May 2011

Battling Lake Superior

The engineering feat of Silver Islet Mine

By Correy Baldwin

Silver Islet Mine, following its closure in 1883 | Thunder Bay Historical Museum Society (No. 972.2.344)


At its height, Silver Islet Mine was the envy of the industry, despite the odds stacked against it. It was, after all, perched on a tiny rock off the northern shore of Lake Superior, where it faced a constant bombardment of storms. Every season was a new battle to keep the waves and the wind-blown ice from flooding or destroying the mine.

The story begins in 1868, when Thomas Macfarlane led an exploration team through the area on behalf of the Montreal Mining Company. In June, they explored a small group of islands not far from Thunder Bay, but found little of interest. Finally, they stopped at an unassuming, wind-swept rock just 27 metres in length. Cutting through it was a promising vein. They set blasting powder and scattered for what little cover they could find. When they emerged, team member John Morgan spotted silver nuggets glittering in the water.

The team followed the vein towards the shore, looking for better access to the ore, but the vein held no silver where it passed through nearby Burnt Island, nor did anything turn up on the mainland. The only access to the silver was from the barren islet. Macfarlane christened it Silver Islet and returned to Montreal with his findings.

Enthusiastic about the quality of the silver, Macfarlane recommended that the Montreal Mining Company develop the site. However, they were not sure that an exposed islet would be an ideal location, no matter the quality of the ore. Mining it would take significant investment, not to mention a feat of engineering. They agreed to develop the site, but only to make it sellable.

Macfarlane was given a tight budget and instructions to improve the property and extract as much ore as possible. He hired two miners and sunk a shaft alongside the vein. He then built a wall of timbers to protect the shaft and a rock-filled crib to support the shaft house.

The first battle with the lake came that fall when a heavy storm tested the strength of Macfarlane’s structures. It did not go well: waves crashed over the shaft house and flooded the shaft. Undeterred, Macfarlane rebuilt and continued extracting the silver. When winter approached, he put Morgan in charge and returned to Montreal to report back to his employers. Triumphantly, he handed over the $6,750 worth of silver they had mined over the previous two months and asked for an additional $50,000.

The company hesitated. European investors had been reluctant to invest, and the rest of their properties were draining their accounts. Despite the promise of the Silver Islet find, they were not willing to gamble. They would look for an American buyer.

Macfarlane was disappointed in the lost opportunity. The first he would hear about the sale of the property was when William Frue arrived by boat in August 1870. Armed with investment money and an enterprising spirit, Frue went about developing the site with gusto. His men bolted logs together to form a 140-metre-long by four-metre-wide breakwater cribbing, filling it with rocks. They built a coffer dam within the breakwater to enclose the mine pit and a platform to serve as a foundation for the mine buildings and machinery.

It was not long before these efforts were put to the test: violent storms raged throughout that fall and winter. An October storm destroyed half the breakwater, halting production for three weeks. Frue doubled the width of the cribbing, but ice smashed through it again during a December storm, dumping almost 3,000 tonnes of rock into the lake. March was unforgiving, with storm after storm destroying a total of 15,000 metres of cribbing.

When spring melted the ice, Frue again extended the breakwater – it was now 22 metres wide and supported by five five-metre-high bulkheads facing out at 45 degrees and holding approximately 50,000 tonnes of rock. The workable area on the islet was expanded to over ten times its original size, and the mine camp and town were growing as well, eventually accommodating 600 workers.

By May 1872, the pit was 40 metres below the lake’s surface and water was constantly seeping in through the pit walls. Occasionally, the mine flooded, once when the drills hit an underground spring and Frue was forced to upgrade the pumping system again and again. The engine pumps were now operating 24 hours a day.

The deeper the mine got, the more nervous the men became about the massive weight of water above them. Many left before freeze-up, fearing the unpredictable destruction of the winter ice. Their concern was not unfounded: every winter, storms hammered Silver Islet. Cribbing was constantly ripped away and buildings were destroyed.

It was an endless battle that pushed Frue’s adaptability and ingenuity as an engineer and businessman. By the time he left Silver Islet after five years as superintendent, it had become the most successful mine in the region, and one of the richest silver mines in the world.

Those were Silver Islet’s best years. When Richard Trethewey took over in 1875, production had already begun to slow. Soon the vein dried up, leaving Trethewey scrambling to locate more ore. A second vein was discovered in 1878 and the mine was reinvigorated. Still, the amount of silver in the mine was dwindling, and the payroll with it.

Meanwhile the familiar struggle with Lake Superior continued. In 1881, a major storm smashed through the breakwater, destroying buildings and flooding the shaft. In the end, Lake Superior would have its way.

In 1883, the winter freeze-up came early and a supply ship carrying the coal for the pump engines failed to arrive, becoming stuck in ice off the coast of Michigan. Silver Islet’s supply would not last until spring. By March, the mine reached its final depth of 384 metres, nearly a quarter mile. The engines stopped and the shaft slowly filled with water.

The mine was abandoned, left to the devices of Lake Superior, which, foot by foot, tore away what remained of the Silver Islet Mine.

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