Diamonds

Diamonds

Alberta's Kimberlite Potential

Prior to the discovery of kimberlites in Alberta, reports of diamond finds were made from central and southern Alberta. The first clue to the presence of possible diamond-bearing source rocks in Alberta was the discovery of a perfect octahedral diamond, estimated at about 1 carat in weight, by farm worker Einar Opdahl in 1958 from the Evansburg area of west-central Alberta. The stone was brought to Dr. R. Burwash at the University of Alberta for positive identification. In 1992 a prospector found two microdiamonds weighing 0.14 and 0.17 carats in recent stream sediment at Etzikom Coulee in southern Alberta. These discoveries led to increased exploration throughout much of Alberta.

The geology of Alberta is favourable for discoveries of diamonds because

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

To March 2015, 55 kimberlitic pipes have been discovered in three separate areas of northern Alberta: Mountain Lake Buffalo Head Hills, and Birch Mountains (figure 1).

Kimberlite Map
Figure 1: Kimberlite occurrences in northern Alberta.


Alberta's Diamond Potential

The Buffalo Head Hills area has the highest diamond content results to date, with 34 of the 47 pipes diamondiferous. At least three of the kimberlites (K14, K91, and K252) contain estimated diamond grades of >11 carats per hundred tonnes (cpht), with one Buffalo Head Hills pipe (K252) having preliminary mini-bulk (22.8 t) sample grades of 55 cpht.
Alberta has a national and 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 hectares); and
  • pipes associated with kimberlite-indicator mineral (KIM) targets in other parts of Alberta, some of which have mantle chemistry indicative of diamondiferous kimberlites.


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.


Significance of Diamond Exploration

Most economic diamond pipes have values of C$400 million to C$4 billion reflecting the size and quantity of mineralisation, but more rarely can be upwards of C$60 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 diamond mine located in the Lac de Gras region of the Northwest Territories contributed over C$5 billion to Canada's GDP between 1996 and 2011 and employed about 1200 people in 2011.

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 C$76 million, of which about $61 million, or 80 per cent of expenditures, was related to diamond exploration.


Alberta Geological Survey Studies

Diamond- and kimberlite-related studies at AGS have 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
  • a structural-emplacement model for kimberlitic diatremes in northern Alberta.

Indicator Minerals

Figure 2: Pyrope and chrome diopside kimberlite indicator minerals.

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