E. Haghighi; S. Alirezaei; E. Ashrafpour
Abstract
The Cheshmeh Hafez deposit in Torud-Chahshirin Range, north-central Iran, consists of a polymetal vein mineralization in Cenozoic volcanic host rocks of dominantly basaltic andesite and dacite compositions. The main ore vein, 1800 m long and <1 – 5 m wide, occurs discontinuously in a north-south ...
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The Cheshmeh Hafez deposit in Torud-Chahshirin Range, north-central Iran, consists of a polymetal vein mineralization in Cenozoic volcanic host rocks of dominantly basaltic andesite and dacite compositions. The main ore vein, 1800 m long and <1 – 5 m wide, occurs discontinuously in a north-south direction, and includes chalcedony, fine- to coarse-grained quartz, and jasperoid, associated with galena and subordinate chalcopyrite, sphalerite, bornite, pyrite, tetrahedrite, specular hematite and siderite. Crustiform bands, consisting of grey chalcedony, jasperoid, milky quartz, and various ore minerals are common, and breccias and comb textures are locally developed, in the vein. Supergene processes led to the replacement of galena by cerussite, and of hypogene copper minerals (chalcopyrite and bornite) by covellite and malachite. The main ore vein is accompanied by several smaller quartz and calcite veins in NE-SW and E-W directions, respectively, where the calcite veins are barren. Alteration related to mineralization is restricted to thin halos bordering the vein, and consists of quartz, chlorite, calcite, kaolinite and sericite (illite). Fluid inclusions in quartz associated with ore minerals are studied. Most inclusions are two-phase, liquid-rich, at room temperatures; few are vapor-dominant, and few consist solely of liquid. Primary fluid inclusions display low to moderate homogenization temperatures (135-285) and salinities (1-13 wt% NaCl equivalents). The δ34S values for the ore fluids in equilibrium with the sulfide minerals fall in the range -1.6 to +4.1‰ and suggest a magmatic source for sulfur. The ore and gangue mineralogy, and the alteration assemblages, suggest that the ore fluids were reduced and near-neutral in nature. This, combined with the metal contents, Ag/Au ratio between 16 to 25, iron- poor sphalerite, the crustiform and colloform textures, and the Th and salinity values, imply that mineralization at Cheshmeh Hafez is of epithermal, intermediate- sulfidation, character. The alteration assemblage at Cheshmeh Hafez is indicative of a sub-type of intermediate- sulfidation epithermal deposits with a tendency towards low-sulfidation type
