James Thomson embodied dedication to the mining industry throughout his 44-year career with the Ontario Department of Mines (ODM), later the Ontario Geological Survey (OGS). He revived, enlarged and modernized ODM, transforming it into an increasingly important body recognized in Canada and internationally for its technical excellence.

Thomson was a talented geologist in his own right, known for his uncanny ability to recognize the mineral potential of a showing, property or region. He discovered and reported on the surface exposures of the copper-zinc orebodies that later became the Geco and Willroy mines and recommended the Hemlo area for prospecting, though he did not live to see the discovery and development of three gold mines in the region. His reports and research generated widespread interest and contributed not only to new discoveries, but to a better understanding of the province’s major mining camps.

Thomson was born in Hensall, a small farming town in southwestern Ontario. He received a science degree from the University of Toronto in 1928 and earned his master’s degree in 1929. He obtained his PhD at the University of Wisconsin in 1932.

While still in the classroom, Thomson demonstrated a remarkable ability to recognize areas with mineral potential. In 1931, while mapping in the Manitouwadge area, he discovered several gossans with sulphide mineralization. Twenty years later, a group of enterprising men read his report and staked showings that soon became the main Geco orebody. In 1970, Thomson reported that the mines of the Manitouwadge camp had produced metals valued at $558 million; the total cost of his field party was a mere $3,000.

The decade between 1938 to 1948 was significant for both Thomson and the Department of Mines. He participated in and supervised the detailed mapping of the Larder Lake-Kirkland Lake area. He also recognized and named the Larder Lake fault, determining, after conferring with colleagues at the Geological Survey of Canada, that it was the eastward extension of the Cadillac Break.

From 1949 to 1960, Thomson focused his mapping efforts on the Sudbury Basin and to the west. In 1953, he began a major mapping project of the Basin that would give rise to radical new theories about the genesis of Sudbury ores.

In 1951, Thomson wrote the first of a series of commodity studies, known as “Base Metal Circulars,” which provided inventories for Ontario prospects and deposits. Over the years, these volumes have proved invaluable to prospectors and explorationists.

In 1961, he was appointed chief geologist of the mines department responsible for all geological mapping by provincial staff. His appointment was followed by a rapid increase in personnel and more aggressive mapping programs.

Thomson ensured that Ontario’s vibrant exploration sector was well- served with multi-disciplinary field programs, commodity inventories and research studies. He kept in close contact with the exploration fraternity, and encouraged his field geologists to do the same. In doing so, he set a higher standard for co-operation between industry and government, one that survives to this day.


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