Geochemical element mobility during alteration/mineralization in the Sungun porphyry copper deposit, Azerbaijan–Iran

Abstract

The Sungun porphyry copper deposit of northwestern Iran is associated with Miocene diorite/granodiorite to quartz-monzonite intrusive into Eocene volcanic–sedimentary and Cretaceous carbonate rocks. Three main mineralization-related alteration episodes (I, potassic; II, transition; and III, phyllic alterations) were studied in terms of mass transfer during hydrothermal evolution of the Sungun deposit. Isocon plots (Grant, J.A. 1986, The isocon diagram – a simple solution to Gresens’ equation for metasomatic alteration: Economic Geology, v. 81, p. 1976–1982) were employed to illustrate these changes quantitatively. These plots illustrate that Al, Ti, and Ga were relatively immobile during alteration, and that the alteration was essentially mass-conservative. At all stages in the evolution of the hydrothermal system, computed volume changes were close to zero. In the potassic alteration zone, an obvious enrichment of K and depletions of Na, Ca, Mn, and Fe took place. These changes were due to replacement of plagioclase and amphibole by K-feldspar and biotite, respectively. Potassic alteration was associated with significant 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 relative to Na reflects replacement of K-feldspar by albite. Phyllic alteration was accompanied 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.