Copper ore is confined to the vesicular tops of Cretaceous porphyritic andesite flows and the immediately overlying calcareous sandstone. The ore shoots are in lobes of the lava flows and are separated, in plan, by linear depressions (channels), up to 10 meters in depth, in which ore is generally absent. Mineral zones are, from bottom to top, bornite, bornite-chalcopyrite, and chalcopyrite-pyrite; the last is primarily in the basal layers of sedimentary rock above the lava. Safflorite is a minor constituent of the ore.

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