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

对贝西型闪锌矿（主要在贝西及其邻近地区、日立和下川）的电子探针分析表明，在接触变质过程中，闪锌矿的Mn/Zn和Co/Zn原子比可能显著增加，而Cd/Zn原子比基本不变，除下川外，溶液沉淀闪锌矿的Mn/Zn和Co/Zn原子比均小于2 × 10 ~（-1）<-3>。在Shimokawa，Mn/Zn和Co/Zn比值变化很大，高Co/Zn比值出现在富铜矿的闪锌矿中。在Shimokawa和Hitachi，Cd/Zn比值大多在2 × 10 - 4以内<-3>。根据<-3>热液与闪锌矿之间的平衡分馏模型，在300-350 ℃时，Besshi及其邻近地区成矿作用的初始溶液中的SIGMAm_<Cd>/SIGMAm_<Zn>和SIGMAm_<Mn>/SIGMAm_<Zn>比值分别估计为2^-3 x 10^<-3>和低于20^-30;它们与EPR 21 ° N时的高温溶液的比值非常相似。低SIGMAm_<Cd>/SIGMAm_<Zn>和SIGMAm_<Co>/SIGMAm_<Zn>比值是日立矿床溶液的特征。下川与铜矿化有关的热液具有较高的<Co>SIGMAm_2/SIGMAm_3<Zn>比值，并对富铜矿石中富钴闪锌矿的形成起了重要作用，结合已有的矿床地质和硫同位素资料，认为下川矿床形成于沉积物覆盖的洋脊上，而别市及其邻近地区的矿床形成于远离陆地的无沉积物洋脊上。日立和柳原矿床可能与长英质火山作用有关。马里亚纳海槽硫化物存款的富铅矿石矿物学可以解释与硅铝壳的成因联系。

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.