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Northwest Territories Geology

Diamond exploration in the Northwest Territories began in the early 1980's and focused on the Lac de Gras Area of the Slave Geological Province, one of the oldest parts of the earths' crust. The Point Lake Discovery in 1991 started Canada's largest claim staking rush, and brought over 300 new explorers to the region, including Canterra Minerals Corporation. With three of the four Canadian diamond mines now operating in the Northwest Territories, Canada is the world's third largest diamond producer - on a value basis - after Botswana and Russia.

Canterra has spent 15 years amassing a large proprietary data set covering much of the southern portion of the Slave Geological Province ("Southern Slave"). A re-analysis of this data, using new advances in technology and techniques, has re-ignited Canterra's interest in diamond exploration. Canterra's properties overlie predominately granitic rocks with minor amounts of Yellowknife Supergroup volcanic and sedimentary rocks scattered throughout the region.

Regional Location Map

Diamonds form deep within the earth's crust in the diamond stability field, which is characterized by pressures ranging from 43-60 kbar and temperatures ranging from 900°C to 1,300°C. Kimberlite magmas generated deep (150 to 450 km) within the earth's crust contain volatile gases that cause the kimberlite magma to explode rapidly at rates of 4 to 10 metres per second through the earth's crust, picking up diamonds as it travels through the diamond stability field and colliding with various rock types on its way to surface. Because the pressures and temperatures required to produce diamonds are quite high, the earth's crust above has to be thick enough to create these conditions. These crustal thicknesses are generally found in very old (Archean) stable cratonic rocks, such as in the Slave Geological Province.

The geology of the Slave Geological Province has been summarized by Padgham and Fyson, 1992*. This relatively small craton (approximately 213,000 km2) contains rocks ranging in age from 4.05 billion years old ("Ga") to 2.55 Ga (throughout the Archean). About one third of the craton is covered by greenstone belts comprised of supracrustal rocks of the Yellowknife Supergroup. These rocks were deposited on a basement of mainly felsic migmatites. The remainder of the Province is largely underlain by granitoid intrusions.

Slave Province Geology

The Slave Province is bounded by major structures. To the northwest, the Wopmay Orogenic Zone forms the boundary between the Slave and Bear Provinces. The boundary between the Slave and Churchill Provinces is defined to the northeast by the Bathurst Fault, and to the southeast by the Macdonald Fault and the Thelon Front Tectonic Zone. Great Slave Lake forms the boundary of the Slave Province to the southwest.

The Slave Province was stabilized approximately 2.5 Ga (at the end of the Archean) however, continued tectonic activity produced linear shear zones which occur throughout the Province as well as several sets of mafic dykes. The most extensive of these is the Mackenzie dyke swarm, dated at 1.27 Ga (during the Proterozoic) and centred in the northwestern part of the Province. These dykes generally strike between 140° and 180°.

Over the last 10,000 years (throughout the Quaternary) the land in Canada's north has been subjected to multiple episodes of advancing and retreating glaciation. As glaciers retreat over the landscape they act like a finger drawing a line in the sand. Glaciers pick up and carry materials over which they travel, dispersing them to a new location down ice and subsequently depositing them as the glacier melts. In the Southern Slave, glaciers move over hard granitic rocks and soft (sometimes unconsolidated) kimberlitic rocks. The soft kimberlite material, including heavy indicator minerals with unique geochemical and physical characteristics, are often picked up by the glacier and transported over 10's of kilometres forming what are commonly known as kimberlite indicator mineral trains. Although, the Southern Slave Region was subjected to multiple episodes of glaciation, one dominant ice flow direction (220° to 260°) is apparent and useful for vectoring towards a kimberlite source.

*Padgham, W.A., and Fyson, W.K. 1992. The Slave Province: a distinct Archean craton. Canadian Journal of Earth Science, 29: 2072-2086