ZHANG Hai, MA Dong-fang, ZHANG Hong, LIU Hong, ZHANG Yu, JIN Can-hai, SHEN Zhan-wu

(Chengdu Institute of Geology and Mineral Resources, Chengdu 610081, China)

Abstract: Xifanping porphyry-copper deposit in Yanyuan County of Sichuan Province, China is located at the west margin of the Yangtze Platform and near the connection between Yanyuan-Lijiang depression zone and Ganzi-Litang suture zone. The rock masses in the mining area are mainly quartz monzonite porphyry (QMP). Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) shows that the zircon U-Pb age of QMP is (100.8±0.7) Ma (MSWD=0.2), indicating the emplacement age of QMP being the Early Cretaceous. The QMP is enriched with large-ion lithophile elements (Rb, Ba, and K) and light rare earth elements (LREEs), but deficient in high-field-strength elements (Nb, Ta, Ti, and P) and heavy rare earth elements (HREEs), indicating the nature of high-K quasi-aluminous granite. The porphyry also contains 64.06%－65.24% w(SiO2), high w(Al2O3) (15.58%－16.55%), high w(Sr) (719 ×10-6－1221 ×10-6) with high Sr/Y ratio (49.2－82.5), low w(MgO) (1.30%－1.63%), low w(Yb) (1.08 ×10-6－1.55 ×10-6), low w(Y) (13.7×10-6－14.8×10-6), unobvious Eu anomaly (0.83－0.90), and significant LREE-HREE differentiation, with (La/Yb)N=29.94－52.14, indicating the properties of adakites. The adakites in Xifanping is characterized with high K and low Na (K2O/Na2O=0.78－2.44); low Cr and Ni; high Th, Th/U, and relatively low Sr/Y, indicating the adakites originated from the partial melting of the thickened lower crust. The crust thickening effect at Early Cretaceous (100.8 Ma) in Xifanping Deposit might be controlled by the orogeny after the Ganzi-Litang ocean closure. The porphyritic masses resulted from the magmatism during the intracontinental extrusion-to-extension transitional period, which appeared after the Indo-Chinese folding orogeny (200 Ma) and before the Himalayan collisional orogeny (65 Ma).

Keywords: quartz monzonite-porphyry; zircon; LA-ICP-MS U-Pb dating; Xifanping of Yanyuan; Sichuan

E-mail：zhanghai1980@sina.com

ACTA MINERALOGICA SINICA Vol. 37, No. 4, 2017, Page 475-485