小秦岭金矿田成因的锶同位素约束  

Sr-isotope constraint on the origin of the Xiaoqinling gold field.

作　　者：祁进平[1] 赖勇[2] 任康绪[3] 唐国军[2] 

机构地区：[1]中国科学院广州地球化学研究所成矿动力学重点实验室,广州510640 [2]北京大学造山带与地壳演化重点实验室,北京100871 [3]中石油塔里木油田分公司勘探开发研究院,新疆库尔勒841000

出　　处：《岩石学报》2006年第10期2543-2550,共8页Acta Petrologica Sinica

基　　金：自然科学基金项目(编号49972035;40352003和40425006);国家重点基础发展规划项目(2006CB403504);科学院百人计划项目的资助

摘　　要：本文报道了前人对小秦岭金矿田部分金矿床流体包裹体、赋矿围岩(太华群)、文峪花岗岩的锶同位素结果以及作者新获得的中-新元古界地层(官道口群-栾川群)的缌同位素测试结果。鉴于小秦岭金矿田的金矿床和文峪花岗岩均形成于130Ma 左右,作者将所有^(87)Sr/^(86)比值返算为130Ma 时的初始值,即 I_(Sr-130)比值。文峪花岗岩的8件 I_(Sr-130)=0.7077～0.7084, 平均0.7082;太华群的12件 l_(Sr-130)=0.7073～0.8090,平均0.7557;中-新元古界地层的15件 I_(Sr-130)=0.7119～0.8373,平均0.7623;赋存于太华群中的金矿床流体包裹体的22件 I_(Sr-130)值变化于0.7334～0.7519,平均0.7440:赋存于文峪花岗岩中的矿脉流体包裹体7件 I_(Sr-130)=0.7135～0.71 85,平均0.7162。由此可见,赋存于太华群的金矿床 I_(Sr-130)值远高于文峪岩体,而落入太华群和中-新元古界地层的 I_(Sr-130)值范围,表明成矿流体不可能源于文峪花岗岩岩浆分异,而源于太华群和/或中-新元古界地层的变质脱水;赋存于文峪岩体中的含矿石英脉 I_(Sr-130)值低于太华群和/或中-新元古界地层,也低于太华群中的金矿床,但显著高于文峪岩体,应是高 I_(Sr-130)的成矿流体与低 I_(Sr-130)值的文峪花岗岩围岩相互作用的结果如此,碰撞造山成岩成矿与流体作用模式可较好阐释小秦岭金矿田的成因,即,中生代扬子与华北板块碰撞过程中,由中-新元古界地层及下伏太华群组成的陆壳板片沿小河断裂向北 A 型俯冲到小秦岭金矿田之下,俯冲板片经变质脱水作用为小秦岭金矿田形成提供了成矿流体,成矿流体与赋矿围岩的相互作用造成太华群中的矿脉与文峪岩体中的矿脉具有明显不同的 I_(Sr-130)值。This paper discusses the Sr isotope data obtained from previous studies on the ore-host rocks （Taihua Group ）, the Wenyu granite and the fluid inclusions of gold-bearing quartz veins in the Xiaoqinling gold field as well as new Sr isotope data recently obtained by the authors for the Neo-Mesoproterozoic strata （Guandaokou and Luanchuan Groups）. All the ^87Sr/^86 Sr ratios are calculated into initial ^87Sr/^86Sr ratios at 130 Ma, i.e. Isr-130, considering that both the Wenyu granite and the gold deposits were formed at about 130 Ma. Eight Isr-130 ratios of the Wenyu granite range from 0. 7077 to 0. 7084 with an average of 0. 7082 ; twelve Isr-130 ratios of the Taihua Group range from 0. 7073 to 0. 8090 with an average of 0. 7557; fifteen Is-130 ratios of the Neo-Mesoproterozoic strata range from 0.7119 to 0. 8373 with an average of 0. 7623 ; twenty-two ISr-130 ratios of the Taihua Group-hosted quartz veins range from 0. 7334to 0. 7519 with an average of 0. 7440; and seven Isr-130 ratios of the Wenyu granite-hosted quartz veins range from 0. 7135 to 0. 7185 with an average of 0. 7162. Obviously, the Isr-130 ratios of the Taihua Group-hosted quartz veins are far higher than those of the Wenyu granite, but accord with the Isr-130 range of the Taihua Group and/or the Neo-Mesoproterozoic strata, suggesting that the ore fluids might be sourced from the metamorphic devolatilization of the Taihua Group and/or the Neo-Mesoproterozoic strata, instead of derivation from the Wenyu granite magma. The Wenyu granite-hosted quartz veins, whose /Sr-130 values are lower than those of the Taihua Group, Neo-Mesoproterozoic strata and the Taihua Group-hosted quartz veins, and higher than those of the Wenyu granite, should be the results of interaction between the high Isr-130 fluids and the low Isr-130 Wenyu granite. Hence a tectonic model that combines collisional orogeny, metallogeny and hydrothermal fluid flow is proposed to interpret the origin of the Xiaoqinling gold field. During the Mesozoic collision between the Yangtz

关 键 词：锶同位素 小秦岭金矿田 太华群 文峪花岗岩 中-新元古界地层 

分 类 号：P597.3[天文地球—地球化学] P588.121[天文地球—地质学]