Philippines’ Deadliest Mining Disaster: A Study on the 1996 Marcopper Mining Incident

The Canadian-owned Marcopper Mining Corporation operated in the province of Marinduque from 1969 to 1996. Its parent company Placer Dome, Inc. managed the mines and took part in the copper exploration of the province. Placer Dome owned 40% of the company’s shares and until 1986, the then-President Ferdinand Marcos secretly owned 50% of the shares and the rest belonged to other stockholders. The mines officially started operation on Mt. Tapian until 1990 when the ore reserve was depleted which prompted the company to move its operation to San Antonio, three kilometers north of Mt. Tapian.

During its time in operation, the company received criticism from the citizens, workers, and labor groups strongly against mining. In its existence, the company has a mixed track record which became apparent in its irresponsible handling of waste and poor treatment of workers.

In 1996, just a year after RA 7942 (Philippine Mining Act of 1995), the collapse of the mine’s drainage pit and tunnel after a minor earthquake caused 2 to 3 million metric tons of mine waste tailings spilling into the Boac River. The incident which became known as the Marcopper Mining Disaster is widely recognized as the worst mining disaster in the country. After the incident, the Philippine government was forced to suspend the company’s permit and the company finally ceased operations.


Due to lax environmental policies and regulations, Marcopper has been known for its irresponsible dumping of toxic wastes, lack of closure and rehabilitation plans, and the absence of environmental risk assessment and management. Until 1972, Marcopper disposed of its waste in land. In 1975, a blanket permit was given to Marcopper, which allowed them to dump mine tailings into the Calancan Bay at the rate of 2.5 tons per second. The amount of tailings produced from mines in Marinduque is high because the ore is low grade, containing only 0.44 percent copper (Hamilton-Paterson 1997). By 1990, a total of 200 million metric tons of mine tailings has been dumped into the shallow marine waters of Calancan Bay that covered a vast number of corals and marine life. The tailings leached metals into the bay and have been found out to be the source of lead contamination of children. The company drew flak from local residents which prompted MGB to question the company’s practices. Despite the protests, Placer Dome, the company that oversees and handles the mine’s disposal denied that their practice affects the livelihood of fishermen. On April 16, 1990, Marcopper’s Environmental Compliance Certificate (ECC) was renewed by the Department of Environment and Natural Resources (DENR) on the condition that Marcopper should find a way to properly dispose its waste. The certificate allowed the company to operate for 10 more years. This lead to the Mt. Tapian pit being the location of tailings disposal from San Antonio mine site.

Before the disaster took place, Maguila-guila dam was constructed in Mogpog River in 1991 to hold out wastes from San Antonio mine as Mt. Tapian Pit might not have enough capacity to store larger quantities. When the construction was finished in 1992, residents started noticing wastes flowing out of the river and large quantities of dead fish. A year later, heavy rain ravaged the area and the dam collapsed. Toxic silt poured into the river and two people died on the incident. Marcopper blamed the unusually heavy rainfall as the cause of the accident.

Three years later on March 24, 1996, a minor earthquake struck Marinduque which fractured the plug that sealed the open-pit tunnel causing 2 to 3 million metric tons of toxic waste to pour into the 27-kilometer long Boac River over the course of 4-5 days with a discharge rate of 5-10 cubic meters/second. At that time, the pit was holding about 23 million metric tons of mine waste tailings. Flash floods isolated 20 of 60 villages in the surrounding area and an estimated 20,000 people were affected. Barangay Hinapulan was buried under six feet of muddy water. The incident was so severe that it left Boac River biologically dead. Fishing and agriculture, the two main livelihoods of the residents were crippled due to inundated fields and rivers contaminated by mine tailings. Residents suffered skin irritations, respiratory problems as a result of the emission of hydrogen sulfide and nitrous oxide. Residents also suffered lead intoxication as a result of contaminated water.

Marcopper claimed that the accident was an act of nature and that the earthquake was to be blamed. Investigations by a team of UN experts proved however that the unconventional use of the Mt. Tapian Site as a pit was a fundamental design mistake due to budget cuts and an environmental impact assessment was never carried out during its operation.

Resolution and Updates

Marcopper did not take responsibility after the incident and did not participate in the cleanup efforts of Boac River. Instead, Placer Dome accepted responsibility and paid an estimated $71 million for the cleanups and reconstruction of damaged property as well as an additional $1 million in monetary compensations as a result of lost income by fishermen and other non-company employees. Then-CEO of Placer Dome John Wilson wrote to then-President Fidel V. Ramos that the residents affected by the Marcopper incident will be quickly and fairly compensated. Thousands of residents however claimed that they did not receive any compensation.

On November 1996, a plug installed on the drainage tunnel was completed. Levees were built along the banks of Boac River to contain the tailings and prevent them from spreading further. Placer Dome plans to dispose of the tailing by means of pumping into the ocean in a process known as Submarine Tailings Disposal (STD), a method banned by the company’s home country of Canada. Citing further environmental damage, citizens of Marinduque disapproved of this method and Placer Dome’s request for disposal was rejected by DENR twice. The tailings are yet to be properly disposed of while residents living near the area are still living in the danger of another possible leakage of the Tapian Pit. As for the other environmental concerns including Mogpog and Calancan Bay, Placer Dome waived any liability claiming a loss of interest over Marcopper by citing that it is the company’s problem.

In 2000, DENR and the provincial government of Marinduque signed a memorandum of agreement (MOA) to finalize a clean-up, rehabilitation and restoration plan that will be reviewed by qualified technical experts and consultants in the hopes that the Boac River will be cleaned up.

In 2005, the provincial government of Marinduque filed a lawsuit on Placer Dome in the Nevada State Supreme Court for $100 million in damages. In the following year, Barrick Gold (Placer Dome’s new owner) offered a $20 million settlement on the condition that the petitioners, including the Philippine government waive any liabilities against the companies involved.

In 2013, a Marinduque Regional Trial Court rejected a case filed by local fishermen against Marcopper for the company’s dumping of mine tailing in Calancan Bay over the course of 16 years.

In 2014, the provincial board of Marinduque discussed with Barrick Gold in Malacañang with relation to the $20 million indemnity being offered.

In 2015, Nevada State Supreme Court rejected the $100 million class suit filed by the provincial government of Marinduque against Placer Dome which has since been acquired by Barrick Gold.

Earlier in 2017, MGB found a leak in one of the tunnels of Marcopper’s Makulapnit Dam. In April 2017, plans were in motion for the filing of case against Marcopper by former DENR Sec. Gina Lopez. The plan never came to fruition as Gina Lopez was rejected by the Commission of Appointments a month later. In the same year, MATA partylist Rep. Tricia Velasco-Catera filed House Bill 6384 that will put an indefinite moratorium on all mining activities in the province of Marinduque in order to prevent a tragedy like the Marcopper incident from happening again.


The tragedy at Marcopper Mining remains a grave testament of the effects of irresponsible mining and lack of law enforcement from the government. While Marcopper has since shut down after the incident and cleanup efforts are being made by DENR and the provincial government of Marinduque, the havoc left by Marcopper still poses a threat among the residents fearing that its dams may collapse again. Proper disposal of the mine tailings is yet to be carried out while justice is yet to be given to the people who witnessed and was affected by the tragedy. 

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