Gold mineralization and environmental impacts of artisanal mining in the Um Araka area, Egypt: Microanalyses and heavy metals assessment

Abstract

Gold-bearing rocks in Um Araka area, south Eastern Desert of Egypt, comprise mineralized quartz veins and wall-rock alterations. Gold mineralized rocks are confined to post-collisional granite that intrudes a variety of island-arc association dominated by amphibolite, mafic schist and marble bands. The paper aims to assess environmental hazards related to extensive artisanal mining, extraction of gold, leaching by poisonous cyanides and the haphazard storage of mine wastes. The latter comprise heaps of dump rocks and tailings. Energy-dispersive X-ray spectroscopy (EDS) coupled with scanning electron microscopy (SEM) confirms the ore paragenesis revealed from the petrographic study. Beside gold, the gold-bearing quartz veins and alteration zones have considerable amounts of sulphides such as pyrite and arsenopyrite, in addition to lesser amounts of galena. Gold-rich samples collected from the excavated pits and shafts show enrichment in an electrum alloy consisting of 71.7 wt% Au and 15.2 wt% Ag, which is washed out totally if subjected to cyanidation. Upon cyanidation, Cl is greatly eliminated from 29,200 ppm to 2300 ppm whereas S is slightly lowered from 33,200 ppm to 27,500 ppm. Trace elements as pollutants in the investigated tailings are distinguished into base metals (Zn, Pb Cu & Ni), and rare-metals (Mo & Nb). The paper emphasizes the need for sustainable mining practices and environmental management to mitigate the random impacts artisanal mining for gold. Data materialized here categorize hazards into the use of cyanide, high concentrations of some heavy metals and appreciable U & Th. It is recommended to use safer alternatives for cyanide (e.g., thiourea CH₄N₂S) to ensure clean environment and sustainable mining of the known and unexplored gold resources in the south Eastern Desert of Egypt.