1 Department of Geology, Faculty of Sciences, University of Sisatna and Baluchestan, Zahedan, Iran
2 Department of Earth and Environment Sciences, Faculty of Sciences, Yamagata University, Yamagata, Japan
The Chah Nali Au-Ag silicic veins are located 160 km northwest of Iranshahr and 70 km north of Bazman town in Lut block. The veins are mainly hosted by basaltic and andesitic rocks that were altered to silicic, phyllic, argillic and propylitic alterations around the veins. Symmetrical crustified structures and colloform, cockade and breccia textures are the common features of the veins. The gold grade is high in the veins (up to 16 ppm Au). The sulfides mainly occur in silicic zone and can be divided into primary and secondary sulfides. The chemistry of sulfides and elemental maps of As, Au and Ag were determined and provided by an electron probe micro analysis (EPMA). The elements that were quantitatively measured are Sb, Zn, Pb, Hg, Cd, Bi, Au, Se, Te, Cu, Fe, Mn, As, Ag and S. Pyrite, chalcopyrite, galena, sphalerite and tetrahedrite occur as primary sulfides and covellite, Ag-rich covellite and an Ag-rich new mineral occur as secondary sulfides. In general, Au concentration is low in the studied sulfides but Ag concentration is relatively high in the sulfide-bearing ores. The investigated Au-Ag mineralization is an Ag-rich low sulphidation epithermal system that was probably formed by hydrothermal solutions that are related to the young volcanic activities.