Continental drilling program develops leading technology

In West Germany, for example, the major effort of a continental drilling program is one “super deep” hole being drilled to a depth of 14 km at a cost of about $230 million(US). The USSR has spent 16 years drilling a hole that reaches a depth of more than 12,000 metres.

But Canada’s Canadian Continental Drilling Program (CCDP) will focus on holes that are less than two kilometres or about 6,500 ft deep. About three-quarters of the proposals received by the CCDP steering committee call for holes of that relatively shallow depth — inexpensive, but with high scientific returns. The CCDP is aimed at gathering scientific information on the North American land mass, but those involved will likely benefit from being on the leading edge of diamond drilling technology. That technology is likely to be put to use eventually on exploration for and development of deep-seated orebodies.

Bradley Bros. Ltd., Heath and Sherwood Drilling (1986) Ltd., JKS.*Boyles Industries, Longyear Canada, Midwest Drilling and Tonto Drilling are six drilling companies involved in the scientific venture as associate members of the CCDP.

The CCDP recently completed a series of six workshops at which proposals for drilling-based studies were presented for discussion. Some 38 proposals have been received to date.

An exception to the shallow hole proposals arose from a workshop held at Laurentian University in Sudbury, Ont. Two proposals were combined into one for drilling a 7-km hole to address a number of aspects of Sudbury geology.

The Sudbury Structure, formed by an explosive event about 1.85 billion years ago, is a well known yet enigmatic feature of the Canadian Shield. Some scientists believe it to be of volcanic origin, but in 1964 R. S. Dietz suggested that it might be the result of a large meteorite impact. Although there is not a consensus, the impact origin is now the majority view.

Coupled with the scientific interest in this unique structure is its major importance as the world’s largest economic source of nickel- copper sulphides.

Another workshop, held at the Geological Survey of Canada in Ottawa, addressed the nature of greenstone belts, which are the source of much of Canada’s mineral wealth, and associated granitoid intrusions.

In spite of the extensive exploration of greenstone belts by the minerals industry, their nature and tectonic history are not yet fully understood. Until this decade it was thought that the belts represented the products of a single formational environment, alternatively either amalgamated island arcs or collapsed continental rifts, or back arc basis later deformed into steep open folds. Several more recently developed models see greenstone belts as the results of a considerably more complex tectonic evolution.

The workshop concluded that a drilling program in granite-greenstone belts should address a number of objectives, including the investigation of problems in the evolution of the early crust, testing of large scale Archaean models, characterization of uniquely Archaean mid-crustal lode-gold hydrothermal systems and resolution of the contradictory values for the apparent thicknesses of the belts obtained by different approaches: several tens of kilometres from stratigraphy, against 5-10 km, consistently, from a variety of different geophysical techniques.

Participants agreed that efforts should be concentrated on the Abitibi belt of Ontario and Quebec since there is already a good base of knowledge of the belt, and because its great mineral potential has led to substantial exploration activity and study through programs such as Lithoprobe.

The next stage in the review of the proposals will be a national discussion meeting in August at which the revised proposals resulting from the workshops will be presented along with a plan for a first, probably 5-year, phase of continental scientific drilling in Canada.

Copies of reports with abstracts of each of the six workshops are available at no charge, while stocks remain, from Dr Malcolm Drury, CCDP Planning Office, Department of Earth Sciences, Carleton University, Ottawa, Ont. K1S 5B6.

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