Study of hydrothermal mineralization in Otaru district, Hokkaido, with special reference to acid sulfate alteration.

日本群岛北部的日本海一侧形成了一个被称为绿色凝灰岩地区的地质省，在那里发生了许多矿化作用，包括金银矿脉、黑子矿床和贱金属矿脉。Otaru位于绿色凝灰岩地区的北端。Akaiwa区是该项目的主要目标，Akaiwa东南13公里处的Asari区也进行了研究。Shimo-Akaiwa(海拔279米)由强烈硅化的火山岩(安山岩？)零星含有明矾石的。在海滨，硅化岩被分带蚀变、泥质(主要是地开石)带、伊利石(绢云母)-蒙皂石带、绿泥石带和丙烷岩所包围。硅化岩石在孔隙中含有尺寸可达2毫米的一水硬铝石晶体。泥质带中含有叶蜡石和/或锆石。矿物的这种分布似乎是含硫酸性热液氧化的结果。“角砾岩管”垂直延伸。管道中硅化碎屑的逆级配表明，它是由上升流体的剧烈运动形成的。用流体包裹体均一化温度、硫化物矿物与硫酸盐矿物的硫同位素分馏、矿物稳定性等方法进行地质测温，得到2 0 0~2 5 0ﾟC.阿凯瓦获得了9.7×0.5 Ma和10.0×0.5 Ma两个K-Ar年龄，Asari获得了6.1×0.6和4.8×0.4 Ma的K-Ar年龄。考虑到浅草以南丰叶报告的较年轻年龄，自中新世以来，热液活动向南迁移。

The Sea of Japan side of the northern part of Japanese Islands forms a geologic province called the Green Tuff region where occur many ore mineralizations including gold-silverveins, kuroko deposits, and base metal veins. Otaru is located at the northern end of the Green Tuff region. Akaiwa district was main target of this project and Asari district, 13 km southeast of Akaiwa was also studied.Mt. Shimo-akaiwa(279m above the sea) consists of intensely silicified volcanic rock (andesite?) containing alunite sporadically. At sea-shore, a silicified rock is surrounded by zoned alteration, argillic(mainly dickite) zone, illite(sericite)-smectite zone, chlorite zone, and propylite. The silicified rock contains diaspore crystals up to 2mm in size in the pore. In the argillic zone contains pyrophyllite and/or zunyite. This distribution of minerals seems to be resulted from oxidation of sulfur-containing acid hydrothermal solution."Breccia pipes" extend vertically. Inverse grading of silicified clast in a pipe suggests that it was formed by vigorous movements of ascending fluid. "Layered parts" are composed of fine-grained powders of quartz and alunite with normal size grading and seem to be formed in small hot lakes.Geothermometry using homogenization temperature of fluid inclusion, sulfur isotope fractionation between sulfide and sulfate minerals, and mineral stability gave 200-250ﾟC.Two K-Ar ages, 9.7*0.5 and 10.0*0.5 Ma have been obtaind from Akaiwa, and two, 6.1*0.6 and 4.8*0.4 from Asari, all for alunite. Considering younger ages reported from Toyoha, south of Asari, the hydrothermal activity migrated southwards since the Miocene age.