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  

Oxygen fugacity of the intrusion Ⅲ-2 in the Baogutu porphyry copper deposit, Xinjiang: evidence from mineral compositions

作　　者：魏少妮[1] 朱永峰[2] 安芳[3] WEI Shaoni;ZHU Yongfeng;AN Fang(College of Geology and Environment,Xi’an University of Science and Technology,Xi’an,710054;School of Earth and Space Sciences,Peking University,Beijing,100871;Department of Geology,Northwest University,Xi’an,710069)

机构地区：[1]西安科技大学地质与环境学院,西安710054 [2]北京大学地球与空间科学学院,北京100871 [3]西北大学地质系,西安710069

出　　处：《地质学报》2020年第8期2367-2382,共16页Acta Geologica Sinica

基　　金：国家自然科学基金项目(No.41403033,No.41602212);陕西省自然科学基础研究计划一般项目(面上)(2019JM-409)联合资助成果。

摘　　要：包古图斑岩铜矿位于新疆西准噶尔地区,是区内规模最大的斑岩型矿床,成矿作用与晚石炭世中酸性侵入体密切相关。Ⅲ-2岩体位于矿区南部,该岩体全岩矿化,但品位较低,是探讨成矿岩浆性质的理想对象。本文结合岩石学和角闪石、锆石等矿物成分分析,通过与典型斑岩铜矿进行对比,探讨了成矿岩浆的氧逸度。研究表明,包古图Ⅲ-2岩体以石英闪长(玢)岩和闪长岩为主,少量辉石闪长岩,主要由斜长石、角闪石、黑云母、石英和钾长石组成,含少量钛铁矿、榍石和磷灰石。石英闪长岩中早期结晶的自形角闪石属于钙质闪石,Mg#较高(0.72~1.00),成分分析指示成矿岩浆的氧逸度为:△NNO+1.4~△NNO+2.6,位于斑岩铜矿含矿岩体的分布范围。从中分选出的锆石REE含量高(338×10-6~959×10-6),具有左倾型稀土配分模式,轻稀土亏损,重稀土富集,显示强烈Ce正异常和Eu负异常。Ce4+/Ce3+比值为29.55~89.50,Eu/Eu*比值为0.32~0.47,分布于斑岩铜矿含矿岩体和未矿化岩体的叠加部位。研究结果显示,包古图斑岩铜矿Ⅲ-2岩体成矿岩浆氧逸度较高,有利于成矿元素的溶解和迁移,对斑岩铜矿的形成有促进作用。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 logfO2 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.

关 键 词：氧逸度 斑岩铜矿 成矿岩浆 包古图 西准噶尔 

分 类 号：P618.41[天文地球—矿床学]