Distribution of platinum-group and chalcophile elements in the Aguablanca Ni–Cu sulfide deposit (SW Spain): Evidence from a LA-ICP-MS study
Distribution of platinum-group and chalcophile elements in the Aguablanca Ni–Cu sulfide deposit (SW Spain): Evidence from a LA-ICP-MS study
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DOI：
10.1016/j.chemgeo.2011.02.010
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发表时间：
2012-04
期刊：
影响因子：
3.9
通讯作者：
R. Piña;F. Gervilla;S. Barnes;L. Ortega;R. Lunar
中科院分区：
文献类型：
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作者：
R. Piña;F. Gervilla;S. Barnes;L. Ortega;R. Lunar
用激光烧蚀-电感耦合等离子体质谱法（LA-ICP-MS）测定了西班牙西南部Aguablanca Ni-Cu存款中贱金属硫化物矿物（BMS）中铂族元素（PGE）和亲铜元素Ni、Co、Au、Ag、Se、Re、Cd、Bi、Te和As的含量。的主要目的是限制的BMS作为主机的铂族元素所发挥的作用，因为这揭示了重要的信息控制这些元素的分布过程中的存款。BMS（磁黄铁矿、镍黄铁矿、黄铜矿和少量黄铁矿）呈半块状、浸染状和少量黄铜矿脉状矿石。根据全岩金属丰度和BMS矿物学，这些矿石类型被解释为不混溶硫化物液体分馏和结晶的结果。铂族和亲铜元素浓度随BMS和矿石类型的变化而变化。这些金属中的一些在硫化物液体分离结晶过程中的分配行为在很大程度上决定了它们在矿石中的分布。铼、锇、铱、钌和铑主要以固溶体形式存在于半块状矿石中的磁黄铁矿和镍黄铁矿中，该矿石被解释为代表单硫化物固溶体（mss）累积。mss结晶产生少量富Cu硫化物液体，其形式为黄铜矿细脉，相对富集Pd-、Au-和Ag的黄铜矿，以及少量贫Re-、IPGE-和Rh-的磁黄铁矿和镍黄铁矿。铂族元素含量的BMS从浸染型矿石，解释为代表原始的未分馏硫化物熔体，大约是中间的半块状和黄铜矿脉矿石。钯和铂主要与铋、碲和砷结合在一起，形成铂族矿物（PGM、Pd-Pt铋碲化物和Pt砷化物）。这种优选位置沿着所采用的结构（通常为圆形颗粒和板条）和结晶温度（推断低于500°C）表明，最初溶解在BMS中的Pd和Pt沿着Bi、Te和As溶出，形成矿石中存在的PGM组合。三种矿石类型的镍黄铁矿中仍有部分Pd（约占总含量的30%）固溶。镍黄铁矿中的Pd的存在可能是有限的硫化物分馏的综合效应，其中一些Pd保留在mss中，并且Pd在冷却时从mss和富Cu部分扩散到镍黄铁矿中。两种结构类型的黄铁矿托管不同的PGE浓度已被描述：（1）大型自形黄铁矿和（2）带状黄铁矿。自形黄铁矿是唯一一种含Pt（高达15 ppm）和Rh（4- 31 ppm）的BMS。相比之下，带状黄铁矿不含Pt，其Os、Ir、Ru和Rh的含量（30- 360 ppb）与其所取代的寄主磁黄铁矿相似。自形颗粒的起源，无论是从mss或磁黄铁矿蚀变产物的出溶产物，是不是众所周知的，进一步的工作将是必要的，以限制这一点。尽管如此，黄铁矿中PGE的存在揭示了这种硫化物作为Ni-Cu-（PGE）矿床中PGE的潜在载体不应被忽视。
The concentrations of platinum-group elements (PGE) and chalcophile elements Ni, Co, Au, Ag, Se, Re, Cd, Bi, Te and As have been determined by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) in base metal sulfide minerals (BMS) from the Aguablanca Ni–Cu deposit, SW Spain. The main aim was to constrain the role played by the BMS as hosts of PGE as this reveals important information regarding the processes controlling the distribution of these elements in the deposit. The BMS (pyrrhotite, pentlandite, chalcopyrite and minor pyrite) occur as semi-massive, disseminated and minor chalcopyrite-veined ores. On the basis of whole rock metal abundances and BMS mineralogy, these ore types have been interpreted to be the result of the fractionation and crystallization of an immiscible sulfide liquid. Platinum-group and chalcophile element concentrations vary as a function of the BMS and ore types. The partitioning behavior of some of these metals during the fractional crystallization of the sulfide liquid largely governed their distribution in the ore. Rhenium, Os, Ir, Ru, and Rh occur mostly in solid solution in pyrrhotite and pentlandite from the semi-massive ore which has been interpreted to represent monosulfide solid solution (mss) cumulates. The mss crystallization gave rise to minor Cu-rich sulfide liquid in the form of chalcopyrite veinlets with relatively Pd-, Au- and Ag-enriched chalcopyrite, and minor Re-, IPGE- and Rh-depleted pyrrhotite and pentlandite. Platinum-group element contents in the BMS from the disseminated ore, interpreted to represent an original unfractionated sulfide melt, are approximately intermediate to the semi-massive and chalcopyrite-veined ores. Palladium and Pt occur mostly associated with Bi, Te, and As forming platinum-group minerals (PGM, Pd–Pt bismuthotellurides and Pt arsenides) within individual BMS grains. This preferential location along with the textures adopted (usually rounded grains and laths) and the temperatures of crystallization (inferred below 500°C) suggests that Pd and Pt, initially dissolved in the BMS, were exsolved along with Bi, Te and As to form the PGM assemblage present in the ore. Some Pd (approximately 30% of the bulk) remains in solid solution in pentlandite for the three ore types. The presence of Pd in pentlandite is likely a combined effect of limited sulfide fractionation with some of Pd remaining in mss and Pd diffusion into pentlandite from the mss and Cu-rich portions on cooling. Two textural types of pyrite hosting distinct PGE concentrations have been described: (1) large idiomorphic pyrite and (2) ribbon-like pyrite. Idiomorphic pyrite is the unique BMS hosting Pt (with contents as high as 15ppm) and also contains relatively high Rh concentrations (4–31ppm). By contrast, ribbon-like pyrite has no Pt and hosts similar Os, Ir, Ru and Rh concentrations (30–360ppb) to those of the host pyrrhotite to that it replaces. The origin of the idiomorphic grains, whether exsolution products from mss or alteration products of pyrrhotite, is not well known and further work will be necessary to constrain this point. Nevertheless, the presence of PGE hosted by pyrite reveals that this sulfide should not be overlooked as a potential carrier of PGE in Ni–Cu–(PGE) ore deposits.