Discovery of 1.2 kg/t gold and 1.9 kg/t silver in mud precipitates of a cold spring from the Takab geothermal field, NW Iran

摘要

The active geothermal system of Takab in the Tertiary―Quaternary Urumieh-Dokhtar volcanic belt of northwestern Iran hosts epithermal gold deposits and a number of thermal springs, sulfotaras, and travertine occurrences with locally anomalous metal contents. Bulk analyses from a cold spring showed extremely high gold and silver concentrations of up to 1160 ppm Au, and 1920 ppm Ag associated with exceptionally high copper (22 wt% Cu) and selenium (14 wt % Se) contents, as well as strong enrichments in Ba, Sb, Pb, As, Hg, Te, Ge, Bi, and Ni. The sulphur content is low (3 wt% S), and is mainly bound to barite. Preliminary mineralogical investigations suggest that the ore minerals are mainly composed of colloidal se-lenides (with minor tellurium and sulphur) of copper and silver, associated with complex oxides and carbonates with barite, strontianite and silica. This new style of gold mineralisation in the region of Takab probably represents the surface manifestation of a deep-seated Cu-Se rich source (magmatic?) rather than being related to supergene enrichment processes.