Preliminary Scrubbing Tests Show Potential To Substantially Increase Diamond Grade At DO-27 Via Pre-Concentration Of Kimberlite

July 24, 2007 PDF version
Vancouver, British Columbia, Canada - Tuesday, July 24, 2007- Peregrine Diamonds Ltd. (TSX-PGD) (“Peregrine”) has received preliminary kimberlite scrubbing test results on its DO-27 kimberlite, NT, Canada, from AMEC Americas. These tests show that the kimberlite can be pre-concentrated 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 9 to 52 metres of depth, the scrubbing tests were conducted on the kimberlite interval from 61-275 metres of depth to ensure no contamination from overburden. In the upper portions of DO-27 (from 61-121 metres of depth) an estimated 90% of the kimberlite was eliminated by way of a relatively quick, 3-4 minute scrubbing test run. All of the kimberlite removed by scrubbing was less than 1mm 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 pre-concentration and would result in the up-grading of the remaining kimberlite by a factor of 10:1 (i.e. if the initial mined grade of the kimberlite is 0.9 carats/tonne, the resulting scrubbed and screened kimberlite concentrate reporting to the processing plant would grade 9 carats/tonne). The same scrubbing test procedures applied to deeper, more competent kimberlite intervals showed up-grading potential of 3.3:1 (from 121-181 metres of depth) and 1.8:1 (from 181-275 metres of depth). The results of these initial tests are shown in the table below.

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                                                     (3-4 minute test)

61-121m                                                            90%

121-181m                                                           70%

181-275m                                                           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, who 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 (<1mm) 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 (i.e. less than 1mm) 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 pre-concentrated and up-graded (significant increase in diamond grade of the remaining material). This pre-concentration can result in a smaller and more efficient processing plant and the minimization of associated infrastructure than typically required for other Lac de Gras, NT kimberlites, or the ability to economically transport the concentrated kimberlite to a third party processing facility, either of which could have a significant positive impact 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 utilizing higher water pressure scrubber technology resulting in an even greater degree of overall pre-concentration 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 impact on po