The Hishikari gold deposit: an airborne EM discovery

CIM Bulletin, Vol. 78, No. 876, 1985

IAN M. JOHNSON, Senior Geophysicist, Scintrex Limited, Toronto, Ontario and MINORU FUJITA, Mining Engineer, Metal Mining Agency of Japan, Tokyo, Japan

A helicopter-borne geophysical survey was flown in 1978 over selected areas on Kyushu Island, Japan. The principal sensors were a moving source electro-magnetic system and a magnetometer. Maps of apparent resistivity were generated from the EM data. Based on the resistivity signature of known deposits within the survey areas, targets were selected for ground follow-up. Drilling of one such target in late 1980 resulted in the discovery of a gold deposit from which full production will begin in the summer of 1985. The deposit contains a minimum 120 tonnes (3.86 million ounces) of recoverable gold and is the largest in Japanese history. The deposit is in a geological setting previously unsuspected of hosting precious metal deposits. The case history suggests a preferred exploration strategy which might be employed in other similar geological environments.

Keywords: Mineral exploration, Electromagnetic survey, Drilling, Gold deposits, Geophysics, Hishikari gold deposits.