LETTERS TO THE EDITOR — Assay accuracy not linked to cost

It is disappointing to see that, for some, cost of analysis is still the indicator of the accuracy of that analysis; that is, the more it costs, the better the result must be. I refer to the front-page article “ASE requests fire assays of Focal drill samples” (T.N.M., May 3/93) where an unspecified wet chemical-based method was used in preference to fire assay to analyze core for gold and platinum.

The reasoning was: “We know we are getting a better job (from the U.S. labs) because we are paying between $200 and $350 for each assay to have it done right, rather than the $50 each the Canadian firms might charge.” There are three points to be made here.

First, the criterion by which the quality of a method should be judged is its ability to produce the “right” result, in terms of accuracy and precision, for well-characterized standard reference materials which are similar in composition to the unknown(s). Largely because of the financial consequences of drill core analyses, rigid examinations were established in Canadian provinces (such as British Columbia) by which labs could be certified as to their competence in the determination of precious metals in a variety of matrices. This is an active process and is not married to the use of old technology or tradition.

Second, charge per analysis to a degree is determined by actual operating cost, but the market (supply and demand) is a powerful influence. Lower charges do not imply “omitted steps,” as suggested in the article. I believe professional assayers would disagree with the contention that eight steps were necessary to produce the correct result. The conditions of fusion must be modified to suit the nature of the sample, and success depends on knowledge and experience rather than following a fixed set of instructions. Canadian labs, highly experienced in fire assay, are extremely competitive today and profit margins are minimal.

I am reminded of a story told to me some years ago by an expert in neutron activation analysis. The charge for uranium in a soil was about $5, I believe, from this geochemically oriented lab. Again, the competition and high throughput (uranium boom days) minimized prices. When asked to quote on an environmental analysis for uranium, the lab still quoted $5 since the same method would be employed as it more than satisfied the criteria of detection limit, accuracy and precision. The environmentalist could not accept this — it simply had to cost more (much more).

The charge finally was raised appreciably, the environmentalist was happy and guess which method was used.

Third, Canadian assay labs are indisputably world leaders in the determination of precious metals. Their vast combined experience in this field and their competitive edge have established this reputation. Much of their workload is derived from off shore as a result.

Gwendy E. M. Hall,

Head, Analytical Method Development,

Applied Geochemistry

Geological Survey of Canada

Ottawa