A comparison of trace element geochemical characteristics between the Platreef deposit of Bushveld Complex and the Jinchuan Cu-Ni-PGE sulfide deposit and its significance
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    Abstract:

    Abstract:Major and trace element geochemistry of rocks and ores from the Platreef deposit of the Bushveld Complex was systemically studied in this paper by using new ICP-MS analytic method for the purpose of making a comparison with geochemistry of the Jinchuan Cu-Ni-PGE sulfide deposit and probing into the genesis of this type of deposits so as to guide their prospecting work. It is concluded that ∑REE values of the Platreef rocks are close to values of lherzolite from the Jinchuan Cu-Ni-PGE sulfide deposit, with very similar REE patterns. Chondrite-normalized REE patterns of the ore-bearing rocks from both deposits assuming right-inclined fractionation, with enrichment of LREE and smoothness of HREE; nevertheless, Platreef rocks have a positive Eu anomaly,whereas Eu negative anomalies are evident for most lherzolite and ores from the Jinchuan deposit. This might be a reflection of insignificantly varying plagioclase/orthopyroxene ratios during the crystallisation of the rocks. it is evident that, relative to the Jinchuan deposit, the Platreef deposit has higher contents of strongly fractionated incompatible elements but shows a trough-shaped profile with pronounced depletion of Nb and Ta,suggesting a model of crustal contamination during mantle plume magma emplacement, evolution and ore formation that resulted in the geochemical features of trace elements similar to arc picrite. Jinchuan ore-bearing magma is enriched in Fe, Ti and highly incompatible lithophile elements, exhibiting geochemical features of Ferropicrites trace elements; and hence it is thought to have been derived from conrrespondingly enriched mantle ( EMI) sources even if there probably also existed some crustal substance contamination during the rock-forming and ore-forming process. The primitive mantle-normalized PGE patterns of platreef rocks are arch-shaped with the enrichment of Pt, Pd and Ru relative to Os, Ir and Rh, and incompatible elements Cs, Rb, Th, U and LREE as well as chalcophile elements Cu and Ni, suggesting that the residual mantle peridotite from which the Bushveld Complex derived has undergone infiltration and contamination-mantle metasomatism by external mineral-enriched fluids containing highly incompatible elements, which may be responsible for the fractionation of PGE from mantale-derived magma.

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GAO Hui, WANG An-jian, CAO Dian-hua, LI Rui-ping, WANG Yong-lei. A comparison of trace element geochemical characteristics between the Platreef deposit of Bushveld Complex and the Jinchuan Cu-Ni-PGE sulfide deposit and its significance[J]. Geology in China, 2009, 36(2): 268-290(in Chinese with English abstract).

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  • Online: March 20,2013
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