黑矿型矿床成矿物质来源:日本上向黑矿铼-锇和氦同位素证据  

Sources of Ore-forming Metals in Kuroko-type Deposits: Evidence from the Re-Os and He Isotopes for the Uwamuki Kuroko Deposit of Japan

作　　者：侯增谦[1] 杜安道[2] 孙卫东[3] 

机构地区：[1]中国地质科学院矿产资源研究所,北京100037 [2]中国地质科学院岩矿测试技术研究所,北京100037 [3]中国科学技术大学地球和空间科学系,合肥230026

出　　处：《地质学报》2001年第1期97-105,共9页Acta Geologica Sinica

基　　金：国家自然科学基金(编号49773711)

摘　　要：上向黑矿(Uwamuki Kuroko)是日本最典型的黑矿型矿床,它形成于日本岛弧中新世夭折岛弧裂谷环境,产于双峰式岩石组合的长英质火山岩系中。矿床由下部筒状硅矿带和上部块状黑矿带构成,后者显示典型的上黑(黑矿)下黄(黄矿)金属分带。为探索研究长期争议的成矿物质来源,系统测定了矿石和主岩的Os,He同位素组成。含矿流纹岩系的 R/R_A值介于0.93～1.14间,证实该岩浆可能主要来源于陆壳重熔。上向黑矿的上部块状黑矿矿石具较高的^(187)Os/^(188)Os值(2.246～7.608),反映矿石Os主体来源于壳源沉积物或矿区基底岩系;下部脉状—网脉状硅矿、块状黄矿和少量黑矿则具低^(187)Os/^(188)Os值(0.423～0.793),证实矿石Os具两源性,估计幔源物质贡献约57％～89％,壳源物质贡献约11％～43％。此外,在上部块状黑矿带内部,矿石^(187)Os/^(188)Os显示清楚的垂向韵律性变化,揭示了成矿流体及成矿物质的周期性混合,据此,本文提出了一个新的两阶段成矿模式。Uwamuki Kuroko is the most typical kuroko-type deposit in Japan. It is located in the aborted island-arc rift zone formed in the Miocene epoch and is hosted in the felsic volcanic package within a bimodal (basalt-rhy-olite) sequence. The Uwamuki deposit consists of underlying pipe-like siliceous ore and layered massive black ore, showing vertical metal zoning from yellow ore upwards to black ore. In order to study the sources of ore-forming metals, which is a long debated and unsolved issue, Re-Os isotope and He isotope compositions of the ore and host rock were systematically analyzed. The rhyolites hosting the siliceous ore yield R/Ra ratios ranging from 0. 93 to 1. 14, suggesting that the felsic magma should be mainly formed by remelting of the continental crust. The massive black ores have relatively high 187Os/188Os ratios (2. 246 - 7. 608), showing the Os came from either crust-derived sediments or underlying basement rocks in the ore district. The stringer or stockwork siliceous ore and massive yellow ore as well as occasional black ore yield relatively low 187Os/188Os ratios (0. 432 -0. 793), indicating that the ore Os has two possible sources, i. e. mantle and continental crust, which contributed about 57%-89% of mantle Os and 11%-43% of crust Os to the Uwamuki deposit, respectively. A clear vertical rhythmic variation of 187Os/188Os ratios in the layered massive black ore has been observed, which suggests the periodically mixing among ore-forming fluids (metals) in various stages. Based on the fluid mixing and metal sources, a new two-stage model is proposed to illustrate ore-forming processes of the Uwamuki kuroko deposit.

关 键 词：日本黑矿 铼-锇同位素 氦同位素 成矿物质 成矿金属 黑矿型矿床 硫化物矿床 

分 类 号：P619.21[天文地球—矿床学]