Rossland’s Geology
What We Mined
Rossland is best known for the gold that was mined during the town’s boom years in the late 1890s to 1920s. Rossland is, in fact, BC’s second largest producer of gold to date, with a estimated $300 million worth of gold extracted. During this time, copper and silver were also extracted in small amounts. Later on, lead, zinc, and molybdenum were also mined.
Photo 2305.0010: The Le Roi Mine Shaft House, c.1904.
If Rocks Could Talk: Rossland’s Geological History
A history much longer than that of the miners who came to Rossland, or the indigenous Sinixt who resided in the area before them, is that of the rocks, minerals, and mountains upon which the town of Rossland was constructed. In order to learn this history, one must start 300 million years ago in the Palaeozoic era.
Colour-coded map of the Rossland area, showing different geological features. Map created by Cominco (now Teck Trail Operations)
See key below.
Map key for mineral map above
200 Million Years Ago (The Jurassic Period)
In the early Jurassic Period, the region that would later become Rossland experienced a stretching of the earth’s crust known as an extension, which caused large bodies of rock to break. This caused a fault-bounded section to form at the bottom of the sea, lifting the area and making it an ‘under sea high’. The Rossland Range now runs on either side of this fault break, leading to some interesting geology. While both sides of the break mountains have an extrusive form, Red Mountain lies on one side of this break, leading to its top being composed of marine sediment, while the Kootenay Columbia Mountain top on the other side of the fault is composed of volcanic material. It is thought that this fault led to the formation of a chain of volcanoes, including the stratovolcano known as the Rossland Volcano, which then rose out of the sea, creating the beginning of the Elise Formation. This Formation along with the Roberts Formation are the basis of the Rossland area’s geology and topography.
During the latter part of the Jurassic Period, the Mount Roberts Formation was lifted above the sea. As such, the area became a volcanic high-point referred to as the Rossland Paleohigh.
300 Million Years Ago (The Palaeozoic Period)
The earliest rocks which remain in the Rossland Range were formed during the Pennsylvanian Period of the Palaeozoic era, around 300 million years ago. This rock was formed as mud and slime sediments settled at the bottom of an ancient semi-tropical sea. This formed the base of the geological layout of the area, known as the Mount Roberts Formation. The rock this formed can be seen today after rains, glinting as polished granite on the middle third of Mount Roberts.
Photo 2311.0010: A moonlight view of Mount Spokane, taken January 9th, 1898. Mount Spokane was renamed Mount Roberts in June 1900 after the Boer War in honour of the famous British General - Lord Frederick Roberts.
Stereograms of a Block of Ore - Bearing Country Rossland, B.C. produced by Canada Department of Mines - 1915.
190 Million Years Ago
It is thought that 190 million years ago, the hot liquid magma of the Rossland Monzonite intruded the Roberts formation. This rock cooled below the surface and the cracking that occurred as the monzonite cooled caused it to become the ‘host rock’ for the copper-gold deposits that later formed. As the cracks and fissures formed, they allowed space for the minerals to enter and create veins of mineral deposits.
180 Million Years Ago
It was about 180 million years ago that the ancestral North America, where the Mount Roberts and Elise Formations lay, and the Intermontane Superterrane began to collide. This collision caused the Intermontane Superterrane to wedge into the side of North America, and push eastward over the Rossland area and beyond, leaving an imprint known as the Kootenay Arc. This arc is a belt of folding and faulting rock caused by the collision. For the Rossland Range, this meant folding and faulting of the Elise and Roberts Formations, and left the Rossland Range on the inner fold of the Kootenay Arc.
180 Million Years Ago
It was about 180 million years ago that the ancestral North America, where the Mount Roberts and Elise Formations lay, and the Intermontane Superterrane began to collide. This collision caused the Intermontane Superterrane to wedge into the side of North America, and push eastward over the Rossland area and beyond, leaving an imprint known as the Kootenay Arc. This arc is a belt of folding and faulting rock caused by the collision. For the Rossland Range, this meant folding and faulting of the Elise and Roberts Formations, and left the Rossland Range on the inner fold of the Kootenay Arc.
Map of the major profitable mineral deposits in British Columbia. (Click for a closer look)
Map showing the locations of the different rock types in Rossland
155 Million Years Ago
About 25 million years after the intrusion of the Rossland Monzonite, the area was invaded by liquid granite magma known as the Trail Pluton. This heat caused thermal metamorphosis of siltstone in the Roberts formation, creating molybdenum. Molybdenum, although not as flashy as gold, was an important mineral mined in the area between 1966 and 1972.
So… What About the Volcano?
Ask a Rosslander the geological history of our town, and there is a good chance they will tell you it lies in the crater of an old, now dormant volcano. Although a very exciting story and once perpetuated by geologists, this, unfortunately, is not the case! Although the area was formed by volcanic activity, including that of the Rossland stratovolcano, the site itself is not in the crater or caldera of a volcano. This legend has its roots in original assumptions of the geological situation. In 1915, the first Canadian Geological Surveys of Rossland were conducted, and it was deduced that 200 million years ago, a continental volcano was present about were Red Mountain currently sires. More recent studies have unfortunately revealed this is not the case, as can be seen in the history outlined above.
Still.. in 2019, Tourism Rossland did a segment asking locals: “Was Rossland built on a dormant volcano?” The result didn’t go as well as we might have hoped!
Of course, we had to respond with our wonderful and VERY knowledgable Camp Black Bear summer camp kids; they’ve learned many times over now the geological development of the region thanks to many school tours, museum/rockhounds clubs, special events, and educational camp opportunities!
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