Abstract

The Chah Zard Ag-Au epithermal deposit, approximately 100 km southwest of Yazd, is located in the central part of the Urumieh-Dokhtar magmatic arc, in Dehshir fault zone. The country rocks consist of a circular complex of polymictic matrix-rich breccias hosted in altered Tertiary intermediate to felsic volcano-plutonic (andesite, trachy-andesite, dacite, porphyritic dacite, porphyritic rhyolite) rocks. Altered rocks at Chah Zard occur in an area greater than 3×3 km. The intense alteration in the area consists of quartz (chalcedony), clay minerals (advanced argillic), K-feldspar and jarosite (alunite). The Ag-Au mineralization appears to be directly related to the intensity of silicified and sulfidic volcanic breccia (hydrothermal and phreatic breccia) and is accompanied by advanced argillic and jarosite (alunite) alterations. Analysis of samples collected from trenches and diamond drill holes indicate gold and silver values up to 21 and 92.2; and 66 and 463.2 g/t, respectively. The principal ore minerals observed in the mineralized zones are native gold, electrum, pyrite, chalcopyrite, tetrahedrite, galena, sphalerite, chalcocite, arsenopyrite, marcasite, skutterudite, loellingite, covellite, digenite; and iron oxides-hydroxides. The major associated gangue minerals are quartz, gypsum and jarosite (alunite). Based on intensity of silicification, advanced argillic and jarosite (alunite) alterations, which are accompanied by gypsum as clasts’ cement as well as gold-bearing vein; Ag-Au mineralization at Chah Zard seems likely as high-sulfidation (acid-sulfate) epithermal mineralization.