Proposed Limpopo West Mine Concept Study ... - SRK Consulting

SRK Consulting: 447493: Limpopo West Geochem Page 255.3.2 NAG TestThe initial paste pH value of the pulverised waste rock and coal samples was measured during ABAtestwork. After completion of the oxidation using hydrogen peroxide, a final pH was measured. Theobjective of this approach is to provide acid generation potential on complete oxidation of sulphidesin the sample. An initial acidic pH indicates that the sample has undergone oxidation prior to testingand might potentially result in acid rock drainage.The initial and final pH is plotted against the Nett Neutralisation Potential (NNP) expressed in kgCaCO 3 equivalent/tonne presented in Figure 5-3.10.09.08.07.06.05.04.03.02.01.00.0-400 -350 -300 -250 -200 -150 -100 -50 0 50 100 150 200NNP in kg/tonne CaCO3Initial pHFinal pHFigure 5-3: Open System Nett Neutralisation Potential (NNP) vs. pH (initial and final)The majority of the samples, approximately 62%, plot in the uncertainty field (- 20 < NNP < +20) ofthe graph, with some of the samples plotting in the negative area (NNP < -20) of the graph whichimply that some of the samples collected from coal zone 2, 3, 4, 5, 6, 7 and two hot spots inWelgelegen (19 to 20m) and Groenfontein samples (79 to 80m) have potential to generate acidity interms of NNP. It is evident that most samples commenced with an alkaline pH condition afteroxidation, the final pH of most samples turned acidic which indicates that these samples are likely toproduce acidity. On the positive side of the graph, the pH of most of the Welegegen samples, at adepth ranging from 14 to 25m, remained alkaline probably indicating excess neutralising minerals.Previous mineralogical study (SRK, 2011 and Bester, 2009) indicated the presence of minerals suchas ankerite and calcite that might participate in acid neutralisation.Summary of ABA and NAG TestsThe following inferences can be made from the results:Paste pH, NAG pH and ABA indicate that the geological materials from Groenfontein,Geelbekpan are potentially acid generating.The rock cores sampled from the Welgelegen farm were collected from a shallow depth rangingfrom 8.0 m to 24.72 m. The final pH (NAG) of most of these samples have not turned acidicafter oxidation and have remained relatively alkaline to circum neutral, indicating low risk of acidgeneration. Hot spots of PAF materials at 18 m, 19 m, 22 m and 24 m were also assessed fromthe final pH of these samples which turned acidic. The NPR values were mostly greater than 3GOGP/LAKJ Report_April2013_19April2013 (1)_Final_Ludi_22052013 April 2013