SIGMA MINES DETAILS GOLD ORE RESERVES <Sigma Mines (Quebec) Ltd>, 65 pct owned by Dome Mines Ltd, said its Sigma Mine had proven and probable reserves at the end of 1986 of 4,902,940 tons, with an average grade of 0.139 ounces of gold a ton. Sigma said the reserves are equivalent to 10 years future production at current milling rates. The reserves comprise 1,640,779 tons proven reserves grading an average of 0.163 ounces of gold a ton and 3,262,161 tons probable reserves grading an average of 0.127 ounces of gold a ton. Sigma said it changed its 1986 reserve reporting method following Dome Mines' previously reported move to adopt general industry practice of reporting proven and probable ore reserves. Prior to 1986, Sigma conservatively reported only proven reserves that could be mined without future development costs. Proven reserves as of December 31, 1985 were 978,000 tons grading an average of 0.194 ounces of gold a ton, equivalent to about two years future production.