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Xu H.,Kunming University of Science and Technology | Cui Y.-L.,Kunming University of Science and Technology | Zhang M.-H.,Nonferrous Metals Geological Survey | Zhou J.-X.,Chinese Academy of science | And 4 more authors.
Kuangwu Yanshi/ Journal of Mineralogy and Petrology | Year: 2015

The Bijiashan Au ore deposit occurred with granite porphyry, quartz-monzonite porphyry and lamprophyre Petrology,petrogeochemistry and zircon U-Pb geochronology of lampro-phyres in the Bijiashan ore deposit are studied. It shows that they are mica lamprophyre and belong to the potassic and ultra-potassic calc-alkaline series, with alkali-rich (ω(Na2O+K2O) = 5. 00%∼9. 26%,average 7. 57%),high-K (K2O/Na2O=l. 92∼19. 02,average 4. 69) and low Ti (ω(TiO2)= 0. 43% ∼0. 77% , average 0.66%) features. The lamprophyre samples display high ratios of ∑LREE/∑HREE (9. 13∼10. 71) and (La/Yb)N(11. 60∼15. 32) .with weak negative Eu anomalies (δEu = 0. 61∼0. 85, average 0. 73). They are enriched in large iron lithophile elements (Rb,Ba,U and Sr) and depleted in high field strength elements (Nb,Ta,Zr and Ti), especially depleted Ta,Nb and Ti,showing "TNT." negative anomalies in trace element spider diagram. Zircon grains from lamprophyres were analyzed by using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS), which yields a U-Pb age of 33. 6 Ma±0. 29 Ma (MSWD = 1. 18,w=16) indicating that it, was formed during Paleogene Eocene,and is consistent with the peak ages (45 Ma∼30 Ma) of the Jinshajiang-Red River alkali-rich porphyry belt. Based on the petrology, petrogeochemistry, zircon U-Pb geochronology and geological setting, It is proposed that the lamprophyres in Bijiashan ore deposit were formed by low degree (2% ∼ 10%) partial melting of phlogopite-hornblend-bearing garnet lherzolite enriched lithospheric mantle under the post-collision tensional setting of India-Eurasian plate.

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