Canadian Rockhound: The Madoc Gold Deposits

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The Gold Deposits in the Madoc Area of Eastern Ontario
By Bob Bredberg

The first discovery of gold in the Canadian Shield took place at the community of Eldorado 6 miles north of Madoc in August of 1866. Originally thought to be copper pyrite, the nuggets were identified as gold in October, and the word spread like a wildfire. The small community soon found itself at the center of a gold rush as thousands of hopeful prospectors arrived from California, Australia, Europe and the United States, all drawn by the "rich" discovery at the Richardson Gold Mine in Eldorado. Even Thomas Edison is said to have come to Madoc in the spring of 1867 with the idea of developing gold recovery equipment for the new mines, but there is no record of the outcome.

Cavern of Gold

During excavation, the amateur prospectors had reached a depth of fifteen feet in a gossan stained quartz vein when the ground beneath their feet gave way and dumped them into a small underground cavern. The ceiling and walls of this cavern were studded with pure gold, and when they came to remove the soft black earth covering the floor of the cavern, it was found to be filled with leaves and small nuggets of gold. Although extremely rich, it was only an isolated pocket, and within a few years the mine was shut down as being unprofitable. None the less, the Richardson Mine fostered the discovery of thirty other gold mines, most of which were clustered 7 miles to the southwest at Deloro.

The Deloro Pluton

These mines encircled the west rim of the Deloro Pluton, a granite body which intruded the metasedimentary crust, and in so doing gave rise to an extensive vent system which appears to have played a role in the accumulation of gold, iron and arsenopyrite. At the Deloro camp, most of the mines carried a gold-arsenopyrite association, though many were discovered because of visible gold found in the surface veins. One of the most productive of the Deloro mines was the Gatling (Five Acre) Mine, owned by the brother of the man whom invented the Gatling gun. Most of these mines played out below 240 feet and were eventually closed except for the manufacture of arsenic from the arsenopyrite. A few years ago, Noranda is said to have explored a gold property just outside Deloro, and a nearby property is now scheduled for drilling by an as yet unknown company.

Bannockburn Gold Deposits

Four miles north of Eldorado, at Bannockburn, another gold discovery in 1868 spawned several other mines but none ever really came into production. Although the area around Bannockburn is bounded by plutons, it appears that a metasedimentary flow wound its way between the plutons like a river. Folded by stress, many of the resultant fractures were filled with quartz, some of which can be traced for 500 feet. Such distinct vein structures were lacking at the Richardson Mine, and thus made the search for gold at Eldorado a hit or miss proposition. Technically classed as a "skarn zone", the Eldorado deposits had no predictable pattern to their occurrence, and were therefore only "where you found them".

In 1983, a prospector discovered that a number of the long quartz veins at Bannockburn contained visible gold. The property is now being explored by the Madoc Mining Company which is currently in the process of extracting a bulk sample from their underground workings. Madoc Mining is part of a recent trend in the mining industry toward small scale operations whose profitability is in fair part due to the absence of expensive offices and debt-loaded capital equipment costs. Typically, this requires clearly defined objectives and highly efficient ore recovery techniques using leased equipment, and if done carefully, an operation of this nature can commercialize many of the smaller deposits passed over by the big guys.

Cooper Gold Deposits

Five miles east of Bannockburn, just past the hamlet of Cooper, two mining companies have drilled for gold, and, a few miles further south near Queensborough, not far from the old Sophia Gold Mine (circa 1890), three other exploration companies have recently drilled potential gold deposits. One of these, Cooper Gold, has apparently identified a medium sized low grade deposit in an alteration zone at the margin of an intrusive structure.

Origins

Though the area to the west, north and east of Madoc has been mined for gold for more than a century, there is still considerable debate as to the original origin of the deposits. While many of the deposits are associated with vent structures at the margins of plutonic intrusions, this is not always true as evidenced by the Madoc Mining deposit at Bannockburn. The absence of alluvial gold could lead one to conclude that the gold was perhaps eroded from older rocks and thence became part of the sedimentary deposits which were remobilised during the extensive periods of metamorphic activity which followed. Whatever the origin, the search for gold has remained alive in this area for more then 130 years.

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