鄂东南铜山口铜(钼)矿床黑云母矿物化学特征及其对岩石成因与成矿的指示  

Mineral chemistry of biotites from the Tongshankou Cu-Mo deposit:Implications for petrogenesis and mineralization

作　　者：刘彬[1] 马昌前[1,2] 刘园园[1] 熊富浩[1] 

机构地区：[1]中国地质大学地球科学学院,湖北武汉430074 [2]中国地质大学地质过程与矿产资源国家重点实验室,湖北武汉430074

出　　处：《岩石矿物学杂志》2010年第2期151-165,共15页Acta Petrologica et Mineralogica

基　　金：2009年湖北省高等学校省级教学研究资助项目(2009108);国家科学技术部国际科技合作项目(2007DFA21230);国家自然科学基金重点资助项目(40334037);教育部和国家外国专家局高等学校学科创新引智计划资助项目(B07039)

摘　　要：在鄂东南铜山口铜(钼)矿床存在着3种产状的黑云母,分别是赋存于花岗闪长斑岩矿物颗粒间的黑云母、钾长石斑晶内的黑云母以及蚀变带内的黑云母。本文运用电子探针(EMPA)和激光剥蚀-等离子体质谱(LA-ICP-MS)技术,对这3种不同产状的黑云母进行了原位成分分析。结果表明,3种产状的黑云母Ti的含量介于0.38～0.45之间,且Mg/(Mg+Fe)介于0.53～0.72之间,类似于岩浆成因黑云母的成分特征。3种产状的黑云母MgO和FeOT值差别较大,但Al2O3、TiO2、SiO2、Na2O和K2O值差别不明显。作为花岗闪长斑岩质熔体中Rb、Ba、Nb、Ta等不相容元素及Sc、V、Co、Ni、Cr等相容元素的主要载体,黑云母的U、Th、Pb、Sr、Zr、Hf、Y等元素含量显著低于主岩,而且高场强元素Nb、Ta受后期岩浆热液作用的影响较弱。黑云母并不是影响全岩稀土特征的主要矿物相。铜山口花岗闪长斑岩的形成与幔源岩浆作用关系密切,并可能与板块俯冲作用相关。黑云母含Cu量的高低并不是衡量侵入体是否成矿的有效指标,但体系中高的氧逸度(logfO2>NiNiO+1),有利于斑岩铜矿的形成。与Cu成矿有关的黑云母具有高镁低铁的特征,与Sn成矿有关的黑云母则具有高铁低镁的特征。Major,rare earth and trace element composition of biotites from the matrix and the intra-K-feldspar phenocrysts of granodiorite porphyry and the alteration zone in the Tongshankou Cu-Mo deposit was measured by the electron probe micro-analyzer （EPMA） and the laser ablation inductively coupled plasma mass spectrometry （LA-ICP-MS）. EPMA analyses of major elements suggest that biotites of different modes of occurrence differ greatly in MgO and FeOT content however,their Al2O3,TiO2,SiO2,Na2O and K2O values do not show remarkable differences. LA-ICP-MS analyses of trace elements demonstrate that biotite is an important carrier of Rb,Ba,Nb,Ta,Sc,V,Co,Ni and Cr in granodioritic melts but has less capability in hosting U,Th,Pb,Sr,Zr,Hf and Y,and thus the concentrations of these elements in biotite are much lower than those in host rocks. Post-magmatic hydrothermal process has insignificant effects on the high field strength elements such as Nb and Ta. LA-ICP-MS analyses of rare earth elements （REE） suggest that the biotites display quite low REE concentrations （∑REE=0.150×10^-6～3.691×10^-6）,and many of the values are even lower than the detection limits. Although there are still some differences between the three types of biotites,these differences fail to accurately reflect the differentiation degree of REE during the post-magmatic hydrothermal process. So biotite is not the main mineral phase affecting the REE features of the host rocks. Geochemical features of the three types of biotites from the Tongshankou Cu-Mo deposit are similar to those of magmatic biotites：Ti=0.38～0.45 and Mg/（Mg＋Fe）=0.53～0.72. Based on the geochemical features,it is suggested that the formation of Tongshankou granodiorite porphyry was related to mantle-derived magmatism and slab subduction. LA-ICP-MS analytical results of Cu in biotites from Tongshankou granodiorite porphyry are low：the highest value is only 8.442×10^-6,and many of the Cu values are lower than 2.121×10^-6. So the Cu content of biotites fro

关 键 词：黑云母 微量元素 花岗闪长斑岩 岩石成因 成矿 

分 类 号：P578.959[天文地球—矿物学] P581[天文地球—地质学]