EXPLORATION METHODS

Regional geological survey should be carried on for the determination of the Kuroko horizon and for discarding unfavourable areas where the ore horizon may have been eroded or uneconomically deeply seated.

" Observation of old mine site and collecting of antique information are also important work, because Kuroko type deposits would be distributed in regular way related to the tectonic setting on that time and have a tendency coming together in rectangle area called Cluster."

" Modern and practical exploration methods such as Element variation, Magnetic susceptibility and Clay mineral assemblage have been devised by means of footwall rocks because of following reasons; "

(1) The footwall rocks were emplaced there before Kuroko mineralization that the rocks must be affected by alteration effect.

(2) The footwall unit is distributed the whole area of all Kuroko cluster therefore the method is expected to be applicable to all Kuroko region.

"(3) Hence the footwall unit is relatively uniform and homogeneous composition, the variation of elements or minerals would be comparative between altered and unaltered area. "

" In case of Fukazawa deposit in the central Hokuroku district, Low magnetic susceptibility anomaly is the most extensive distribution as extended as 3Km in long and 1.5Km in width compaired to the other modern exploration methds mentioned above. The anomaly is resulted from substitution of Pyrite after Magnetite affected by the high sulfur condition during Kuroko mineralization. "

" Low Na2O anomaly defined by the content less than 0.4% is the most effective, because the boundary is very clear and abruptly changes to the un-altered rock contained 3 to 5% Na2O. The anomaly is considered to be generated by the decay of Na rich plagioclase. "

Clay mineral assemblage is also useful and easy to detect by naked eye. There are two trends of zonation; One is lateral change in the footwall unit from Sericite-Chlorite zone in central part to mixed layered clay mineral assemblage in the peripheral part. Anther is vertically changing from mixed layered clay mineral zone in the ore horizon to smectite zone in the hanging wall unit.

"In consequence of argilization and pyritization, Geophysical anomaly such as low registivity and high conductivity anomaly could be detected as a inverted 'V' form by means of surface exploration. "



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