Canadian Rockhound: Collecting at the Black Lake Mine, Quebec

The Black Lake Mine consists of several mines owned by the Chrysotile Labs Cie. The mines are located between the cities of Asbestos and Thetford Mines, and all are concentrated in one area. Each year the Mineralogical Club of Montreal and other clubs in the province of Quebec are given permission and access by the mines to collect minerals. Normally, the mines only allow one collecting day per year. So when you do get access to the mine, there is no time to talk with friends while collecting. In 1999, however, the mines made an exception. Because of the high demand from many collectors, they allowed two days of collecting. Luckily, since I was a member of both the Asbestos and Montreal mineralogical clubs, and because the collecting trips occurred on different weekends, I had two great opportunities to find minerals. Both trips took place at the beginning of April. On the first weekend trip, I went to the mines with the Asbestos club, but found nothing special – or should I say, nothing for my collection.

Rock Pile
Looking for minerals at the Black Lake Mine.

During that trip, however, one collector found a small quantity of specimens with medium-green andradite garnets, about 4 mm in diameter (Figure 1). These were associated with gemmy dark-green vesuvianite crystals from a boulder he found in a pile of boulders probably dumped by the trucks. While going back to our car in the bus, he explained to me that the boulder was very hard to brake apart and he was only able to obtain the small specimens he collected. When I asked him what kind of tool he was working with, he showed me a typical geologist's hammer! The guy explained to me approximately where the boulder was situated. But, as you may know, this mine is huge, so my chances of finding that very boulder during another trip were slim – more like finding the obelisk needle in Central Park, New York. I left the mine with my father and continued to think of the boulder that would probably be there waiting for me – or someone else!

Figure 1. Andradite garnets from the Black Lake Mine.

I returned with the Montreal club on the following weekend. This time our guide changed – she was not aware of the unique garnets we could find there. The other guide told her to bring us to where the latest blast occurred, which was at the upper level of the mine. As soon as we arrived, I realized that I was in a different pit. Oh my God! At this level, the only thing you'd find would be zeolite minerals or some calcite, if you are lucky. We were about 40 collectors, so as soon as the bus opened the doors, we all rushed to the walls of the pit. Naturally, most of the collectors were new members and they were told to follow the experienced one. So what do you think happened?

I was always busy answering questions like "where do we find crystals?" or "can you show me one so I'll know what I am looking for?" I am always happy to explain to new members where and how to collect minerals, but when you get access only once or twice a year, time flies by quickly. I decided to walk real fast and find a contact with minerals like apophyllite that would satisfy their needs. But walking fast did not help. A couple collectors always followed close behind me, and every time I stopped, they would come to me and ask "so, anything good here?"

The funniest moment that day was when I stopped near some boulders for a little nature's emergency. Well, you know what I mean. When those same guys caught up to me and asked me whether I found something good, I replied, "yes, I'm holding it in my hand, but I won't show it to you!"

Figure 2. Golden calcite, from the Black Lake Mine.

Figure 3. A single crystal of golden calcite.

Finally, I found many contacts with very nice golden calcite crystals, like the ones you see in this article (Figures 2-4), and a minor apophyllite vein with small crystals. Everyone went to dig for the calcite. The calcite crystals are interesting, because some of them show two generations of growth. After that, I left with my father and my friend Sylvain Roy to find garnets at another pit. On our way we met the guide who offered to bring us to the area where I was last week. Just as I suspected, I couldn't remember the exact level or even the side of the pit I was in the previous weekend, because the mine had been worked and now all the rocks appeared the same. We decided to start from the highest level and walk down into the mine until we found something interesting.

Figure 4. Another golden calcite specimen. Calcite crystals from the Black Lake Mine are interesting, because some show two generations of growth.

At the second level I discovered a big pile of boulders with serpentine. I decided to jump from boulder to boulder in the center, while my two partners took the top and the bottom. The boulders looked all the same – hundreds of them – and there was not much time left for me to find something. Suddenly, I noticed a different boulder with beige and white lines with smaller pieces of rock scattered around it. It certainly appeared as if someone had struck the boulder and left some material there. Could that be the one I was looking for? I climbed to it and sure enough, that was it! At first glance I recognize the andradite garnets, the vesuvianite and the matrix. I started to call my partners to come and see.

Figure 5. The boulder containing the andradite and demantoid garnets.

This boulder was about 3 x 3 feet, and one third of it was made of a contact filled with andradite garnets. With a hammer and good tools, it wasn't difficult to open it. The boulder itself was very hard, but the section containing the crystals gave me some problems, because it was flaky. It was difficult to obtain a big plate from it without braking the specimens. My two partners were looking at me like little puppies without a toy to play. I decided to separate the boulder into three parts so they could collect some of their own specimens. When I lifted part of the boulder, I had the biggest surprise of the day. A giant demantoid crystal (Figure 6), about 1 cm in diameter and bright Irish-green in colour fell onto the ground between my knees! We searched every inch of that boulder to find similar crystals. The picture above (see Figure 5) shows myself and my father opening that boulder.

Figure 6. Large demantoid crystal, approx. 1 cm in diameter, that was obtained from the boulder.

I was able to find 10 crystals of demantoid, but all were detached from the matrix. Later, the group of collectors joined us after the guide saw some of the specimens we obtained. Unfortunately, the boulder we found was the only one with garnets, and no one found another.

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The preceding article is also available online at the Daniel Comtois' Quebec Minerals web site.