On the Geology and the Ore Deposit of the Takatama Mine

Especially on the Rock Alteration

Abstract

The Takatama Mine, located in Fukushima Prefecture is a typical epithermal ore deposit. The deposit consists of nearly one thousand veins. Quartz gangue comprises two-thirds of the veins and adularia gangue the remaining one-third. This mine, the largest gold producing unit in Japan, has in the past thirty-five years produced 1, 690, 000 tons of ore containing 21 tons of gold and 204 tons of silver.
The eight types of vein quartz into which the writer has classified the gangue material appear clearly selective—above the veins, in between and below—in the central portions or extremities —in the bonanzas and in the barren parts.
It was ascertained that the habit, size and fineness of the gold particles and quartz crystals contained in the veins adhere to a formula and can be accurately predicted by the position of the gold in the vein.
Statistical studies made on the habits and textures of the gold and quartz in correlation with their position in the ore veins have proved very helpful in prospecting. From a segment of newly discovered veins at an outcrop or underground it can be determined by such studies, whether these veins would be worth while further prospecting and in case considered so, in which direction the prospecting adits should be driven.
The country rocks of the Takatama deposit were formed by severe and extensive alternation of liparitic tuff and shale by silicification and alkalization (adularization). Only two or three other cases in Japan can be cited of instances where the gangue minerals contain a high percentage of adularia. The adularization of the country rock is a type of alteration rather uncommon in Japan.
From the results of a detailed survey and observation of both types of alterations, it can almost no longer be said that the country rock alteration was the result of infiltration of the mineral solutions through both walls of the fissures at the time of ore formation. In the writer's opinion the excessive siliceous solutions, barren in nobles, ascended before the mineral solutions and first silicified to a high degree the coarse textured rocks. Immediately after both types of alteration were completed, the residue, namely the mineral solutions bearing gold and silver ascended, depositing many gold and silver bearing ore veins in the alkalized areas. The highly silicified country rock is found extensively on the summits of hills as cap rock. Alkalization took place below this area where silicification was weaker.