Concentration Mechanism of Base Metal Elements in Vein-Type Deposits of Tertiary Age

本项目旨在阐明分布于日本第三纪火山岩区的浅成热液脉型矿床的基本金属元素的富集机制和环境条件。为此，我们对这些矿床进行了多方面的研究。取得的主要成果如下：(1)对金银矿区(伊豆半岛西部、福岛县与泽区、北海道西南部)的地质环境进行了研究；(2)获得了基本金属和金银矿区(绿凝灰岩、伊豆、九州)的硫、碳、氧同位素组成；(3)研究了金银矿床(青凝灰岩、伊豆、九州)中的流体包裹体。(4)获得了矿石矿物(如Au-Ag矿物、闪锌矿)的化学成分；(5)研究了金银矿区(伊豆半岛西戈什)的热液蚀变，利用(1)至(5)的数据，建立了最可能的热液系统伴生脉型矿床的模型。将该模型与活动地热系统的模型进行了比较。浅成热液脉型矿床与活动地热系统特征特征的不同，是气-液-岩相互作用的不同表现，有必要对脉型矿床中贱金属元素的富集机理进行进一步的理论和实验研究。

The purposes of this project are to clarify concentration mechanism of base metal elements and environmental conditions for epithermal vein-type deposits which are distributed in Tertiary volcanic regions in Japan.For these purposes we have studied several aspects of these deposits. They are: (1) geology, (2) mineralogy, (3) stable isotopes, (4) fluid inclusions, and (5) hydrothermal alterations.main results obatained are as follows:(1) Geologic environments of gold-silver mining districts (western part of Izu peninsula, Yonezawa district of Fukushima Prefecture, Southwestern part of Hokkaido) have been eleucidated, (2) Sulfur, carbon and oxygen isotopic compositions of base metal and gold-silver mining districts (Green tuff region, Izu, Kyushu) have been obtained, (3) Fluid inclusions in gold-silver deposits (Seigoshi, Yatani deposits) have been studied. (4) Chemical compositions of ore minerals (e.g. Au-Ag minerals, sphalerite) have been obtained, (5) Hydrothermal alteration in gold-silver mining district (Seigoshi in Izu peninsula) has been studied.Using these data from (1) to (5), the most likely model for hydrothermal system accompanied by vein-type ore deposition was constructed. This model was compared with that for active geothermal system. The differrences in the characteristic features of epithermal vein-type deposits and active geothermal system were different behavior of gas-liquid-rock interactions.Further theoretical and experimental works on the concentration mechanism of base metal elements in vein-type deposits are necessary.