1983 Volume 33 Issue 178 Pages 73-86
In the Nakatatsu mine of pyrometasomatic lead and zinc deposits, the recent systematic exploration activities in the Kurotodo area have resulted in the discovery of new minable orebodies with further ore potentials to be explored. The Kurotodo deposits are located in the westernmost part of the Nakatatsu mine area. It is revealed that in the Kurotodo area the Fujikuradani limestone formation of possible hosts of ore deposits is emplaced in a wider area at the depth.
In the northern, central and southern areas of the Fujikuradani formation are found new mineralized zones associated with skarn minerals which consists mainly of garnet with some clinopyroxene, wollastonite, etc.
In the mineralized zones in the northern area are found promissing orebodies, several of which in the east are now under development.
In the northern area the skarn minerals consist largely of garnet in the east mineralized zone, and are relatively rich in clinopyroxene in the west mineralized zone.
In the central and southern area the mineralized zones consist predominantly of garnetiferous Shiroji, composite of quartz calcite and ore minerals, and wollastonite. The Kurotodo deposits comprise lead and zinc orebodies of irregular masses in shape in the same manner as the main deposits of Nakatatsu mine. On the other hand in the central area are partly found vein-like orebodies in shape.
The study of Pb: Zn: Cu ratio [π-Pb=Pb(%)×10×100/(Zn(%)×1+Pb(%)×10+Cu(%)×100)] has revealed that the Kurotodo deposits are remarkably higher in π-Pb than the main Nakatatsu deposits and that the areas high in π-Zn or π-Cu are confined only to small areas in the east mineralized zone of the northern area.
It has been also revealed that the Kurotodo deposits are of low value in Ag/Pb ratio with the exception of a part of the north mineralized zone.
In these respects, the Kurotodo deposits are different from the main deposits in the Nakatatsu mine. The mineralization in the area is controlled by faults such as the Ohno fault and the Uwaban fault with a east-west trend and by fissure systems with a north-south and northeast-southwest trend.
The igneous rock related to the mineralization in the area is presumed to be quartz porphyry which is located northeast of the Senno deposits and is considered to be the related igneous rock of the main ore deposits in the Nakatatsu mine.
