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2007-07-24 10:00 ET - News Release: Peregrine Diamonds Ltd. has received preliminary kimberlite scrubbing test results on its DO-27 kimberlite, Northwest Territories, Canada, from AMEC Americas. These tests show that the kimberlite can be preconcentrated by using simple, relatively inexpensive, water-based scrubbing technology with minimal crushing, resulting in a substantial increase in diamond grade of the resulting concentrate. This could have important positive implications on operating and capital costs of a potential future mining operation at DO-27. As the top of the DO-27 kimberlite varies from approximately nine metres to 52 metres of depth, the scrubbing tests were conducted on the kimberlite interval from 61 metres to 275 metres of depth to ensure no contamination from overburden. In the upper portions of DO-27 (from 61 metres to 121 metres of depth) an estimated 90 per cent of the kimberlite was eliminated by way of a relatively quick, three- to four-minute scrubbing test run. All of the kimberlite removed by scrubbing was less than one millimetre (mm) in size meaning that only very small and economically insignificant diamonds would be lost in the scrubbing process. This is considered a substantial degree of preconcentration and would result in the upgrading of the remaining kimberlite by a factor of 10:1 (that is, if the initial mined grade of the kimberlite is 0.9 carat per tonne, the resulting scrubbed and screened kimberlite concentrate reporting to the processing plant would grade nine carats per tonne). The same scrubbing test procedures applied to deeper, more competent kimberlite intervals showed upgrading potential of 3.3:1 (from 121 metres to 181 metres of depth) and 1.8:1 (from 181 metres to 275 metres of depth). The results of these initial tests are shown in the scrub test results table. SCRUBBING TEST RESULTS
DO-27 test depth interval (m) % of kimberlite removed by scrubbing
(three- to four-minute test)
61 to 121 90
121 to 181 70
181 to 275 57
The laboratory-scale scrubbing tests were completed using 352 kilograms of kimberlite core from DO-27. The tests were conducted at SGS Lakefield, Ontario, and overseen by AMEC Americas, which is completing an internal preliminary technical assessment (PTA) report on the DO-27 kimberlite. The PTA is investigating various potential mining and processing scenarios for DO-27. The scrubbing tests consisted of exposing various intervals of DO-27 kimberlite to water scrubbing in a screened (less than one millimetre) revolving trommel, analogous to a placer mining operation's washing plant. As DO-27 kimberlite is quite soft and fine-grained, the engineering concept is to remove as much of the finer (less than one millimetre) kimberlite as possible prior to further diamond recovery processing (crushing, dense media separation and X-ray sorting). As this softer and finer kimberlite material is removed by scrubbing, the remaining kimberlite is preconcentrated and upgraded (significant increase in diamond grade of the remaining material). This preconcentration can result in a smaller and more efficient processing plant, and the minimization of associated infrastructure than typically required for other Lac de Gras, NWT, kimberlites, or the ability to economically transport the concentrated kimberlite to a third party processing facility, either of which could have a significant positive effect on potential project economics. These preliminary test results are encouraging and the feasibility of using this procedure in a full-sized commercial mining operation is being investigated through additional testwork. Further tests are also being planned to determine if more of the kimberlite, including more competent kimberlite from the deeper regions of DO-27, can be further concentrated by using higher water pressure scrubber technology resulting in an even greater degree of overall preconcentration from this prospective mineral deposit. The current PTA engineering work will also examine the concept of mixing (co-mingling) the scrubbed kimberlite waste slurry with the granite from mine stripping. Co-mingling of the processed kimberlite waste with the granite, as opposed to a conventional processed kimberlite containment facility, could also have a significant positive effect on potential project economics and mine reclamation/closure costs. The PTA is expected to be completed in September, 2007, although optimization studies will be continuing beyond that date. In addition, the processing of the 2007 bulk sample (2,651 wet tonnes) is currently on schedule to be completed at the end of August, 2007 (see news release in Stockwatch dated June 6, 2007). AMEC Americas' Dr. Lynton Gormely has reviewed the content of this news release. Dr. Gormely is a qualified person as defined by National Instrument 43-101. |
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