE of the rocks show trend of partial melting, similar to that of mantle peridotite, which shows that magma formation occurs during rock-forming and ore-forming processes. The chondrite normalized PGE patterns of the rocks and ores are well related to each other, which signifies the signatures of multi-episode magmatic intrusion, melting and differentiation in the formation processes of rocks and ores. In addition, analyses about the relation between PGE and S, and study on Re-Os isotopes indicate that few contamination of the crustal substances occurred during the magmatic intrusion and the formation of deposit. However, contamination by crustal substances helps to supply part of the S for the enrichment of PGE. Meanwhile, the hydrothermal process is also advantageous for the enrichment of PGE, especially lbr Pt and Pd, due to deep melting segregation. The characteristic parameters （such as Pt/（Pt＋Pd）, （Pt＋Pd）/（Ru＋Ir＋Os）, Pd/Ir, Cu/（Ni＋Cu）, and so on.） for platinum-group elements for Jinchuan sulfide copper-nickel deposit show the same features as those for sulfide copper-nickel deposit related to basic magma, which also illustrates its original magma property representative of Mg-high tholeiite. Therefore, it is the marie （not ultramafic） magma that resulted in the formation of the superlarge sulfide copper-nickel deposit enriched in Cu and PGE. To sum up, the geochemical characteristics of platinum-group elements in rocks and ores from Jinchuan copper-nickel sulfide deposit are constrained by the continental rift tectonic environment, the parent magma features, the enriched mantel magma source, the complex metallogenesis and PGE geochemical signatures, and this would be rather significant for the study about the genetic mechanism of copper-nickel sulfide deposits.     

The Avebury Ni deposit,Tasmania: A case study of an unconventional nickel deposit

The Avebury Ni deposit, which has a resource of 260,000 tons of Ni at a grade of 0.9%, is a unique example of a significant Ni sulfide deposit associated with an ophiolite sequence; the deposit is unique because it was formed by hydrothermal processes and also because ophiolites are generally considered unprospective for magmatic Ni sulfide mineralization. The deposit is hosted by Middle Cambrian cumulate peridotite and dunite rocks that were most probably formed from S-poor boninitic magmas. The mineralization, which consists principally of pentlandite, occurs in both serpentinites and skarns in the ultramafic cumulates. The ultramafic rocks are variably metasomatised as the result of the intrusion of the Late Devonian Heemskirk granite. Sulfide-rich and sulfide-poor portions of the ultramafic rocks are variably enriched in W, Bi, U, Pb, Mo, Sn and Sb relative to the primitive mantle. Modest to strong correlations between Cu, Au, Pd, REE, Sn, Mo, W and Ni provide strong evidence that the mineralization is hydrothermal in origin. In situ metasomatism of a magmatic Ni sulfide deposit is ruled out on the basis of poor or negative correlations between Ir, Ru, Rh and Pt when compared to Ni. Although the sulfide-free ultramafic rocks have high Ni contents, this Ni would have been unavailable to the ore-forming fluids as it was hosted in inaccessible sites, such as oxides and silicates. The strong correlations between Au, Pd and Ni suggest that the source of the Ni was magmatic sulfides somewhere at depth that not only have high Ni but also elevated Pd and Au contents.     

金川铜镍硫化物矿床岩浆通道型矿体地质地球化学特征

金川铜镍硫化物矿床6行富铜（铂族）矿体曾因Cu、Pt、Pd等含量明显高于相邻其它矿体而被认为是岩浆期后热液叠加作用的产物,研究发现,空间上该矿体受断层构造控制,在矿石组构、矿物组成和硫同位素组成方面与相邻岩浆融离型1号矿体一致,显示了该矿体岩浆成矿作用的特征。在元素地球化学方面,6行富铜（铂族）矿体的Cu、Ni、Pt、Pd含量及Cu/Ni比值明显高于1号主矿体,而Os、Ir、Rh、Ru却明显低于后者,同时,前者相对富含LREE,轻、重稀土分异程度高于后者。根据硫化物结晶分异过程中金属元素分配规律及稀土元素特征,阐明了6行富铜（铂族）矿体为岩浆通道型矿体,是岩浆硫化物晚期结晶的产物。矿区中西部存在的Cu、Ni、Pt、Pd、Au等含量高,而Os、Ir、Rh、Ru含量低的部位,是寻找岩浆通道型矿体的有利部位。     

Genesis of the Jinchuan PGE deposit, China: evidence from fluid inclusions, mineralogy and geochemistry of precious elements

Summary The Jinchuan deposit is a platinum group element (PGE)-rich sulfide deposit in China. Drilling and surface sampling show that three categories of platinum group element (PGE) mineralization occur; type I formed at magmatic temperatures, type II occurs in hydrothermally altered zones of the intrusion, and type III in sheared dunite and lherzolite. All ore types were analyzed for Os, Ir, Ru, Rh, Pd, Pt and Au, as well as for Cu, Ni, Co and S. Type I ore has (Pt + Pd)/(Os + Ir + Ru + Rh) ratios of <7 and relatively flat chondrite-normalized noble metal patterns; the platinum group minerals (PGM) are dominated by sperrylite and moncheite associated with chalcopyrite, pyrrhotite and pentlandite. Type II has (Pt + Pd)/(Os + Ir + Ru + Rh) ratios from 40 to 330 and noble metal distribution patterns with a positive slope; the most common PGM are sperrylite and Pd bismuthotelluride phases concentrated mostly at the margins of base metal sulfides. Type III ores have the highest (Pt + Pd)/(Os + Ir + Ru + Rh) ratios from 240 to 710; the most abundant PGM are sperrylite and phases of the Pt–Pd–Te–Bi–As–Cl system. It is concluded that the Jinchuan deposit formed as a result of primary magmatic crystallization followed by hydrothermal remobilization, transport, and deposition of the PGE.     

Genesis of PGE mineralization in the Wengeqi mafic–ultramafic complex, Guyang County, Inner Mongolia, China

The Wengeqi complex in Guyang County, Inner Mongolia, is one of several Pd–Pt-mineralized Paleozoic mafic–ultramafic complexes along the north-central margin of the North China. The complex comprises pyroxenites, biotite pyroxenites, amphibole pyroxenites, gabbros, and amphibolites. Zircons extracted from a pyroxenite yield a U–Pb SHRIMP age of 399?±?4?Ma. Several 2–6-m wide syngenetic websterite dikes contain 1–3?ppm Pd?+?Pd and are dominated by pyrite–chalcopyrite–pyrrhotite–magnetite–(pentlandite) assemblages with minor sperrylite, sudburyite, and kotuskite. Textural relationships indicate that pyrite has replaced magmatic chalcopyrite and that magnetite has replaced magmatic pyrrhotite. The mineralization is enriched in Pd–Pt–Cu > Au >> Rh–Ir–Os–Ni > Ru, similar to other occurrences of hydrothermally modified magmatic mineralization, but very different from the much less fractionated compositions of magmatic PGE mineralization. Textural, mineralogical, and geochemical relationships are consistent with alteration of an original magmatic Fe–Ni–Cu sulfide assemblage by a S-rich oxidizing high-temperature (deuteric) hydrothermal fluid.     

Re–Os isotope and platinum-group element geochemistry of the Pobei Ni–Cu sulfide-bearing mafic–ultramafic complex in the northeastern part of the Tarim Craton

A number of mafic–ultramafic intrusions that host Ni–Cu sulfide mineralization occur in the northeastern Tarim Craton and the eastern Tianshan Orogenic Belt (NW China). The sulfide-mineralized Pobei mafic–ultramafic complex is located in the northeastern part of the Tarim Craton. The complex is composed of gabbro and olivine gabbro, cut by dunite, wehrlite, and melatroctolite of the Poyi and Poshi intrusions. Disseminated Ni–Cu sulfide mineralization is present towards the base of the ultramafic bodies. The sulfide mineralization is typically low grade (<0.5 wt.% Ni and <2 wt.% S) with low platinum-group element (PGE) concentrations (<24.5 ppb Pt and <69 ppb Pd); the abundance of Cu in 100 % sulfide is 1–8 wt.%, and Ni abundance in 100 % sulfide is typically >4 wt.%. Samples from the Pobei complex have εNd (at 280 Ma) values up to +8.1, consistent with the derivation of the magma from an asthenospheric mantle source. Fo 89.5 mol.% olivine from the ultramafic bodies is consistent with a primitive parental magma. Sulfide-bearing dunite and wehrlite have high Cu/Pd ratios ranging from 24,000 to 218,000, indicating a magma that evolved under conditions of sulfide saturation. The grades of Ni, Cu, and PGE in 100 % sulfide show a strong positive correlation. A model for these variations is proposed where the mantle source of the Pobei magma retained ~0.033 wt.% sulfide during the production of a PGE-depleted parental magma. The parental magma migrated from the mantle to the crust and underwent further S saturation to generate the observed mineralization along with its high Cu/Pd ratio at an R-factor varying from 100 to 1,200. The mineralization at Poshi and Poyi has very high γOs (at 280 Ma) values (+30 to +292) that are negatively correlated with the abundance of Os in 100 % sulfide (5.81–271 ppb) and positively correlated with the Re/Os ratios; this indicates that sulfide saturation was triggered by the assimilation of crustal sulfide with both high γOs and Re/Os ratios. When compared to other Permian mafic–ultramafic intrusions with sulfide mineralization in the East Tianshan, the Poyi and Poshi ultramafic bodies were formed from more primitive magmas, and this helps to explain why the sulfide mineralization has high Ni tenor.     

Extreme enrichment of Se,Te, PGE and Au in Cu sulfide microdroplets: evidence from LA-ICP-MS analysis of sulfides in the Skaergaard Intrusion,east Greenland

The Platinova Reef, in the Skaergaard Intrusion, east Greenland, is an example of a magmatic Cu–PGE–Au sulfide deposit formed in the latter stages of magmatic differentiation. As is characteristic with such deposits, it contains a low volume of sulfide, displays peak metal offsets and is Cu rich but Ni poor. However, even for such deposits, the Platinova Reef contains extremely low volumes of sulfide and the highest Pd and Au tenor sulfides of any magmatic ore deposit. Here, we present the first LA-ICP-MS analyses of sulfide microdroplets from the Platinova Reef, which show that they have the highest Se concentrations (up to 1200 ppm) and lowest S/Se ratios (190–700) of any known magmatic sulfide deposit and have significant Te enrichment. In addition, where sulfide volume increases, there is a change from high Pd-tenor microdroplets trapped in situ to larger, low tenor sulfides. The transition between these two sulfide regimes is marked by sharp peaks in Au, and then Te concentration, followed by a wider peak in Se, which gradually decreases with height. Mineralogical evidence implies that there is no significant post-magmatic hydrothermal S loss and that the metal profiles are essentially a function of magmatic processes. We propose that to generate these extreme precious and semimetal contents, the sulfides must have formed from an anomalously metal-rich package of magma, possibly formed via the dissolution of a previously PGE-enriched sulfide. Other processes such as kinetic diffusion may have also occurred alongside this to produce the ultra-high tenors. The characteristic metal offset pattern observed is largely controlled by partitioning effects, producing offset peaks in the order Pt+Pd>Au>Te>Se>Cu that are entirely consistent with published D values. This study confirms that extreme enrichment in sulfide droplets can occur in closed-system layered intrusions in situ, but this will characteristically form ore deposits that are so low in sulfide that they do not conform to conventional deposit models for Cu–Ni–PGE sulfides which require very high R factors, and settling of sulfide liquids.     

黑龙江省五星Cu-Ni-Pt-Pd矿床的PGE-Au元素地球化学特征与成因探讨

对黑龙江省东部五星Cu-Ni-Pt-Pd矿床的矿体和与成矿有关的镁铁质杂岩的PGE-Au以及铁族、亲铜元素的地球化学特征研究表明：它们均以亏损Cr、IPGE和富集Ni、Co、Cu、Pt和Pd（Pt     

岩浆Cu-Ni-PGE矿床研究现状及发展趋势

从全球视野分析研究了世界岩浆铜镍硫化物矿床的大地构造分布和成岩成矿类型,特别是通过上世纪末新发现的加拿大Voisey′s Bay矿床与俄罗斯Noril′sk等世界级矿床特征的对比研究,突出强调了大火成岩省(LIPs)对大规模岩浆硫化物矿床形成的意义,从更加宏观的角度审视了世界级岩浆硫化物矿床形成的地质背景和岩浆作用条件,为中国金川等岩浆Cu-Ni-PGE硫化物矿床的深入研究提供了参照背景。评述分析了当代岩浆硫化物矿床成矿研究中,幔源岩浆中硫化物液相不混溶(熔离)的演化轨迹,对岩浆萃取地壳中的硫改变硫化物饱和度促成不混溶作用发生的可能性和条件进行了探讨,进一步讨论了岩浆演化过程中,亲铜元素(Ni、Cu、Co、Pt和Pd等)进入硫化物液相成为金属硫化物或先期进入先结晶的橄榄石、辉石矿物成为氧化物的物理化学行为,并通过加拿大Sudbury陨石撞击构造成因矿床复合热液对硫化物矿体形成贡献的讨论,提出了热液作用对岩浆硫化物矿床成矿的可能贡献。分析判断了中国岩浆Cu-Ni-PGE硫化物矿床的成矿特点和金川超大型岩浆Cu-Ni-PGE矿床外围的找矿潜力。     

Controls on variations of platinum-group element concentrations in the sulfide ores of the Jinchuan Ni-Cu deposit, western China

Ongoing underground exploration in the giant Jinchuan Ni-Cu sulfide deposit in western China is beginning to emphasize the potential for Cu-, Pt-, and Pd-rich sulfide ores that may have formed by sulfide liquid fractionation. The success of such an effort relies on whether or not fractional crystallization of sulfide occurred in the Jinchuan system. In this paper, we used available PGE data to evaluate such a process. We found that about two thirds of the 126 samples analyzed to date exhibit significant decoupling not only between Pt and Pd but also between Ru, Rh, and Ir. The best explanation for the decoupling is postmagmatic hydrothermal alteration, which affected not only silicates but also sulfides. The effects of postmagmatic alteration must be considered when using metal and isotopic ratios to evaluate primary mineralization. PGE variations in the remaining one third of the samples with Ir/(Ir + Ru) = 0.3–0.7, Ir/(Ir + Rh) = 0.4–0.8, and Pt/(Pt + Pd) = 0.3–0.7 indicate variable R-factors within individual ore bodies as well as the entire deposit, consistent with the interpretation that multiple sulfide-bearing magmas from depth were involved in the formation of the Jinchuan deposit. The mantle-normalized PGE patterns of the least-altered samples from the Jinchuan deposit are similar to the picrite-related Pechenga Ni-Cu sulfide deposit in Russia. PGE variations that can be related to sulfide liquid fractionation are observed in orebody-1 and orebody-24 but not in orebody-2 at Jinchuan. Exploration for Cu-, Pt-, and Pd-rich sulfide ores that may have been expelled into fractures in the footwalls of orebody-1 and orebody-24 appears to be justified.     

Distribution of noble metals in ore mineral assemblages of the Volkovsky gabbroic pluton, central Urals

Relationships between noble-metal and oxide-sulfide mineralization during the origin of the Volkovsky gabbroic pluton are discussed on the basis of geochemical data and thermodynamic calculations. The basaltic magma initially enriched in noble metals (NM) relative to their average contents in mafic rocks, except for Pt, is considered to be a source of Pd, Pt, Au, and Ag in the gabbroic rocks of the Volkovsky pluton. The ores were formed with a progressive gain of NM in the minerals during the fractionation of the basaltic magma. The active segregation of NM in the form of individual minerals (palladium tellurides and native gold) hosted in titanomagnetite and copper sulfide ore occurred during the final stage of gabbro crystallization, when the residual fluid-bearing melt acquired high concentrations of Cu, Fe, Ti, and V, along with volatile P and S. Copper sulfides—bornite and chalcopyrite—are the major minerals concentrating NM; they contain as much as 22.65–25.20 ppm Pd and 0.74–1.56 ppm Pt; 4.39–8.0 ppm Au, and 127.2–142.6 ppm Ag, respectively. The copper ore and associated NM mineralization were formed at a relatively low sulfur fugacity, which was a few orders of magnitude (attaining 5 log units) lower than that of the pyrite-pyrrhotite equilibrium. The low sulfur fugacity and the close chemical affinity of Pd and Pt to Te precluded the formation of pyrrhotite, pyrite, and PGE disulfides. The major ore minerals and NM mineralization were formed within a wide temperature range (800–570°C), under nearly equilibrium conditions. Foreign elements (Ni, Co, and Fe) affected the thermodynamic stability of Pd and Pt compounds owing to the difference in their affinity to Te and to elements of the sulfur group (S, Se, and As). The replacement of Pd with Ni and Co and, to a lesser extent, with Pt and the replacement of Te with S, As, and Se diminish the stability field of palladium telluride. Comparison of Pd tellurides from copper sulfide ores at the Volkovsky and Baronsky deposits showed the enrichment of the former in Au, Sb, and Bi, while the latter are enriched in Pt, Ni, and Ag. The enrichment of Pd tellurides at the Baronsky deposit in Ni is correlated with the analogous enrichment of the host gabbroic rocks.     

PGE mineralization in Archean volcanic systems: geochemical evidence from thick, differentiated mafic-ultramafic flows, Abitibi greenstone belt, Ontario, and implications for exploration

PGE-rich disseminated zones with discrete platinum-group minerals (Pd, Pt and Rh mineral phases) have been discovered in three thick (80–130 m), differentiated (peridotite-gabbro) mafic-ultramafic flows of the Archean Abitibi greenstone belt, Ontario. Three mineralization zones (whole-rock ∑PGE + Au = up to 1000 ppb) occur along four stratigraphic cross sections through a 2 km strike-length of the Boston Creek Flow ferropicritic basalt. Their occurrence most strikingly correlates with lenticular-podiform concentrations of disseminated chalcopyrite (1 %) and clinopyroxene + interstitial magnetite-ilmenite intergrowths (15–20% oxide), high concentrations of related metals (3000 ppm Cu, 3000 ppm S, 1200 ppb Ag, and 1000 ppm V), strong PGE depletion in adjacent rocks and along strike, and lithological and textural complexity in the margins of the central gabbro-diorite layer. The mineralization zone (whole-rock Ir + Pt + Pd + Au = 110 ppb) within Theo's Flow tholeiitic basalt is somewhat similar in occurrence, style, and composition to those within the Boston Creek Flow. In contrast, the mineralization zone (whole-rock Ir + Pt + Pd + Au = 340 ppb) in Fred's Flow komatiitic basalt most strikingly correlates with vesicle-filling intergrowths of pyrrhotite + pentlandite ± chalcopyrite (2 modal %) and high whole-rock concentrations of Ni (2500 ppm), Cu (700 ppm), and S (1.1%) in the upper chilled margin of the flow.Although apparently uneconomic, these flow-hosted PGE mineralization zones are of interest in exploration, because they are more similar in stratigraphie setting, style, and composition to PGE-rich disseminated Fe-Cu sulfide mineralization zones within thick differentiated intrusions than to mineralization zones in other Archean volcanic rocks. The characteristics of the mineralization zones and their host rocks, especially high degrees of PGE enrichment, vertical and horizontal patterns of PGE depletion, and accumulation of clinopyroxene + magnetite-ilmenite intergrowths, indicate a critical genetic role for variations in the regime of melt flowage. The mineralization zones in the Boston Creek and Theo's Flows are interpreted to have formed by simultaneous in situ formation of PGE-rich Fe-Cu sulfide and Fe-Ti oxide from flowing silicate liquid in the margins of internal lava channels. The mineralization zone in Fred's Flow is interpreted to have formed by ponding and coalescence of PGE-enriched sulfurous vapor bubbles in the upper chilled margin during olivine accumulation on the base of a dynamic lava channel. The relative abundance of PGE mineralization zones and high degree of PGE enrichment in the Boston Creek Flow suggest that the most favorable exploration targets are rocks crystallized from late-stage, highly fractionated derivative liquids in large differentiated terropicritic units.     

Geochemical Constraints on the Origin of the Ni–Cu Sulfide Ores in the Tejadillas Prospect (Cortegana Igneous Complex,SW Spain)

After the discovery of the Aguablanca ore deposit (the unique Ni–Cu mine operating in SW Europe), a number of mafic‐ultramafic intrusions bearing Ni–Cu magmatic sulfides have been found in the Ossa–Morena Zone of the Iberian Massif (SW Iberian Peninsula). The Tejadillas prospect is one of these intrusions, situated close to the border between the Ossa–Morena Zone and the South Portuguese Zone of the Iberian Massif. This prospect contains an average grade of 0.16 wt % Ni and 0.08 wt % Cu with peaks of 1.2 wt % Ni and 0.2 wt % Cu. It forms part of the Cortegana Igneous Complex, a group of small mafic‐ultramafic igneous bodies located 65 km west of the Aguablanca deposit. In spite of good initial results, exploration work has revealed that sulfide mineralization is much less abundant than in Aguablanca. A comparative study using whole‐rock geochemical data between Aguablanca and Tejadillas shows that the Tejadillas igneous rocks present a lower degree of crustal contamination than those of Aguablanca. The low crustal contamination of the Tejadillas magmas inhibited the assimilation of significant amounts of crustal sulfur to the silicate magmas, resulting in the sparse formation of sulfides. In addition, Tejadillas sulfides are strongly depleted in PGE, with total PGE contents ranging from 14 to 81 ppb, the sum of Pd and Pt, since Os, Ir, Ru and Rh are usually below or close to the detection limit (2 ppb). High Cu/Pd ratios (9700–146,000) and depleted mantle‐normalized PGE patterns suggest that the Tejadillas sulfides formed from PGE‐depleted silicate magmas. Modeling has led us to establish that these sulfides segregated under R‐factors between 1000 and 10,000 from a silicate melt that previously experienced 0.015% of sulfide extraction. All these results highlight the importance of contamination processes with S‐rich crustal rocks and multiple episodes of sulfide segregations in the genesis of high‐tenor Ni–Cu–PGE ore deposits in mafic‐ultramafic intrusions of the region.     

铜、镍、铂族元素地球化学性质及其在幔源岩浆起源、演化和岩浆硫化物矿床研究中的意义

Ni、Cu和PGE具有不同于其他微量元素的特殊的地球化学性质,这些特殊的性质使得它们在幔源岩浆起源和演化以及岩浆硫化物矿床的成因研究中具有不可替代的作用。在S不饱和的条件下,Ni、Os、Ir和Ru具有相容元素的特性,而Cu和Pd是强不相容元素,因此,它们在玄武岩浆分离结晶过程中常常发生分异。一旦体系达到S饱和,这些元素则会强烈地进入硫化物熔浆,特别是PGE具有极高的硫化物熔浆/硅酸盐熔浆分配系数,极微量的硫化物熔离便可导致残余岩浆中PGE的显著亏损,因此,PGE是玄武岩浆硫化物熔离作用最敏感的示踪元素。硫化物熔离和成矿实质上是幔源岩浆特殊演化过程的结果,所以,Ni,Cu和PGE的特殊性质可用来探讨岩浆硫化物成矿的关键控制因素。Ni、Cu和PGE具有不同的单硫化物固溶体/硫化物熔浆分配系数,因此,它们也是硫化物熔浆结晶分异的重要示踪元素。本文试图从Ni、Cu和PGE地球化学性质和行为入手,并借助一些研究实例,对它们在幔源岩浆起源和演化以及岩浆硫化物矿床成因研究中的示踪意义进行系统介绍。     

Sulfide oxidation as a process for the formation of copper-rich magmatic sulfides

Typical magmatic sulfides are dominated by pyrrhotite and pentlandite with minor chalcopyrite, and the bulk atomic Cu/Fe ratio of these sulfides is typically less than unity. However, there are rare magmatic sulfide occurrences that are dominated by Cu-rich sulfides (e.g., bornite, digenite, and chalcopyrite, sometimes coexisting with metallic Cu) with atomic Cu/Fe as high as 5. Typically, these types of sulfide assemblages occur in the upper parts of moderately to highly fractionated layered mafic–ultramafic intrusions, a well-known example being the Pd/Au reef in the Upper Middle Zone of the Skaergaard intrusion. Processes proposed to explain why these sulfides are so unusually rich in Cu include fractional crystallization of Fe/(Ni) monosulfide and infiltration of postmagmatic Cu-rich fluids. In this contribution, we explore and experimentally evaluate a third possibility: that Cu-rich magmatic sulfides may be the result of magmatic oxidation. FeS-dominated Ni/Cu-bearing sulfides were equilibrated at variable oxygen fugacities in both open and closed system. Our results show that the Cu/Fe ratio of the sulfide melt increases as a function of oxygen fugacity due to the preferential conversion of FeS into FeO and FeO_1.5, and the resistance of Cu₂S to being converted into an oxide component even at oxygen fugacities characteristic of the sulfide/sulfate transition (above FMQ?+?1). This phenomenon will lead to an increase in the metal/S ratio of a sulfide liquid and will also depress its liquidus temperature. As such, any modeling of the sulfide liquid line of descent in magmatic sulfide complexes needs to address this issue.     

Mineralogy, geochemistry and stratigraphy of the Maslovsky Pt–Cu–Ni sulfide deposit, Noril’sk Region, Russia

We report new data on the stratigraphy, mineralogy and geochemistry of the rocks and ores of the Maslovsky Pt–Cu–Ni sulfide deposit which is thought to be the southwestern extension of the Noril’sk 1 intrusion. Variations in the Ta/Nb ratio of the gabbro-dolerites hosting the sulfide mineralization and the compositions of their pyroxene and olivine indicate that these rocks were produced by two discrete magmatic pulses, which gave rise to the Northern and Southern Maslovsky intrusions that together host the Maslovsky deposit. The Northern intrusion is located inside the Tungusska sandstones and basalt of the Ivakinsky Formation. The Southern intrusion cuts through all of the lower units of the Siberian Trap tuff-lavas, including the Lower Nadezhdinsky Formation; demonstrating that the ore-bearing intrusions of the Noril’sk Complex post-date that unit. Rocks in both intrusions have low TiO₂ and elevated MgO contents (average mean TiO₂ <1 and MgO?=?12?wt.%) that are more primitive than the lavas of the Upper Formations of the Siberian Traps which suggests that the ore-bearing intrusions result from a separate magmatic event. Unusually high concentrations of both HREE (Dy+Yb+Er+Lu) and Y (up to 1.2 and 2.1?ppm, respectively) occur in olivines (Fo_79.5 and 0.25% NiO) from picritic and taxitic gabbro-dolerites with disseminated sulfide mineralization. Thus accumulation of HREE, Y and Ni in the melts is correlated with the mineral potential of the intrusions. The TiO₂ concentration in pyroxene has a strong negative correlation with the Mg# of both host mineral and Mg# of host rock. Sulfides from the Northern Maslovsky intrusion are predominantly chalcopyrite–pyrrhotite–pentlandite with subordinate and minor amounts of cubanite, bornite and millerite and a diverse assemblage of rare precious metal minerals including native metals (Au, Ag and Pd), Sn–Pd–Pt–Bi–Pb compounds and Fe–Pt alloys. Sulfides from the Southern Maslovsky intrusion have δ ³⁴S?=?5–6‰ up to 10.8‰ in two samples whereas the country rock basalt have δ ³⁴S?=?3–4‰, implying there was no in situ assimilation of surrounding rocks by magmas.     

煎茶岭硫化镍矿床的铂族元素地球化学特征及其意义

采用ICP-MS分析方法对煎茶岭硫化镍矿床岩石及矿石的铂族元素地球化学研究表明,煎茶岭矿床蛇纹岩的Cu/Pd值低于原生地幔岩浆的Cu/Pd值,说明岩浆熔离作用较弱,其Au/Pd值反映存在后期变质热液成矿作用镍矿石的Pd/Ir比值变化较小,指示其多数矿石属于岩浆型,尽管岩浆活动弱,但以岩浆成矿作用为主。该硫化镍矿床的铂族元素特征参数(Pt/(Pt Pd)、(Pt Pd)/(Ru Ir Os)、Pd/Ir及Cu/(Ni Cu)等)具有过渡特征,这与其处于过渡的构造环境、特殊的岩浆性质和复杂的成矿作用有关煎茶岭镍矿床成矿过程中有壳源物质的混染,整体上岩、矿石铂族元素含量较低,这与其岩浆熔离作用弱,PGE成矿作用不发育等因素有关