Resource World Magazine

16 www.resourceworld.com F E B R U A R Y / M A R C H 2 0 1 7 Again, considering 1% of a tonne equals 22 pounds then we would need 4.5% zinc to be interesting and 10% zinc to be high- grade. Since zinc deposits are generally flat, and bedded layers have thicknesses of less than 100 metres, we are generally looking for 10% or better. Using $500 per tonne gross metal value as a high-grade metal value on a per tonne basis gives the follow - ing parameters for other commodities: COPPER: 10% copper would be very high-grade, but very often copper occurs with other base and precious metals, so I would consider a value of 5% copper to be a rule of thumb threshold for thicknesses of 2 metres and up. The Nevsun Resources Timok Project in Serbia has indicated resources for the Upper Zone estimated to be 1.7 million tonnes averaging 13.5% copper and 10.4 g/t gold – exceptionally high grades. The Ivanhoe Mines Kakula deposit in the DRC has returned very high copper grades, including 11.91 metres (true width) of 6.23% copper at a 3.0% copper cut-off. GOLD: One ounce, or roughly 30 grams/ tonne is high-grade and can be expected to move markets in most cases. Several ounces of gold per tonne is considered to be high- grade for underground mining, although 5 grams gold/tonne is usually economically viable. The most well-known example of narrow high-grade is in Goldcorp's Red Lake, Ontario mine where gold grades of 18-20 grams gold/tonne are being mined from its deep workings. URANIUM: The Athabasca Basin in northern Saskatchewan has high-grade uranium which can run from 1-3% ura - nium and higher in deposits buried 200 metres or more below surface. These are among the highest grade uranium mines in the world, so we will define 1% ura- nium as high grade for small tonnage style deposits. Fission Uranium has reported fantastically high grades at its Triple R deposit, including hole PLS16-504 on zone R840W with 25.95% U 3 O 8 over 4.0 metres and 10.03% U 3 O 8 over 11.0 metres. DIAMONDS: There is no separate rule of thumb I can define for small tonnage high-grade diamond deposits as to carat value, or diamond counts; the rule stated previously of one carat/tonne should suf - fice for all scenarios. PLATINUM AND PALLADIUM: These precious metals almost always occur as narrow seams, and one would look for grades of 6 grams platinum + palladium/ tonne over 2 metres as a reasonable thresh - old for high-grade. The previous guidelines should give the reader a general idea of what is high- grade in a news release. It is important to think of assays in terms of what they mean in dollars per tonne, using the idea that a deposit is generally profitable if the metal value is twice the mining cost. Also it is necessary to determine if the deposit can be mined as a bulk tonnage or low tonnage project before considering whether a news release 'makes the grade' or not. n

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