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Gold/Mining/Energy : ZINC The base metal. News and Views. Symbol Zn -- Ignore unavailable to you. Want to Upgrade?

To: CLK who wrote (99)	2/15/1999 4:54:00 PM
From: Ray Hughes	Read Replies (1) \| Respond to of 3270

CLK: A mining engineer wrote an article in Engineering And Mining Journal a few years ago in which he reported on the statistics of trying to attempt to drill and assay old tailings or waste dumps. A chief problem he noted is that most waste is not crushed to its comprised of large rocks. These may simply move aside from a drill bit so only isolated rocks, statistically un-representative of the pile, are sampled. Also, the distribution of mineral within waste varies according to the time when the material was mined and what grade material was mined then and how efficient the ore vs waste selection was in the mine. Hence, any estimation of grade in waste is, at best, a crude assumption. Remember, there was little incentive during the mining to assertain what was in the waste. To adequately sample a waste dump to determine remaining grade requires processing large tonnages from statistically adequately dispersed pits, right to the bottom of the dump. Generally, that requires too much investment because one is processing extremely low grade (if any)which will give an adequate return on investment only if initial investment is kept very low. Catcha-22, financially, and there are lotsa other gremlins lurking, like clay lenses that blind off the waste so solutions won't percolate and so can't disolve the mineral. But, sometimes the old timey miners were so inefficient that they left high grade mineral in waste and...in Bolivia hordes of locals sit all day hand picking bits of tin and antimony ore out of old tin waste dumps. RH