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Zhao Y.S.,China University of Geosciences | Zhao Y.S.,Gold Geological Institute of CAFF | Yang L.Q.,China University of Geosciences | Chen Y.F.,Gold Geological Institute of CAFF | And 5 more authors.
Acta Petrologica Sinica | Year: 2012

The Jinchang Cu-Au deposit, a super-large ore deposit explored in the latest, is mainly of breccia-type ore body and is spatially closely associated with diorite porphyry which is apophysis like and porphyry structure with mainly plagioclase, hornblende and litde pyroxene as phenocrysl. Major element data show that the SiO2 content of diorite porphyry is 54, 62% ∼ 67.82%, average as 60.33% : Al2O3 content is 14.52% ∼ 18.25%, an average of 16.62%, and ratio of k2O/Na2O is 0.06 ∼0.31, less than 0.5. All these indicate that diorite porphyry belongs to sub-alkaline series and have a calc-alkaline evolutionary trend with a lower potassium content. While the LREE/HREE ratio ol the porphyry diorite is relatively higher, between 5.06 and 14.24 with an average of 9.16 and the δEu of 0.85 to 1.46 shows a positive anomaly. Then, trace elements of porphyry diorite shows low Y and Yb, but high Sr. The ratio ol Sr/Y is between 35.87 and 111.4, average as 57.57 ( >40). Moreover, the primitive mande-normalized trace element spider diagram shows that the diorite porphyry enriched in large ion lithophile elements ( OLE) while depleted in high field strength elements ( HSFE), especially Nb, Ta and Ti depletion, besides some enrichment of Pb. The geochemical data suggests that the diorite porphyry is probably adakitic rock and were produced by crustal contamination and fractionation of mafic magmas generated from partial melting of mantle source which had been metasomatismed by the subduclion tluid. In addition, an 118.1 ± 1.6Ma to 115.7 ±2.OMa diagenelic age and an 118.1 ± 1.6Ma mineralization age ol diorite porphyry in Jinchang deposit, consistence with the 120 ∼ 110Ma magmatic activities epoch in the eastern part of Jilin and Heilongjiang provinces, revealed that the Jinchang porphyry Cu-Au metallogenesis possiblely related to the Early Cretaceous subduction of the Pacific plate. It is potential to exploration the porphyry-epithemal system copper-gold deposit of the same period in the eastern part of Jilin and Heilongjiang provinces.

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