Geochemical Study on the Granite and Ore Fluids in the Tohoku District.

作为解决花岗岩类是否成矿问题的第一步，选取了东北地区的一些花岗岩类岩体。通过野外考察、显微镜观察、模态分析和流体包裹体的加热/冻结实验，对花岗岩体进行了检验。结果如下：1、和田花岗闪长岩：晚第三纪至早古近纪的花岗闪长岩伴生有铜铅锌钼铋金银矿化。根据野外观察和显微镜观察，该花岗闪长岩为较均一的中粒岩类。花岗闪长岩的东南部角闪石较富，西北部钾长石较富。这些结果表明，西北部是花岗岩体的后期和(或)上部的固化。这与西北部K-Ar年龄矿床的存在丰富而年轻的事实相一致。2、日正花岗岩杂岩(山形县莫高岗)：这种第三纪花岗杂岩伴生有铜铅锌矿化。花岗岩杂岩由石英闪长岩和花岗闪长岩组成，后者侵入前者。由于花岗闪长岩为半斑状，其周缘部分为流纹岩，花岗杂岩被认为侵入地壳浅层。花岗闪长岩石英中的流体包裹体由三相包裹体和气液比差异较大的两相包裹体组成。NaC l当量浓度与均一温度呈正相关，这表明沸腾伴随着浅层花岗闪长岩的上升而发生，沸腾时释放的流体非常咸。矿床是盐化成矿流体的稀释作用形成的。

As a first step to obtain the answer of the problem that a granitoids is mineralized or not, some granitic bodies in the Tohoku district were chosen. The granitic body was examined on the basis of field survey, microscopic observation, modal analysis, and heating/freezing experiment of fluid inclusion. The results obtained are as follows.1, Wasada granodiorite (Higashi-Tagawa-gun, Yamagata Prefecture) : The granodiorite of late Ceata-ceous to early Paleogene age accompanies Cu-Pb-Zn-Mo-Bi-Au-Ag mineralization. According to field servey and microscopic observation, the granodiorite is relatively homogeneous and medium grained. Hornblende is richer in the southeastern part and potash feldspar is richer in the northwestern part of the granodiorite. These results indicate that the northwestern part is solidified later and/or upper part of the granitic body. This is in harmony with the fact that the existence of the ore deposits is abundant and younger in K-Ar age in the northwestern part.2, Nissho granitic complex (Mogami-gun, Yamagata Prefecture) : This granitic complex of Tertiary age accompanies Cu-Pb-Zn mineralization. Quartzdiorite and granodiorite composes the granitic complex and the latter intrude into the former. Because the granodiorite is semi-porphyritic and its peri-pheral part grade into rhyolite, the granitic complex is considered to be intruded into shallow level of the crust. The fluid inclusion in quartz of the granodiorite is composed of three-phase inclusion including NaCl daughter mineral and two-phase inclusion having large different vapor/liquid ratio. NaCl-equivalent concentration is positively correlated with homogenization temperature.These results lead that the boiling occurred accompanied with ascending of the granodiorite in the shallow level, and the fluid released on the boiling is very saline. The ore deposits were formed by the dilution of the saline ore fluid.