MISIMA
Location
Misima Island, Milne Bay Province.
Latitude 10°39'52.16"S Longitude 152°48'17.59"E
Status
Misima mine opened in 1990. Mining was completed in May 2001 but the processing of ore continued into 2004 until the mine closed.
Type of Mine and Waste Disposal
The Misima mine was the first mine outside of Canada to employ Submarine Tailings Disposal (STD) from the beginning of operations. Its waste management has been used as a precedent for other mines where tailings disposal is problematic. Misima exploited low-grade ore that was left in the ground by past mining operations. The deposit was mined in a series of economic stages in which those parts of the ore body with higher than average grades and low strip ratios were mined first. Conventional open pit mining was used and the milled product underwent cyanide leaching. The tailings were treated to recover some of the reagents and reduce dissolved metal concentrations prior to STD. This was carried out by an undersea pipeliune at a depth of approximately 112 metres into a 1,500-metre ocean basin in Milne Bay. The tailings were piped to a coastal mixing tank where they were diluted 15:1 with seawater. Over 50 million tones of tailings waste were disposed of onto a near shore coral reef during the life of the project. Other options for waste disposal considered for Misima including a tailings dam, milling and then discharging, and shoreline dumping. None of these were deemed to be viable due to the terrain, high rain fall, high occupancy rate and high rates of land use for agriculture. This type of tailings disposal set a precedent for other mines to follow.
Past Production
Gold average annual production from1989-2004 was 252.178 ounces (7,149,130 grams) and silver average annual production for 1989-2003 was 146, 215, 7 ounces (41,451,477 grams).
Ownership and Finance
Misima Mines Ltd was formerly a joint venture between Placer Dome (80%) and PNG State company Orogen Minerals (20%). In 2006 Barrick acquired Placer Dome and its mines, including Porgera and Marinduque Philippines.
Environmental Setting
Misima Island is a volcanic island and is characterized by extremely steep submarine slopes and a narrow, fringing coral reef on the shoreline. It is an eastward extension of the Papua New Guinea mainland and is essentially a large mountain jutting out of the ocean floor. The island is 40 kilometres long and 10 kilometres wide at its broadest point and covers an area of 280 square kilometres. The climate is tropical and the annual rainfall ranges from 3000 mm on the coast to 3750 mm near the mine. The island is subject to cyclones bringing high winds and extreme rainfall. About 10,000 people live on the island, mostly on the less rugged eastern end where the mine was also located.
Environmental Impacts
During the lifetime of the mine over seventy-five metres of thick deposits of tailings and soft waste from the Misima mine had covered over 20 square kilometres of ocean. The dumping of soft waste rock and soil alone has had direct impact to the near shore marine environment. Approximately 53 million tonnes of soft waste rock and soil was dumped into the ocean over a 5 year period, smothering a coastal coral shelf over 1 kilometre long and having an impact on coastal reefs extending along 9 kilometres of coast. This process killed the corals in the immediate impact zone and thus eliminates the subsistence fish resource in that area.
Heavy metal contamination of the marine environment is a common problem with STD. At the Misima mine tailings contained residual cyanide from the gold extraction process. Before being released into the sea the tailings were first diluted with seawater to reduce the concentration of cyanide and other contaminants. Even after this dilution, the tailings contain such high levels of cyanide that they do not meet Papua New Guinea’s water quality criteria for seawater. Because of this Placer Dome were granted a very large area in the sea around the outfall of the pipe, called a “mixing zone,” within which the seawater is polluted with cyanide and other chemicals at levels not otherwise permitted. The Mixing Zone extended 42 metres above the end of the pipe (which is at a 112 metre depth), and 488 metres below the pipe. The mixing zone is about 2.5 km wide at the top, tapering down to about a kilometre wide at the bottom. The concentration of some metal contaminants at the boundaries exceeded a range of USEPA and Australian environmental criteria.
Two validation surveys had shown that the system complied with regulatory conditions and meets ambient standards for contaminants well within a submerged mixing zone that extends to 1200-m radius from the mix tank location. However, in 1997 a submarine landslide broke the tailings pipe, spewing waste pipe into higher levels in the ocean. This is a common occurrence in STD operations and illustrates the risk associated with submarine tailings disposal. It took Placer Dome six months before the pipe was fixed. The submarine section of the tailings pipe at Misima broke at 55 metres depth. In the meantime the discharge system was reversed and the seawater intake pipe was used to pump out the tailings at only 60 metres depth. During each of these pipe breaks at sea, cyanide and metal enriched tailings particles were pumped into shallow zones where they should not be discharged. The discharge s of these tailings and cyanide at the shallow depths was not in compliance with the conditions of its permit as these shallow areas fall outside of the a permitted “mixing zone”.
In 1999 there was a cyanide leak through the submarine tailings pipes from the Misima mine, killing marine life from shallow and deep waters in Milne Bay. Landowners reported that the whole of the Port Maika areas was filled with dead fish. Sharks feeding on the dead fish also died and there were reports of a whale close to Misima dying shortly after the spill. Mine workers were found clearing dead fish out of the water and burning them. Workers were also cleaning the chemical holding tanks at the mine site until they were ordered to stop so that an investigation could establish the cause of the fish deaths. A subsequent investigation found that there was a number of non compliance issues including the absence of authorized environmental officers, and that reporting procedures were not followed prior to the flushing of sodium cyanide into the bay.
Social Impacts:
Misima was particularly vulnerable to the social impacts of large-scale mining as the island had not been exposed to a large-scale development before, nor had the island experienced a cash economy. Misima was geographically isolated from where decisions were being made. Local people were not privy to information on the impacts of mining social impacts throughout the life of the Misima mine.
Social impacts included the disruption of the indigenous society and culture, disruption of the physical environment, local inflation or hyper-inflation, problems of revenue distribution, increased cost of government services, increased prevalence of disease, the creation of "haves" and "have nots", the introduction of "outsiders" and expatriates who are not necessarily welcomed by local residents, and unequal distribution of decision making authority between local and national authorities. Access to productive land was a major issue during the life of the Misima mine, due to housing developments and mining occurring on land that had previously been used for agriculture. Women in particular had to travel further to harvest their food.
Local people also felt that the system of disposal they are using was not properly explained to the people. They felt that if these explanations had been forthcoming at the start of the project then they would have been opposed to the practice of STD. The cyanide spill also caused immediate and long-term, perhaps permanent, community psychological damage.