The discovery of gold 1983 in the unpopulated Mt Diwata, the Philippines, resulted in that the mountain within a few years became populated with up to 200 000 persons, making their living from gold extraction. The methods used, amalgamation with mercury and cyanide leaching with rudimentary equipment, result in large emissions of mercury and cyanide and related deterioration of environment and health. Our objective is to relate
observations made in 2005 in relation to mercury supply and use in Mt Diwata and propose possible actions to reduce the deterioration of health and environment. There are no reliable records on Hg actually used or emitted in Mt Diwata. In 2004, the
Environmental Management Bureau in Davao City certified 367 tonnes Hg for the enduse of mining in Mt Diwata. The quantities actually used were much smaller, but not registered. Sales from authorized Hg dealers in neighboring cities and smuggled Hg, notably via Indonesia, complicates the inventory. Based on documents, interviews, package labels, and quantities of gold extracted, the following observations were made.
The consumption of Hg for gold mining has decreased by up to 50% since 2003 as a result of the increased Hg price. Still, more than 10 t Hg is annually used for gold mining in Mt Diwata. A significant fraction of this originates from the EU, notably the Spanish state company MAYASA. The continued use of Hg is not technically or economicly motivated, because amalgamation recovers only a minor part of the gold available, resulting in subsequent cyanide treatment of the ore. Moreover, the cyanide leaching is less efficient on amalgamated ores. Magnetic sluices could replace Hg for partial recovery of gold before submission of the ore to an environmentally adapted cyanidation process. Economic means in form of credits are necessary to permit investment in safer cyanidation equipment. Information is needed to the miners about safer extraction methods and a general use of retorts could reduce but not eliminate hazardous mercury exposure. Restricting the present Hg supplies from Spain and other countries of the EU and from the USA would intensify the transition to Hg free gold mining methods.
2006. 574- p.