Diamond-bearing Kimberlites in Saskatchewan, Canada: The Fort a la Come Case History

Exploration & Mining Geology, Vol. 1, No. 4, 1992

KLAUS LEHNERT-THIEL, ROLAND LOEWER, RODNEY G. ORR and PHIL ROBERTSHAW, Uranerz Exploration and Mining Limited, Saskatoon, Saskatchewan, Canada

This paper documents the 1988 discovery and subsequent evaluation (to 1991) of diamond-bearing kimberlites in the Fort a la Corne area, Saskatchewan, by Uranerz Exploration and Mining Limited. Cameco Corporation began participating as a joint venture partner (50%) in mid-1989. The first indications that kimberlite-type intrusions might exist in the area came from Geological Survey of Canada aeromagnetic maps. Because of the overburden thickness (over 100 m), magnetometer surveys continue to be the main exploration tool in defining pipe locations and sizes. Magnetometer surveys in varying levels of detail have outlined one main cluster and two sub-clusters, the main group being some 10 km by 50 km in size. In excess of 70 individual targets have been interpreted from the magnetics as probably representing kimberlites. The size range of the individual magnetically-defined bodies is between 1 ha and 74 ha. Proof that the magnetic anomalies were kimberlite intrusions came in 1989 when each of seven test holes, all drilled on different targets, intersected the potential diamond host rock. The majority of the targets tested were diamond-bearing, with the indicator mineral chemistries suggesting that both peridotitic and eclogjtic diamond parageneses could be expected. To date, 18 individual kimberlite bodies have been drill-tested. A total of 39 bulk samples, amounting to 1861 (representing 3601 of theoretical sample recoveries) were processed in 1990 and 1991. One hundred and sixty diamonds were recovered, averaging 0.04 carats in weight, the largest being 0.6 carats. Most of the bulk sample grades are less than 2 carats/100 t; only three bulk samples have higher grades, the best being approximately 10.5 carats/100 t. The diamonds are predominantly gem-quality stones.