A Study of Geochemistry, Heavy Minerals, Genesis and Gold Potential in Hangaran Listweanites, Mokhtaran Area, Iran

The widespread listweanites (carbonatized serpentinites) outcrop in Birjand-Nehbandan axis in the east of Iran and south of Khorasan province. listweanites cover an area extending more than 25000 km2, and occur along the major faults and between flysch-colored mélange-ophiolite complex. The most extensive outcrop is in the south of Mokhtaran map (scale 1:100000). On the basis of lithology, listweanites, occurring mostly close to ultrabasic rocks, are divided into four categories: breccia cryptocrystalline silicic listweanite bearing sulfide minerals, silicic listweanite, and silicic-carbonatic listweanite. Among these, breccia silicic listweanite bearing sulfide can be a suitable case for gold exploration. Sulfide minerals such as pyrite, chalcopyrite, bornite, arsenopyrite and covelite occur in this listweanite. With respect to mineralogy, listweanite rocks consist of major minerals such as cryptocrystalline quartz (opal, jasper), calcite, dolomite, magnesite, siderite, serpentine, chlorite, and minor minerals such as pyroxene, chromite, magnetite, cinnabar, chalcopyrite, bornite, arsenopyrite and Fe-oxide-hydroxide. Some of the sulfide minerals have altered to Fe-oxide and hydroxides.Heavy mineral studies, on the samples taken from river sediment, show that the particles of gold (30-150 microns) are associated with pyrite, chalcopyrite, cinnabar and native copper. Significant alterations in the listweanitic complex are silicification, hematitization, and slight argillitization. The origin of gold, silver, arsenic and other associated elements are from serpentinized ultrabasic rocks. With development of regional metamorphism, fluid bearing anions like (CO3)2-, Cl-, and (SO4)2- form complexes with metallic elements such as Au, Ag, Sb, As, Hg, Cu, Ni, Cr, and Co. This fluid ascends to the upper parts, forming gold-bearing sulfide-silicic vein deposit in breccia zones and in the geochemical bars of carbonatic parts (carbonatic listweanite with silica deposition).