GEOCHEMICAL STUDIES ON MINERALIZATION ACCOMPANIED BY TERTIARY GRANITOIDS

本研究的目的是寻找花岗岩类矿化或不矿化的因素。为此，我们选取了日本东北部的几个第三纪成矿花岗岩类--大山花岗岩、黑森花岗岩和日商花岗岩，以及山阴地区的一个贫瘠花岗岩类--云木花岗岩，对其岩石结构、岩石矿物化学和热液蚀变进行了研究。从铁钛氧化物矿物结构和斜长石的化学成分和分带来看，黑森花岗岩是在高温下侵入并迅速冷却的。大山花岗岩与黑森花岗岩同时或稍晚侵入，冷却缓慢，热液蚀变影响。这些结果是基于磁铁矿中钛铁矿-板钛矿细、长石化学成分范围宽、Rb和K富集以及Myrmeite发育的事实。泰山花岗岩北方热液蚀变强烈，导致镁铁质矿物绿泥石化，Sr富集，形成脉状矿化。日商花岗岩以较长英质成分侵入，冷却缓慢，在较长的温度范围内形成脉状矿化，而云木花岗岩为等粒花岗岩，成分较均匀，结晶分异范围小。Kumogi花岗岩中的钠长石环发育程度很小。研究表明，Kumogi花岗岩是在高氧化环境下快速冷却的，通过对花岗岩的矿物结构、矿物和岩石化学成分以及热液蚀变的详细研究，可以获得岩浆期和热液期的结晶和成矿信息。将这些方法应用于其它花岗岩类，可以得到花岗岩类矿化或不矿化的充分必要条件。

This study aims to search the factors which provide a granitoid is mineralized or barren. For this aim, we selected some mineralized Tertiary granitoids, the Daiyama, Kuromori and Nissho granites, in Northeast Japan, and a barren granitoids, Kumogi granite, in San-in district, and examined their rock texture, bulk rock and mineral chemistry and hydrothermal alteration.From texture of Fe-Ti oxide minerals and chemical composition and zoning of plagiocalse, the Kuromori granite intruded in a high temperature and cooled rapidly. The Daiyama granite intruded at the same time or a slightly later than the Kuromori granites, and cooled slowly with affecting hydrothermal alteration. These results are based on the fact that fine ilmenite-lamellae in magnetite, wide chemical composition ranges of feldspars, enrichment of Rb and K,and development of myrmekite. The hydrothermal alteration occurs strongly in the northern part of the Daiyama granite, resulting in chloritization of mafic minerals, reaching of Sr and formation of vein-type mineralization. The Nissho granite intruded in a more felsic composition and cooled slowly, resulting in a vein-type mineralization in a long temperature range.On the other hand, the Kumogi granite is equi-granular and has rather homogeneous composition, meanin small range of crystallization differentiation. Development of albite-rim in the Kumogi granite is small. It is concluded that the Kumogi granite cooled rapidly in a high oxidized conditions.Detailed examination of mineral texture, mineral and bulk rock chemistry, and hydrothermal alteration can obtain the information of crystallization and mineralization during the magmatic and hydrothermal stages. Adopting these methods to other granitoids, we can obtain necessary and sufficient conditions whether the granitoids are mineralized or barren.