Geodynamic significance and genesis of chromitites from the Islahiye ophiolite(Gaziantep,SE Anatolia)as constrained by platinum group element(PGE)compositions and mineral chemistry characteristics

Chromitites associated with intensely altered dunites and harzburgites from fourteen dif ferent localities in the Islahiye ophiolites(SE Anatolia)is reported here for the first time.These chromitites were observed as lenticular and banded bodies with disseminated and massive textures and containing magnesiochromite grains with the following composition:CrO=58.91–59.74 wt%,Al_(2)O_(3)=10.85–11.20 wt%,and TiO=0.09–0.13 wt%.The Mg#[Mg/(Mg+Fe)]values of magnesiochromite from the Islahiye ophiolite range between 0.52 and 0.60 and their Cr#[Cr/(Cr+Al)]values vary from 0.7802 to 0.7844.These contents vary with a constant pattern,coincident with the estimated parental liquids that have originated from the derivative of a single bulk of boninitic magma together with Al,Ti-poor,and Cr-rich initial contents.The chromitites are serpentinised in almost all parts of the study area,and harzburgite and dunite can be observed in different locations.Although the overall composition of platinum group elements(PGE)in most examined chromitites varies between 97 and 191 ppb,three chromitites from the Islahiye region present enrichments in overall PGE(up to 214 ppb).The mineralogical and geochemical features of chromitites from the Islahiye region exhibit a robust similarity to podiform chromitites in the mantle fragment of supra–subduction zone type ophiolitic bodies.The estimated parental magmas of the investigated chromites are consistent with the diff erentiation of arcrelated melts and do not suggest an oceanic spreading centre tectonic environment.The Islahiye chromites are enriched in IPGE(Ir,Os,Ru),with the occasional presence of Ru and Ir and higher Os contents in chromite.Furthermore,we did not find any platinum group minerals(PGM)associated with the serpentine silicate sample matrix,which would have stated a secondary enrichment in PGEs.All chromitites in the investigated region have high Cr and low Ti values,are defined as magnesiochromite and were crystallised from a characteristic boninitic magma.

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.

Adsorption kinetics of platinum group elements onto macromolecular organic matter in seawater

Adsorption kinetics of the interaction between Pt, Pd and Rh(defined here as platinum group elements, PGEs)ions and macromolecular organic compounds(MOCs,>10 kDa), including humic acid, carrageenan and bovine serum albumin, and different cutoff fractions of natural organic matter(>1 kDa and >3 kDa) obtained from seawater using centrifugal ultrafiltration devices were investigated. For a given element, all the adsorption kinetics did not reach equilibrium except the interaction between Pt and >1 kDa cutoff, and between Pd and humic acid.For all the tested MOCs, the adsorption kinetics could be divided into two stages, a rapid adsorption process in the first 8 h and the desorption stage after the first 8 h until the equilibrium. The change trend of partition coefficient(log10Kd) values with experiment time was consistent with that of the kinetic curves. However, in the interaction between PGE ions and natural dissolved organic matter(NDOM), an obvious difference in the change trends of log10Kd and kinetic curves was observed. It indicated that the partition behavior of PGE ions interacting with NDOM in seawater was a combined effect of different organic constituents. The adsorption and log10Kd of PGEs in the >1 kDa NDOM fraction were higher and more stable than those in the >3 kDa NDOM fraction. The results also indicated that the 1–3 kDa NDOM may dominate the interaction between PGEs ions and NDOM. Moreover, no kinetic model could perfectly simulate the adsorption process. It indicated that the colloidal struction and morphology of MOCs or NDOM in seawater might be inhomogeneous. Hence, the interaction between PGE ions and organic matter in seawater was a complicated process and needs further research.

Recent Development in Simultaneous Multi-Element Determination of the Platinum Group Elements and Gold in Geological and Environmental Samples

In recent years, the modern methods of multi-element analysis of precious metals have attracted wide attention in scientific research and industry. The application and development in the decomposition of samples, separation and enrichment, and modern instrumental analysis of the platinum-group elements (PGEs) and gold in geological and environmental samples have been reviewed. Finally, the tendency of analysis of precious metals is also prospected.

Geochemistry of Platinum Group Elements in Mafic-Ultramafic Rocks of Xinjie Intrusion

The platinum group elements (PGE) in the mafic ultramafic suite in the Xinjie layered intrusion and associated basalts and syenites were analyzed using neutron activation techniques after fire assay preconcentration. On this basis, the geochemistry of the platinum group during the magmatic stage is discussed. With respect to PGE distribution, the Xinjie layered intrusion is similar to the Bushveld ferruginous ultramafic series and is distinct from komatiite and Alpine type peridotite. It is also similar to the Emeishan basalt in PGE characteristics, implying that the original magmas of them may be of the same type.

Concentration of Platinum Group Elements during the Early Earth Evolution: A Review

Numerous unique geological processes [1] took place during the early Earth evolution;several of them, especially those occurring in the Hadean—Early Archean and later, are reflected in the modern geological (geophysical, geochemical, etc.) pattern. One such significant enigmatic feature is the preservation of extremely dense and heavy platinum group elements (PGEs): Pt, Pd, Rh, Ru, Ir, Os. Concentration of PGEs during this period could have taken place in two ways: 1) presence of particular matter capable of preserving PGEs near the earth's surface, 2) transportation of PGEs by magma flows from deep lithospheric (asthenospheric) layers (slabs) to the subsurface. Clearly, much of the dense and heavy PGEs did not sink through to the Earth’s mantle (core) at the time of the magma-ocean, and occur near Earth’s surface in abundances for formation of ore deposits with PGE concentrations found to be 2 - 3 orders of magnitude greater than those in their host media. Their enrichments are associated in numerous cases with such enigmatic phenomena as formation of anorthosites and anorthosite-bearing layered magmatic intrusions. PGE deposits and mineralization zones are also found in associations with chromitites, dunites and serpentinites. In this review, problems related to the initial concentration and preservation of PGEs, their association with anorthosites, and formation of layered intrusions are discussed in detail. The main aim of this article is analysis of the requirements—initial concentration and preservation of PGE and PGM (Platinum Group Minerals) during the early Earth evolution, as well as examination of the distribution behavior of some PGEs in different ore deposits and meteorites. It is supposed that meteoritic bombardment of Earth has played a significant role in formation of PGEs deposits. Some conclusions made in this article may be useful for developing and enhancing strategies of prospecting for PGEs deposits.

Geochemistry of platinum-group elements in the podiform chromitites and associated peridotites of the Nain ophiolites,Central Iran:Implications for geotectonic setting

The Nain ophiolite complex with an extent of[600 km2 is a part of the Central Iranian ophiolite,which is related to the opening and subsequent closure of the Neo-Tethys Ocean.Dunite and serpentinized harzburgite in the Nain area host podiform chromitites that occur as three(eastern Hajhossein,western Hajhossein,and Soheil Pakuh)schlieren-type tabular and aligned massive lenses with various sizes.The most common chromitite ore textures are massive,nodular,disseminated,and banded,reflecting crystal settling processes.The Cr#[Cr/(Cr+Al)]ranges from 0.43 to 0.81(average 0.63).The Mg#[Mg/(Mg+Fe2+)]varies from 0.25 to 0.78(average0.62).The Nain ophiolite and hosted chromitite are generally characterized by high Cr#,reflecting crystallization from a very hot boninite magma in a MORB setting.The high Cr#in the Nain chromitite also indicates a high degree of melting(15%–35%)of the depleted peridotite.The average total PGE content in the ophiolitic host rock(harzburgite and dunite)and chromite are 107 and 221 ppb,respectively.The Nain ophiolite and chromitite have high IPGE/PPGE and negative Pt*(Pt/Pt*=0.6)anomaly,which is a characteristic of high Cr#chromitite.The U-shaped REE pattern of dunite host rock suggests the interaction of depleted mantle peridotite with boninitic melt.Geochemical data suggest that the Nain chromitites are related to the boninitic magma emplacement in a suprasubduction zone.

Platinum-group Element Geochemistry of Magnetite from Porphyry-Cu-Mo Deposits and their Host Rocks(Siberia,Russia)

The concentrations of platinum-group elements （PGE） have been analyzed in primary magmatic magnetite samples from the Zhireken, Shakhtama and Aksug porphyry Cu-Mo deposits （Siberia, Russia） by laser ablation-inductively coupled plasma mass spectrometry to determine the range of PGE contents in magnetites and to check whether magnetite from two main rock suites （barren plutonic suite and mineralized porphyry suite） has distinct PGE composition. The results presented here indicate that magnetites are enriched in PGE relative to whole-rocks. Comparison of ore-related porphyry and barren plutonic suites shows that magnetite exhibit relatively similar PGE distribution patterns in both suites. Variations in Rh and Ru contents were controlled by the oxygen fugacity during magma crystallization.

Geochemistry and mineralogy of platinum-group elements(PGE)in chromites from CentralnoyeⅠ,Polar Urals,Russia

The Polar Urals region of northern Russia is well known for large chromium （Cr）-bearing massifs with major chromite orebodies, including the Centralnoye I deposit in the Ray-Iz ultramafic massif of the Ural ophiolite belt. New data on platinum （Pt）-group elements （PGE）, geochemistry and mineralogy of the host dunite shows that the deposit has anomalous iridium （Ir） values. These values indicate the predominance of ruthenium--osmium--iridium （Ru--Os--Ir）-bearing phases among the platinum-group mineral （PGM） assemblage that is typical of mantle-hosted chromite ores. Low Pt values in chromites and increased Pt values in host dunites might reflect the presence of cumulus PGM grains. The most abundant PGM found in the chromite is erlichmanite （up to 15 μm）. Less common are cuproiridsite （up to 5 μm）, irarsite （up to 4--5 μm）, and laurite （up to 4 μm）. The predominant sulfide is heazlewoodite, in intergrowth with Ni--Fe alloys, sporadically with pentlandite, and rarely with pure nickel. Based on the average PGE values and esti- mated Cr-ore resources, the Centralnoye I deposit can be considered as an important resource of PGE.

Platinum-Group Element Geochemical Characteristics of the Picrites and High-Ti Basalts in the Binchuan Area,Yunnan Province

The Binchuan area of Yunnan is located in the western part of the Emeishan large igneous province in the western margin of the Yangtze Block. In the present study, the Wuguiqing profile in thickness of about 1440 m is mainly composed of high-Ti basalts, with minor picrites in the lower part and andesites, trachytes, and rhyolites in the upper part. The picrites have relatively higher platinum- group element （PGE） contents （PGE=16.3-28.2 ppb）, with high Cu/Zr and Pd/Zr ratios, and low S contents （5.03-16.9 ppm）, indicating the parental magma is S-unsaturated and generated by high degree of partial melting of the Emeishan large igneous province （ELIP） mantle source. The slightly high Cu/Pd ratios （11 000-24 000） relative to that of the primitive mantle suggest that 0.007% sulfides have been retained in the mantle source. The PGE contents of the high-Ti basalts exhibit a wider range （~PGE=0.517-30.8 ppb）. The samples in the middle and upper parts are depleted in PGE and have ~Nd （260 Ma） ratios ranging from -2.8 to -2.2, suggesting that crustal contamination of the parental magma during ascent triggered sulfur saturation and segregation of about 0.446%-0.554% sulfides, and the sulfide segregation process may also provide the ore-forming material for the magmatic Cu-Ni-PGE sulfide deposits close to the studied basalts. The samples in this area show Pt- Pd type primitive mantle-normalized PGE patterns, and the Pd/Ir ratios are higher than that of the primitive mantle （Pd/Ir=l）, indicating that the obvious differentiation between Ir-group platinum- group elements （IPGE） and Pd-group platinum-group elements （PPGE） are mainly controlled by olivine or chromites fractionation during magma evolution. The Pd/Pt ratios of most samples are higher than the average ratio of mantle （Pd/Pt=0.55）, showing that the differentiation happened between Pt and Pd. The differentiation in picrites may be relevant to Pt hosted in discrete refractory Pt-alloy phase in the mantle; whereas the differentiation in the high-Ti basalts is probably associated with the fractionation of Fe-Pt alloys, coprecipitating with Ir-Ru-Os alloys. Some high-Ti basalt samples exhibit negative Ru anomalies, possibly due to removal of laurite collected by the early crystallized chromites.

Analysis of platinum-group elements in drill core samples from the Meishan Permian-Triassic boundary section, China

There is a long-standing controversy of what triggered the extinction at the Permian-Triassic boundary, the most severe mass extinction in the geologic record, including flood basaltic volcanism and/or bolide impact hypothesis. In order to clarify various pieces of evidence for the mass extinction event at the Permian-Triassic boundary, some researchers from some laboratories throughout the world have made a comprehensive study on a group of samples from the Meishan area of China. Some fresh core samples from the Permian-Triassic boundary in the Meishan area were analyzed in this study. The results showed that there is no Ir anomaly. Moreover, the PGEs patterns of those samples show obvious differentiation characteristics, that is different from the case encountered in meteorites. So no evidence supports the hypothesis of extraterrestrial impact. In contrast, the PGEs patterns are similar to those of Siberian and Emeishan basalts, which indicates that those PGEs are derived mainly from the basalts, lending a support to the correlation between mass extinction at the Permian-Triassic boundary and flood basaltic volcanism. This study has also confirmed the results for samples from section C prior to the analysis of the samples.

Platinum-Group Elements Geochemistry and Chromian Spinel Composition in Podiform Chromitites and Associated Peridotites from the Cheshmeh-Bid Deposit, Neyriz, Southern Iran: Implications for Geotectonic Setting

Dunite and serpentinized harzburgite in the Cheshmeh-Bid area, northwest of the Neyriz ophiolite in Iran, host podiform chromitite that occur as sehlieren-type, tabular and aligned massive lenses of various sizes. The most important chromitite ore textures in the Cheshmeh-Bid deposit are massive, nodular and disseminated. Massive chromitite, dunite, and harzburgite host rocks were analyzed for trace and platinum-group elements geochemistry. Chromian spinel in chromitite is characterized by high Cr#（0.72-0.78）, high Mg#（0.62-0.68） and low TiO2 （0.12 wt%-0.2 wt%） content. These data are similar to those of chromitites deposited from high degrees of mantle partial melting. The Cr# of chromian spinel ranges from 0.73 to 0.8 in dunite, similar to the high-Cr chromitite, whereas it ranges from 0.56 to 0.65 in harzburgite. The calculated melt composition of the high-Cr chromitites of the Cheshmeh-Bid is 11.53 wt%-12.94 wt% A1203, 0.21 wt%-0.33 wt% TiO2 with FeO/MgO ratios of 0.69-0.97, which are interpreted as more refractory melts akin to boninitic compositions. The total PGE content of the Cheshmeh-Bid chromitite, dunite and harzburgite are very low （average of 220.4, 34.5 and 47.3 ppb, respectively）. The Pd/Ir ratio, which is an indicator of PGE fractionation, is very low （0.05- 0.18） in the Cheshmeh-Bid chromitites and show that these rocks derived from a depleted mantle. The chromitites are characterized by high-Cr#, low Pd ＋ Pt （4-14 ppb） and high IPGE/PPGE ratios （8.2- 22.25）, resulting in a general negatively patterns, suggesting a high-degree of partial melting is responsible for the formation of the Cheshmeh-Bid chromitites. Therefore parent magma probably experiences a very low fractionation and was derived by an increasing partial melting. These geochemical characteristics show that the Cheshmeh-Bid chromitites have been probably derived from a boninitic melts in a supra-subduction setting that reacted with depleted peridotites. The high-Cr chromitite has relatively uniform mantle-normalized PGE patterns, with a steep slope, positive Ru and negative Pt, Pd anomalies, and enrichment of PGE relative to the chondrite. The dunite （total PGE = 47.25 ppb） and harzburgite （total PGE =3 4.5 ppb） are highly depleted in PGE and show slightly positive slopes PGE spidergrams, accompanied by a small positive Ru, Pt and Pd anomalies and their PdJIrn ratio ranges between 1.55-1.7and 1.36-1.94, respectively. Trace element contents of the Cheshmeh-Bid chromitites, such as Ga, V, Zn, Co, Ni, and Mn, are low and vary between 13-26, 466-842, 22-84, 115- 179, 826-1210, and 697-1136 ppm, respectively. These contents are compatible with other boninitic chromitites worldwide. The chromian spinel and bulk PGE geochemistry for the Cheshmeh-Bid chromitites suggest that high-Cr chromitites were generated from Cr-rich and, Ti- and Al-poor honinitic melts, most probably in a fore-arc tectonic setting related with a supra-subduction zone, similarly to other ophiolites in the outer Zagros ophiolitic belt.

Geochemical characteristics of the platinum-group elements in the Abulangdang ultramafic intrusion,Sichuan Province,China

The contents of the platinum-group elements (PGEs: Os, Ir, Ru, Rh, Pt, Pd) in the Abulangdang ultramafic intrusion have been determined using ICP-MS after nickel sulfide fire assay preconcentration. Different samples show significant differences in absolute PGE abundance. They display a pronounced negative incline in mantle-normalized patterns which are characterized by strong enrichment in IPGEs (Os, Ir, Ru) and depleting to slight enrichment in PPGEs (Rh, Pt, Pd). The characteristics of PGE distribution in the Abulangdang rocks are due to the combined action of sulfide and non-sulfide (spinel/chromite or alloy or micro-granular aggregation of metals). In comparison with the mafic-ultramafic rocks which host Ni-Cu-PGE deposits in the Emeishan Large Igneous Province (ELIP), it is assumed that the Abulangdang ultramafic intrusion may be the product of early-stage magma activity in the ELIP.

Study of Interfering nuclear reactions in determination of platinum group elements by neutron activation analysis

Eighteen interfering nuclear reactions that likely occur in neutron activation analysis of platinum group elements are studied. Their degrees are calculated by the basic principle of activation analysis. The calculation results indicate that most of the nuclear interferences become significant only if the interfering elements exist in major amount and the elements of interest in trace amount. However, the second\|order interference to platinum analysis from gold and the fission interference to analysis of ruthenium and palladium from uranium cannot be neglected even if the gold and uranium exist as trace constituents in samples.

ABUNDANCE AND DISTRIBUTION OF PLATINUM-GROUP ELEMENTS (PGE) IN PERIDOTITE FROM THE DAGZHUKA OPHIOLITE IN TIBET:IMPLICATIONS FOR MANTLE METASOMATISM

Information on abundance and distribution of platinum\|group elements (PGE) in peridotite from ophiolite is relevant to understand the nature and evolution of the upper mantle. The ophiolite suite outcropping along the famous suture zone of Yarlung Zangbo River, Tibet, has attracted wide attention of geologists both in China and abroad. The Dagzhuka ophiolite of in the suture zone is thought to display a complete ophiolitic sequence. The peridotite from the Dazhuka ophiolite is composed of fairly fresh or unaltered lherzolite, harzburgite and minor dunite which are the upper mantle residuum formed by 15%～35% partial melting. In this paper we have mainly studied the abundance and distribution of PGE in the harzburgites and lherzolites. The harzburgites and lherzolites preserve total PGE contents of 28 37×10 -9 ～50 67×10 -9 respectively higher than Primitive mantle or the peridotite from some typical ophiolites and Alpine. They all have fractionated chondrite\|normalized PGE patterns with positive slopes from Ir to Pd (Fig.1), and Pd/Ir=1 13～2 40>1, Pd/Rh=2 23～7 49>1, and Pd/Pt=0 26～1 16 (average 0 67) higher than Primitive mantle (1 11, 2 35, 0 57) or CI\|chondrite (1 01, 2 73, 0 53). Consequently, the Dagzhuka peridotite are PGE\|enriched, but otherwise possess residual characteristics arising from a minimum of 15% partial melting. It is suggested that mantle residuum by partial melting have low total PGE contents, fractionated chondrite\|normalized PGE patterns with negative or slightly flat slopes from Ir to Pd, and Pd/Ir<1. But, the total PGE contents, chondrite\|normalized PGE patterns and Pt/Ir, Pd/Rh and Pd/Pt values of the Dagzhuka peridotite are completely inconsistent with a residual origin. Partial melting would have partitioned all sulfide in the source into the melt. In fact, no sulfide or silicate melt remained in the Dagzhuka peridotite. Therefore, PGE in Dagzhuka peridotite are not present in sulfides. The PGE\|enrichment and fractionation of the Dagzhuka peridotites seem to arise from mantle metasomatism of melts/fluid enrich incompatible elements include Pt and Pt, but not from residual or percolation of sulfides. The enrichment of Cs, Rb, Ba, Th, U and LREE in Dagzhuka peridotite also give a hint of the mantle metasomatism. The abundance and distribution of PGE in the peridotite from the Dagzhuka ophiolite show the nature and evolution of the Dagzhuka upper mantle are distinctive.

Characteristics of platinum-group elements in basalts from spreading axis of Mariana Trough

Total platinum-group elements （PGEs） abundances in basalts from the spreading axis of Mariana Trough ranged from 0.418 × 10^9 to 1. 022 × 10^-9, and primitive mantle-normalized PGE patterns are of positive slope showing the relative enrichment of PPGE （ platinum, palladium, rhodium） and gold relative to IPGE. Compared with other mantle-originated rocks, these basalts have lower PGE contents and wider ranges of primitive mantle-normalized ratios of palladium content to iridium one, palladium content to platinum one and palladium content to gold one exhibiting relative platinum and iridium depletion. Characteristics of PGE patterns indicated that the studied Mariana Trough basalts originated from low partial melting, and the MORB mantle beneath the spreading center had been contaminated by the are-island mantle. In the aspect of trace elements, Mariana Trough basalts showed the enrichment of LILE, lead and LREE, indicating that they had been influenced by subduetion compositions. All these demonstrated that Mariana Trough basalts are products of partial melting from a mixed mantle （ the contamination of MORB mantle by are-island mantle）.

K/T boundary: Discussion of the platinum group elements as indicators of extraterrestrial materials

Whether the platinum group elements (PGE) can be taken as the indicators of extraterrestrial materials is a very important and interesting scientific problem. It is discussed on the basis of systematic investigation and study of a great amount of related literature. The following conclusions can be obtained: (ⅰ) extraterrestrial impact event can cause the PGE anomaly; conversely, the PGE anomaly may not represent the existence of extraterrestrial impact event, because the PGE anomaly can be caused by many terrestrial events (e.g. volcanic activity); (ⅱ) the PGE anomaly, especially the global PGE anomaly can inspire us to think it from extraterrestrial event, but it may not be as useful as previously thought as unambiguous identifiers of large extraterrestrial impact event in the earth’s history.

陕西略阳南部何家垭镍钴含矿岩体铂族元素特征——对硫化物熔离过程的约束

陕西何家垭镍钴含矿岩体位于南秦岭碧口地块,是近年来秦岭造山带中镍、钴战略性矿产找矿取得的重要新发现之一。该岩体由辉长岩、辉长闪长岩和少量辉石岩、角闪石岩组成,矿(化)体主要赋存在蚀变辉长岩中。基于对不同结构类型矿石铂族元素地球化学和硫化物原位硫同位素分析,探讨了岩浆性质和硫化物熔离过程。结果表明,各类矿石铂族元素(PGE)丰度均较低(3.93×10^(-9)~87.85×10^(-9),平均为27.88×10^(-9))。铂族元素地球化学特征反映,岩体母岩浆为高镁玄武质岩浆,受后期热液作用影响较弱。铂族元素和原位硫同位素特征显示,镁铁质矿物分离结晶是引起矿床中硫演化至饱和并发生深部硫化物熔离的重要因素。矿石中Pt元素的显著亏损可能是含Pt矿物结晶导致。南秦岭略阳何家垭岩体具有较好的镍钴成矿条件和找矿潜力,有望在秦岭造山带岩浆型铜镍硫化物矿床勘查评价方面取得重大突破。

金川铜镍硫化物矿床2号矿体铂族元素地球化学特征及其意义

以金川铜镍硫化物矿床2号矿体为研究对象,开展了主量元素、微量元素以及铂族元素(PGE)地球化学特征研究,探讨金川矿床岩浆演化和成矿机制。结果显示,研究区岩矿石(La/Yb)_(N)值为4.1,富集轻稀土;(La/Lu)_(N)值为3.8,轻重稀土分馏;亏损高场强元素Nb、Th和Zr,表明矿体形成过程中存在地壳混染。2号矿体矿石中PGE总量高于岩石,是由于矿化作用导致PGE发生富集。岩矿石中存在PGE分异,主要富集低熔点组PGE(Rh、Pt、Pd)。基于研究结果,推测研究区母岩浆为地幔中等部分熔融形成的玄武质岩浆,主要成矿机制是深部熔离--贯入机制。