LETTER TO THE EDITOR — Geological controls affect geostat evaluations

I was somewhat dismayed by the recent letter of Edward Isaaks (“Credentials, training essential for competent geostat evaluation,” T.N.M., Feb. 15-21/99). In his long letter, not once did he mention the importance of geology to the geostatistical evaluation of ore reserves.

One can have all the theoretical mathematical models in the world, but if they do not coincide with a sound understanding of the geological setting and controls on mineralization, they can be dangerously misleading.

I agree with Isaaks that there are numerous case studies showing the successful application of geostatistical ore reserve models, production schedules and the like. Many of these have been confirmed against actual mine production.

Isaaks then went on to attribute perceived failures of geostatistical studies to a lack of geostatistical training. He states that “inaccurate geostatistical ore reserve assessments are generally the product of theory being incorrectly applied by practitioners who have little formal geostatistical education.”

Was this indeed the cause of the failures? Was it a lack of geostatistical education on the part of geologists and mining engineers? Perhaps we should also look at the geological training of the geostatisticians. Were they placing their theoretical models into a real-world framework? Were they overselling the capabilities of the methods? Were they communicating the strengths and weaknesses of their numerical models to their geology and engineering colleagues?

Graham Clow, in his letter of Oct. 12, 1998, stated it best when he said ore reserve calculation “involves both quantitative and qualitative assessment. Geostatistical methods certainly look after the former, but the latter remains a judgment call and is easily overlooked when one is banging away on a computer.”

In his letter of Nov. 16, 1998, Alastair Sinclair also discussed the credible nature of many geostatistical applications and the necessity for evolving improvements in the field. As stated by Sinclair and Tomasz Postolski in the February 1999 CIM Bulletin, “Geology is the fundamental basis of all resource /reserve estimation and must be thoroughly integrated into the system of procedures used in practice.”

This argument highlights the necessity of co-operation within a work team throughout the process — geologists, to define the deposit; geostatisticians, to quantify the grade-quality distributions; and mining engineers, to ensure it fits into the positive economic extraction criteria of ore.

Ben Whiting, P.Geo.

Department of Geological Sciences

Queen’s University