Mineralogy and geochemistry of mineralized veins and wast rocks of Chokdee epithermal gold Prospect, Phitsanulok province

Abstract

The Chokdee prospect is located about 20 km northeast of Chatree gold mine, Phitsanulok province. The mineralization occurs as quartz veins, stockworks and minor breccia hosted in volcaniclastic rocks. Base on stratigraphic study, the host volcanic sequence can be grouped into 3 units namely, 1) Tuffaceous sandstone unit, 2) Polymictic volcanic breccia unit and 3) Siltstone unit. Base on cross-cutting relationship, mineral assemblages and textures, mineralization consists of 3 stages namely, 1) quartz-sulfide veins, 2) quartz ± carbonate-sulfide-gold veins and 3) quartz ± carbonate veins. Quartz ± carbonate-sulfide-gold veins (Stage 2) is the main gold mineralization stage which occurs as quartz veins with or without carbonate. Pyrite and chalcopyrite are major sulfide minerals with minor sphalerite. For environmental study, a Synthetic Precipitation Leaching Procedure (SPLP) was used to leach out heavy metals from host rock and veins samples. This procedure was performed at pH level of 4. The following elements were selected for analysis: copper, zinc, arsenic, lead, manganese, mercury, cadmium and chromium. The results reveal that the mineralized veins samples have leached out arsenic and mercury exceeding the Surface Water Quality Standard (SWQS) whereas, waste rocks has leached out cadmium exceeding SWQS. Copper, zinc, lead, manganese, and chromium leach out below SWQS and Industrial Effluent Standard (IES) for both types of samples. Although, arsenic and mercury are elevated in in mineralized veins and cadmium in waste rocks when used pH level 4. However, petrographic studied suggested that the amount of sulfides present in both types of samples are very low in comparison to some other mineral deposits. Therefore, there is less chance that these types of material will cause acid mine drainage even exposed to the surface. Furthermore, pH level in natural area in this region is far higher than 4. It is further suggested that there is very low chance that both types of materials from Chokdee prospect will pollute the environment if it were mined. The results of this study will also help in managing waste rocks during the mine operation if it became a mine in future.