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Looking Back: Tracing the Cadomin Conglomerate


John Kinnear

Nov 2, 2022

The Kootenay geological formation holds the key to how the communities of the Pass developed

The location of the Kootenay geological formation, which trends north to south throughout the Crowsnest Pass, holds the key to why the communities of the Pass developed where they did. In Bellevue, Hillcrest, Frank, Blairmore and Coleman, out-cropping fault repeats of this coal bearing zone led to mines being driven into the coal seams of the Kootenay, and as they say, the rest is history.    

In the case of Coleman, the first mine to be developed was the International in 1903. Across the valley, south of the deteriorating remains of its turn of the century tip-ple complex, you will find the sealed entries to this mine, which produced over 13 million tons of coal before it was shut down in 1952. The original entries were driven in south of the Crowsnest River, at somewhat of an angle, to make contact with the massive Cadomin Conglomerate, a predominant sandstone feature here in the Pass. The Cadomin is an integral part of the Kootenay and where-ever you find it, the coal seams are usually close by.

Incredibly, that entry was eventually driven for over a mile into this super-hard version of nature’s cement. The cost of driving that amount of rock tunnel these days would be astronomical. This strategic move ensured that the International entry would remain very intact and it still does, to this day. A few years back the once buried entrances were re-exposed and permanently sealed with a concrete block wall some distance inside and then giant metal doors added at the entrance as a second seal.    

The Cadomin conglomerate outcrop itself is in evidence in several places along a north/south trend in the Coleman area. As you leave town on the highway you pass by it on the first curve going west.  Directly below the highway there is a giant exposure of the Cadomin that the road to West Coleman wends around.    

This massive bluff is, in reality, pebbles cemented together with microcrystalline quartz.  Author and geologist Ben Gadd has observed in his geological tour book ‘Canadian Rockies’ that the green pebbles of chert, that the Cadomin is known for, are similar to the deep-green chert found in the Cache Creek Terrane . That terrane is a landmass hundreds of kilometers to the west which suggests that rivers once flowed from central BC into Alberta a very long time ago.  

Further to the south of that bluff, on the Crowsnest River, the conglomerate surfaces slightly and creates a lovely waterfall/rapid very near the easternmost side of the trailer city.  This small waterfall demonstrates the hardness of this upper Kootenay measure, as it has resisted erosion for hundreds of years. Immediately south and east of there is where the now sealed International tunnels entered into its trend.  

When one views this area on Google earth the Cadomin formation jumps out at you as a prominent treeless, 10 metre-plus wide, rock highway that trends south from the Crowsnest River to where it crosses York Creek. Once again its appearance creates a beautiful water-resistant step we all know as York Creek Falls.  

Back north of the falls just south of the York Creek staging area the International Mine installed its main air supply fan, an important building tasked with ensuring that those working deep within the Kootenay formation had an adequate air supply. It is a massive concrete structure only a hundred feet off the road’s west side and is orientated in an east/west direction. It, like the entries down by the river, was deliberately positioned just on the east edge of the Cadomin rock tunnel. It had an outside enclosed concrete airway to carry the air up the hill and into a tunnel driven into the conglomerate.    

I have heard of only one other coal mine in Alberta that took the rock tunnel approach and that was the Cadomin Mine south of Hinton that operated from 1917 to 1952.  It utilized what was known as IPRT (Isolated Panel Rock Tunnel) method. This method minimized hazards by dividing the mine into separate, independent districts. When the coal in each district was exhausted, that section of the tunnel was filled with concrete and sealed off from the rest of the mine, reducing methane gas build-up and the risk of an explosion.  

The International Mine, throughout its lifetime, lost 55 men to accidents, which is just over one man per year. One father or son that didn’t come home to their family. It was by all reports considered a safer mine than the McGillivray Mine to the north of it which suffered 58 losses in 46 years.  The International Mine was amalgamated with the McGillivray Mine in 1935 for economic reasons and in 1951 the entity known as Coleman Collieries acquired both mines and the Hillcrest/Mohawk Collieries. The Mohawk and Hillcrest Mines were then shut down to cope with the dwindling markets and their manpower absorbed into Coleman Collieries wherever possible.    

I have mentioned in previous columns, like my April one entitled “Boulders I Have Known”, that conglomerate remains can be found scattered all throughout the Pass, on hill tops and at the golf course. It is always a treat to come across one in some remote section of bush in the middle of nowhere. The interesting thing about this occurrence is that you will not find conglomerate erratics west of its outcrop in Coleman. This verifies that the last glacial flow, about 10,000 years ago, was from west to east through the Pass and was responsible for shoving and depositing these giant fusions of pebbles everywhere.  

There exists yet another example of a conglomerate outcropping here in the Pass and that can be found in and around the Frank Slide Interpretive Center. It is not, how-ever, connected to the Kootenay Formation and is known as the igneous-clast conglomerate of the Mill Creek Formation which occurs up higher formation-wise than the Kootenay. If you have walked the lower or upper Frank Slide trails you have either walked on top of or alongside it. This conglomerate is not as hard or as consolidated at the Cadomin and tends to fall apart easily in some areas. The perfectly rounded clasts within it or those that have dislodged and are lying near the trail are clear evidence that they are from an alluvial fan of an ancient river flowing from the west.

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