Part of the problem may lie in the almost paranoid North American aversion to the unfortunate word “ore,” which is apparently regarded as a cast-iron guarantee of future fortune, instead of its everday usage for “rock that may be, is hoped to be, will be, is or has been mined” (profit must come from the activity of mining, not from the static raw material). Then, junior companies tend to think they can get away with murder and call literally any estimate of tonnage a “reserve,” as long as they don’t call it an “ore reserve,” even though the latter sense remains by implication.
I support very strongly your condemnation of the practice of quoting a reserve only as so many ounces of gold; frequently this is the gross content of the geological reserve, without allowing for design, mining or treatment losses. This deplorable practice first arose some decades back, because I recall mention of a reserve of billions of pounds of copper (Americans seem to have a weakness for using astronomical numbers of absurdly small units). It has long been standard in the uranium industries of North America and Australia, and seems to have spread into gold about two years ago, I suspect from the activities and methods of speculative stock- market analysts. But isn’t the remedy partly in your own hands? Many of the offending announcements appear regularly in The Northern Miner newspaper. Worse, one has only to go to the September issue of your magazine to find the same crime in an article on Echo Bay Mines compiled by your own assistant editor, Thom Loree] Hugh Taylor, Mining Consultant, West Vancouver (Editor’s Note: On this general topic, Hugh Taylor will be giving the keynote address at a meeting of the Institution of Mining and Metallurgy in London, England, next April.) A Measure of Confusion It was with great disappointment that I read in your November, 1988, issue a letter to the editor regarding the confusion between metric and other weights and measures. Lorne Ross, president of Taseko Mines, stated that in your August issue “you have made an outstanding contribution to the prevailing confusion about the relationship of the metric system to other systems of weights and measures.” I am afraid it is Mr Ross who has given the outstanding contribution this time, as his letter had several inaccuracies, which I;ve corrected:
. One troy ounce is approximately 31.103 g.
. One gram is approximately 0.032 troy ounces.
. One gram per tonne is roughly 0.0292 troy ounces per tonne.
. One troy ounce per ton is equal to 34.286 grams per tonne or 34,286 parts per billion is roughly equal to one troy ounce per ton as one gram per tonne is equal to one part per million and one part per million is equal to 1,000 parts per billion.
Thus, to convert parts per billion to troy ounces per ton, multiply parts per billion by 0.0000292.
All these factors can be found in the 1988-1989 Canadian Mines Handbook on page 495. It should also be noted that Taseko Mines can be found on page 432 of the same handbook. Thus, I can only conclude that Ross is as confused as are many others in the mining industry. It sure makes me suspicious if a president of a mining company cannot get these conversions correct. Stephen Davies, Mining Engineer, James Wade Engineering For the Record As one of those “geologists and other people with scientific training,” I read with interest the letter in the November issue entitled “A Weighty Matter” by Lorne E. Ross, which purported to clarify the confusion engendered by an earlier article (“Unconventional Grading,” in the August issue). As a result of Ross’s contribution, readers are now faced with both confusion and, more importantly, inaccuracies. Since some of Ross’s figures invoke errors as large as 20%, a clear statement of imperial to metric conversion for precious metals is required. After all, a conversion error of 20% in grade and tonnage calculations could (on the low side) relegate a potentially economic prospect or mining venture to oblivion or (on the high side) lead to accusations of salting or illegal stock promotion.
One troy ounce is approximately 31 g (not 38 g as stated) and, given the precision required in conversions, at least three decimals of the true value should be used. The true value is 31.1034768 g. Taking the reciprocal of 31.103 g gives the following relationship: 1 g equals 0.032 troy oz (not 0.028 troy oz, as stated). Ross states that 1 g per tonne is roughly 0.03 troy oz per short ton (i.e. 2,000 lb); close, but a better figure is 0.029 troy oz per short ton. He also states that one tonne equals one long ton (i.e. 2,240 lb); incorrect, one tonne equals 2,205 lb. Perhaps the most glaring error, and the one with impact on grade and tonnage calculations, is his statement that 41 parts per million is roughly equal to one troy oz per short ton; no way. Taking one troy oz per short ton and converting to g per kg yields 31.103 g per 907.185 kg, which is equivalent to 34.285 g per 1,000 kg (i.e. one tonne), or about 34 parts per million.
In summary, 34.285 x (m troy oz per short ton) = n g per tonne (i.e. ppm), or 0.029 x (m g per tonne) = n troy oz per short ton: where m is known and n is to be calculated.
In conclusion, obtaining the figures given above from a book dealing with metric-imperial conversions reminded me of the antiseptic nature of metric as compared with idiosyncratic imperial. Where in metric does one come across such delightful standard units as an ell, a slug, a coal tub, a herring barrel, a salt tub, a sand barrel, a barrel of us dry cranberries, three different nautical miles, or the Paris foot, a measure used in Quebec for certain land deals, which measures 12.789 inches? G. R. Parslow, Dept. of Geology, University of Regina, Regina, Sask. Oversight In the October, 1988, issue in an article entitled “Pointers for Planners” you reviewed a paper entitled “The Changes in the Concepts of Maintenance for a Large Mechanized Surface Mine and its Cost-effectiveness: A Case Study.” You gave credit for the paper to two authors, namely Jan Rutquist and Per-Eric Jadmolm. Even though I am the first author of the paper out of the three, it seems you have omitted my name. I would appreciate some recognition for my contribution. Uday Kumar, Division of Mining Equipment Engineering, Lulea University, Sweden Editor’s Note: Mr Kumar’s significant contribution to the paper was inadvertently overlooked.
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