Two largest diamonds recovered in Saskatchewan

Shore Gold, sponsor of the cover of International Mining’s July issue which includes a feature on Canadian diamonds, has received the sixth set of diamond results from Phase 3 of the underground bulk sampling of the Star Kimberlite (Phase 1 being the original 25,000 t bulk sample and Phase 2 being the 18,000 t bulk sample). These results include the two largest diamonds (49.50 and 22.56 carats) recovered in Saskatchewan to date. The diamond recoveries total 205.37 carats from 987.26 t processed. A total of 689 commercial sized diamonds (greater than 1.18 mm square mesh screen), collectively weighing 205.20 ct, has been recovered from the three batches. Thirty-three diamonds greater than one carat have been recovered and the four largest stones are: 49.50, 22.56, 5.45 and 5.34 ct, respectively. In addition, eight diamonds (0.17 ct) were recovered down to 0.85 mm square mesh. The colour of 71% of the diamonds has been classified as white, with a further 17% classified as off-white.

These kimberlite batches were recovered from the Cantuar Kimberlite, which was mined at the southwest end of the South 7 drive, some 200 m southwest of the shaft, within Star West – the portion of Star within the claims of the Fort a la Corne Joint Venture (Shore 60%, Newmont 40%). Diamond results are still awaited from a total of 1,400 t of Cantuar Kimberlite, of which some 900 t has been processed through the onsite plant and 500 tonnes remains to be processed. The processing of this Cantuar Kimberlite is currently underway.

Senior Vice President Exploration and Development, George Read: "The 49.50 carat stone is a fragment of a considerably larger stone and the crystal shape suggests that less than 50% of the original stone has been recovered. There are multiple breakage surfaces on this stone and the freshest breakage, probably incurred in the processing plant, only accounts for a small loss of carat weight. Fragments comprising 3 ct that are most likely broken from the 49.50 ct stone were found in Batch 225. This large stone confirms the statistical modeling by Shore geologists that diamonds in excess of 100 ct occur in the Star diamond population. The high proportion of plus one carat diamonds and the resultant coarse size frequency distribution for the Cantuar diamond population will have a positive effect on the economics of this kimberlite lithology. The two largest stones were both recovered from a coarse breccia unit within the Cantuar. Present estimates suggest that Star contains some 20 to 23 Mt of Cantuar Kimberlite. This is a geological estimate based on pattern drilling and is conceptual in nature. The collection of data which will be used to determine the presence of a National Instrument 43-101 compliant mineral resource is proceeding on schedule with the potential definition of a mineral resource on Star in early 2008."

The diamond recovery procedure includes on-site processing of kimberlite through the modular Dense Media Separator (DMS), after which DMS concentrates are batch fed through an X-ray Flow-sort. In order to ensure the recovery of low luminosity diamonds, the Flow-sort tailings are processed over a grease table. Flow-sort and grease table concentrates are transported by a secure carrier to SGS Lakefield Research for final diamond recovery. The SGS Lakefield Research process includes drying, screening, magnetic separation, manual sorting and diamond weighing and description.

The Star Kimberlite is currently being evaluated using a combination of pattern core drilling, underground bulk sampling and large diameter drilling. This evaluation programme, with a budget of some C$60 million, will determine the presence of a NI 43-101 mineral reserve for the Star Kimberlite.