Alto Cuilo - MBS Results

Petra Diamonds Ld
29 May 2007

29 May 2007

                             Petra Diamonds Limited


               Alto Cuilo Project; First Mini Bulk Sample Results


Petra Diamonds Limited ('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.pdf

The 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       Total       Total      Sample      Average
                                                 tonnes     stones to   carats to     grade    stone size
                           metres     metres                  sieve       sieve      (cpht)     (carats)
AC63-MB1          S4        170        200        4.56          3         0.51        11.18       0.17
AC63-MB1          S5        200        230        4.56          3         1.62        35.51       0.54
AC63-MB1          S6        230        260        4.56          8         0.98        21.48       0.12
Total over sample interval:                       13.69        14         3.11        22.72       0.22
AC63-MB12        S10        360        390        4.56          9         0.82        17.97       0.09
AC63-MB12        S11        390        397        1.06          3         0.25        23.48       0.08
Total over sample interval:                       5.63         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.



For further information, please contact:
Parkgreen Communications, London
Cathy Malins / Annabel Leather
Tel [phone]


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