引用本文：魏少妮,朱永峰,安芳.2020.新疆包古图斑岩铜矿III- 2岩体氧逸度研究：来自矿物成分的指示[J].地质学报,94(8):2367-2382. WEI Shaoni,ZHU Yongfeng,AN Fang.2020.Oxygen fugacity of the intrusion III- 2 in the Baogutu porphyry copper deposit, Xinjiang: evidence from mineral compositions[J].Acta Geologica Sinica,94(8):2367-2382.
Abstract:Baogutu porphyry copper deposit, the largest porphyry type deposit of the area, is located in the west Junngar, Xinjiang. The ore- forming processes are closely associated with the late Carboniferous in termidate- acidic intrusions. The intrusion III- 2, located in the south of the mine, with the characteris tics of wholly mineralized and low grade, is an ideal sample for investigation of the nature of the ore- forming magma. In thispaper, oxygen fugacity of ore- forming magma was disscussed on the basis of petrology and mineral compositions of amphibole and zircon, by comparison with typical porphyry copper deposits. The results show that the Baogutu intrusion III- 2 is mainly composed of quartz diorite (porphyry) and diorite, with a small amount of pyroxene diorite. Plagioclase, amphibole, biotite, quartz and potassium feldspar are the major ore- forming minerals, with minor ilmenite, sphene and apatite. Early stage euhedrae amphiboles from quartz diorite are classified as calcic amphibole with high Mg# (0. 72~1. 00). The oxygen barometer based on amphibole compositions provides log f O2 values ranging from △NNO+1. 4 to △NNO+2. 6, which is in the variation range of ore- bearing intrusions from porphyry copper deposits worldwide. Zircons from quartz diorite are characterized by high REE content (338×10-6~ 959×10-6). With depleted LREE and enriched HREE, these zircons display left- leaning REE patterns and strongly positive Ce and negtive Eu anomalies. The moderate Ce4+/Ce3+(29. 55~89. 50) and Eu/Eu* ratios (0. 32~0. 47) are in the overlapping portion of ore- bearing and ore- barren intrusions from porphyry copper deposits. These data indicate that the oxygen fugacity of the ore- forming magma of the Baogutu intrusion III- 2 are relatively high, which is beneficial for the dissolution and migration of metal elements, and also facilitates the formation of poyphyry copper deposits.