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28 <br />0 variation of the drainage is that the highest concentrations <br />of Zn, Cd, and Pb occur in the central zone even though <br />sphalerite and galena, the ore minerals which concentrate <br />these elements, occur in greatest abundances in the inter- <br />mediate and peripheral zones. The impact of this conclusion <br />is increased when it is coupled with the observation that <br />mines of greatest economic importance occur in the inter- <br />mediate zone or on the margin of the central zone (11). <br />Thus, there is not necessarily a correlation between the <br />economic grade of an ore extracted from a mine and the harm- <br />fulness of the water draining from a mine. On the other <br />hand, there is a direct correlation between the abundance <br />• of pyrite in the veins and the harmfulness of the water <br />draining from the mine and it is felt that this is an <br />important parameter for determining the harmfulness of <br />drainages from base metal deposits. <br />What the results show is a confirmation of the sulfide <br />mineral weathering scheme that was summarized previously. <br />For some reason, it is necessary to oxidize the pyrite first. <br />Its dissolution will lower the pH of the water so that biologi- <br />cal catalysts can operate. Also, the Fe(III), HS04 , and H* <br />catalyze the dissolutions of the other sulfides. So the <br />primary criterion relating petrology to water quality is <br />the abundance of pyrite. <br />Na, K, Mg, and Ca are normally considered as the major <br />metal constituents in water. The zonal variation in concen- <br />tration of these cations is much less severe than those of