Resource evaluation of mineral deposit in southern Hokkaido, Japan, utilizing airborne magnetic and radiometric data

摘要

The Metal Mining Agency of Japan carried out the helicopter-based magnetic and radiometric survey using a stinger mounted magnetometer over the Shakotan Peninsula referred to as Block 2 region in the southwest Hokkaido last year. Magnetic data and also potassium, uranium and thorium gamma-ray spectral data with high resolution were acquired along flight lines oriented 30 degree clockwise from the North, spaced 200m apart and with a mean terrain clearance of 60-80m.The hydrothermal activities associated with mineralization and alteration might have led the destruction and redistribution of magnetic minerals such as magnetite in the host rocks, and the formation of various K-bearing minerals such as adularia, illite and alunite. These the hydrothermal alteration halos can often cover an area of at least several square kilometers, and can be detected by reconnaissance surveys utilizing high resolution airborne magnetic and radiometric sensors.The magnetic data were processed using the vertical derivative filter, pseudo-depth slicing, Euler deconvolution and analytic signal in order to obtain information on lineament and fault systems. Some promising sites were recognized by interpreting some maps in terms of magnetic data and those related to radiometric data. By considering these promising sites, we set five highly prospected areas with the known geologic information, the images of Landsat-TM and SPOT, and geochemical anomalies on the stream sediment.At least 25 small discrete zones of potassium enrichment are observed within the very large semicircular volcanic complex located at the southeast of Yoichi in the Yamato-Otarumatsukura Prospect. In the Todoroki-Nakanosawa Prospect, several zones of anomalous potassium, uranium and thorium gamma-ray spectral values are present topographically below volcanic rocks of the Yobetsu Formation and along the prominent NNW-trending fracture zone within which the Todoroki and Nakanosawa mineralizations are placed. In the Tamagawa-Taishu Prospect, Cenozoic pultons intrude the main NW-trending anticlinal dome. There are some mineralizations at the boundaries between plutons and the anticline. These areas are rated as having a very high potential for hosting mineralization.