Bloom commentary misses mark

Lynda Bloom’s commentary, Fusion key step in fire assaying for PGEs (T.N.M., Feb. 25-March 3/02), is plagiarism at its worst.

Bloom is brazen enough to start her article with “Fire assay is the preferred method for assaying rocks for platinum group elements (PGEs),” the very title of John Van Loon’s paper given at a Geological Association of Canada meeting in Vancouver 10 years ago.

Not only does she copy Van Loon’s work; she gets it wrong. The following paragraph is incorrect: “The next step in the fire assay process is cupellation, in which the lead button, which contains the PGEs, is heated again until the lead is lost by volatilization.” Ninety-eight per cent of the lead is absorbed by the cupel as lead oxide, and 2% goes up the chimney. This is easily verified by weighing a preheated cupel after cooling and re-weighing it after cupellation. The difference is multiplied by lead divided by lead oxide and then multiplied again by 100.

An assaying course at the University of Idaho used a page-by-page copy of Bugbee’s A Textbook of Fire Assaying, first published in 1922. The book was the first scientific look at modern fire assaying using Gay-Lussac pot fusion, also known as classical lead fusion. Bugbee, a metallurgist from the Massachusetts Institute of Technology, and not a seasoned assayer, leads us down the garden path with classical lead fusion by using half-assay ton weight. He does not show how to formulate a flux; instead, he balances the equations of known fusion charges from different sites.

The assay ton measurement was developed in the U.S. A troy ounce divides into a ton (2,000 lbs.) 29,166 times. A representative weight of 29.166 grams of sample yielding 1 milligram of pure gold equals 1 ounce per ton.

It is obvious that, in earlier times, assayers had a better understanding of the nature of gold. They split the assay ton in two, and if after fusion, cupellation and parting, the gold prills were not in agreement and a third sample was employed. Somehow, a gold determination became a single half-assay ton.

A twofold error occurs by doubling the weight of the prill. This was brought about by down times in gold mining and by people with no formal education in assaying.

Pierre Gy’s sampling of Particulate Material’s Theory and Practice sent Canadian geologists into a whirlwind. The sample weight was increased to a full assay ton, but the flaw still remains, because single fusion constitutes a gold determination in custom assay laboratories.

All academics and researchers use Bugbee as a reference but fail to see the forest for the trees. An assay, often described as the sum of its errors (resulting in low assay determinations), can be blamed on poor assaying and not the “nugget” effect.

William Johnson

Assay Consultant

Toronto