- journal_title：Economic Geology
- Contributor：Jérémie Lehmann ; Nicholas Arndt ; Brian Windley ; Mei-Fu Zhou ; Christina Yan Wang ; Chris Harris
- Publisher：Society of Economic Geologists
- Date：2007-
- Format：text/html
- Language：en
- Identifier：10.2113/gsecongeo.102.1.75
- journal_abbrev：Economic Geology
- issn：0361-0128
- volume：102
- issue：1
- firstpage：75
- section：Articles
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-Cu-platinoid 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 near-vertical 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.