ABSTRACT

The vertical zoning of minerals in porphyry copper deposits was discussed in the preceding chapter. Horizontal zoning of the hypogene primary deposit is also typical of these ore bodies, with a protore core surrounded by a mineralogically different halo. The protore core contains a low pyrite to chalcopyrite ratio (Py/Cp = 1/1), and most of the molybdenite. The halo contains higher pyrite to chalcopyrite ratios, typically Py/Cp = 10/1, and lower copper concentrations. Mining of ore for milling is usually confined to the protore region where copper concentrations exceed an economic cut-off grade.