Copperfields Mine (Temagami Mine) Comprehensive History
Discovery and Early Exploration
Copperfields Mine, originally known as the Temagami Mine, was discovered in the early 1950s on Temagami Island in Lake Temagami, Ontario. Copper showings on the island had been noted by geologists as far back as the late 19th century, but modern exploration began in 1951 after a strong geophysical anomaly was detected. Prospectors and companies quickly staked the ground, and Desrosier Nickel and Copper Mines Ltd. conducted ground magnetometer surveys and drilled the first diamond drill holes from 1951–1954.
Their work was soon followed by Frontenac Exploration and Development Co. in 1952–1953, which completed extensive geophysical surveys and 49 drill holes (totaling ~26,000 feet) to delineate the deposit. These early programs confirmed a spectacular high-grade copper-sulfide deposit. In 1954, Abex Mines Ltd. carried out additional geophysics and drilling, further proving the continuity of the orebody.
Geologists reported that the discovery drill cores were rich in chalcopyrite (CuFeS₂), indicating exceptionally high copper grades. By August 1954, the Temagami Mining Company Limited was incorporated (amalgamating the earlier Temagami prospectors and Desrosier Nickel & Copper Mines) to develop the find. Initial geological assessments touted the deposit as possibly the largest occurrence of nearly pure chalcopyrite ever found in Canada, with early assays showing ore averaging ~28% copper – extraordinarily rich by industry standards.
Geological Overview
The Copperfields deposit is hosted within the Temagami Greenstone Belt, a 2.7 billion-year-old sequence of metavolcanic and intrusive rocks in the Canadian Shield. Geologically, the mine’s mineralization occurs at the contact between an altered gabbro intrusion and rhyolite volcanics. This lower contact zone provided a structural and chemical trap for metal-rich fluids, resulting in lenses and veins of massive sulfides. The principal ore mineral is chalcopyrite (a copper-iron sulfide), which in this deposit formed unusually pure concentrations (the ore averaged ~6% Cu over the mine’s life). Associated minerals include pyrite and bornite (iron and copper sulfides) and secondary copper carbonates like malachite in the oxidized zones. Notably, the Copperfields ore also carried significant by-products: gold and silver were present in economic quantities, and minor amounts of nickel, cobalt, platinum, and palladium were found in the ore body. Nickel occurs as minerals such as millerite and gersdorffite, often with cobalt-nickel arsenides, indicating a complex magmatic sulphide origin. The gabbro host rock is a steeply dipping sill about 250 m thick, traced for at least 5 km along strike. This large intrusive body created a conduit for metal-bearing fluids. The structural geology includes steep fractures and breccia zones that the copper-rich fluids exploited, forming fissure-filling quartz-carbonate veins with massive chalcopyrite. The combination of a mafic-ultramafic intrusion and volcanic rocks classifies this deposit as a magmatic sulfide occurrence, somewhat akin to contact-style or feeder deposits in Archean greenstone belts. The extreme purity of the chalcopyrite resulted in an average copper content of 28% in select zones, eliminating the need for heavy onsite processing initially. In 1973, a new mineral species named temagamite (a palladium-mercury telluride) was discovered in ore samples from the mine, underscoring the geological uniqueness and mineral diversity of the deposit.
Mining Operations
Active mining at Copperfields spanned 1955 to 1972, during which both open-pit and underground methods were employed. After the official mine opening in 1955, surface stripping and a small open pit were developed to access the shallow high-grade ore. Simultaneously, an internal shaft (No. 1 shaft) was sunk to exploit deeper extensions; ultimately this vertical, four-compartment shaft reached a depth of about 2,535 feet (773 m) below surface with multiple production levels established (e.g. at 2175′, 2375′ levels). In the early years, mining was seasonal: ore was stockpiled on site until winter when ice roads could support trucking heavy ore off the island. High-grade ore was direct-shipped to smelters without milling because of its exceptionally high copper content. By 1964, a significant infrastructure milestone was achieved – the construction of the Lake Temagami Access Road (nicknamed “the Mine Road”). This road allowed year-round transport: ore could be barged to the mainland landing and hauled by truck, vastly improving logistics. Underground, miners followed the rich chalcopyrite veins using cut-and-fill and shrinkage stoping methods, typical for narrow, high-grade deposits.
Ownership and Corporate History
The Copperfields Mine passed through several corporate hands and played a pivotal role in Canadian mining corporate history. The initial development was led by the Temagami Mining Company Limited, which had been formed in 1954 specifically to consolidate the discovery holdings. Temagami Mining Co. was an amalgamation that included the interests of the original prospectors (Desrosier Nickel & Copper Mines) and new investors, positioning it to raise capital for mine construction. Notably, mining entrepreneur Dr. Norman B. Keevil Sr. was heavily involved in the project. By the late 1960s, Copperfields became closely associated with Teck Corporation – in fact, Copperfields Mining Corp. effectively became a part of Teck. Eventually, Copperfields Mining Corp. was rolled into Teck Corporation, making Temagami Mine one of Teck’s operating assets.
Production Data
During its 17-year life, Copperfields Mine was a prolific producer of copper with valuable precious metal credits. In total, the mine milled just over 900,000 tons of ore averaging ~6.0% Cu, yielding approximately 80 million pounds of copper, 230,000 ounces of silver, and 13,271 ounces of gold.
Probable Nearby Deposits
The Copperfields deposit is part of a broader metallogenic system within the Temagami Greenstone Belt, which remains highly prospective for additional copper and nickel deposits. Notably, geophysical surveys indicate that similar conductive anomalies exist east of the Copperfields deposit, suggesting potential extensions or parallel mineralized zones. Exploration drilling in the 1980s and 1990s identified disseminated chalcopyrite and pyrrhotite-bearing gabbroic intrusions eastward from the mine, though grades were generally lower than those at Copperfields.
To the east, several untested airborne electromagnetic anomalies remain, particularly near Net Lake and the eastern arm of Lake Temagami, indicating potential for further massive sulfide lenses at depth. The presence of nickel-cobalt occurrences in the same belt suggests a possible polymetallic system extending beyond the known mine footprint. Further deep-penetration geophysical surveys and drilling would be needed to confirm the size and economic viability of these targets, but the geological setting remains highly favorable for additional copper-nickel discoveries.