Abstract

Chemical analyses of the wall rock gneiss at Ore Knob reveal that iron decreases toward the ore body. Biotite, the principal iron-bearing mineral in the wall rock gneiss, decreases in iron content and abundance toward the ore. Along a given drill core there is a correlation between the percentage of iron in biotite and in the total rock, and the thickness of the ore body; a similar correlation exists between the N (sub gamma ) index of biotite and the thickness of ore.Biotite averages only 8 ppm of copper, and the amount of copper in biotite from drill core samples does not show a significant increase or decrease toward the ore. Chalcopyrite and sulfur, however, increase toward the ore. The distributions of copper and sulfur in the wall rock gneiss support the idea of introduction of these elements from a distant source, whereas the distribution of iron does not support this idea. Calculations indicate that enough iron was removed from the wall rock gneiss to account for all the iron in the ore body. It is suggested that during metamorphism sulfurization was an important ore-forming process at Ore Knob, and that copper and sulfur introduced in hydrothermal solutions combined with iron from the biotite of the wall rock to produce the massive sulfide copper ore body at Ore Knob.

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