南秦岭西坝花岗质岩体矿物学特征及成岩意义  

Mineralogy of the Xiba Granitoid Pluton in the Southern Qinling Orogenic Belt and Its Implications for Petrogenesis

作　　者：汪欢[1,2] 王建平[1,2] 刘家军[1,2] 曹瑞荣 惠德峰 程建军 贺志春 高创 赵新江 齐峰 张国刚 王罗 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室,北京100083 [2]中国地质大学岩石圈构造深部过程及探测技术教育部重点实验室,北京100083 [3]陕西太白黄金矿业有限责任公司,陕西太白716000

出　　处：《现代地质》2011年第3期489-502,共14页Geoscience

基　　金：国家自然科学基金项目(41030423);中国黄金集团公司科技项目"陕西省太白县双王金矿床地质特征;成矿规律及找矿靶区再研究"

摘　　要：西坝花岗质岩体位于南秦岭构造-岩浆带中部,为南秦岭印支期花岗岩带五龙岩体群的重要组成部分,与双王金矿有密切的空间关系。该岩体主要由石英二长闪长岩和花岗闪长岩组成,岩体中发育较多的镁铁质包体。通过对岩体及镁铁质包体的系统的矿物学特征研究发现,本区花岗质岩体属于I型花岗岩类,成岩物质主要来源于地壳,并且有地幔物质的加入。岩体及镁铁质包体显示有多种壳-幔岩浆混合的岩相学证据:如包体的冷凝边、斜长石环带成分显示核部和边缘偏基性,而幔部偏酸性,包体中见大量的长针状磷灰石及角闪石,包体中有两种产状的角闪石等。根据矿物温度压力计计算,西坝岩体的结晶温度为646.72~703.84℃,压力为1.67×108~3.66×108Pa,平均为3.12×108Pa。岩体形成于相对高氧逸度(lgfO2为-16.16×105^-17.06×105Pa)、中等水逸度(fH2O为46.82×105~136.85×105Pa)和氢逸度(fH2为0.32×105~0.91×105Pa)环境。岩体的这种高氧逸度条件有利于金进入熔体相或流体相,是金矿形成的有利条件。The Xiba granitoid pluton,as an important part of the Indo-Chinese Wulong granitoid series,is located in the middle section of the Southern Qinling orogenic belt and spatially related to the Shuangwang gold deposit.It mainly consists of quartz monzodiorite and granodiorite containing many mafic microgranular enclaves（MME）.Systematic petrological and mineralogical studies indicate that the rocks belong to I type granite.The petrographical studies of granite and MME suggest that magma mixing plays a great role during magma crystallization.The pressure of the granite estimated by Al-in-hornblend barometer is from 1.67×108 to 3.66×108 Pa.Amphibole-plagioclase thermometry yields a forming temperature of 649.72~703.84 ℃.The plutons equilibrated under high oxygen fugacities（lg fO2） ranging from-16.16×105 to-17.06×105 Pa,moderate water fugacities（fH2O） between 46.82×105 and 136.85×105 Pa,and also moderate hydrogen fugacities（fH2） from 0.32×105 to 0.91×105 Pa.The high oxygen fugacities provide suitable conditions for Au entering into melt and fluid,thus favor the formation of gold deposit.

关 键 词：西坝花岗质岩体 镁铁质包体 矿物学 岩浆混合 物理化学条件 南秦岭 

分 类 号：P588.121[天文地球—岩石学]