GSC studies gold, PGE anomalies in Alberta

The Geological Survey of Canada (GSC) and the Alberta Geological Survey are participating in a research project to evaluate reported occurrences of gold and platinum-group elements (PGE) in the Fort MacKay region of Alberta.

Interest in the region was triggered by Focal Resources (ASE), which last spring reported attention-grabbing values from drilling on its Bradley prospect, including a 5-ft. interval grading 0.41 oz. gold, 0.53 oz. silver, 1.99 oz. platinum, 0.08 oz. rhodium, 2 oz. osmium, 1.68 oz. ruthenium, 0.17 oz. palladium and 6.74 oz. iridium.

Because the results came from unconventional assay techniques, the Alberta Exchange asked that Focal conduct the more conventional fire assay technique to verify its earlier results. Fire asssays, however, failed to confirm the high values returned from non-conventional techniques.

“I don’t see that as an indictment, I see that as a challenge,” said GSC geochemist Hugh Abercrombie of the ASE’s request for check fire assays. (Abercrombie recently co-authored a paper on mineralogical studies of the Fort MacKay region.) “We are seeing anomalous gold concentrations by our micro-analytical techniques,” he said.

The surface and core samples analyzed by the GSC were provided by HMS Properties (a private company and property vendor) and three public companies active in the region. The latter are Focal and two Toronto-listed juniors, Tintina Mines and NSR Resources, associated by way of common management. According to the GSC report given by Abercrombie to The Northern Miner, GSC scientists analyzed the samples by two methods: dissolution and analysis by solution mode Inductively Coupled Plasma-Mass Spectrometry (ICP-MS); and direct analysis by in-situ laser ablation microsampling ICP-MS. Of the 13 surface samples tested by the first method, nine returned values at or below 0.01 grams gold per tonne. The highest value was 0.03 grams gold. Four core samples from Tintina drilling were tested, returning values of 0.02, 0.13, 0.04 and 0.01 grams gold per tonne. One drill core sample from the Bradley (Focal) drilling returned a value of 0.01 grams gold. No PGE values were reported. (Very generally, background levels of gold in rocks run about 0.005 grams per tonne, or 5 parts per billion.)

Surface samples from six sites were tested by laser ablation ICP-MS analysis, returning results from each respective area averaging:

* 1.08 grams gold per tonne with no PGE values (range: 0.02-3.48 grams); * 0.08 grams gold per tonne (range: 0.05-0.14 grams) and 0.02 grams palladium; * 0.45 grams gold (range: 0.05-2.17), 0.01 grams rhodium and 0.01 grams palladium;

* 1.60 grams gold (range: 0.51-3.71), 0.01 grams rhodium and 0.03 grams palladium;

* 0.27 grams gold (range: 0.12-0.53), 0.02 grams rhodium and 0.01 grams palladium; and

* 0.23 grams gold (range: 0.02-1.05).

The results of ICP-MS analysis revealed a systematic discrepancy between results obtained by the solution method versus laser ablation. As an example, sample WK15 returned 0.001 grams gold from the first method (solution method) and 1.60 grams gold from the second (laser ablation).

“We don’t question that there are problems with reproducibility,” Abercrombie said. But he considers this “an analytical problem” related to the composition of the rock, rather than the result of nugget effect or sampling bias, which are concerns, given the small size of sample tested by the laser ablation technique (an estimated 2,250 micrograms from every 400-by-400 micrometer raster).

The Alberta Geological Survey has also been working on the project and collected its own samples during a 3-week program last summer. “We did not find any gold or PGEs in any of our samples analyzed to date,” said Michael Dufresne, consulting geologist for the AGS, adding that samples were analyzed at a Canadian laboratory using fire assay and neutron activation analysis. But he said results from more recent sampling will be released shortly.

Abercrombie said the microanalytical techniques do not lend themselves to testing of larger samples (such as drill core intersections). But he suggested the results of this mineralogical work could be used by the analytical community to design appropriate techniques for larger-scale testing, which could be “scaled up” for extractive purposes. Abercrombie also said his methods are being supported by work done on samples from the Fort MacKay region by John van Engelen of Chauncey Laboratories in Toronto. Some of these samples have run as high as 0.3 oz. gold per ton using van Engelen’s techniques. Van Engelen said he charges $1,000 per lb. to test samples.

Van Engelen, who formerly was with Assayers (Ontario) Ltd., refused to identify the chemicals he adds to the sample at the chemical roast stage. “I have been working on these kinds of (unassayable) deposits for 10 years and I would rather keep that information to ourselves,” he said.

Van Engelen’s previous work includes his assaying of samples from the Moapa region of Nevada in the mid-1980s. An engineering firm, relying on the facilities of several Canadian labs, could not duplicate positive results obtained by van Engelen’s techniques on the Moapa project. The labs that use traditional assay methods returned zero or near-zero values.