Stockwork siliceous ores at Kosaka mine, Akita prefecture-With special reference to distri-bution of ore metals and relation to bedded ores

Abstract

The kuroko deposits of Kosaka mine consist of several types of ores such as black ore (BO), semi-black ore (SBO), yellow ore (YO), and siliceous ore (SO). The SO may be subdivided into black-SO (BSO) and yellow-SO (YSO) on the basis of ore mineralogy and further into massive-SO and stockwork-SO from the structural and textural characteristics. Present study on the stockwork-SO has provided the following information:
(1) Orebodies of stockwork-SO in general display a sort of cylindrical form with average dimension of about 40m×20m×70m.
(2) In terms of ore types included, they are classified into two groups, i.e., Uchinotai type characterized by the combination of YSO-YO-SBO-BO and Uwamuki type of YSO-BSO-BO. The Uchinotai type are developed dominantly in the central portion of the deposits, while the Uwamuki type are restricted in occurrence to their marginal portion.
(3) Distinct chemical zoning is recognized in some orebodies named as 4D-W (Uwamuki type), P-O (Uchinotai type) and 2D-W (Uwamuki type), i.e., Cu→Cu+Zn→Cu+Zn+Pb in the former two and Cu→Cu+Zn→Zn+Pb in the latter, in vertically ascending order. The zoning patterns in the orebodies 4D-W and 2D-W are obviously asymmetrical on the vertical section.
(4) Paying attention to total composition, the P-O orebody is slightly enriched in Cu and depleted in Zn+Pb as compared with the 4D-W orebody. In view of the distribution of Cu, Pb, Zn and Ag among different ore types, the ore type BSO in the 4D-W orebody is assumed to be chemically equivalent to the sum of YO, SBO and a part of BO in the P-O orebody.