Sydney, May 30, 2007 (ABN Newswire) - Petra Diamonds Limited (ASX: PDL)('Petra' or 'the Company') announces encouraging first results from the mini bulk sampling ('MBS') campaign at Project Alto Cuilo ('Alto Cuilo' or 'the Project') in Angola. The MBS programme is important as it is the next step in estimating the economic viability of the various kimberlites at Alto Cuilo and hence their potential to be developed into mines. These first results are for kimberlite AC63, the first of the priority kimberlites to be sampled; the MBS programme will now continue with the sampling of other priority kimberlites at Alto Cuilo, namely AC98 and AC60.
Highlights
- AC63 drilled and sampled as the first priority kimberlite in the MBS campaign
- Encouraging results received, with one hole at AC63 (MB1) recording a grade of 22.7 carats per hundred tonnes ('cpht') for an intersection of 90 metres; this drill hole peaked at a grade of 35.5 cpht over an intersection of 30 metres
- Other high grade zones at AC63 were identified; these results mean that AC63 will be further investigated by geophysical techniques and is likely to be sampled further during the MBS campaign
- Recovery of 222 diamonds (greater than 1mm square mesh screen), yielding 18.49 carats from a cumulative sample weight of 549 tonnes of material*; this sample included crater facies sandstones which will have significantly diluted the overall average grade
- Two stones of 1.52 and 1.05 carats were recovered - the sample also included 3 white stones of 0.83, 0.68, and 0.33 carats
- The highest grade areas correspond with those that have previously exhibited high potential results from kimberlitic Heavy Mineral Analysis ('HMA'), supporting the exploration model developed by Petra and joint venture partner BHP Billiton
- The large diameter drill ('LDD') rig is now drilling at AC98, the next priority kimberlite target
- Now that the MBS campaign is underway, it is expected that MBS results will be announced with regards to other priority kimberlites at Alto Cuilo on a regular basis; further, a second LDD rig has been ordered and is expected to be on site by the end of July, which will assist the speed and efficiency of the MBS campaign further
Chairman Adonis Pouroulis commented, 'The best exploration result for any diamond mining company is naturally to recover diamonds and these results further demonstrate the potential of Alto Cuilo. Given the volume, size and complex internal morphology of the kimberlites at Alto Cuilo, grade is likely to vary over the priority targeted kimberlites and therefore more work is required to establish which areas will offer the best economics for a producing mine or mines. We are delighted with the grades already identified by this initial programme and in particular we are heartened that these first results vindicate the integrity of our exploration strategy. We will now move quickly forward with BHP Billiton into the next stage of our bulk sampling programme.'
Background
Alto Cuilo is located in north eastern Angola, in an area which many experts believe will become a prolific region for the production of diamonds. The Catoca mine, which is approximately 90 kilometres from Alto Cuilo, is expected to produce around 7 million carats in 2007. Petra and BHP Billiton have to date discovered 73 kimberlites at Alto Cuilo and a prioritisation process has ranked certain of these kimberlites for mini bulk sampling by large diameter drilling.
There are a substantial number of kimberlites at Alto Cuilo that exhibit diamond indicator mineral chemistry and other features conducive to the kimberlites hosting economic quantities of diamonds. The exploration programme is in the first instance taking mini bulk samples from a range of the kimberlites currently ranked as the most prospective (given the size of the Alto Cuilo project, it is possible this ranking will change based on further exploration work); stage two will then involve the taking of larger samples from the kimberlites that return the most prospective mini bulk sample results.
Results - Kimberlite AC63
AC63 was selected as the first target for LDD mini bulk sampling. All kimberlitic material drilled below the Kalahari sand layer has been processed, including crater facies sandstones and sand diluted resedimented volcaniclastic kimberlite ('sRVK'). These units are not usually included in resource grades as they will not host economic concentrations of diamonds; the focus is instead on resedimented volcaniclastic kimberlite ('RVK') and volcaniclastic kimberlite ('VK') layers, which is where the lowest dilution of diamond-bearing kimberlite is expected to be found.
As previously announced AC63 has an estimated surface area of 20.8 hectares. For the MBS programme, 13 large diameter holes were drilled, 11 of which were sunk in an area of 90 metres by 60 metres (less than 1 hectare), sampling less than 5% of the total surface area of the AC63 pipe. The holes were grouped in an area which had previously returned good HMA and Microdiamond Analysis ('MiDa') results.
One hole (MB1) was drilled in the eastern area of AC63 and intersected a 90 metre section containing an average grade of 22.7 cpht, having a peak of 35.5 cpht over a 30 metre zone. This intersection coincides with the previously reported encouraging HMA analysis results, lending confidence to the prioritisation and exploration model developed by Petra and BHP Billiton to identify kimberlites with the best diamond potential in this part of the Lunda-Kasai Craton.
For schematics of AC63 illustrating the relative positioning of the drill holes
and related information, please go to the following link:
http://www.rns-pdf.londonstockexchange.com/rns/3183x_1-2007-5-29.pdfThe grouping of holes in the north of the kimberlite (MB3 to MB13), drilled in response to previous HMA and MiDa results, resulted in sporadic higher grade zones with a peak grade of 19 cpht in a 37 metre intersection at a depth of 390 metres.
Two stones of 1.52 (irregular shape) and 1.05 carats (dodecahedron) were recovered. The sample also included three larger white stones of 0.83, 0.68, and 0.33 carats. A total of 18.49 carats was recovered, a parcel size that is not large enough to estimate diamond value.
Given the high grade recovered from certain of the RVK samples processed, the potential for similar results at other locations in AC63 is considered likely. Both Petra and BHP Billiton are confident that substantial intersections of relatively high-grade RVK and VK remain to be drilled at AC63.
Summary results for the AC63 RVK kimberlite intersections are listed in the table below. To view a table showing full detailed results for all AC63 drill holes, please go to the following link:
http://www.rns-pdf.londonstockexchange.com/rns/3183x_2-2007-5-29.pdf
AC63 BEST MINI-BULK SAMPLE INTERSECTIONS
Hole ID Sample From To Final
tonnes
metres metres
AC63-MB1 S4 170 200 4.56
AC63-MB1 S5 200 230 4.56
AC63-MB1 S6 230 260 4.56
Total over sample interval: 13.69
AC63-MB12 S10 360 390 4.56
AC63-MB12 S11 390 397 1.06
Total over sample interval: 5.63
Hole ID Total Total Sample Average
stones to carats to grade stone size
sieve sieve (cpht) (carats)
AC63-MB1 3 0.51 11.18 0.17
AC63-MB1 3 1.62 35.51 0.54
AC63-MB1 8 0.98 21.48 0.12
Total over sample interval 14 3.11 22.72 0.22
AC63-MB12 9 0.82 17.97 0.09
AC63-MB12 3 0.25 23.48 0.08
Total over sample interval 12 1.07 19.02 0.09
Information pertaining to the Drilling Method and Plant
The Reverse Circulation Flood Drilling method is employed, which uses drilling muds to assist in sidewall stability and material lift. A selection of three 31 centimetre drill bits is used, depending on formation. The drilled sample is passed through a cyclone, de-gritted on a 1mm slotted screen, then collected in bags and transported to the DMS plant where it is stored and presented for treatment. Initially samples were treated in 10 metre batches but the sampling interval was subsequently increased to 30 metres for convenience of treatment. This may need to be modified in the future as the processes become more refined. The drill rig is operating very satisfactorily and has reached depths of 586 metres.
The mini-bulk DMS plant is a stationary, self contained unit that is designed to treat 10 tonnes per hour. Samples that are received from the large diameter RB40 drill rig are washed and screened to a bottom size cut of 1.0mm square mesh, which is then discarded. Thereafter, there is a closed circuit comprising a 2 stage crushing system with tailings being discarded at 4mm. Concentrate feeds into a 219 Flowsort X-ray diamond recovery machine that has a grease table backup. Diamonds are hand-picked from these concentrates, weighed, acidized and then sized. The plant is thoroughly cleaned between processing of each 30 metre sample.
BHP Billiton Joint Venture
The costs of exploration and associated activities at Alto Cuilo continue to be funded by BHP Billiton in accordance with the Alto Cuilo JV agreement. As reported on 14 May 2007, BHP Billiton's cumulative spend with regards to Alto Cuilo as at 30 April 2007 amounted to US$40.33 million.
* estimated tonnage from uncalipered borehole dimensions
Ends
Notes
1. The information in this update that relates to Exploration Results, Mineral Resources or Ore Reserves is based on information compiled by Jim Davidson, Pr. Sci Nat (reg No 400031/06), who is a Member of the Geological Society of South Africa, a 'Recognised Overseas Professional Organisation' ('ROPO'). Jim Davidson is the Qualified Person for the purposes of the AIM Guidance Note on Mining, Oil and Gas Companies dated March 2006. Jim Davidson is a full-time employee of the Company and has sufficient experience which is relevant to the style of mineralisation and type of deposit under consideration and to the activity which he is undertaking to qualify. Jim Davidson has given his written consent to the inclusion in this announcement of the matters based on his information in the form and context in which it appears.
2. It should be noted that the potential quantity in this report is conceptual in nature, there has been insufficient exploration to define a Mineral Resource and it is uncertain if further exploration will result in the determination of a Mineral Resource.
