Ore reserve estimation at the Enterprise Gold Mine, Pine Creek, Northern Territory, Australia. Part 2: the multigaussian kriging model

CIM Bulletin, Vol. 81, No. 909, 1988

NEIL SCHOFIELD, Applied Earth Sciences Department, Stanford University, Stanford, California

The estimation of recoverable ore reserves for feasibility in precious metal deposits such as Pine Creek must account not only for the extreme variability of the ore grade but also for the complexity of the geology. Compatible models for both must be adopted. Further, very selective mining demands reserve estimates be based on small selection units whose individual grades cannot be estimated reliably from the exploration drilling data. Multigaussian kriging is one method based on a multivariate normal model, for estimating recoverable reserves under such conditions. In this paper, a non-mathematical description of the multigaussian model is presented together with its application to the Pine Creek Gold Deposit. The results, when compared to the first year of production, are encouraging for the model but not without surprises. Together, Part 1 and Part 2 of this study combine a detailed and geologically conditioned variogram analysis with an appropriate estimation method for a highly variable low-grade gold deposit. This and other studies of gold deposits familiar to the author show convincingly both that while the appropriate geostatistical skills and techniques are necessary to tackle the question of reserves, equally important but of ten discounted is the need for an appropriate and compatible geological model.

Keywords: Ore reserve estimation, Geology, Kriging, Multigaussian model.