This is a bit of a random collection of facts because I can't be bothered editing it and everyone should do their own research... I take no responsibility for inaccuracy or misinterpretation.
BDI are calling it as an epithermal deposit, but it must be far from your standard epithermal. The last subduction in Madagascar was about 800Mya, as far as I can tell, and the basalt host rock here is from ~250Mya. Their description of the host mineralisation sounds more like flow top breccias, but looking at the interpretations of the genesis of Keweenaw (briefly and without paying for research papers because my stake in this isn't worth it), it was originally interpreted as downdip burial metamorphism but there is a different interpretation that it an influx of meteoric brine (brine due to dissolved evaporites) which then mixed with the fluid generated by burial metamorphism to form a "hybrid evolved meteoric-metamorphogenic ore-forming hydrothermal brine". It sounds like the cooler, denser brine mixing with the metamorphic fluid caused it to rise, cool and copper drop out of solution. But I've only read over this briefly so don't quote me on it.
At from Keweenaw it appears most of the copper came from conglomerate rather than breccia or fault/fracture zones, and BDI don't mention conglomerates. It appears that the pore spaces in the conglomerate at Keweenaw facilitated the concentration of copper to economic levels. As there's no mention of conglomerate, we should stick to looking just at breccias at Keweenaw. That means we're looking at long, wide, flat sheets in layers. Not very conducive to open-cut (because we all like open-cut).
The only successful modern mine at Keweenaw was White Pine, which was conglomerate-hosted so that's no good to us. The original fissure vein mining at Keweenaw was uneconomic then and will be even less so now. Quincy mine (1850ish to 1945ish) is possibly our shining light - 53 consecutive years of profit from mining the flow tops. That should cheer you up... Whether that style of underground mining would be economic now is a completely difference matter.
TL;DR Give me a copper porphyry or sedex any day, but here's hoping.
BDI Price at posting:
0.1¢ Sentiment: None Disclosure: Held
