Historical geochemical profiles of Sonne 140 cores from Lingayen Gulf, The Philippines: Some imprints of mine wastes from the past

摘要

Mine wastes input of the Baguio Mineral District into the Lingayen Gulf can be traced in the gulf sediments using Cu and SO_4 historical profiles of SONNE 140 cores from representative sites in the gulf. Two watersheds, the Bued-Pantalan and the Agno, cover the mine sites and serve as major contributors of sediments to the gulf. Sediment core representative of the Bued-Pantalan watershed provides a well-defined geochemical profile of the mine wastes, which delineate correlative relationships between Cu and SO_4 to be highly significant (r=0.95). Elevated Cu concentrations in these sediments average 203 mg/kg for, at least, the last ten years based on reported sedimentation rates. Sediment core representative of the Agno watershed, on the other hand, yielded a lower average Cu load of 89 mg/kg and a lower correlation (i=0.64). Its historical geochemical profile depicts dilution of Cu concentrations, which we interpret as the combined results of Cu sequestration in the watershed by agriculture, the intermixing of the Pinatubo ash with the watershed sediments, and the gradual closure of mines in the Baguio Mineral District during the last ten years.