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Gold/Mining/Energy : Manhattan Minerals (MAN.T) -- Ignore unavailable to you. Want to Upgrade?

To: Elizabeth Andrews who wrote (2965)	7/9/1999 3:13:00 PM
From: Claude Cormier	Read Replies (1) \| Respond to of 4504

<<But if the stress exists in the rock at depth isn't drilling through it or opening up a stope going to release the stress and cause spalling? >> If such was the case, there would be no VMS underground mines, and there are plenty. None that I know with the problems you suggest.

To: Elizabeth Andrews who wrote (2965)	7/9/1999 4:01:00 PM
From: Jeff Dickson	Read Replies (1) \| Respond to of 4504

And, my new dictionary says that exfoliation is also produced by chemical forces producing differential stress within the rock. It doesn't say that it is strictly a surface phenomenon. It does say it is noticeable on surface where eroded. The exfoliation is caused by weathering, so the rock has to been exposed at the surface. It could I guess be covered up again by a volcanic flow or deposition by other means. In fact, the notion that it is caused by the rock that was formed at depth subsequently being exposed at the surface and no longer experiencing compressive forces is now out of favor. So too are large temperature cycles during the day. Exfoliation occurs due to water penetrating the surface of the rock, resulting in clay which expands and flakes off the surface of the rock. The exfoliation that takes place underground is small scale, and is also called spheroidal weathering.

To: Elizabeth Andrews who wrote (2965)	7/9/1999 5:15:00 PM
From: Bruce Robbins	Respond to of 4504

Dictionaries tend to be concise- exfoliation is caused by weathering and weathering occurs near surface. Spalling is due to exfoliation (in the dictionary, I am sure it says see Exfoliation).. >>But if the stress exists in the rock at depth isn't drilling through it or opening up a stope going to release the stress and cause spalling?<< It would be better to say caving instead of spalling and rock burst instead of exfoliation. The stress in the surrounding rock resulting from a small opening at the depth of the TG-3 mineralization are weaker than the strength of the rock (we are talking about a very fine grained felsic volcanic). The resulting strain will not cause rock bursts. IMO every hole in TG will remain open for the rest of our lives- I hope they are cementing them after they are completed. The large openings will not remain open for long enough to have to be supported- even so, they will scale and use rock bolts to support the walls. Every underground mine in the world scales and uses rock bolts. Lets use an example of a producing mine where I have alot of info: Hudson Bay Mining and Smelting Co. Ruttan Mine, Leaf Rapids, Manitoba, Canada. An underground Cu-Zn VMS with proven and probable reserves of 11.5 million tonnes averaging 1.1% Cu and 1.7% Zn as at Jan 1, 1998. The mine began producing in 1973 and is still in operation today. It produces 5,900 tonnes per day (approximately 13 million lbs) of ore which is now situated well below 150 meters depth. Their mining costs were Canadian $5.02 per tonne in 1996, using blasthole open stopes with delayed backfill. Of that cost, ground support and backfill costs were C$0.07 and C$0.41 respectively. That makes ground support and backfill only 10% of total mining costs. As you can see, what we have been talking about in these posts is really a very small issue. The Ruttan Mine was discovered in 1969 by drilling a single hole on a target delineated by regional electromagnetic and magnetic surveys. Subsequent drilling outlined an an orebody containing 45.5 million tonnes of sulfide ore with a grade of 1.47% copper and 1.61% zinc to 600 meters below surface. Production commenced at 9,000 tonnes per day from an open pit in 1973 and moved underground in 1979. As far as I know, Sherrit (the discoverer of the Ruttan, also a publically traded company) never published their core logs.