Investigation on the Distribution of Gold Across the Ahar Area (NW Iran) Using Stream‐Sediment and BLEG Methods

Abstract

AbstractThe Ahar area is located in NW Iran. The main part of the area is covered by Eocene andesitic and andesi‐basaltic rocks within which several granitoid intrusives of Oligocene age are emplaced. This caused vast hydrothermal alterations and Cu and Au mineralization. In this regard, this contribution aims to explore the distribution of gold across the region based on systematic sampling of stream sediments and using the secondary geochemical halos, as well as the bulk leach extractable gold (BLEG) method. Meanwhile, the results obtained from these two methods will be compared in order to find out if the anomalous zones match with each other. For this, 620 stream sediment samples of −80 mesh grain size and 422 BLEG samples were collected and analyzed by Fire Assay and atomic absorption spectroscopy (AAS) methods, respectively. For BLEG samples, gold was first dissolved using KCN before being analyzed by the AAS method. Furthermore, 84 rock samples were also collected during the field control surveys and were analyzed by Fire Assay and ICP‐OES methods for gold and other elements, respectively. After determining the distribution characteristics and statistical parameters of gold in each group of samples, anomaly maps of gold for each method were prepared, revealing almost similar anomalous zones across the region. Based on these maps, most of the discovered anomalies correlate well with granitoid intrusives of Oligocene age and the related hydrothermal alterations, which have occurred within the intrusives and the host andesitic‐basaltic rocks of Eocene age, especially at the NE and central parts of the area and east of Ahar. Some silicic veins and veinlets have been observed during field surveys in these parts, within which high concentrations of Au and sometimes Cu are determined. Another anomalous zone is located over the hydrothermal alterations within trachy‐andesitic and andesitic volcanics of Pliocene age at the SE part of the quadrangle, where vast alterations caused by volcanic fumaroles and epithermal mineralization of gold and Pb–Zn is discovered. In this regard, the SE and NE parts of the area and the east Ahar area are proposed, in order of importance, for further detailed investigations.