Tapian reserve was depleted in 1990, Marcopper moved its operations to the San Antonio copper mine, three kilometers north of the Mt.
[4] The Marinduque Mines operated by Marcopper dumped waste into the shallow bay of Calancan for 16 years, totaling 200 million tons of toxic tailings.
[5] When exposed to ocean breezes, the tailings, which partially floated, become airborne and landed on rice fields, in open water wells, and on village homes.
"[6] This "Snow from Canada," consisting of mine tailings, forced 59 children to undergo lead detoxification in the Philippine capital of Manila.
The effects of the incident were so devastating that a United Nations assessment mission declared the accident to be a major environmental disaster.
Officials of the DENR (Department of Environment and Natural Resources) claimed they did not know of the presence of the drainage tunnel that measured 2.6 kilometres long and 1 metre wide which was located underneath the pit, which led to the Makulapnit and Boac river system.
[9] The toxic spill caused flash floods which isolated five villages, with populations of 4,400 people each, along the far side of the Boac river.
One village, Barangay Hinapulan, was buried under six feet of muddy floodwater, causing 400 families to flee to higher grounds.
[10] On 17 April 1996, a Department of Health (DOH) report said that residents may already be harboring quantities of zinc and copper beyond tolerable limits.
Residents complained of skin irritations and respiratory problems which could have been caused by poisonous vapors such as hydrogen sulfide and nitrous oxide from mine wastes.
[1] The disaster prompted government to revise the rules of the Mining Act to focus more on the protection of the environment and address social issues.
[1] Oxfam, an international development and humanitarian aid agency with projects in the Philippines was approached by Marinduque community members for help.
[7] The report calls on Placer Dome to complete an environmental clean-up, adequately compensate affected communities, and take steps to prevent future disasters.
[14] On October 4, 2005, the provincial government of Marinduque sued Marcopper's parent company, Placer Dome, for $100 million in damages.
[15][16] As of 2017, the provincial government had been preparing to file a new case against Placer Dome and Barrick Gold for environmental damage in the municipalities of Boac and Mogpog.