The Red Lake mine: the richest gold mine in the world: Balmertown, Ontario, Canada

The Red Lake mine: the richest gold mine in the world: Balmertown, Ontario, Canada

David K. Joyce

In 1989 Goldcorp, Inc. took over Dickenson Mines, Ltd., a venerable gold mining company that, since 1948, had operated the Arthur White mine in the Red Lake mining camp, located north of Lake Superior, near the Ontario-Manitoba border. Robert McEwan, chairman of Goldcorp, felt that the adage “the best place to look for a new orebody is near an old mine” had some credence. Was he right! Goldcorp initiated an exploration program while the old mine rolled along as a break-even or money-losing gold mining operation. During early 1995, while testing Goldcorp’s geological theory, diamond drillers cut across a high-grade body of mineralization that was soon to become the fabulous “High-Grade Zone” (HGZ). Diamond drilling continued, and the HGZ has proved (at the time of this writing) to contain more than 1.96 million tons of high-grade ore containing 4.6 million ounces of gold. That is an average grade of 2.35 troy ounces per ton! Most gold mines in the world average well under 0.5 troy ounce per ton. So prolific was the change in fortune of the mine that the Arthur White mine was renamed the Red Lake mine.

There are other orebodies in the world that, being larger, contain more troy ounces of gold. However, to our knowledge, no other gold mines contain the average grade of ore that the Red Lake mine does. These sorts of orebodies come along only once every several decades or so.

The HGZ changed the economics of the old mine so much that Goldcorp decided to build a new mine around the new orebody to optimize its extraction. A milling complex and offices were built along with a camp to house contract workers. The only significant parts of the original mine that remained in use were the headframe and shaft needed to access the orebody. Recently, however, Goldcorp also has decided to replace the old shaft and winze with a new 7,500-foot single lift, vertical shaft in an effort to speed up the mining of the orebody and to improve the overall efficiency of the mine.

The impact of the discovery of the new orebody on Goldcorp, the Red Lake mine, and the surrounding area has been dramatic. With millions of dollars surging into the local economy from the Red Lake mine and the exploration efforts of other companies hoping to duplicate the feat, the Red Lake area has experienced a surge of prosperity and confidence not felt since the heydays of gold mine discoveries in the 1940s and 1950s. Now, cash rich with no debt, Goldcorp is one of the most profitable mining companies in the world.

It became apparent early in the exploration of the orebody that visible native gold would often be encountered. The senior management of Goldcorp decided, to its credit, that if specimen-grade native gold was encountered, some of it should be preserved as specimens to serve as a legacy of Goldcorp, the Red Lake mine, and the fantastic orebody that produced it. One of the authors (DKJ) was retained to prepare specimens, on site, and then to market and sell them. Since production commenced, hundreds of beautiful, rich native gold specimens have been recovered and sold to museums, shareholders, collectors, and universities around the world.

Many mines have zones of high-grade ore that are very profitable to mine. Few have had a zone like the HGZ, however, which is still open at depth and, although smaller in width at depth, appears to be increasing in grade.

The property on which the Red Lake mine is located comprises fifty-eight patented mineral claims held by Goldcorp that cover approximately 2,348 acres, which, on the west side, share a common boundary with Placer Dome, Ltd.’s Campbell mine. Goldcorp also holds mineral claims covering approximately 56,125 additional acres of prospective mineral ground in the Red Lake area. Access to the mine is by road and by air, with the closest major cities being Winnipeg, Manitoba, and Thunder Bay, Ontario.

The Red Lake mine is currently operating at a rate of 550 tons of ore per day. Mining is accomplished using mostly a mechanized cut-and-fill mining method utilizing jumbo drills and 5-cubic-yard scoop trains. At the present time, ore is being mined between the 31 and 37 levels, at a depth of about 4,000 and 5,500 feet below surface. This ore, averaging about 2.28 troy ounces of gold per ton, is being hoisted to the surface. When the new shaft is finished in 2006, production will increase to 1,000 tons per day.

The mill at the Red Lake mine uses several techniques to separate gold from the waste rock. One circuit uses centrifugal force and gravity, employing Knelson concentrators and a Diester jig table, respectively, to separate coarse gold from the rock. Another circuit employs flotation to float gold-rich sulfides to produce a gold-rich sulfide concentrate. Third, a carbon-in-pulp circuit is used to capture the fine gold that is not tied up in sulfides. Much of the concentrates produced by the above methods contains bits of rock and other impurities. The concentrates are refined by smelting–they are melted, and the impurities are removed as a slag. The finished products at the mine are dore bars, which are poured molten into molds after the refining is complete. Dore is a mixture of gold and silver with some other minor impurities and, at the Red Lake mine, contains, on average, about 87 percent gold and 13 percent silver. The dore bars are sold to refineries that further purify the gold and sell it to end-users, financial institutions, and investors. Goldcorp actually does not sell but retains a certain percentage of its gold, in the belief that gold is undervalued. Currently, Goldcorp owns more gold bullion than many governments of the world!

Security is very tight at the Red Lake mine. All people and vehicles enter and leave the mine through a single gate. Guards are diligent in searching all belongings and vehicles to ensure that gold is not smuggled out of the mine. Everyone leaving the mine is required to undergo a search, similar to those undertaken at airports, with subjects selected at random. All briefcases and pieces of luggage leaving the mine are searched.

Geology

Regional Geology

Ontario and Quebec occupy much of the Canadian Shield, a prolific, Precambrian-age geological formation and home of many of the world’s greatest mines, past and present. There are many belts of greenstone (highly contorted, Precambrian volcanics and sediments) throughout the Canadian Shield. These greenstone belts are the geological environments where gold deposits have been found; they include, among others, those at Campbell, Hollinger, Dome, Sigma, Kerr Addison, Lakeshore, Macassa, McIntyre, Hemlo, Doyon, Bousquet, Malartic, and Camflo, all multimillion-ounce producers. Goldcorp’s Red Lake mine lies in the eastern part of the Red Lake Greenstone Belt, which is composed of an assemblage of ultramafic, mafic, and felsic volcanic rocks with a sedimentary sequence. These rocks are cut by a number of felsic and mafic dikes.

Mine Geology

Most of the gold mineralization within the Red Lake mine’s boundaries is within, or adjacent to, major deformation zones. Two deformation events are recognized in the Red Lake Area, D1 and D2; both were imposed after 2,742 Ma. The D1 event occurred syn- or pre-Huston Conglomerate (2,733 Ma or earlier), whereas D2 is estimated–based on field relationships involving intrabelt plutons–at 2,718 Ma or earlier. D2 was a protracted event involving brittle-ductile reworking during extensive hydrothermal alteration and metamorphism, which ultimately led to syn- to late-tectonic precipitation of gold to form the ore structures mined in the Red Lake mining camp.

The deposit at the Red Lake mine is made up of a number of subparallel groups of linear mineralized zones, hosted by sequences of altered mafic volcanic rocks, which are interpreted to lie along the north and south limbs of a major antiform. Ultramafic rocks, which are rarely host to ore, are spatially related and important in acting as impermeable zones that trapped the gold-rich hydrothermal solutions in fracture systems.

Ore lenses may vary from a few inches to several feet in width and may be from tens of feet to more than 100 feet in length. Overlapping lenses have permitted orebodies to be developed and mined over lengths, in some instances, in excess of 1,000 feet and widths of up to 60 feet.

The orebodies generally strike from northwest to southeast and dip to the southwest. Individual lenses in the orebodies plunge to the west. Fifteen major and thirteen minor, steeply dipping zones have been identified to date. Current ongoing underground and surface exploration work indicates that other major zones exist. Each zone consists of several parallel to subparallel mineralized zones. Apart from variations in physical attributes and dimensions, the zones vary from well-defined veins to more indistinct zones of silica-sulfide mineralization. The zones vary mineralogically in sulfide content and gold distribution.

Styles of Gold Emplacement

The two major types of gold mineralization consist of high-grade quartz-carbonate-sulfide mineralization, grading 2.35 troy ounces of gold per ton (opt), and the lower-grade sulfide zones, grading 0.37 opt. To reflect that variation, the zones have been grouped into two categories, the high-grade zones (the HGZ) and the sulfide zones (the Sulfide Zone).

Within each group, gold can be emplaced within fabric parallel structures or in structures occurring at a high angle to rock fabric. Generally, the high-angle structures represent dilatant ore environments allowing for protracted fluid-wallrock interaction and enhanced gold grades. Within the HGZ, mining horizons can average up to 5.00 opt and locally grade in excess of 10.00 opt! Although the fabric parallel structures as a whole are not as high grade, locally grades can be significant and specimen-quality mineral samples abundant. Most often, the gold specimens are collected from mining horizons within the high-angle structures. Not only are the grades generally higher in those structures, but also more quartz and carbonate exist as host to the visible gold.

Mineralogy

Gold is the principal ore mineral at the Red Lake mine and the mineral that is the most interesting to collectors. The gold in the HGZ was largely emplaced as a result of gold-rich, siliceous replacement of carbonate veins and also by injection into volcanic rocks. Large masses of native gold–up to many hundreds of troy ounces–have been encountered during mining. On occasion, knobs or masses of native gold can be seen protruding from stope backs or wails. These are rich sights to behold! It is from such places that the most impressive specimens of native gold have been recovered.

There appears to have been some subsequent remobilization of native gold into fractures in quartz and carbonates (calcite, ferroan dolomite) and into intensely altered volcanics. Arguably, the best specimens of native gold result when the gold has formed as veinlets in these fractures. The gold forms more coherent, solid veinlets or “leaves” in the calcite and quartz than it does in the altered rocks. These veinlets, when exposed, become the leaves and plates of the specimens from the Red Lake mine. A large percentage of the native gold at the mine occurs only as fine fracture fillings or as coarse masses in altered volcanic rock that are not suitable as specimens other than as examples of fantastic high-grade ore!

On occasion, masses of coarse gold are encountered in dark gray-black quartz. This type of high-grade is slabbed and sold to lapidaries for use in jewelry. Geologists and others interested in ore textures also find the slabbed high-grade specimens interesting.

Berthierite and stibnite are the only other species that occur at the mine that are of interest to collectors. Rich, high-grade gold is, on occasion, associated with metallic black masses of coarse berthierite and stibnite. Crystals of these minerals have not been observed, but their association with coarse gold makes for interesting specimens.

Other minerals commonly occur at the mine as coarse to fine, massive aggregates, including arsenopyrite, pyrite, pyrrhotite, chalcopyrite, and sphalerite. In addition, a number of species have been reported from petrographic studies of polished sections. They include electrum, tetrahedrite, aurostibite, boulangerite, galena, bournonite, jamesonite, andorite, gudmundite, ullmannite, zoubekite, hessite, benleonardite, acanthite, coloradoite, gersdorffite, lollingite, millerite, and pentlandite. Some other minerals that are occasionally observed in the ore are magnetite, actinolite, rutile, the tourmaline group, chlorite group, mica group, garnet group, and iron-calcium-magnesium carbonates.

Specimen Recovery

Company geologists regularly visit stopes and development headings to gather samples, map local geology, and give direction to miners. The geologists are accustomed to seeing native gold in the HGZ but are constantly on the lookout for the extra-high-grade areas that are occasionally encountered. These super-rich areas are erratically distributed throughout the mine and often run locally in the many hundreds of ounces per ton over distances of tens of feet. They are also often the sources of specimen-quality high-grade that can be prepared to produce the beautiful gold specimens for which the Red Lake mine is becoming famous. When geologists encounter the super-high-grade areas, they collect any likely looking gold-bearing ore and place it in locked, metal boxes, which are then moved to the shaft, taken to the surface, and stored in the vault.

One of the authors (DKJ) periodically visits the mine and works on each individual piece of high-grade to, if possible, better expose the beautiful gold leaves, plates, and other interesting formations that are enclosed in the matrix rock and vein material. He “reads” the grain of the rock and the directions of gold emplacement and then, using a host of tools, breaks, chips, and chisels away the minerals that cover the gold in an effort to produce aesthetic specimens that are coveted by collectors, investors, and museums around the world. The vault can be a spectacular sight when full of native gold-bearing high-grade ore and finished specimens!

Interestingly, Goldcorp has retained one specimen in particular; it consists of a thick vein of nearly solid gold traversing altered volcanic rock. The specimen is estimated to contain 298 troy ounces of gold! Goldcorp often brings this large specimen to trade shows to tantalize people.

Conclusions

Based on the very high average grade of current ore and life-of-mine ore reserves, the Red Lake mine is, to our knowledge, the richest gold mine in the world. To its credit, Goldcorp has decided to recover and market beautiful specimens of high-grade ore, specimens that will serve as a legacy of this orebody. They will continue to delight collectors, prospectors, museum visitors, and others who marvel at the occurrence of so much gold, in one place, at one time!

ACKNOWLEDGMENTS

We would like to thank Mr. R. M. McEwan, chairman and CEO, and the management of Goldcorp for the opportunity to be involved with specimen recovery at the Red Lake mine, for permission to publish this article, and for its foresight to save excellent gold specimens from the mine. We also thank the following people for assisting or contributing to the article: Bruce Humphrey, chief operating officer; Chis Bradbrook, vice president of corporate development; Gilles Filion, vice president of exploration; Claude Lemasson, mine manager; Tim Twomey, senior geologist; Gabriela Sanchez, assistant to the chairman, and Arlene Connolly, graphic artist. In addition, we thank Dr. Robert Cook and Dr. Carl Francis for their invaluable reviews of the manuscript.

ADDITIONAL READING

Andrews, A. J., and H. Hagon. 1985. Alteration, metamorphism and structure associated with Archen volcanic-hosted gold deposits, Red Lake district: Studies in the Campbell and A. W. White mines. In Summary of field work and other activities 1985, 193-200. Ontario Geological Survey miscellaneous paper 126.

Dube, B., K. Williamson, and M. Malo. Geology of the Goldcorp Inc. High Grade Zone, Red Lake mine, Ontario: An update. Geological Survey of Canada current research 2002-C26, catalogue No. M44-2002/C26E-IN.

MacGeehan, P., and C. J. Hodgson. 1982. Environments of gold mineralization in the Campbell, Red Lake and Dickenson mines, Red Lake district, Ontario. In Geology of Canadian gold deposits, 184-207. Canadian Institute of Mining and Metallurgy special volume 24.

Outlook, 2002. 2002. Balmerton, Ontario, Canada: Goldcorp publication.

Parker, J. R. 2000. Gold mineralization and wall rock alteration in the Red Lake Greenstone Belt: A regional perspective. In Summary of field work and other activities, 1-28. Ontario Geological Survey open-file report 6032.

Sanborn-Barrie, M., T. Skulski, J. Parker, and B. Dube. 2000. Integrated regional analysis of the Red Lake Greenstone Belt and its mineral deposits, western Superior Province, Ontario. Geological Survey of Canada current research 2000-C18.

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DAVID K. JOYCE

Box 95551, Newmarket, Ontario

Canada L3Y 8J8

dkjoyce@allstream.net

STEPHEN McGIBBON

Goldcorp, Inc.

Balmertown, Ontario

Canada P0V 1C0

Smcgibbon@goldcorp.com

David K. Joyce, a graduate of the Haileybury School of Mines, is a mineral dealer, adjunct professor at the University of Toronto, and a mining business development consultant.

Stephen McGibbon is exploration manager at Goldcorp’s Red Lake mine. He holds a bachelor of science degree from Queen’s University and has been active in exploration and mining for twenty-two years.

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