FENG Qian1,2, HUANG Ming-liang, XU Lei-luo1*, BI Xian-wu1, ZHANG Xing-chun1, WANG Xin-song1
(1. The State Key Laboratory of Ore Deposit Geochemistry, Institute of geochemistry, Chinese Academy of Sciences, Guiyang 550081, China;
2. University of Chinese Academy of Sciences, Beijing 100049, China)
Abstract: The Pulang porphyry copper deposit is the largest one in the Zhongdian area, Yunnan Province, China. Its mineralization has closely genetic relationship with the Pulang complex, primarily composed of the mineralized quartz diorite porphyry (Phase 1) and quartz monzonite porphyry (Phase 2), and the barren diorite porphyry (Phase 3). In this study, the in-situ analysis of trace elements of zircon crystals, and the in-situ analysis of major elements of apatite grains from porphyries of the Pulang complex have been carried out. The Ce/Ce* values, Ce4+/Ce3+ratios, and Ce/Nd ratios of zircon grains indicate that the relative oxidation state of magma of the barren diorite porphyry is similar to that of magma of the mineralized quartz diorite porphyry, but clearly higher than that of magma of the mineralized quartz monzonite porphyry. Cl, OH and SO3 components of apatites indicate that magmas of all porphyries of three phases have similar H2O contents, but magmas of mineralized quartz diorite porphyry (Phase 1) and quartz monzonite porphyry (Phase 2) have higher Cl contents and sulfur fugacities than magma of the barren diorite porphyry (Phase 3). The high oxygen and sulfur fugacities and enrichment of H2O and Cl in magmas of porphyries are all the key factors for the porphyry copper mineralization. Magmas of porphyries of three phases in the Pulang complex are all characterized with the high oxygen fugacity and enrichment of H2O. However, magma of the barren diorite porphyry (Phase 3) has clearly lower Cl contents and sulfur fugacity than magmas of mineralized quartz diorite porphyry (Phase 1) and quartz monzonite porphyry (Phase 2). The differences in Cl contents and sulfur fugacity between magmas of the mineralized and barren porphyries are most likely one of the significant causes leading to mineralization in the quartz diorite porphyry (Phase 1) and quartz monzonite porphyry (Phase 2), but no mineralization in diorite porphyry (Phase 3).
Keywords: Pulang complex; Zircon; Apatite; In-situ geochemical compositions
ACTA MINERALOGICA SINICA Vol. 39, No. 6, 2019, page 681-689
