Field Relationships and Geochemical Constraints on the Emplacement of the Jinchuan Intrusion and its Ni-Cu-PGE Sulfide Deposit, Gansu, China
Field Relationships and Geochemical Constraints on the Emplacement of the Jinchuan Intrusion and its Ni-Cu-PGE Sulfide Deposit, Gansu, China
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DOI：
10.2113/gsecongeo.102.1.75
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发表时间：
2007
期刊：
影响因子：
5.8
通讯作者：
J. Lehmann;N. Arndt;B. Windley;Mei‐Fu Zhou;C. Wang;C. Harris
中科院分区：
文献类型：
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作者：
J. Lehmann;N. Arndt;B. Windley;Mei‐Fu Zhou;C. Wang;C. Harris
通过对金川岩体的野外填图和岩石地球化学研究，阐明了金川岩体的侵位过程，并提供了一种新的模式，解释了金川岩体中大型、丰富的镍铜铂矿床的形成。侵入体沿上覆盖层序列底部的不整合面沿着侵位到高级片麻岩和大理石中，表明它是作为岩床侵位的，而不是如先前所提出的近垂直岩脉。侵位后，岩体旋转至现今方位，并在绿片岩相条件下变形变质。不相容微量元素的相对富集，以及U-Th和Nb-Ta的负异常，证明了母岩浆同化了下地壳的花岗岩类岩石。丰富的大理石捕虏体，现在脱碳酸富透辉石矽卡岩，和化学指标，如高CaO/SiO2的存在下，表明岩浆同化碳酸盐到达其目前的网站。这种污染可能与镍铜铂族矿石的形成有关。我们认为，富碳酸盐流体的同化作用增加了岩浆的氧逸度，并导致富金属硫化物的分离。
Field mapping and petrological-geochemical investigation of the Jinchuan intrusion in north-central China clarifies how the intrusion was emplaced and provides a new model that explains how its large and rich Ni-Cuplatinoid deposits may have formed. The intrusion was emplaced into high-grade gneisses and marbles along a disconformity at the base of an overlying cover sequence, indicating that it was emplaced as a sill, not a nearvertical dike, as previously proposed. After emplacement the intrusion was rotated to its present orientation and deformed and metamorphosed under greenschist-facies conditions. Relative enrichment of incompatible trace elements coupled with negative U-Th and Nb-Ta anomalies in all samples from the intrusion provide evidence that the parental magma assimilated granitoid rocks in the lower crust. The presence of abundant marble xenoliths, now decarbonatized to diopside-rich skarns, and chemical indices such as high CaO/SiO2, indicate that the magma assimilated carbonate on reaching its present site. This contamination may be linked to the formation of the Ni-Cu platinoid ores. We propose that the assimilation of carbonate-rich fluids increased the oxygen fugacity of the magma and led to the segregation of metal-rich sulfides.