Mineralogical and Geochemical Comparison between Non- and Weakly- Metamorphosed Besshi-type Deposits and Ridge Sulfide Deposits

非变质和弱变质别子型矿床与脊状硫化物矿床的矿物学和地球化学比较

基本信息

批准号：
06640616
负责人：
KASE Katsuo
金额：
$ 1.41万
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：
1994
资助国家：
日本
起止时间：
1994 至 1996
项目状态：
已结题

项目摘要

Electron microprobe analyzes of sphalerites from Besshi-type deposits, mainly at Besshi and its vicinity, Hitachi, and Shimokawa, revealed that the Mn/Zn and Co/Zn atomic ratios may have markedly increased during contact metamorphism, while the Cd/Zn ratios remained unchanged.Except for Shimokawa, the Mn/Zn and Co/Zn ratios of sphalerite precipitated from solutions are found to be both mainly lower than 2 x 10^<-3>. At Shimokawa, the Mn/Zn and Co/Zn ratios are highly variable, and high Co/Zn ratios occur in sphalerite of Cu-rich ores. The Cd/Zn ratios are mostly within 2 x 10^<-3> at Shimokawa and Hitachi. The ratios display a wide variation within 8 x 10^<-3> in the deposits at Besshi and its vicinity.Based on the equilibrium fractionation model between hydrothermal solution and sphalerite, the SIGMAm_<Cd>/SIGMAm_<Zn> and SIGMAm_<Mn>/SIGMAm_<Zn> ratios in the initial solutions responsible for the mineralizations at Besshi and its vicinity are estimated to be 2^-3 x 10^<-3> and lower than 20^-30 at 300-350ﾟC,respectively ; they are quite similar to the ratios of high-temperature solutions at EPR 21ﾟN.Low SIGMAm_<Cd>/SIGMAm_<Zn> and SIGMAm_<Co>/SIGMAm_<Zn> ratios characterize the solutions for the deposits at Hitachi. At Shimokawa, the hydrothermal solution related with Cu-mineralization was high in the SIGMAm_<Co>/SIGMAm_<Zn> ratio and contributed to the formation of Co-rich sphalerite in the Cu-rich ores.These data coupled with available ones including ore geology and sulfur isotope ratios suggest that the deposits at Shimokawa formed on sediment-covered ridge, and those at Besshi and its vicinity on sediment-free ridge far-off from land. The deposits at Hitachi and Yanahara may be genetically related with felsic volcanism. Lead-rich ore mineralogy of the sulfide deposit at Mariana Trough may be explained by the genetical connection with sialic crust.

对Sshi型seposits sphalyz的电子探针分析E MN/Zn和CO/Zn原子比可能没有变化。 <-3>在Shimokawa，Mn/Zn和Co/Zn比率高度可变，Zn比率在Cu富矿石的SphaLite中出现。在Besshi的沉积物中，在水热溶液和SphaLite之间的平衡分级模型上。据估计，在300-350 ey时估计为2^-3>，低于20^-30，与EPR 21°N.LOW SIGMAM_ <ZN>和SIGMAM_ <CO的高温解决方案的比率非常相似。 >/sigmam_ <zn>比率是在shimokawa的s的解决方案。 Shimokawa在泥沙覆盖的山脊上形成，Tet Besshi及其OTS OTS OT-FREEE RIDGE远离土地，与Felsic火山矿相关。唾液壳。