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 ...
Read More
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
E. Ashrafpour; K. M. Ansdell; S. Alirezaei
Abstract
Arghash gold district includes five gold-bearing vein systems, (Au-ItoAu-V) and one antimony-rich vein hosted by intermediate to silicic volcanic rocks, tuffs, granite, and diorite. Pyrite is the main sulfide mineral consisting of four generations (Py-ItoPy-IV). Py-I toIII are intimately ...
Read More
Arghash gold district includes five gold-bearing vein systems, (Au-ItoAu-V) and one antimony-rich vein hosted by intermediate to silicic volcanic rocks, tuffs, granite, and diorite. Pyrite is the main sulfide mineral consisting of four generations (Py-ItoPy-IV). Py-I toIII are intimately associated with gold; however, Py-IV is barren. The δ34S values of pyrites in conventional bulk analyses fall into two groups, one highly enriched in 34S (δ34S= +9.3 to +21.8‰), and the other less enriched to slightly depleted in 34S (δ34S= +5.1 to -4.3‰). In-situ laser probe experiments were carried out to characterize various generations of pyrite. The results indicate a relatively narrow range for Py-I to Py-III (δ34S= -5.8 to +0.1‰) consistent with a magmatic source for sulfur. Py-IV is highly enriched (δ34S= +8.9 to +23.7‰), implying contributions of sulfur from sources enriched in 34S, like evaporites. The high δ34S values in the enriched group can be attributed to a significant occurrence of Py-IV in this group.
The δ34S values of two stibnites from Sb ore (-18.8 and -14.4‰) suggest a different sulfur, and possibly metal source, and/or radical changes in the physicochemical conditions of the fluid during deposition of stibnite. Metasedimentary basement rocks could contribute sulfur and metal to the circulating fluids. δ13CPDB values of vein calcites are near 1 per mil suggesting a sedimentary source for carbon. Carbonate units and interlayers in the area are a suitable source for CO2 in the ore fluids. The stable isotope data suggest that hydrothermal fluids experienced a complex history of water/rock interaction and that ore components, were derived, at least partly, from country rocks.
