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Gold/Mining/Energy : Gold Price Monitor -- Ignore unavailable to you. Want to Upgrade?

To: goldsheet who wrote (86785)	6/11/2002 11:16:12 PM
From: E. Charters	Respond to of 117011

Macassa was deep but had a lot of contiguous ore adjacent to veins. Its structures were originally mined with stulls, which are posts put between adjacent walls of the stope to keep the walls stable. This is because the ore was in X-faults that ran at a shallow dip (45 degrees) and reversed direction every so often as you went up on the vein. Consequently wall support was back support. The veins are hard to drill, as the ore is very nuggety. You had to drill for structure or the existence of a vein, but could not rely on the numbers, as often you had to drift over and mine it to find out the grade. Traditionally you found the best average ore below the 4000 foot level in Kirkland lake, although some surface pillars at the Lakeshore were rich. They will face two challenges at Macassa -- ore or grade determination and ground control. Both will demand innovative engineering approaches. I think the ore demands a whole new mining method. I have suggested short wall mining, freezing and keyhole stress relief. Such methods may well be the only option they have as the stopes are not large in size, so gallery mining methods such as vertical crater retreat and the like are difficult to employ in these kind of structures. Ore determination requires some kind of petrological or geological correlation that is ordinarily not done. I found that in identifying veins in the Kirkland lake area there were two clues that should yield success if examined with some caution: environment and mineral character. In some cases, normally geologically denied environments such as a host of conglomerate with hairline crack structures, with no quartz or sulphides, had rich ore. In other cases quartz and sulphides, looking juicy as hell, had average 0.25 ounce values. Parallel structures of different kinds abounded. But only a trial mining or bulk determination could correlate. Obviously a mineral correlator such as crystabolite (high temparature quartz), a greenschist precipitation-temperature mineral, or telluride may help. It may be that X-ray fluorescence or other petrological examination of bulk vein material or core, may develop a correlator such as was used in Manitoba mines with high temperature pyrite. Such mineral correlators may yield only to the microscope readily. On the other hand very careful bulk type assaying of large core may be the ticket. I have seen that work-- just upping the correlational effect of the assay method to catch nuggets. There may be some ore in the mine that is kind of low grade to mill but of good tonnage. This ore may yield to techniques of sorting by automated equipment to increase the grade if bulk mined to reduce the costs. Rejection rate may be high, but in the end dollars saved on hoisting and milling may make it worth it. I have seem grade increased routinely for very large tonnages by 3 times in some environments. EC<:-}