Exploration and development of the Fukusen vein group of the Yamada deposit， Hishikari Mine

Abstract

The Fukusen vein group， a low-sulfidation style epithermal gold-silver vein system， is located in the southeastern area of the Yamada deposit， the Hishikari Mine.
The Fukusen vein group， hosted by the andesitic volcanic rocks， consists of nine sub-parallel quartz veins including six undeveloped veins so far with minor amount of adularia and smectite and generally strike N30° E-N50° E and dip 70° SE-90°.
Exploration activities indicate that the Fukusen No.1 vein extends at least 650m horizontally and 90m vertically with the average thickness of 1.65m and average gold grade of 25 grams per ton. The veins striking N50° E tend to be thicker and higher grade than the veins striking N30° E. Further exploration and development revealed that the Fukusen vein group is strictly controlled by the sub-horizontal argillized layer at the shallower part of the veins.
Volcanic rock samples are taken from the underground drill cores and X-ray diffraction analysis was applied to identify the hydrothermally altered clay mineral assemblages to delineate the thermal gradient responsible for the mineralization of the Fukusen vein group. It is suggested that the northeastern part of the Fukusen vein group is within the quartz-chlorite zone and further exploration is recommended.