Friday Fragment: Cobalt, Ontario Silver

I found this sample at a mine dump at Cobalt, Ontario. The two major minerals are quartz and cobaltite (mineral data, very nice crystal)
The Cobalt deposit is the result of volatile escape from late-stage aplites in the Nipissing Diabase. These aplites intruded the overlying Gowganda Formation, which is itself a fascinating unit of diamictites and other glacial sediments. The Gowganda has been regionally metamorphosed, but only at low T and P; surprisingly subtle sedimentary features are still preserved. So the mineralization is intimately associated with the diabase, but actually located in the sedimentary units.
The texture of this rock strikes me as probably representing a thoroughly replaced breccia, but the patchy nature of the quartz and cobaltite distribution may simply be the original texture, not a texture of the protolith.
Now the thing that excited me about this speciman can be seen in the second and third pictures (crops above and below respectively). Those little black streamers are native silver.
There is a wonderful loop you can do in Ontario if you ever have the opportunity; Sudbury is the world's largest nickle deposit, a sizable copper deposit, and an enormous meteorite impact. Go north to Timmins and tour a gold mine in one of the richest gold deposits of North America. Travel southeast to Cobalt; the area is largely worked out in terms of silver, but my sense is that there is still quite a bit of cobalt, and the mine dumps are a kick in the pants. From there travel south, with a stop near Temagami. On the road's crest on the hill just north of town, there's a great outcrop of banded iron formation and pyrite-bearing black slates. Then head to Bancroft, Ontario to check out some of the most exotic and extreme minerals on the planet.

I had the opportunity to do just this loop with a friend and fellow geology student in 1988; it was truly a wonderful experience.