Lithoprobe has implications for mineral exploration

Lithoprobe, an integrated geoscience research program created in 1987, is providing new insights into mineral exploration in several mining camps in the Abitibi greenstone belt in Ontario and Quebec. Scientists are using seismic data to create three dimensional models of the earth’s crust to search for deep ore zones.

The Lithoprobe program was designed to study the earth’s lithosphere in a variety of geological and tectonic settings. The program has brought together a multidisciplinary team of geoscientists from government, university and industry to study eight areas or transects across Canada.

Lithoprobe has adapted seismic techniques and technology used in oil exploration to study crystalline rocks to depths of 50-100 km. Sound waves triggered at the surface penetrate the earth and bounce off rock layers of differing physical characteristics and return to the surface. Computer processing and modelling of the sound wave reflections and refractions provide depths and positions of buried structures and rock formations. Whenever possible, seismic data are integrated with gravity, magnetic and electrical and thermal conductivity data. Geological mapping, structural geology, age dating, and petrology are also used to further refine the three dimensional models of the earth’s interior.

Most of the new insights into mineral exploration have come from the Abitibi-Grenville transect. The primary focus of the transect is the Abitibi greenstone belt in northeastern Ontario and northwestern Quebec. The Abitibi sub-province is the largest belt of Archean-aged volcanic, sedimentary and plutonic rocks in the world and contains a large proportion of Canada’s mineral wealth, including major gold and base metal deposits. Lithoprobe research shows that the Cadillac and Porcupine-Destor fault zones that are associated with most of the major gold deposits were generated by crustal scale thrust and or strike slip faulting. Their steep dips can be traced to depths of 10-15 km. By studying the new profiles of these fault zones, deeper mineralized zones may be discovered.

In the Matagami mining camp in northern Quebec, a seismic survey was carried out to map the contact between the predominantly felsic Watson Lake group and the overlying Wabassee basalts. This contact is important since it hosts all known economic deposits discovered to date in the camp.

Seismic surveys were conducted around the active Les Mines Selbaie mine site in northern Quebec to obtain an image of the east-dipping contact between the granite and underlying andesite and volcanic rocks hosting the copper-zinc-gold-silver orebodies.

Three profiles were also completed over the Sudbury structure. The new seismic data show that the Sudbury structure is asymmetrical at depth and suggest that some of the copper-nickel sulphide ore-bearing mafic units on the southern rim of the Sudbury structure may be repeated at depth. The Lithoprobe project is funded by the Natural Science and Engineering Research Council of Canada, Geological Survey of Canada and private industry.