Abstract

Quartz porphyries, keratophyres, and dacites are altered to sericite-quartz schists in a discrete envelope around the ore body (earlier arsenopyrite and later pyrite). The varieties of altered rock closest to ore (sericite rock, andalusite rock) also constitute the core of the alteration channel in depth below the ore body. An outer zone of chloritic and pyrite-banded schist surrounds this inner zone at and below the level of the ore body. The distribution density of quartz phenocrysts is the same in altered and unaltered rocks, showing that no significant volume changes are involved. The central alteration zone has gained Al, K, Ti, Si, and water, and lost Fe and Mg, compared to unaltered rock. The outer zone has gained Mg, Fe, water, and S. Both zones have lost Ca and Na. Iron lost from the altered rocks as a whole, particularly in depth, may now be fixed in the ore; Mg and Al distributions also suggest upward migration. Zoning is viewed as the result of continuous action of an ascending solution.

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