Alto Cuilo Drilling Results
Petra Diamonds Ld
08 October 2007
8 October 2007 AIM: PDL
Petra Diamonds Limited
Alto Cuilo - Favourable Drilling Results From Kimberlite AC98
Petra Diamonds Limited ('Petra' or 'the Company') announces further encouraging
results from the mini bulk sampling ('MBS') campaign at Project Alto Cuilo ('
Alto Cuilo' or 'the Project') in Angola. These results are for kimberlite AC98,
the second of the selected kimberlites to be sampled. The MBS programme will
now continue, with kimberlite AC60 the next to be sampled.
Highlights
MBS Campaign
• Kimberlite AC98, (estimated surface area of 174.8 hectares) drilled and
sampled as the second selected kimberlite in the MBS campaign
• Encouraging results recorded, with one hole achieving a sample grade of
33.13 carats per hundred tonnes ('cpht') over an intersection of 33 metres
• Other higher grade zones identified including intersections of 12.1 cpht
over 137 metres and 10.8 cpht over 90 metres
• These results are consistent with the exploration model and targeting
system being developed at Alto Cuilo
• Recovery of 508 diamonds (greater than 1mm square mesh screen) from the 11
holes drilled, yielding 22.9 carats from a cumulative sample weight of 562
tonnes of material*; it is important to note that the cumulative sample
included crater facies sediments which will have significantly affected the
overall average grade; the sample included a white stone of 1.88 carats
• A second large diameter drill ('LDD') rig is in transit to site and will
assist in the speed and efficiency of the MBS campaign
• Mini bulk sampling has now commenced at AC60 (estimated surface area of 30
hectares)
Core drilling programme
• Number of kimberlites indentified at Alto Cuilo increases to 78
(previously 73)
Chairman Adonis Pouroulis commented, 'AC98 is the second kimberlite to be tested
in the mini bulk sampling campaign and this is a good follow up to the positive
results we received from the first targeted kimberlite, AC63. As we saw before,
the grades vary but this is only to be expected given the very large size of the
kimberlites at Alto Cuilo. AC98 alone covers an estimated 174.8 hectares and
therefore we were only able to test an extremely small proportion of its surface
area. Of utmost importance is that we have identified high grade intersections
and these incidences, along with the encouraging diamond recoveries, support our
view that Alto Cuilo will be a significant source of diamonds.'
Results - Kimberlite AC98
AC98 was selected as the second target for large diameter drilling and mini bulk
sampling. All kimberlitic material drilled below the Kalahari sand layer has
been processed, including crater facies sediments ('CF') 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
'), volcaniclastic kimberlite ('VK') and tuffisitic kimberlite ('TK'), which is
where the lowest dilution of diamond-bearing kimberlite is expected. Therefore
it is important to note that the inclusion of CF sediments in the cumulative
sample will have significantly affected the overall grade.
As previously announced, AC98 has an extremely large surface area, estimated to
be approximately 174.8 hectares. For the MBS programme, 11 large diameter holes
were drilled in an area of 125 metres by 25 metres ((less than 0.5 hectares),
sampling less than 0.2% of the total surface area of the AC98 kimberlite. The
holes were grouped in an area which had previously returned encouraging Heavy
Mineral Analysis ('HMA') and Microdiamond Analysis ('MiDa') results. Given the
higher grade recovered from certain of the RVK samples processed, the potential
for similar results at other AC98 locations is considered likely.
The MBS results for AC98 further increase Petra's confidence in the exploration
model developed to identify kimberlites with the best economic diamond potential
in this part of the Lunda-Kasai Craton.
Summary results for selected AC98 RVK kimberlite intersections are listed in the
table below. A table of full detailed results for AC98 is included in Appendix A
at the end of this release.
AC98 BEST MINI-BULK SAMPLE INTERSECTIONS
Total Total Sample Average
From To Final stones to carats to grade stone size
Hole ID Sample metres metres tonnes sieve sieve (cpht) (carats)
AC98-MB1 S7 270 300 6.29 9 1.16 18.43 0.13
AC98-MB1 S9 330 360 6.16 13 0.70 11.37 0.05
AC98-MB1 S10 360 390 5.40 13 0.45 8.33 0.03
AC98-MB1 S11 390 420 4.12 13 0.55 13.35 0.04
Total over MB1 sample interval (S9 to S11): 15.68 39 1.70 10.84 0.04
AC98-MB6 S7 270 300 5.17 4 0.45 8.75 0.11
AC98-MB6 S8 300 330 4.74 11 1.01 21.24 0.09
AC98-MB6 S9 330 360 4.38 11 0.33 7.46 0.03
AC98-MB6 S10 360 390 4.50 6 0.15 3.43 0.03
AC98-MB6 S11 390 407 2.49 14 0.64 25.85 0.05
Total over MB6 sample interval (S7 to S11): 21.27 46 2.58 12.13 0.06
AC98-MB8 S1 87 120 5.79 3 1.92 33.13 0.64
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. Petra and
its joint venture partner BHP Billiton have to date discovered 78 kimberlites at
Alto Cuilo. 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. Refinements to the kimberlite MBS
selection process are continually being made with reference to the data acquired
as the MBS programme continues.
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 selected 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 taking larger samples from those kimberlites
that return the most prospective mini bulk sample results.
Information pertaining to the Drilling Method and Plant
The Reverse Circulation Flood / Airlift 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. Samples are treated in increments of nominal 30 metre
depth, typically yielding 5 tonnes per sample intervals. The drill rig is
operating very satisfactorily and has reached depths of over 580 metres. At
least two separate security departments monitor the process ensuring a
continuous chain of custody.
The mini-bulk DMS plant is a stationary, self contained unit that is designed to
treat 10 tonnes per hour. Samples 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 twice from these concentrates, weighed, acidised 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 Joint Venture
agreement. BHP Billiton's cumulative spend with regards to Alto Cuilo as at 30
June 2007 amounted to US$45.20 million.
* estimated tonnage from calipered 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:
Louise Goodeve / Justine Howarth Telephone: +44 (0) 20 7851 7480
Parkgreen Communications, London
Adrian Hadden Telephone: +44 (0) 20 7523 8000
Collins Stewart, London
Appendix A: Full Results for all AC98 Kimberlite Intersections (Abbreviations:
CF- crater facies, RVK - resedimented volcaniclastic kimberlite, VK -
volcaniclastic kimberlite, TK - tuffisitic kimberlite, SDST - sandstone, Kar -
Karoo sediments):
Average
From To Geological Final Total Stones Total Carats Sample Grade Stone Size
Hole ID Sample (m) (m) Domain Tonnes To Sieve To Sieve (CPHT) (cts)
AC98-MB01 S1 90 120 CF 7.34 0 0.00 0.00 0.00
AC98-MB01 S2 120 150 CF 6.89 0 0.00 0.00 0.00
AC98-MB01 S3 150 180 CF 6.93 1 0.02 0.29 0.02
AC98-MB01 S4 180 210 RVK 6.50 4 0.10 1.54 0.03
AC98-MB01 S5 210 240 VK 6.16 8 0.25 4.06 0.03
AC98-MB01 S6 240 270 VK 6.16 6 0.20 3.25 0.03
AC98-MB01 S7 270 300 VK 6.29 9 1.16 18.43 0.13
AC98-MB01 S8 300 330 CF 6.75 2 0.04 0.59 0.02
AC98-MB01 S9 330 360 VK 6.16 13 0.70 11.37 0.05
AC98-MB01 S10 360 390 TK 5.40 13 0.45 8.33 0.03
AC98-MB01 S11 390 420 TK 4.12 13 0.55 13.35 0.04
AC98-MB01 S12 420 427 TK 0.96 2 0.06 6.26 0.03
Total: 69.65 71 3.53 5.07 0.05
AC98-MB02 S1 92 130 CF 6.32 1 0.02 0.32 0.02
AC98-MB02 S2 130 160 CF 4.86 1 0.03 0.62 0.03
AC98-MB02 S3 160 190 CF 4.92 3 0.13 2.64 0.04
AC98-MB02 S4 190 220 RVK 4.37 6 0.26 5.95 0.04
AC98-MB02 S5 220 250 VK 4.24 8 0.20 4.71 0.03
AC98-MB02 S6 250 280 VK 4.22 10 0.20 4.74 0.02
AC98-MB02 S7 280 310 CF 4.52 11 0.25 5.53 0.02
AC98-MB02 S8 310 340 RVK 4.21 5 0.16 3.80 0.03
AC98-MB02 S9 340 370 VK 4.11 1 0.01 0.24 0.01
AC98-MB02 S10 370 400 VK 4.11 8 0.25 6.08 0.03
AC98-MB02 S11 400 430 VK 4.90 4 0.13 2.65 0.03
Total: 50.78 58 1.64 3.23 0.03
AC98-MB03 S1 91 120 CF 5.12 0 0.00 0.00 0.00
AC98-MB03 S2 120 150 CF 4.78 2 0.03 0.63 0.02
AC98-MB03 S3 150 180 CF 4.75 2 0.02 0.42 0.01
AC98-MB03 S4 180 210 RVK 4.40 5 0.16 3.64 0.03
AC98-MB03 S5 210 240 RVK 4.13 0 0.00 0.00 0.00
AC98-MB03 S6 240 270 VK 4.10 6 0.31 7.55 0.05
AC98-MB03 S7 270 300 VK 4.10 4 0.12 2.92 0.03
AC98-MB03 S8 300 330 SDST/VK 4.33 0 0.00 0.00 0.00
AC98-MB03 S9 330 332 VK 0.27 0 0.00 0.00 0.00
Total: 35.99 19 0.64 1.78 0.03
AC98-MB04 S1 90 120 CF 7.63 2 0.14 1.83 0.07
AC98-MB04 S2 120 150 CF 5.86 0 0.00 0.00 0.00
AC98-MB04 S3 150 180 CF 5.82 0 0.00 0.00 0.00
AC98-MB04 S4 180 210 RVK 4.70 4 0.12 2.55 0.03
AC98-MB04 S5 210 240 VK 4.22 5 0.18 4.26 0.04
AC98-MB04 S6 240 270 RVK/VK 4.14 5 0.59 14.26 0.12
AC98-MB04 S7 270 300 VK 4.22 8 0.23 5.45 0.03
AC98-MB04 S8 300 330 RVK 4.40 4 0.17 3.87 0.04
AC98-MB04 S9 330 360 VK 4.12 16 0.54 13.12 0.03
AC98-MB04 S10 360 390 VK 4.10 12 0.25 6.09 0.02
AC98-MB04 S11 360 406 VK 6.29 7 0.41 6.51 0.06
Total: 55.50 63 2.63 4.74 0.04
AC98-MB05 S1 88 120 CF 7.30 1 0.03 0.41 0.03
AC98-MB05 S2 120 150 CF 6.03 1 0.02 0.33 0.02
AC98-MB05 S3 150 186 CF 6.29 0 0.00 0.00 0.00
AC98-MB05 S4 186 210 RVK/VK 3.76 3 0.06 1.60 0.02
AC98-MB05 S5 210 240 RVK 4.60 8 0.26 5.66 0.03
AC98-MB05 S6 240 270 RVK/VK 4.59 3 0.12 2.62 0.04
AC98-MB05 S7 270 300 VK 4.79 5 0.09 1.88 0.02
AC98-MB05 S8 300 330 VK 4.72 12 0.38 8.05 0.03
AC98-MB05 S9 330 360 VK 4.79 14 0.71 14.83 0.05
AC98-MB05 S10 360 390 Kar 5.24 0 0.00 0.00 0.00
AC98-MB05 S11 390 402 Kar 2.08 0 0.00 0.00 0.00
Total: 54.17 47 1.67 3.08 0.04
Average
From To Geological Final Total Stones Total Carats Sample Grade Stone Size
Hole ID Sample (m) (m) Domain Tonnes To Sieve To Sieve (CPHT) (cts)
AC98-MB06 S1 88 120 CF 6.60 5 0.11 1.67 0.02
AC98-MB06 S2 120 150 CF 5.62 1 0.03 0.57 0.03
AC98-MB06 S3 150 180 CF 5.16 1 0.02 0.40 0.02
AC98-MB06 S4 180 210 VK 4.72 2 0.05 1.10 0.03
AC98-MB06 S5 210 240 VK 4.62 0 0.00 0.00 0.00
AC98-MB06 S6 240 270 VK 4.69 1 0.04 0.89 0.04
AC98-MB06 S7 270 300 SDST/VK 5.17 4 0.45 8.75 0.11
AC98-MB06 S8 300 330 VK 4.74 11 1.01 21.24 0.09
AC98-MB06 S9 330 360 TK 4.38 11 0.33 7.46 0.03
AC98-MB06 S10 360 390 TK 4.50 6 0.15 3.43 0.03
AC98-MB06 S11 390 407 TK 2.49 14 0.64 25.85 0.05
Total: 52.68 56 2.84 5.39 0.05
AC98-MB07 S1 88 120 CF 5.93 1 0.02 0.34 0.02
AC98-MB07 S2 120 150 CF 5.30 0 0.00 0.00 0.00
AC98-MB07 S3 150 180 CF 5.17 0 0.00 0.00 0.00
AC98-MB07 S4 180 210 RVK/VK 4.97 3 0.06 1.21 0.02
AC98-MB07 S5 210 240 VK 4.69 5 0.23 4.90 0.05
AC98-MB07 S6 240 270 VK 4.62 3 0.15 3.24 0.05
AC98-MB07 S7 270 300 SDST/VK 4.85 8 0.25 5.15 0.03
AC98-MB07 S8 300 330 VK 4.65 4 0.16 3.44 0.04
AC98-MB07 S9 330 360 VK 4.52 2 0.04 0.88 0.02
AC98-MB07 S10 360 390 VK 4.56 4 0.14 3.07 0.04
AC98-MB07 S11 390 420 VK 4.66 4 0.16 3.44 0.04
AC98-MB07 S12 420 434 VK 2.17 0 0.00 0.00 0.00
Total: 56.09 34 1.21 2.16 0.04
AC98-MB08 S1 87 120 CF 5.79 4 1.95 33.65 0.49
AC98-MB08 S2 120 150 CF 5.10 0 0.00 0.00 0.00
AC98-MB08 S3 150 180 CF 5.08 0 0.00 0.00 0.00
AC98-MB08 S4 180 210 RVK/VK 4.69 3 0.12 2.56 0.04
AC98-MB08 S5 210 240 VK 4.47 3 0.49 10.95 0.16
AC98-MB08 S6 240 270 VK 4.60 2 0.04 0.87 0.02
AC98-MB08 S7 270 300 VK 5.02 14 0.61 12.15 0.04
AC98-MB08 S8 300 330 VK 4.76 3 0.22 4.62 0.07
AC98-MB08 S9 330 360 VK 4.55 7 0.28 6.16 0.04
AC98-MB08 S10 360 390 RVK/VK 4.56 3 0.06 1.32 0.02
AC98-MB08 S11 390 401 VK 1.67 0 0.00 0.00 0.00
Total: 50.31 39 3.77 7.49 0.10
AC98-MB09 S1 89 120 CF 7.06 2 0.03 0.43 0.02
AC98-MB09 S2 120 150 CF 6.84 0 0.00 0.00 0.00
AC98-MB09 S3 150 180 CF 5.22 0 0.00 0.00 0.00
AC98-MB09 S4 180 210 RVK/VK 4.87 4 0.08 1.64 0.02
AC98-MB09 S5 210 240 VK 4.67 10 0.26 5.57 0.03
AC98-MB09 S6 240 270 VK 4.63 7 0.55 11.88 0.08
AC98-MB09 S7 270 300 VK 4.56 3 0.06 1.32 0.02
AC98-MB09 S8 300 330 RVK 4.50 3 0.11 2.45 0.04
AC98-MB09 S9 330 360 VK 4.66 4 0.11 2.36 0.03
Total: 47.01 33 1.20 2.55 0.04
AC98-MB10 S1 92 120 CF 6.38 3 0.16 2.51 0.05
AC98-MB10 S2 120 150 CF 5.60 1 0.02 0.36 0.02
AC98-MB10 S3 150 180 CF 5.03 1 0.03 0.60 0.03
AC98-MB10 S4 180 210 RVK 4.65 3 0.08 1.72 0.03
AC98-MB10 S5 210 240 RVK 4.52 7 0.35 7.75 0.05
AC98-MB10 S6 240 270 VK 4.30 8 0.25 5.81 0.03
AC98-MB10 S7 270 300 VK 4.49 2 0.04 0.89 0.02
AC98-MB10 S8 300 330 RVK 4.71 3 0.19 4.04 0.06
AC98-MB10 S9 330 360 VK 4.50 11 0.41 9.10 0.04
AC98-MB10 S10 360 380 Kar 3.15 0 0.00 0.00 0.00
Total: 47.33 39 1.53 3.23 0.04
Average
From To Geological Final Total Stones Total Carats Sample Grade Stone Size
Hole ID Sample (m) (m) Domain Tonnes To Sieve To Sieve (CPHT) (cts)
AC98-MB11 S1 92 120 CF 5.11 4 0.20 3.92 0.05
AC98-MB11 S2 120 150 CF 4.86 0 0.00 0.00 0.00
AC98-MB11 S3 150 180 CF 4.53 1 0.02 0.44 0.02
AC98-MB11 S4 180 210 VK 4.16 2 0.04 0.96 0.02
AC98-MB11 S5 210 240 VK 4.10 11 0.57 13.90 0.05
AC98-MB11 S6 240 270 VK 4.10 5 0.32 7.80 0.06
AC98-MB11 S7 270 300 SDST/VK 4.28 3 0.24 5.60 0.08
AC98-MB11 S8 300 330 SDST/VK 4.25 7 0.28 6.58 0.04
AC98-MB11 S9 330 360 VK 4.10 8 0.40 9.75 0.05
AC98-MB11 S10 360 382 TK 3.15 8 0.17 5.40 0.02
Total: 42.64 49 2.24 5.25 0.05
Grand Total 562.16 508 22.90 4.07 0.05
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