When it comes to gold, think outside the box

Gold prospects abound, but economic deposits are rare. There is a rule of thumb among explorationists to the effect that it takes 1,000 prospects to yield a single mine.

Canadian gold deposits have been discussed for a 100 years. Most recently their geology received a detailed ‘going over’ in Economic Geology (Vol. 103, No. 6). The interpretation repeats the 1930s shear zone model in various forms.

As a field geologist, how useful is this established model for finding new gold deposits and the response invariably will be “not at all.”

From my work as an exploration geologist who has spent almost 40 years studying the structural history of mineral deposits, I have concluded that conformable gold deposits always predated the shearing along with their host rocks.

Here is a brief rundown on what several others have said.

T. Bottrill, a Toronto geologist teaching at the University of Toronto, did a paper entitled “Shear Zone Hosted Gold Model, an Economic and Scientific Failure.” He said it was a ‘failure’ scientifically because it had never produced criteria to guide exploration, and was a ‘failure’ economically because it had never led to a gold discovery.

Given the amount of money spent and the lack of discoveries, I agree.

A Russian geologist, Y. Bilibin, in a 1952 study showed that similar mineral deposits in unrelated Greenstone belts were situated in similar geological settings. The age of the belt was irrelevant. This finding suggests that the host rocks are the best guide to understanding the contained mineral deposits.

Wm. Karinven, a former resident geologist for the Ontario Geological Surevy in Timmins, went at the famous Timmins gold deposits which he concluded were related to iron carbonate iron formation. This author saw a similar relationship in the Saddle Reef gold deposits of Nova Scotia.

In 1987, this author published a paper on the “Gold Mineralization and its Position of Gold Deposits in the Geological Evolution of the Beardmore-Tashota Area (CIMM Bulletin, April 1987).” This study concluded that the gold deposits were formed before the shearing as part of the forming rock sequence. Based on all the economic deposits and prospects in the camp, it provided guidelines to identify areas with then potential to discover gold mines not just showings.

There is other key evidence that these gold deposits are part of the normal geological sequence. A very common feature in gold deposits is the presence of graphite or amorphous carbon which colours the rock grey to black. Elemental carbon can only be formed by organic activity. Carbon and graphite strongly suggest a syngenetic origin elemental carbon or graphite is reported from Goldcorp’s rich Red Lake mine, Richmond’s Nugget Pond Gold Mine, the Belleterre, Sturgeon River, McvIntyre and Chibougamau Mines.

My paper (inset, above) from the CIMM on the Beardmore area concluded that both the rock and contained gold were deposited and deformed. This is an important guide for gold exploration. The correct criteria provide a guide, the wrong criteria waste investors’ money!

Let’s return to the Timmins gold mining camp in light of the Beardmore criteria. I think that the Beardmore criteria explain the distribution of the Timmins gold mines.

All the mines are conformable and can be shown to lie in a limited stratigraphic stratisection.

All have subsequently been bent around the major early folds. Mine plans show this relationship on all scales.

The CIMM Special Volume One “Structural Geology of Canadian Deposits” (1948) is an excellent source for the mine geology of these closed and flooded mines even if it is a bit dated.

Does this model work and can the criteria interpreted from it be applied elsewhere? The answer is “yes.”

At the time of publication, claims were being staked 2000 miles away in similar rocks but 2000 million years younger. The target was explored using the recommended exploration techniques and the Nugget Pond Gold Mine was discovered in the correct geological setting. Discovery cost was $140,000 and the cost to feasibility was less than $15.00 per ounce in 1989. I have concluded that this success demonstrates that thinking outside gold exploration box can significantly improved exploration success and efficiency.

This brief article combines scientific data from the literature and my own experience and suggests that Archean gold mines and by projection any conformable or stratabound gold deposit with superimposed regional structural deformation or shearing is best explored incorporating a syngenetic component in the exploration model.