Understanding the baseline geochemistry of stream waters in a prospective mining area is the key to responsible life-of-mine planning and the protection of local rivers. This can be sometimes challenging due to the presence of abandoned mines, small scale mining, and geogenic sources of metals in the same area, particularly under a tropical humid climates with rivers carrying intermittently high solid loads. This study is focused on the Pula Bato, Danlag, Altayan, and Taplan Rivers in such a climatic setting in Philippines. The rivers are located in the vicinity of the Tampakan ore deposit. It was observed that elemental concentrations in water samples from Pula Bato were generally higher when compared to concentrations from Danlag, Taplan, and Altayan samples. In particular, SO42-, TDS, Al, Cu, Fe, Mn, Ni, and Zn present considerably higher concentrations in the water samples from Pula Bato. It was shown that water quality of Pula Bato is influenced by the natural weathering of sulphide minerals which is further enhanced by the small scale mining activities and old underground workings. The mining effects on the water of Pula Bato River were not apparent in the water of the Altayan due to the possible dilution of the uncontaminated water from Danlag River and sorption processes occurring during the course of contaminants transport. The geochemical indicators and water distinctions can be used in future for catchment-scale geochemical balance modelling.
Keywords: Geogenic; Mining; Stream; Tropical; Water quality.