Introduction

The site of the former Britannia Mine is located approximately 48 km north of Vancouver, British Columbia, adjacent to the fjord of Howe Sound. The mine was operated from 1902 to 1963 by the Britannia Mining and Smelting Company Ltd., and from 1963 to 1974 by Anaconda Mining Company. Mining activity ceased in 1974 because of the exhaustion of economic ore (Price et al., 1995). The orebodies mined were located in Mineral Ridge, the east-west divide between Britannia Creek to the north and Furry Creek to the south, which rises to an altitude of 4600 feet (1400 m) from Howe Sound (NTS map 92G/11, 1981). During the life of the mine, ore was extracted from underground workings that included 80 km of development and five open pits (Photograph 1). Mineralization was predominantly copper as chalcopyrite (copper-iron sulphide), with some economic zones of zinc as sphalerite (zinc sulphide) and extensive occurrences of pyrite (iron sulphide). Approximately 47 million tonne of ore was extracted from the mine during its 72 years of operation. Details of mine geology and production statistics may be found in Minfile Number 092GNW003 (BC Ministry of Energy, Mines and Petroleum Resources, 1996).

All ore was concentrated by milling in Britannia Beach, with concentrate shipped to smelters and refiners in the United States. Milling originally consisted of crushing, grinding and gravity concentration, with froth flotation being added when the technology became available. Most mill tailings, in excess of 44 million tonne, were deposited sub-aqueously in Howe Sound from an intertidal discharge at Britannia Beach. This method of tailings disposal was a form of Sub-Aqueous Tailings Disposal or Submarine Tailings Disposal (STD), but current practice requires such a discharge must place tailings well below the photosynthetic productive zone, where the tailings must remain.

Copper was also recovered, by cementation with scrap iron, from mine water issuing from the 2200 Level and 4100 Level portals (at Britannia levels are measured downwards from 4300 feet above sea-level, the highest point of the mine). Cementation launders were located at Mount Sheer (5 km inland and 2000 feet (600 m) higher than Britannia Beach) and at Britannia Beach. These cementation operations have been described in detail by the United States Bureau of Mines (1935), who report a 2200 Level portal discharge containing 980 mg/l copper, 170 mg/l ferrous iron and 1.61 g/l ferric iron with a pH of about 3. Current knowledge and terminology would consider such a flow to be Acid Rock Drainage (ARD).

Photograph 1: Arial View of Open Pit Complex (from Price et al., 1995)

Current Site Physical Status

The current physical status of the Britannia site has been well documented in reports by Steffen, Robertson and Kirsten (1991) and Price et al. (1995) and summarized by McCandless (1995). The present owners of the site are Copper Beach Estates Ltd. A 16 hectare parcel of land that includes former administrative, assay laboratory and other buildings, the remains of the ore processing mill and a small underground section of the mine were donated to the British Columbia Museum of Mining in 1979.

Mine water flows from the 2200 Level and 4100 Level portals and has the elevated metal content, particularly copper and zinc, and low pH characteristic of ARD. The 2200 Level portal discharge (Photograph 2) is no longer treated by the cementation plant at Mount Sheer, but flows directly into Jane Creek (Photograph 3) which is a tributary of Britannia Creek.

Photograph 2: 2200 Level Portal and Discharge (from Price et al., 1995)

Photograph 3: Jane Creek after entry of 2200 Level Portal Discharge

Attempts were made to divert the 2200 Level flow inside the mine to lower levels, away from the portal, but these measures appear to be currently ineffective. Even though the copper (40 to 100 mg/l) (Figure 1) and other metal concentrations in the 2200 Level portal discharge are now less than 10% of concentrations reported by the United States Bureau of Mines in 1935, they remain an environmental hazard, and are the major contributor to the concentration of copper (typically 0.5 to 3 mg/l) (Figure 1) in Britannia Creek at its discharge to Howe Sound (monitoring station at Townsite Bridge).

Figure 1: Britannia Water Quality Monitoring Data - 1995: 2200 Level Discharge, Britannia Creek at Townsite Bridge and 4100 Level Discharge (data courtesy of G. Ford, B.C. Ministry of Environment)

The 4100 Level portal discharge flows via a submerged pipeline to an outfall 30 m below the surface of Howe Sound. Copper concentration in the 4100 Level discharge is typically in the range of 15 to 20 mg/l (Figure 1). The fresh water from Britannia Creek and from the submerged outfall are of lower density than the saline waters of Howe Sound and tend to remain on or rise to the surface of the Sound. The pH of both Britannia Creek and the 4100 Level discharge to the outfall are lower than the pH of Howe Sound, resulting in some neutralization of the flows and precipitation of copper hydroxides and related compounds. These precipitates within the flows are often visible as plumes (Photograph 4).

Photograph 4: Arial Photograph of Britannia Beach and Britannia Creek at Howe Sound (from Price et al., 1995)

There are also several portals on the Furry Creek (south) side of Mineral Ridge (Price et al., 1995), but their volumetric discharge rate and metal concentrations are relatively insignificant in comparison with the 2200 and 4100 Level Portal discharges. Photograph 5 shows the discharge from the Beta Portal.

Photograph 5: Secondary Copper Minerals Precipitation Below the Beta Portal in the Furry Creek Drainage

(from Price et al., 1995)

For further information on metal concentrations in 2200 Level Portal discharge and Britannia rock samples, see Trace Element Geochemistry in Acid Rock Drainage page.

Current Site Regulatory Status

The site is currently subject to a Pollution Abatement Order (established in the early 70s and revised in 1981) under the B.C. Waste Management Act (Price et al., 1995). This order directs that:

As noted above, the 2200 Level portal discharge now enters Jane and Britannia Creeks, and is not directed to the 4100 Level. The copper recovery (cementation) plant at Britannia Beach (Photograph 6) appears to have seen sparse use in recent years.

Photograph 6: 4100 Level Cementation Launders above the Townsite Bridge and Britannia Creek, Britannia Beach (from Price et al., 1995)

The federal Metal Mine Liquid Effluent Regulations (MMLER, 1977), while prohibiting the discharge of coastal metal mine tailings to submarine receiving environments, permit the discharge of liquid effluents that comply with the MMLER (Golder Associates Ltd., 1996b). The MMLER apply only to mines that commenced operations after 1977 (Mills and Jambor, 1995), and therefore cannot be applied to Britannia with regard to either tailings or aqueous effluent. The Canadian Water Quality Guidelines developed by the Canadian Council of Resource and Environment Ministers (1987) apply only to fresh water receiving environments.

The B.C. Ministry of Environment has not developed specific Water Quality Assessment and Objectives for the Britannia site, as it has, for example, for such former and proposed mines as Mount Washington (Deniseger and Pommen, 1995), Nickel Plate (Swain, 1987) and Cinola-Misty Mountain (Nijman, 1990). The general Approved and Working Criteria for Water Quality - 1995 (B.C. Ministry of Environment, 1995) has copper, cadmium and zinc concentration criteria for both fresh and marine water, but the absence of any pre-mining baseline data for a heavily mineralized watersheds such as Britannia Creek and Howe Sound (Thompson, 1975 and Sibbick et al., 1992) makes the applicability of such general criteria questionable.

It is likely, however, that the Contaminated Sites Regulation (1996) of the B.C. Waste Management Act (1997) applies to the Britannia site.

Acid Rock Drainage Generation

Conditions within the mining complex at Britannia are, and have been since the commencement of mining, highly conducive to the production of ARD. Both the open pits and underground workings contain substantial quantities of exposed pyrite. The open pit bottoms are connected to underground workings by "glory holes", so that much of the substantial precipitation of rain and snow on Mineral Ridge is funnelled underground. Precipitation is cyclic, being high during the spring and late autumn, and low during summer and mid-winter, and most of the exposed pyrite has an adequate supply of oxygen since neither the pits, nor the underground workings above sea level, are flooded. Presumably, also, there are established colonies of bacteria such as Thiobacillus ferrooxidans that accelerate pyrite oxidation and ferric iron generation. Residual mineralization corresponding to sub-economic ore contains significant amounts of the copper and zinc minerals chalcopyrite and sphalerite, from which the copper and zinc are readily leached by the acidic ferric iron solution produced from the oxidation of pyrite. ARD has, therefore, almost certainly been a mine product since the early years of production, and was a major source of copper production by 1935 (United States Bureau of Mines).

However, ARD is produced in the natural environment as well as by mining activity (Downing and Mills, 1998, Slim, 1995, Termuende, 1995). Ramsey (1967) records that the Britannia ore deposits were initially discovered because of their surface outcrops, as were smaller, but similar, deposits in (what is now) Lynn Headwaters Regional Park on Vancouver's North Shore (Minfile Numbers 092GSW001 and 092GSW003, BC Ministry of Energy, Mines and Petroleum Resources, 1996, NTS map 92G/6, 1983, Freeman and Freeman, 1986). Armstrong (1990) dates the age of Howe Sound as about 10,000 years (i.e. since the end of the last ice-age and the retreat of glaciers). It is therefore a reasonable supposition that natural ARD was generated from exposed copper ores in the Britannia Creek valley during the 10,000 years prior to mine startup, and that the copper in this ARD may have contributed significantly over this extended period to the copper loadings in both the sediments and the waters of Howe Sound. Ford (1995) has noted anecdotal evidence that ochre (a mixture of iron oxides and hydroxides) was taken from the mouth of Britannia Creek for trade in pre-mining days, and ochre is a clear sign of iron compound precipitation from ARD. Steffen Robertson and Kirsten (1991) and Price et al. (1995) note that natural ARD would have been generated prior to mining. In the absence of pre-mining baseline water quality data only speculation is possible regarding metal concentrations and pH of watercourses such as Jane and Britannia Creeks, and whether such concentrations and pH may or may not have prevented the development of aquatic species such as fish in these watercourses.

Water Quality and Aquatic Effects Monitoring

Over the last eight years extensive water quality monitoring data for the Britannia Creek system has been collected by Steffen Robertson and Kirsten, the B.C. Ministry of Environment, Environment Canada and Norecol Dames & Moore (1996) that has established metal concentrations and loadings on a seasonal basis. Studies of the waters and sediments of Howe Sound have been conducted by Thompson and McComas (1974), Thompson (1975), Thompson and Paton (1976, 1978), Syvitsky and Macdonald (1982), Drysdale (1990), Chretien (1997) and others (see bibliography in Golder Associates Ltd., 1996a).

With regard to the submerged tailings, Drysdale has concluded:

"In summary, while it is well known that Howe Sound has a trace metal problem, it has been shown conclusively that the buried tailings deposit on the fjord floor is not the source of the dissolved metals"

Acid Base Accounting (Price, 1997) data for three Britannia tailings samples of unknown provenance have been reported by Lawrence and Harries (1996) that suggest that the tailings would be acid generating if deposited on the ground surface, rather than under cover of water. Drysdale's conclusions support the widely accepted fact that water is an effective oxygen barrier that prevents the onset of ARD.

Syvitsky and Macdonald (1982), Figure 15 report copper sediment concentrations that clearly indicate the location of the submerged tailings, but also show a tongue of elevated copper levels extending from Britannia Creek along the fjord coastline almost to Murrin Provincial Park. It is possible that the copper in these sediments is the result of Britannia Creek waters mixing with those of Howe Sound, since this tongue approximates the position of plume visible in the aerial photographs 8 and 9 of Price et al. (1995). A similar tongue of copper enriched sediments in seen in Figure 2 of Thompson and Paton (1976).

Thompson and Paton (1976) also found that the influence of the Britannia mine was detectable in the sediments of the main channel of Howe Sound at a point 13 km distant from Britannia Beach. The authors conclude that anomalously high levels of copper in Pacific oysters (Crassostrea gigas) taken from Howe Sound are due to the assimilation of geochemically insoluble particles in sediment and suspension, rather than the dissolved copper content of Howe Sound waters.

Chretien (1997) found that the mixing of Britannia Creek with estuarine waters occurs only at the surface, and that metal concentrations in Britannia Bay are markedly higher at the surface than at depth in both the vicinity of the mine and at 2 km offshore. He also found that the discharge from the submerged outfall is trapped below the surface of Howe Sound until winter, when density stratification breaks down and the discharge water rises to the surface where it can occasionally be observed as a light blue patch.

Monitoring studies to date have demonstrated that it is the dissolved metals in ARD released into Howe sound that represent a long-term environmental problem if left unmitigated, rather than the metal content of the submerged tailings.

Acid Rock Drainage Mitigation and Remediation

The ARD problem at Britannia has been recognized for a very long time. Initially it was welcomed as an additional source of copper product by cementation, but by 1974 Anaconda were investigating a lime-based neutralizing treatment plant (Steffen Robertson and Kirsten, 1991). This, unfortunately, was never built because of impending mine closure.

In their 1991 report, Steffen Robertson and Kirsten examined a number of mitigation and remediation options that included:

None of the copper recovery processes would increase the pH of the ARD significantly, while any neutralization process would generate large volumes of potentially chemically unstable sludge that would require a safe disposal site.

A series of studies and reports funded by Environment Canada (Process Research Associates, 1995, Ground Control Consulting Engineers, 1996, 1998, Cominco Engineering Services Ltd. (CESL), 1997, H.A. Simons, 1997, 1998) have been undertaken to develop the process parameters and engineering design of a lime-based high-density sludge plant. This project involves the storage of sludge at the former Mount Sheer townsite and the use of partially dammed underground workings as a storage reservoir to even out seasonal ARD flows.

Other successful precipitation/neutralization metal immobilization studies have been undertaken on Britannia ARD by the Klean Earth Environmental Company (KEECO) using their proprietary reagent KB-1 (Gormely Process Engineering, 1994, CSM Associates Limited, 1994)

NTBC Research Corporation successfully demonstrated their Biosulphide Process at the pilot plant level on ARD flows from the 4100 Level portal at Britannia Beach (NTBC Research Corporation, 1994, Rowley et al., 1997). This process produces only a small volume of metallic sulphide sludge in a two-stage process. Sulphate reducing bacteria (SRB) convert the sulphate in the ARD to hydrogen sulphide, which is then used to precipitate copper, zinc and cadmium.

Other approaches that have been considered are:

In reality there are a number of proven technologies that could be utilized to mitigate and remediate the ARD flows at Britannia so that they cease to pose environmental risks to the aquatic life of Howe Sound. No matter which approach, or combination of approaches, is taken to resolve the ARD problem at Britannia the monetary cost will be high for both initial installation and operation. It remains for the people, government and courts of British Columbia to determine whether ARD mitigation and remediation is necessary at Britannia, and, if so, what will be the source of the financing.

 

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