Sample bias and conditional probability ore reserve estimation at Valley

CIM Bulletin, Vol. 81, No. 911, 1988

G.F. RAYMOND* Placer Development Limited, and W.P. ARMSTRONG Cominco Limited

At the time of this study, the Valley mine was producing 23 000 tonnes of ore per day from a large, low-grade porphyry copper orebody. Sulphide mineralization, principally bornite and chalcopyrite, occurs in a stockwork of quartz veins in one phase of the Guichon Creek batholith. The property was explored from 1967 to 1982, and was placed in production in 1983. Using a three-parameter lognormal approximation developed by G.F. Raymond at Similkameen and Mount Isa Mines, a geostatistical conditional probability ore reserve was estimated prior to mining. Comparisons with blasthole kriging and milled ore for the first 17 months of production showed close agreements at all cut-offs between conditional probability estimates and mineable ore. This was not true of either kriging or polygon estimates. An important part of this work was identifying and correcting for bias in both exploration and blasthole samples.

Keywords: Ore reserve estimation, Valley, Copper, Highland Valley, Grade estimates, Kriging, Geostatistics.