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28 <br /> 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 />• l <br />f <br />i <br />i <br />h <br />h <br />f <br /> ness o <br />n <br />e <br />arm <br />u <br />ng t <br />important parameter for determ <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 <br />0