Mineralogical and geochemical characterization of mining wastes: remining potential and environmental implications, Muteh Gold Deposit, Iran

Muteh Gold Deposit is the biggest active gold district in Iran consisting of two mines, Senjedeh and Chah-Khatoun, and seven mineral occurrences. Senjedeh has been mined about 20 years ago and was recently closed because of the depletion of the reserves. Chah-Khatoun went into operation few years ago. During the previous decades, more than 22 Mt of low-grade wastes has been produced from both mines. The wastes are assumed to be a possible source of gold, especially with recent increase in the world gold prices. In this research, 62 surface and subsurface samples were taken from four waste dumps in Senjedeh and two dumps in Chah-Khatoun mines. The optical mineralogy, XRD, ICP-MS analysis, SEM, and electron probe microanalysis (EPMA) studies were carried out to investigate the mineralogical and geochemical characteristics of the waste rocks. In addition to identification of major and minor primary and secondary phases, the mode of occurrence of minerals and also the content of precious and economic elements have been studied. The main opaque mineral was found to be pyrite. Among the economic elements, Au was recognized in the pyrite lattice as well as electrum. The Au grades are higher than 0.5 mg/kg in some waste piles. Zinc and Cu revealed concentrations above 5000 and about 1400 mg/kg, respectively. It is for the first time that electrum is reported in Muteh. Therefore, regarding the economically recoverable content of Au, the studied waste rocks may be considered as potential ores of coming years. Among the environmentally significant elements, As showed concentrations of up to 25 mg/kg which may be of pollution concerns.