【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。更多还原

【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 logf_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.更多还原