Calculation of Mass Transfer and Element Mobility During the Hydrothermal Alteration in the Sungun PORPHYRY Copper Deposit Iran

The Sungun porphyry copper deposit is located in northwestern Iran and is associated with diorite/granodiorite to quartz-monzonite of Miocene age, which intruded Eocene volcanosedimentary and Cretaceous carbonate rocks. Copper mineralization was accompanied by both potassic and phyllic alteration. Three main mineralization related alteration episodes (potassic, transition, and phyllic alterations) have been studied in terms of mass transfer and element mobility during the hydrothermal evolution of the Sungun deposit. In order to illustrate these changes quantitatively, isocon plots [1] have been applied. Isocon plots illustrate that Al, Ti and Ga were relatively immobile during alteration, and that mass was essentially conserved alteration. At all stages in the evolution of the hydrothermal system, the volume change is close to zero. In the potassic alteration zone, there is an obvious enrichment of K, and depletions of Na, Ca, Mn and Fe. These changes were due to replacement of plagioclase and amphibole by K-feldspar and biotite, respectively. Potassic alteration was associated with large addition of Cu as might be expected from the occurrence of disseminated chalcopyrite and bornite in this zone. In the transition alteration zone, Ca was added, Na, Fe and Mg were relatively unchanged, and K, Ba and Cu were depleted. The loss of K and Ba relatively to Na reflects replacement of K-feldspar by albite. Phyllic alteration wasaccompanied by the depletion of Na, K, Fe and Ba and enrichment of Si and Cu. The losses of Na, K and Fe reflect the sericitization of alkali feldspar and destruction of ferromagnesian minerals. The addition of Si is consistent with the widespread silicification, which is a major feature of phyllic alteration and the addition of Cu with mobilization from the transition zone which is depleted in this element.