Promising exploration margins around known kuroko deposits can well be evaluated in terms of the Na2O anomaly reported previously (HASHMOUCHC et al., 1981). In the present study, using 662 samples from 61 drill holes in the Fukazawa mine area, an attempt has been made to figure out statistically the metallic contents and their variations in the footwall mineralization zone, which is essentially included within the promising margin delimited from the Na2O anomaly. The results obtained are as follows.
1) Two economically significant thresholds in metallic distribution can be set at Cu 0.07%, Pb 0.18% and Zn 0.29% as a lower limit and at Cu 0.5%, Pb 1.4% and Zn 3.1% as a higher one.
2) The anomalous zones delimited by the lower thresholds are about two times as large as the presently known deposits in scale and are quite similar to them in both distribution and shape.
3) The higher thresholds obtained are virtually the same as the experiential cut-off values for the "siliceous ores" of the mine.
4) The "siliceous yellow ores" and the "siliceous black ores" appear to be different in their spatial distribution. The former tends to be predominated in the central portion of the mineralization zone and the latter in the peripheries of the zone.
5) The footwall mineralization zone thus defined extends rather regionally along the NW-SE direction, which is in harmony with what are given from our knowledges of magnetic susceptibility anomaly, alteration zoning and distibutions of so-called "Fe-chert" and post-ore basalt flows.
