抄録
The Kamioka Mine, working the largest lead-zinc deposits in Japan, lies in the eastern corner of the Hida gneiss complex. Around the mine, lenticular crystalline limestone beds are often intercalated among biotite-hornblende gneiss which is generally disposed in a NE direction and has NE fold axes which pitch 45°SW.
The ore deposits are closely related to the crystalline limestone beds by pyrometasomatic replacement which attacked some minor folding crests to form typical skarn ores of the so-called "Mokuji ore body". The "Shiroji ore body" is a peculiar type of deposit intimately related to the skarn Mokuji ore body. It carries the distinct features of a hydrothermal deposit and is localized in narrow spaces controlled by fissure intersections which are quite different from those of the Mokuji ore body.
The Shiroji ore body includes sphalerite, galena, chalcopyrite, pyrite, hematite, arsenopyrite, and silver minerals as ore, and quartz, chlorite, sericite, and carbonate as gangue. The ore is enclosed in a zone of silicification consisting of quartz-(adularia)-sericite-carbonate. All surrounding rocks have been strongly altered by silicification, sericitization, chloritization, feldspathization and argillization.
The fracture system controlling the Shiroji ore body is disposed regularly in three directions, namely, NE, NS and EW. The intersections of the fractures trend NE and pitch 45°SW, and offer excellent room for ore deposition.
Based on the field occurrence, the mineral assemblages and the nature of the wall rock alteration, the writer concludes that Shiroji ore bodies were produced under hydrothermal(mesothermal) conditions which followed deposition of the pyrometasomatic Mokuji ore bodies.
