New discovery of epithermal gold at Chahnali prospect, Bazman volcano, SE-Iran

Abstract

Recent exploration in the region of Bazman in SE-Iran led to the discovery of gold mineralization in different prospects. The epithermal gold mineralization at Chahnali prospect is hosted by late Tertiary andesites and dacites which had been affected by a widespread and intense alteration including propylitization, argillitization, and silicification. The propylitization was of regional scale and predated the mineralizing events.

A first-stage gold mineralization occurs along a series of N-S to N30E trending tensional structures, mainly quartz veins. Trace amounts of gold can be found in individual quartz veins and stockworks that exhibit colloform banding and cockade textures, typical of open-space filling. Native gold, both visible and refractory (< 10 <m) is present, and a considerable portion of it occurs in grains < 5 <m (first gold stage). Minor quantities of sulfides (mainly pyrite) are associated with this event too.

The main gold-forming event, a second-stage gold mineralization is associated with a late-stage brecciation and subsequent silicification, which most likely were produced as a result of sinistral faulting along NNE-trending zones. Visible and refractory gold formed together with base metals, which include galena, chalcopyrite, sphalerite, and pyrite. Locally, weathering has led to the formation of jarosite-type minerals, which may contain very fine-grained gold. The gold mineralization is closely associated with quartz-adularia alteration. Therefore it is of low-sulfidation type and was generated in an epithermal environment. The initial results of a first reconnaissance study in Chahnali prospect indicate a remarkable potential for gold in the Bazman region. Further studies are needed to confirm the economic significance with an estimated gold grades averaging at 3–4 ppm.