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Sulfur isotope geochemistry of Besshi-type deposits

别子型矿床硫同位素地球化学

基本信息

批准号：
08640610
负责人：
YAMAMOTO Masahiro
金额：
$ 1.47万
依托单位：
Okayama University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1996
资助国家：
日本
起止时间：
1996 至 1998
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-08640610/
关键词：
Besshi-type deposit Sulfur isotope ratio Tsuchikura mine Pyrite Chalcopyrite 工倉鉱山キ-スラーガー

项目摘要

The deposit of the Tsuchikura mine, located near Lake Biwa, occurs in an Early Jurassic non-metamorphosed accretionary complex that contains basaltic volcanic rocks, probably of Carboniferous age, and Carboniferous to Triassic chert. The Tsuchikura deposit consists of three deposits : the Eastern, Middle and Western deposits. Each deposit consists of a number of lenticular or fusiform orebodies. The size of the orebodies is very variable, ranging from pebble to 20,000 tons. Sulfur isotope ratios of sulfide minerals in the ore specimens from the deposit of the Tsuchikura mine are distributed in a range from -0.8 to +5.4*, mostly from +0.5 to 3.0*, close to the previous data (from +1 to +3*) by Miyake and Sasaki (1980). The distribution range is also similar to the major Besshi-type deposits of the Sambagawa terrain. Sulfur isotope fractionation between coexisting pyrite and chalcopyrite is not uniform. Of 11 pairs, 5 pairs show the normal fractionation (that means the delta^<34>S value of pyrite is higher than that of chalcopyrite), whereas 6 pairs show the reverse fractionation. This may be largely due to spatial rearrangement of the initial orebodies to the present form. Sulfide minerals mostly pyrite from host rocks (siltstones, sandstones, basaltic rocks) exhibit remarkably low delta^<34>S values ranging from -49.3 to -2.6*, distinctly different from the delta^<34>S values for sulfide minerals of ores. The low delta^<34>S values may indicate the bacteriogenic origin of host rock sulfides, although it seems peculiar that basaltic rocks also have extremely low delta^<34>S values. Ridge basalts usually have sulfur isotope ratios around 1* or so. The sulfides in the present samples may have been migrated from the nearby sediments. More detailed discussion will be done in near future, when sulfur isotope data are obtained for rock specimens of low sulfur contents.

土仓矿的存款位于琵琶湖附近，产于一个早侏罗世的非变质增生杂岩中，该杂岩含有玄武质火山岩，可能是石炭纪的，以及石炭纪至三叠纪的硅质岩。土仓存款由三个矿床组成：东部、中部和西部矿床。每一个存款都由若干透镜状或纺锤状矿体组成。矿体的大小变化很大，从卵石到2万吨不等。土仓矿存款矿石样品中硫化物矿物的硫同位素比值分布在-0.8 ~+5.4* 之间，大部分在+0.5 ~3.0 * 之间，与Miyake和Sasaki（1980）的数据（+1 ~+3*）接近。其分布范围也类似于Sambagawa地形的主要Besshi型矿床。共生黄铁矿和黄铜矿之间硫同位素分馏不均匀。在11对中，有5对表现为正分馏（即黄铁矿的δ ^<34>S值高于黄铜矿），6对表现为反分馏。这在很大程度上可能是由于初始矿体在空间上重新排列成现在的形式。含矿岩石（粉砂岩、砂岩、玄武质岩石）中的硫化物矿物（主要是黄铁矿）具有非常低的δ ^<34>S值，范围为-49.3 ~-2.6*，与<34>矿石中硫化物矿物的δ ^ S值明显不同。低δ ^<34>S值可能表明寄主岩石硫化物的细菌成因，尽管玄武岩也具有极低的δ ^ S值似乎很奇怪<34>。脊玄武岩的硫同位素比值通常在1* 左右。目前样品中的硫化物可能是从附近的沉积物中迁移而来的。今后在获得低硫岩石样品的硫同位素数据时，将作更详细的讨论。