Assessing the environmental impacts of open pits of artisanal and small scale gold mines :

Abstract

ASM open pit mining is a form of mining characterized by Open cut techniques.to extract easily accessible near-surface ores covered by relatively thin layers of overburden soils or bedrock. In the area of Tiira consists of 100pits and 10pits where mapped and the samples were collected from. 3pits out of 10pits using the random sampling method, because the. mineralogy is the same. The study shows the negative impacts of open pits to the environment and their mitigation measures. From the results indicate the pits angle of inclination ranges from (470 - 67) which is above the recommended pit slope angle of 450 there is pit failure. The PH levels of the water in the 5 sampled pits ranges from (6.23-6.49) which is below the recommended PH levels of (6.58) USEPA 2010, the concentration of the metal elements in the. water is above the recommended standards by the WHO and EPA. Thus there a potential of Acid generation in the pits. The plasticity results carried on the over burden indicate that the plasticity index is above the rainfall intensity of 23.42% to 23.27% thus the rainfall does not affect the overburden to flow as slurry to the nearby gardens to Cause soil infertility. The mitigation measures according to the research findings include the following, acid buffering using lime and open lime channels should be constructed around the active pits, for abandoned pits backfilling using the waste. rock from the pits and process tailings for saprolite a backfill of 293 14.897T/m3 of saprolite and for laterite a backfill of 49704.192T/m3 is required to block the contact between the water and the soil rocks. For pit failure proper pit slope design whereby for miners working in saprolite rocks and laterite rocks the width to height ratio of the pit slopes is 3:2 and 4:3 respective to reduce on pit wall failure. Construction of a rock fall protection catch fence in the pits to reduce on falling rocks and also pit wall scaling