Gold Mineralization and Impacts of Its Mining on Environment

Abstract

Abstract Mining makes a significant contribution to the national economy and local communities. This research briefly places the contribution of gold mining into the context of the wider economy and then focuses on the impact of its mining on the environment. Broadly, Sudan is endowed with multi-metal resources of which gold is the most economically attractive mineral. The gold mineralization is found, widespread in Sudan and confined primarily to the Archaean basement rocks and the Late-Proterozoic greenschist belts of the Arabia-Nubian shield. The recent studies of the Nubian-Arabian greenstone indicated that the Ariab metallogenic province is becoming one of the premier areas in the world for the development of poly-metallic base metal sulfide deposits, which contain substantial economic gold potential. Moreover, the secondary re-worked placer concentrates and detritus small nuggets of the pre-existing gold mineralization, attracted most of the present indigenous activities. The rapid expansion of formal and indigenous gold mining activities, particularly in the event of gold rushes after boom increase of gold prices, constituted one of the recent dominant challenges to economics, social developments and regional environmental impacts. Ariab open pit and Gebeit abandoned mines, which exhibited different gold extraction techniques of two genetically different ore formations, were taken as two study cases in this research. The study was based.on_the hypothesis that, mining .operations in the study areas have damaging impacts on the natural environment due to cumulative negative impacts generated from mine acidic water, leaching of heavy minerals from mine waste, relic tailings and the associated chemical effluents into the ecosystem. The results of the study have identified several features showing, positive and negative impacts, which are rather paradoxical in nature. From one side, the mining activities supported the increase of the national economy with appreciable sustainable social development as in Ariab disnict, but on the other side, undeniable negative effects at the mining sites have also accompanied these activities. Based on defined criteria, the impacts of mining and mineral processing operations were classified of low impacts at Ariab, and comparatively high at Gebeit with diiferent magnitudes on the ecosystem and communities.

The chemical analysis and statistical correlations showed that, the mineral concentrations in mine waste and processed heaps, exhibit distinctive, elevated concentrations exceeding the local background and global limits by 46.1 and 99.2 times in arsenic, 4.6 and 8.4 in copper and 8.1 and 12.1 in lead respectively. The correlations between heavy minerals, Pb/Zn, Pb/Cd and As/Cd in the study area have shown also peculiar reaction behaviors due to cyanide influence and the pH level existing. Most of the heavy metals existed in the form of stable carbonate compounds of copper, lead, zinc, cadmium and as oxides of chromium, arsenic and antimony. However the drainage soil around Ariab gold mining sites has showed insignificant heavy metal pollution or acidification, derived fi'om the operation. That was, attributed to the advanced technology used and management control exerted during the mining operation. The qualitative and quantitative review of the heavy metals are presenting high elevated concentration values in the central zone where mining and processing were performed compared with the normal background (threshold) concentrations at up-stream zone. The down-stream zone concentration values were showing a close and analogous mineral distribution to the local backgroimd (threshold) and global concentration limits. This phenomenon has concluded with facts that the influence and the effects of heavy metals generated from mine waste, heap-leached tailings and mine acid water on the ecosystem is negligible. In contrast, abandoned mines tend to have far more extensive and accumulated impacts to the environment context. The dust emission has been, significantly reduced by the new installation of dust suckers and the surveillance results of dust threats on resident’s health is insignificant. Although indigenous mining has positive socio-economic contributions, but it also contributes to land degradation, loss of biodiversity, destruction of natural resources, deforestation , water and soil mercury pollution . The study showed that it is difficult to prevent pollution altogether during mining, but it is advisable to determine the optimal level of pollution or pollution connol by balancing the cost and threats of polluting activities against the improvement of the national economy and social development as strategy.