摘要
选择西南太平洋冲绳海槽（ＯｋｉｎａｗａＴｒｏｕｇｈ）现代海底烟囱硫化物矿床、日本小坂矿山上向（Ｕｗａｍｕｋｉ）黑矿（第三纪）和中国西南呷村黑矿型矿床（三叠纪）进行了矿石地球化学比较研究。黑矿型矿床矿石吨位－品位模式与其他火山成因块状硫化物（ＶＭＳ）矿床类似，矿田（２０－５０ｋｍ２）矿石吨位与单个喷气－沉积型（Ｓｅｄｅｘ）矿床相当，金属总量４－６Ｍｔ，为矿田范围内热液流体搬运的最大金属量。与洋脊环境ＶＭＳ矿床相比，岛弧裂谷环境产出的黑矿型矿床相对富Ｐｂ、Ａｓ、Ｓｂ、Ａｇ、Ａｕ等，相对贫Ｃｕ、Ｆｅ、Ｓｅ等。不同时代的黑矿型矿床的矿石化学存在一定差异。矿床硫化物成分受岛弧张裂程度制约，与岛弧壳层物质及海相火山岩系密切相关，证实成矿物质来源于壳层火山岩系。古代与现代黑矿型矿床块状矿体内元素化学分带型式十分一致，揭示硫化物堆积过程高度类似。基于现代海底烟囱－硫化物生长过程实地观察和古代黑矿的具体剖析，建立了古代黑矿硫化物淀积新模式，强调硫化物堆积发生于已固结的结壳或烟囱及火山碎屑堆下部，表现为开放空间的充填、交代与动态迁移。
A comparative study have been made on geochemistry of sulfide ores from sulfide mounds in the Okinawa trough,Pacific, Uwamuki kuroko deposit in Kosaka mine, Japan and Gacun kuroko-type deposit,S.W. China. The ore tonnage-grade model of Kuroko-type deposits is similar to that of other volcanogenic massive sulfide deposits. The tonnage of sulfide ores from Kuroko-type deposits or ore clusters in a field with 20-50 km2 equals to that of indivdual Sedex-type deposit, the total metal amount is about 4-6Mt for the two type deposits, suggesting that the hydrothermal fluids could carry about 4-6Mt metals.Comparing with volcanogenic massive sulfide deposits in the mid-oceanic ridges,Kuroko-type massive sulfide deposits occurred in intrar-arc rifting zone and back-arc rifting basin show enrichment in Pb, As, Sb, Ag, Au, etc,and depletion in Cu,Fe, Se,etc. The chemical compositions of Kuroko-type sulfide ores are controlled by the intra-arc rifting degree,and related to submarine volcanic rocks and crustal naturecontinental or oceanic), indicating that the ore-fonning metals derived from volcano-sedimentary rocks through which hydrothermal fluid circled and discharged. The patterns of chemical zoning for major and minor metal elements in the ancient massive orebodies are identical to those in modern analogue, suggesting a similarity in processes of sulfide deposition on ancient and modern seafloor. Based on observation on growth processes of sulfide chimneys on seafloor and investigation on ancient Kuroko-type deposits, a new model on sulfide deposition have been established,in which sulfides fill and accumulate in open space beneath solidifying crust or pyroclastic layer and replace low-temperature sulfide assemblage to result in outward migration of metal components.
出处
《地球化学》
CAS
CSCD
北大核心
1996年第3期228-241,共14页
Geochimica
基金
"古代与现代黑矿型块状硫化物矿床比较研究"中日合作项目
日本"国际产业技术研究事业"基金
