Environmental geochemistry of the Bingham Canyon porphyry copper deposit, Utah

Abstract.

At the Bingham Canyon porphyry copper deposit, sulfide mineralization progresses outward from a low-grade core through the following general zones: (1) molybdenite, (2) chalcopyrite–bornite, (3) chalcopyrite–pyrite, (4) pyrite, and (5) sphalerite–galena. The low-grade core and the molybdenite zone are composed of net neutralizing rock and will generally not acidify when exposed to surface weathering conditions. The copper-bearing zones of the orebody and the surrounding pyrite halo are net acid-generating and so will tend to acidify when exposed. Rocks in the lead–zinc halo are typically net neutralizing. In plan view, the distribution of net neutralization potential (NNP) is doughnut-shaped, with a positive (net neutralizing) 1,000-m-diameter core surrounded by a negative (net acid-generating) 3,000-m-diameter ring. Rock exposed in the lower 100 m of the current pit has a positive NNP and is overlain by 500 m of rock with a negative NNP.