British Columbia Mine Reclamation Symposia

Acid mine drainage in British Columbia : today and tomorrow Errington, John 2009

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Proceedings of the 11th Annual British Columbia Mine Reclamation Symposium in Campbell River, BC, 1987. The Technical and Research Committee on Reclamation -7- ACID MINE DRAINAGE IN BRITISH COLUMBIA TODAY AND TOMORROW By Dr. J.C. Errington, P.Ag. Ministry of Energy, Mines and Petroleum Resources Engineering and Inspection Branch Room 105, 525 Superior Street Victoria, British Columbia V8V 1X4 Mr. K.D. Ferguson, P.Eng. Environmental Protection Service Conservation and Protection Environment Canada Kapilano 100, Park Royal South West Vancouver, British Columbia V7T 1A2 ABSTRACT Of the 16 metal mines currently operating in British Columbia, five generate acid mine drainage.  At least five abandoned mines also produce acid mine drainage.  Acid mine drainage flows from underground workings, tailings, open pits and waste rock dumps.  The production of acid mine drainage from open pits and waste rock dumps is a major concern in B.C. The date of initial release of acid mine drainage is uncer- tain for most mines, but is known to be as rapid as one year and as slow as 11 years.  Significant levels of Thiobacillus ferrooxidans have been found in all acid mine drainage. Release of acid mine drainage has resulted in some major impacts on the environment in B.C.  The five operating mines have instituted comprehensive pollution abatement programs to address the problem while little has been done to control the abandoned mines. New mine proposals are now reviewed in detail.  Many of the properties currently under active exploration have the poten- tial for acid generation.  Potential acid generating mines are primarily massive sulphide deposits although there are three possible coal mines with acid mine drainage potential. Proceedings of the 11th Annual British Columbia Mine Reclamation Symposium in Campbell River, BC, 1987. The Technical and Research Committee on Reclamation -8- ACID MINE DRAINAGE IN BRITISH COLUMBIA - TODAY Mining is a major resource industry in British Columbia. There are currently 23 mines operating in British Columbia. Of the 16 metal mines, five, or about 30 percent, generate acid mine drainage.  In addition, at least five abandoned metal mines produce acidic drainage.  None of the seven operating coal mines produce acid mine drainage as the coal contains relatively low levels of sulphur (mean 0.37 percent sulphur). The acid generating metal mines are distributed throughout the province (Figure 1).  Sources of acid mine drainage include underground workings, tailings, open pits, and waste rock dumps.  The number of cases associated with open pits and waste rock is unique to British Columbia as the remain- der of Canadian provinces have few large open pit operations and associated waste rock dumps.  In B.C., the total quan- tity of acid generating tailings is about 72,000,000 tonnes (Table 1) and waste rock is 229,000,000 tonnes (Table 2). These figures do not consider other sites suspected by the authors but unconfirmed.  Acid generating tailings generally contain higher concentrations of sulphur than waste rock. Two acid generating waste rock dumps apparently contain less than two percent sulphur.,  The porous nature of waste rock Proceedings of the 11th Annual British Columbia Mine Reclamation Symposium in Campbell River, BC, 1987. The Technical and Research Committee on Reclamation -9-  Proceedings of the 11th Annual British Columbia Mine Reclamation Symposium in Campbell River, BC, 1987. The Technical and Research Committee on Reclamation -10- TABLE 1 ACID GENERATING TAILINGS IN BRITISH COLUMBIA  * most of the Anyox tailings were deposited under water TABLE 2 ACID GENERATING WASTE ROCK IH BRITISH COLOMBIA  Proceedings of the 11th Annual British Columbia Mine Reclamation Symposium in Campbell River, BC, 1987. The Technical and Research Committee on Reclamation -11- dumps allows oxygen penetration to much greater depths than in tailings.  As such, waste rock dumps may generate as much acid mine drainage per unit surface area as tailings though sulphur levels are much lower. The date of initial release of acid mine drainage is unknown for most mines.  However, lag from mine start-up to the dis- covery of acid mine drainage is known to be about 11 years for the Gibraltar mine and only about 1 year for the Equity mine (Table 3).  All mines have been generating acidic drainage for several years and four have done so for more than a decade.  At the Britannia mine, the acidic minewater was reported to contain from 20 to 170 mg/1 dissolved copper in 1955, similar to levels found in 1966 (Figure 2).  Since 1966, levels have generally decreased although there is evidence of a levelling off since 1979.  A smooth curve through the data suggests elevated levels of copper will continue to be released for several more decades. Virtually all acid mine drainage produced exceeds federal and provincial effluent discharge .criteria by several orders of magnitude (Table 4).  The quality is variable reflecting differences in the mineralogy of the mining wastes.  As a general rule, mines that are, or were, copper mines have Proceedings of the 11th Annual British Columbia Mine Reclamation Symposium in Campbell River, BC, 1987. The Technical and Research Committee on Reclamation  -12- Proceedings of the 11th Annual British Columbia Mine Reclamation Symposium in Campbell River, BC, 1987. The Technical and Research Committee on Reclamation -13-  Proceedings of the 11th Annual British Columbia Mine Reclamation Symposium in Campbell River, BC, 1987. The Technical and Research Committee on Reclamation -14- TABLE 4 EXAMPLES OF SOME ACID MINE DRAINAGE IN BRITISH COLUMBIA (Adapted from Ferguson and Mehling, 1986) OPERATING MINES  CONTINUED . . . Proceedings of the 11th Annual British Columbia Mine Reclamation Symposium in Campbell River, BC, 1987. The Technical and Research Committee on Reclamation -15- TABLE 4 EXAMPLE OF SOME ACID MINE DRAINAGE IN BRITISH COLUMBIA (Adapted from Ferguson and Mehling, 1986) ABANDONED MINES  * Data from EPS surveys except Britannia (B.C. Waste Management Branch). Peak concentrations are undoubtedly higher than those found during infrequent EPS surveys. Units are og/1 for metals, acidity is mg/1 as CaCO3. Proceedings of the 11th Annual British Columbia Mine Reclamation Symposium in Campbell River, BC, 1987. The Technical and Research Committee on Reclamation -16- acid mine drainage with particularly elevated copper values while lead/zinc mines produce drainage high in those metals. Iron values are surprisingly low in the acidic drainage from some mines.  Elevated concentrations of iron would be expected since the oxidation of pyrite is believed to play the critical role in acid mine drainage formation. At mines with low iron, ferric iron may precipitate in the waste or galvanic reactions between sulphide minerals may hinder pyrite oxidation.  Eventually iron could be released from these wastes as the geochemical process matures. The strongest acid mine drainage is produced from a waste rock dump at the Equity Silver mine.  Very low pH, high acidity and metal values are found in the acid nine drainage through most of the year. Elevated internal temperatures and steaming vents indicate the great activity of the biolo- gically catalyzed process at that mine. Significant levels of the bacteria, Thiobacillus ferrooxidans, have been found in all acid mine drainage tested (Table 5).  By contrast, neutral drainage contains low levels.  These data illustrate the important role of bacteria in producing acid mine drainage.  The iron oxidiz- ing Thiobacillus ferrooxidans is believed responsible for acid generation at most mines. Tests for the sulphur oxi- dizing Thiobacillus thiooxidans and thermophilic sulfolobus Proceedings of the 11th Annual British Columbia Mine Reclamation Symposium in Campbell River, BC, 1987. The Technical and Research Committee on Reclamation -17- TABLE 5 THIOBACILLUS FERKOOXIDANS IH DRAINAGE FROM SOME MINES IN BRITISH COLUMBIA Thiobacillus ferrooxidans Mine         pH of Drainage Acidic Drainage in Drainage* Gibraltar        2.0 - 4.0 9,200 - 540,000 Noranda (Bell)   2.8 - 4.0 160,000 - 3,500,000 Mt. Washington   3.5 - 4.0 790 - 540,000 Sullivan         2.7 - 3.1 2,400,000 - >2,400,000 Equity           2.4 - 2.8 130,000 - >24,000,000 Neutral Drainage Noranda (Bell)       7.3 230 Sullivan             7.0 < 20 Equity               5.1 <200 Premier Silbak       6.2 <200 * MPN/100 ml Proceedings of the 11th Annual British Columbia Mine Reclamation Symposium in Campbell River, BC, 1987. The Technical and Research Committee on Reclamation -18- bacteria in acidic drainage from the Gibraltar mine indi- cated insignificant levels of those organisms (Kay, 1986). Seasonal variations in contaminant concentration and loading have been observed at all mines.  Seeps from the waste rock dump at the Mount Washington mine exhibit elevated copper concentration and load in the spring and fall associated with freshet and rainfall events respectively (Figure 3). The long relatively dry summer period allows the production and accumulation of soluble metal sulphate salts which are flushed from the dump during the first major precipitation event.  In 1986, this waste rock dump produced about 20 tonnes of sulphuric acid from only 250,000 tonnes of waste rock based on the sulphate concentrations in the drainage from the dump. The release of acid mine drainage has resulted in some major impacts on the environment in British Columbia.  A review by Clark and Morrison (1982) of receiving water quality data collected near the Westmin mine indicated that zinc and copper levels in Buttle Lake and downstream waters had significantly increased.  Both of the metals were in concentrations which posed an immediate threat to aquatic life in the watershed.  A reduction in fishing success, and a general decrease and change in plankton community structure was also noted.  Subsequent investigations found acid mine drainage Proceedings of the 11th Annual British Columbia Mine Reclamation Symposium in Campbell River, BC, 1987. The Technical and Research Committee on Reclamation    Proceedings of the 11th Annual British Columbia Mine Reclamation Symposium in Campbell River, BC, 1987. The Technical and Research Committee on Reclamation -20- from waste rock dumps and an open pit at the mine to be the primary sources of metals to the lake.  Receiving water quality dramatically improved following the institution of a comprehensive acid mine drainage abatement program (B. Kelso and R. Van Dyk, personal communication). At the abandoned Mt. Washington mine, acid mine drainage is affecting water quality in the Tsolum River, some 11 kilo- metres downstream.  Total copper concentrations in the river are at times acutely toxic to salmonids, suggesting that poor fish returns to a local hatchery, and a declining steelhead fishery, may be partly due to acid mine drainage (Kangasniemi and Erickson, 1986). The five operating mines in British Columbia have instituted comprehensive pollution abatement programs to address the problem while little has been done to reduce acid mine drainage from the abandoned mines.  The five abandoned mines are severely impacting eibout 30 kilometres of streams.  In addition, the marine environment adjacent to the Britannia and Anyox mines is impacted up to 18 kilometres and 6 kilo- metres from the minesites as indicated by elevated metal levels in molluscan bivalues (mussels, oysters, etc.) (D. Goyette, personal communication). High precipitation in some parts of the province result in Proceedings of the 11th Annual British Columbia Mine Reclamation Symposium in Campbell River, BC, 1987. The Technical and Research Committee on Reclamation -21- the formation of large volumes of acid mine drainage.  Many British Columbia streams support valuable fisheries resources and are extremely sensitive to acid and metal pollution as they have low buffering and metals complexing capacities. None of the operating acid-producing mines have reached a maintenance free state where they can be safely abandoned. At least 150 kilometres downstream of the Equity mine could be severely impacted by acid mine drainage if collection and treatment were to be suspended based on current acid produc- tion rates (F. Rhebergen and B. Wilkes/ personal communica- tion).  Concern over long-term responsibility and potential environmental impacts has lead to more stringent review of new mining proposals, and may present serious impediments to the future development of British Columbia's sulphide min- eral resources. Proceedings of the 11th Annual British Columbia Mine Reclamation Symposium in Campbell River, BC, 1987. The Technical and Research Committee on Reclamation -22- ACID MINE DRAINAGE IN BRITISH COLUMBIA - TOMORROW Potentially acid generating wastes are currently being pro- duced in British Columbia although no evidence of acidic drainage has yet been found.  Tailings deposited at the Westmin mine have very high levels of sulphur and show segregation of sulphide and carbonate minerals based on particle size and density (Figure 4).  These tailings are deposited by the subaerial method where thin layers of tailings are discharged from a spray bar system and allowed to drain and consolidate.  Westmin hopes to produce a dense unsaturated tailings mass with low horizontal and vertical permeability.  These physical parameters may limit acid mine drainage production.  No acid mine drainage has been found from the tailings after two years of operation of the subaerial system.   Further studies are required to ensure design criteria are met and these conditions prevent acid formation. Tailings from the Equity, Scottie, and Island copper mines in British Columbia are also reported to be acid generating, but no acid mine drainage has been found to date.  The for- mer mine has maintained the alkalinity of the tailings pond supernatant and flooded most of the tailings during its operation.  The latter two mines have placed tailings under- water.  Although unconfined underwater disposal of tailings Proceedings of the 11th Annual British Columbia Mine Reclamation Symposium in Campbell River, BC, 1987. The Technical and Research Committee on Reclamation - 2 3 -  Proceedings of the 11th Annual British Columbia Mine Reclamation Symposium in Campbell River, BC, 1987. The Technical and Research Committee on Reclamation -24- is a controversial issue in British Columbia, involving several potential impacts on the environment, the practice appears to be successful in preventing acid mine drainage generation. The recent history of Acid Mine Drainage in British Columbia has indicated, if nothing else, the importance of assessing each individual mine on its own merits.  There are certain criteria based upon the type of mineral deposit which pro- vide a general indication of whether or not acid mine drain- age could occur. Massive sulphide deposits These deposits are one of the major sources of acid mine drainage in British Columbia.  Three of the five operating and four of the abandoned mines are massive sulphide deposits.  Proceedings of the 11th Annual British Columbia Mine Reclamation Symposium in Campbell River, BC, 1987. The Technical and Research Committee on Reclamation -25- The authors know of no massive sulphide mines which have not become acid producers.  There are a number of properties which have been discovered and are undergoing feasibility studies at present, all of which are a major concern. Porphyry Copper There are nine large open pit porphyry copper mines in British Columbia.  Two of these, Bell Copper and Gibralter are acid producers and at least one of the others has the potential for producing acid mine drainage.  Equity Silver can be considered a transition between a shallow porphyry and a massive sulphide deposit.  The future of large low- grade copper producers is not bright in British Columbia and no future porphyry copper mines are anticipated for the next decade. The existing porphyry copper producers should continue to be monitored closely. Vein Deposits The Duthie property is an example of a mesothermal vein sys- tem and the authors could find no other good example of vein system which has the potential for acid mine drainage. Proceedings of the 11th Annual British Columbia Mine Reclamation Symposium in Campbell River, BC, 1987. The Technical and Research Committee on Reclamation -26- Skarn Deposits Both Craigmont and Giant Mascot are example of skarn depo- sits and neither operation has shown any signs of acid generation.  While pyrite levels are high, the high carbon- ate associated with skarn replacement deposits has undoubt- edly neutralized any acid generation. Epi thermal Gold Deposits With the current high price of gold, exploration for epi- thermal gold deposits has accelerated in B.C.  Generally, epithermal deposits are relatively low in sulphide, however, as the depositional environment becomes lower, the concen- tration of sulphide increases.  The Cinola property on the Queen Charlotte Islands is an example of an ephithermal type where acid generation is definitely a possibility.  Epither- mal deposits may be associated with carbonate rich or poor host rock. Proceedings of the 11th Annual British Columbia Mine Reclamation Symposium in Campbell River, BC, 1987. The Technical and Research Committee on Reclamation -27- Coal Deposits As previously discussed, the seven operating coal mines in the southeast and northeast regions of British Columbia do not generate acid mine drainage.  However, coal mines pro- posed in north central B.C. and on Vancouver Island have encountered sulphur levels from 0.6% to 4.2%. MINE SULPHUR LEVEL IN RAW COAL Weighted Mean         Range operating mines* 0.37%     0.20 - 0.59% proposed mines** - Quinsam 1.40%     0.6 - 3.20% - Telkwa 1.50%     0.7 - 4.20% - Nuspar 0.6 - 2.30% * from Paine and Blakeman, 1983 ** from Environmental Impact Statements from respective nines Concerns for possible acid generation from the Quinsam and Telkwa mines resulted in the preparation of comprehensive acid mine drainage prevention plans (Sturm, Environmental Services 1983 and 1985). The proposed mines have not proceeded due to depressed world wide coal markets.  Monitoring of drainage from a reclaimed bulk sample backfill at the Quinsam mine, however, found low levels of contaminants and suggests the acid mine drainage prevention plan could be successful for the full scale oper- ation. Proceedings of the 11th Annual British Columbia Mine Reclamation Symposium in Campbell River, BC, 1987. The Technical and Research Committee on Reclamation  -28- DISCLAIMER  The view presented in this paper are solely those of the authors and may not be those of the Environmental Protection Service, Conservation and Protection, Environment Canada or the British Columbia Ministry of Energy, Mines and Petroleum Resources. Proceedings of the 11th Annual British Columbia Mine Reclamation Symposium in Campbell River, BC, 1987. The Technical and Research Committee on Reclamation -29- REFERENCES  Clark, M.J.R. and T.O. Morrison, 1982.  Impact of the Westmin Resources Ltd.  Mining Operation on Buttle Lake and the Campbell River Watershed.  Ministry of Environment, Victoria B.C. Ferguson, K.D., 1986.  The Geochemistry of Westmin Resources Ltd. Myra Creek Mine Tailings.  Environmental Protection, Environment Canada, West Vancouver, B.C. Ferguson, K.D. and P.E. Mehling, 1986.  Acid Mine Drainage in B.C. - The Problem and Search for Solutions. Presented at:  Tenth CIM District Six Meeting, October 2 - 4, 1986, Victoria, B.C. Kangasniemi, B.J. and L.J. Erickson, 1986.  A Preliminary Assessment of Acid Mine Drainage from an Abandoned Copper Mine on Mount Washington.  B.C. Ministry of Environment, Victoria/Nanaimo, B.C. Kay, B., 1986.  Summary of Bacteriological Results - Gibraltar Mines June 1986.  Environmental Protection, Environment Canada, West Vancouver, B.C. Paine, P.J. and W.B. Blakeman, 1983.  The National Coal Wastewater Study - Trace Elements and Organic Compounds in Canadian Coal Wastewaters.  Environmental Protection, Environment Canada, Ottawa, Ontario. Sturm Environmental Services, 1983.  Evaluation of Acid Generation Quinsam Coal Project.  For B.C. Ministry of Environment.  Bridgeport, West Virginia, U.S.A. Sturm Environmental Services, 1985.  Geochemical Evaluation of Soils and Overburdens for Crows Nest Resources Ltd., Telkwa Coal Project, British Columbia, Canada. Bridgeport, West Virginia, U.S.A.

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