Kimberlites, Indicator Minerals and Diamonds

The Kimberlite-Diamond Connection Kimberlite is a rock type first categorized over a 100 years ago based on descriptions of the diamond-bearing pipes of Kimberley, South Africa. Kimberlite is characterized as a hybrid, volatile-rich, potassic, ultrabasic igneous rock. Although volumetrically insignificant on a global scale, kimberlite commonly occurs in fields, or clusters, comprising up to 100 individual, steep-sided intrusions. Kimberlites are only the mechanism by which diamonds are brought to the surface. Diamonds form much earlier than the kimberlite in the diamond stability field at depths of 110 km to 150 km and temperatures of 900°C to 1200°C. Because kimberlites are derived from deep within the earth (>150 km below the surface), they are able to transport mantle and possibly diamonds to the surface. Kimberlitic rocks are the most important primary source of diamonds and the main rock type in which significant, economically viable diamond deposits capable of sustained profitable mining have been found so far. Economic concentrations of diamonds only occur in about one per cent of known kimberlites worldwide.

Model of an idealized kimberlite magmatic system.

Alberta's Kimberlite Potential

The geology of Alberta is favourable for discoveries of diamonds because:

1. most of Alberta constitutes a younger, flat-lying sedimentary platform underlain by an older (>2 billion years) craton;
2. Alberta contains tectonic features that may have provided pathways for kimberlite intrusion;
3. there is evidence of several ages of volcanic activity in Alberta, including late Cretaceous, which was the most prolific period for world-wide kimberlite volcanism; and
4. there are a large number of geological, geophysical and geochemical anomalies in Alberta that may have been, or are related to, emplacement of potentially diamondiferous kimberlites.

To September 2003, 48 kimberlitic pipes have been discovered in three separate areas of the northern Alberta kimberlite province:

1. Mountain Lake cluster: two pipes discovered in 1989 to1990 by Monopros Limited (the then Canadian exploration subsidiary of De Beers).
2. Buffalo Head Hills field: 38 pipes discovered between 1997 and January 2003 by Ashton Mining of Canada Inc., in a joint venture with EnCana Corporation and Pure Gold Resources Ltd.

Birch Mountains field: eight pipes, which includes seven pipes discovered in 1998 by Kennecott Canada Exploration Inc., Montello Resources Ltd. and Redwood Resources Ltd., and one pipe discovered in December 2000 by New Blue Ribbon Resources Ltd.

Location of kimberlites discovered in northern Alberta with anomalous kimberlite-indicator mineral ‘trends', which show the potential for future kimberlite discoveries in northern Alberta is high.

Alberta's Diamond Potential The Buffalo Head Hills area has the highest diamond content results to date. Twenty-six of the 48 pipes are diamondiferous, and at least three of the kimberlites (K14, K91 and K252) contain estimated diamond grades of >11 carats per hundred tones (cpht) with one Buffalo Head Hills pipe (kimberlite K252) having preliminary mini-bulk (22.8 t) sample grades of 55 cpht. Alberta has a national/international reputation as having tremendous potential for the discovery of an economic diamond deposit, and will have a mine if explorers can discover a favourable combination of: a ‘near-surface' pipe with diamond grades similar to, or better than, the estimated 55 carats per hundred tonnes in pipe K252, Buffalo Head Hills; an economic pipe, or marginal-grade pipe, with diamonds of similar quality to some that have been found to date within Alberta (e.g., a gem quality, 0.76 c, yellow diamond from K6, Buffalo Head Hills); a marginal-grade pipe, but with aerially extensive near-surface dimensions similar to many of the pipes discovered to date (e.g., several Alberta pipes crop out and have an aerial extent of up to 48 ha.); and pipes associated with kimberlite-indicator mineral (KIM) targets in other parts of Alberta, some of which have mantle chemistry indicative of diamondiferous kimberlites.

Significance of Diamond Exploration

Most economic diamond pipes have 'values' of US $500 million to $5 billion, but can be upwards of $75 billion and attain mining life spans ranging from 20 years to more than 100 years. Discovery of an economic diamond deposit in Alberta would produce considerable wealth for the province in jobs, royalties, mining investment and economic spin-offs for companies supplying the mining industry. For example, the Ekati, NT, mine will contribute about CAN $5.1 billion to Canada's GDP and will create between 675 and 1000 jobs (Venture, May 1997).

Alberta, which has been mainly dependent on revenue from the oil and gas sector, has already experienced a dramatic increase in exploration expenditures from diamond seekers. Between 1995 and 2001, mineral exploration companies in Alberta spent a total of CAN $76 million, of which about $61 million, or 80 per cent of expenditures, was related to diamond exploration.

Alberta Geological Survey Studies

Current kimberlite-related studies at the AGS are focused on

• kimberlite geochemistry and petrography;
• geochemical orientation surveys over exposed and buried kimberlite pipes;
• kimberlite-indicator mineral geochemical compilation, distribution patterns and summary maps; and
• structural-emplacement model for kimberlitic diatremes in northern Alberta.

The AGS is the custodian for publicly available mineral assessment reports submitted by exploration companies and made available through AGS Information Sales (see the Publications page). As well, Alberta kimberlite core is available for viewing at the Mineral Core Research Facility.

 

Last modified: May 7, 2008