Cheshmeh Gaz (Nasim) copper deposit, NW Bardaskan: mineralogy, alteration, geochemistry, and determination of model

Cheshmeh Gaz (Nasim) copper deposit is located in northwest of Bardaskan, Khorasan Razavi province. Geology of the area is consist of andesite, basalt, nummulitic limestone, and marl with gypsum intercalations Eocene in age, Pliocene conglomerate, and Quaternary sediments. Mineralization has been formed in andesites and contact between andesitic units and limestone as stratabound with disseminated, veinlets, and open space filling textures. Orebody consist of primary minerals such as chalcocite, native copper, and pyrite and secondary minerals including malachite, covellite, azurite, and goethite. Based on microscopic studies and XRD analysis, mineralogy of alteration zones is chlorite, calcite, zeolite (natrolite, thomsonite, and analcime), quartz, and minor epidote. Considerable anomaly of Cu (up to 3.36%) is present in the area. The hosted volcanic rocks are calc-alkaline type and are formed in subduction zone volcanic arc. Host rock type and geochemical features, alteration, structure and texture of mineralization, and ore types in Cheshmeh Gaz deposit are similar to Manto-type deposits and epigenetic-diagenetic model is suggested for formation of it.