What is a porphyry copper deposit ?
Porphyry copper deposits are large relatively low grade deposits that occur in the roof zones of igneous intrusions in island arc and continental margin settings (Figure 1). The mineralisation is fracture controlled and comprises copper and copper-iron sulfides with variable concentrations of gold and/or molybdenum. Figure 1: Major Copper Deposits – World Distribution Rock and mineral types are especially important for plant design and mine planning because porphyry copper systems are typically zoned upwards and outwards from a central potassic core through sericitic, argillic and propylitic alteration assemblages (Figures 2). Hypogene copper and copper-iron sulfides are associated with potassic and sericitic alteration. Figure 2: Schematic Section through a Porphyry Copper Deposit showing typical alteration zonation Many of the early deposits exploited had well developed supergene enrichment zones immediately beneath the leached surface outcrops. These zones are higher grade than the
