Cullinan is one of the world’s most celebrated diamond mines and the source of the two largest diamonds in the British Crown Jewels
Cullinan is renowned as a source of large, high-quality gem diamonds, including Type II stones, as well as being the world’s most important source of very rare blue diamonds.
Cullinan earned its place in history with the discovery of the Cullinan diamond in 1905, the largest rough gem diamond ever found at 3,106 carats, which was cut to form the two most important diamonds in the British Crown Jewels. Many of the world’s most famous diamonds herald from Cullinan, and it continues to produce world-class diamonds under Petra’s stewardship.
Cullinan contains a world-class gross resource of 154.9 Mcts as at 30 June 2019, which suggests its mine life could be significantly longer than the current mine plan to 2030.
The Company’s development plan led to underground ROM throughput increasing from 3.7 Mt in FY 2018 to 4.1 Mt in FY 2019, which delivered 1.6 Mcts ROM and 0.07 Mcts from surface tailings production.
Plant optimisation at Cullinan is ongoing, with the recovered ROM grade improving from 35.9 cpht in FY 2018 to 38.6 cpht for FY 2019. ROM grade is expected to remain in the 38-42 cpht range for FY 2020.
In FY 2020 the C-Cut Phase 1 project is planned to contribute ca. 3.5 Mt and 0.5 – 0.7 Mt will be sourced predominantly from the CC1E and remnant B-Block areas. The Company will on an ongoing basis investigate the optimal plan to utilise the full extent of the large Cullinan orebody (ca. 16 hectares at current production depths). .
|Location||Gauteng Province, South Africa|
|Size of kimberlite pipe at surface||32ha|
|Mine start date||1903|
|Acquisition by Petra Diamonds||July 2008|
|Acquisition cost||ZAR 1bn|
|Ownership||Petra Diamonds Limited: 74%1
Kago Diamonds (Pty) Ltd: 14%
Itumeleng Petra Diamonds Employee Trust: 12%
(inclusive of Reserves)
|Current depth of Resources||1,073m|
|Mining Method||Block cave|
|Depth of current mining||880m|
|Mine Plan||To 2030|
|Potential Mine Life||+50 years|
1. Refer to Petra’s ‘Effective Interest in Mines’ in the following document: Analyst Guidance – Explanatory Notes.
The Cullinan kimberlite pipe was discovered in 1902 and open pit mining commenced at the ‘Premier’ mine (as it was then known) in 1903. Ore extraction has been by underground mining methods since 1946. Ore extraction has varied between 2 and 5 Mt per annum and ore treatment between 2 and 7 Mt per annum.
The mine was renamed ‘Cullinan’ as part of its centenary celebrations and to link the mine to the illustrious heritage of the Cullinan diamond, which provided the two main polished diamonds within the British Crown Jewels (the 530 carat Great Star of Africa and the 317 carat Lesser Star of Africa).
Petra initially acquired a 37% interest in the Cullinan mine from De Beers in 2008, but increased its direct interest in the mine to 74% in late 2009 when it acquired Al Rajhi’s holding in the mine. Petra continues to mine the underground resource using block cave mining methods.
Cullinan is renowned as a source of large diamonds and frequently yields diamonds larger than 10 carats. Furthermore, it has produced over 800 stones weighing more than 100 carats, 140 stones weighing more than 200 carats, and around a quarter of all diamonds weighing more than 400 carats.
Cullinan is also renowned as the world’s most important source of blue diamonds, providing the collection of 11 rare blues displayed in 2000 at London’s Millennium Dome alongside the Millennium Star and which included the fancy vivid blue ‘Heart of Eternity’ (27 carats polished).
Since we acquired the mine in 2008, Cullinan has produced the following important diamonds:
Other notable diamonds historically produced from Cullinan include the Premier Rose (353 carats rough), the Niarchos (426 carats rough), the De Beers Centenary (599 carats rough), the Golden Jubilee (755 carats rough) and the famous Taylor-Burton diamond (69 carats polished).
|Category||Tonnes (millions)||Grade (cpht)||Contained Diamonds (Mcts)|
1. Resource bottom cut-off: 1.0mm.
2. Reserve bottom cut-off: 1.0mm.
3. B-Cut resource tonnes and grade are based on block cave depletion modelling and include external waste.
4. C-Cut Resource stated as in-situ.
5. Reserves based on PCBC simulations on C-Cut phase 1 and Mine2-4D schedules for CC1E and other remaining pillar retreats.
6. Factorised grades and carats are derived from a calculated Plant Recovery Factor (“PRF”). These factors account for the efficiency of sieving (bottom cut-off), diamond liberation and recovery in the ore treatment process.
7. The PRF has been revised in line with the new Resource model, and plant commissioning in 2018. The PRFs currently applied for the new mill plant per rock type are, Brown kimberlite = 73.8%, Grey kimberlite = 67.9%, Black kimberlite = 70.6% & Coherent kimberlite = 68.0%.
8. An interim Resource estimate has been completed, and will be updated once the C-Cut bulk sampling programme is completed in December 2019.
9. US$/ct values of 110-120 for ROM, excluding exceptional stones, and 35-45 US$/ct for tailings based on FY 2019 sales values and production size frequency distributions.
|Unit||FY 2019||FY 2018||Variance|
|Average price per carat||US$||1101||1252||-12%|
|On-mine cash cost per tonne treated||ZAR||234||239||-2%|
|Borrowing Costs Capitalised||US$m||2.3||11.2||-79%|
1 The Company is not able to precisely measure the ROM / tailings grade split because ore from both sources is processed through the same plant; the Company therefore back-calculates the grade with reference to resource grades.
Production increased 21% to 1,655,929 carats (FY 2018: 1,368,720 carats) mainly due to underground throughput increasing from 3.7 Mt in FY 2018 to 4.1 Mt in FY 2019 and further supplemented by an increase in ROM grades from 35.9 cpht in FY 2018 to 38.6 cpht in FY 2019.
FY2019 production from the newly established C-Cut and CC1 East mining areas increased to ca. 3.6 Mt in FY 2019 (FY 2018: ca. 2.46 Mt) with the remaining tonnage being supplemented from older B-Block mining areas.
A total of 0.9 Mt of tailings were treated with an average grade of 6.9 cpht.
The Company is guiding 4.0 – 4.2 Mt of ROM material to be treated during FY 2020, higher than previous guidance of 4.0 Mtpa due to a further contribution of B-Block areas which remain available to be mined and treated. The ROM grade is guided at 38 – 42 cpht for FY 2020.
The Company will investigate the optimal plan on an ongoing basis to utilise the full extent of the large Cullinan orebody (ca. 16 ha at current production depths). The C-Cut Phase 1 project is planned to contribute ca. 3.5 Mt for the year. A further 0.5 – 0.7 Mt will be sourced predominantly from the CC1E and remnant B-Block areas.
Tailings production was curtailed for FY 2020 by ca. 0.1 Mcts compared to previous guidance, due to price pressure on smaller, lower quality diamonds. ROM production will be prioritised, supplemented by low volumes of higher grade recovery tailings. The economic evaluation of Cullinan’s substantial tailings resource will be monitored continuously and could be included in future mine plans should the market conditions and pricing of smaller diamonds improve.
Cullinan contains a ‘Tier 1’ diamond resource of 154.88 Mcts and the Company will on an ongoing basis investigate the optimal plan to utilise the full extent of the large Cullinan orebody (ca. 16 ha at current production depths).
The Company’s current mine plan has a life to 2030, but the major residual resources at the mine indicate that the actual LOM could extend beyond 2030.
Cullinan Diamond Mine (Pty) Ltd (“CDM”) holds a valid new order mining right (the ‘‘Cullinan Mining Right’’) dated 4 December 2007. The Cullinan Mining Right was initially granted to De Beers pursuant to Item 7 of Schedule II of the MPRDA and was ceded to CDM by a notarial deed of cession on 1 July 2008 pursuant to section 11 of the MPRDA and duly notarially executed and registered in the Mineral and Petroleum Titles Registration Office. .
The Cullinan Mining Right confers on CDM the exclusive right to mine for diamonds in relation to the areas it refers to until 3 December 2037. Pursuant to the MPRDA, the Cullinan Mining Right is renewable (for periods of up to 30 years for each renewal) on the basis more fully set out in section 24 of the MPRDA.
Section 2 of the Royalty Act requires CDM to pay the South African Government a royalty for minerals recovered under the Cullinan Mining Right. Pursuant to section 4 of the Royalty Act, the royalty is to be paid on gross sales in accordance with a defined formula set out in the Royalty Act. The formula applicable to rough diamonds is as follows: 0.5% + (earnings before interest and taxes, as defined in Section 5 of the Royalty Act / (gross sales x 9) x 100) but not exceeding 7%.
In addition, South Africa has a rough diamond export levy requirement of 5% as set out in section of the Diamond Export Levy Act 15 of 2007 (“Export Levy Act”). Producers are however exempt from this levy in respect of production that is exported provided that a certain percentage of their production is sold to local diamond beneficiation licence holders, on the basis more fully set out in sections 7, 8 and 9 of the Export Levy Act.
CDM is also subject to corporate tax in South Africa at the rate of 28% in terms of section 5 and other provisions of the Income Tax Act 58 of 1962.
There are no fiscal stabilisation provisions in place in relation to Cullinan Diamond Mine.
In September 2017, Petra completed the construction and commissioning of a modern, fit-for-purpose processing plant at Cullinan, with a throughput capacity of 6 Mtpa.
This has replaced the previous plant at Cullinan, which was originally commissioned in 1947 and which had undergone numerous refurbishments over the years. Due to its age and operational complexity, it had become expensive to maintain, requiring significant stay-in-business capex, and costly to operate, particularly given the large size of its 26 ha footprint. The plant was also based on old crushing technology, which is known to impact large stone recoveries as while diamond is the hardest substance known to man, it cannot take impact and therefore very large stones can be shattered using conventional processing techniques. At the same time, the energy efficiency of the old plant was not aligned with the Company’s vision.
The design of the new plant was therefore planned to address these shortcomings and was considered an important factor in setting out a long-term sustainable future for the mine.
The new plant utilises gentler processing methods (comminution via attrition) instead of extensive crushing in the form of autogenous milling and high pressure grinding rolls, which are expected to reduce diamond breakage and improve recoveries across the full spectrum of diamonds, including the larger/exceptional stones for which the mine is rewnowned (the top-cut of 75mm will cater for diamonds of +3,000 carats, such as the Cullinan diamond).
In addition, the new plant has been designed to improve the efficiency of the material flow, thereby significantly lowering operating costs, and has a significantly smaller footprint of just 5 ha, with the associated reduction of engineering infrastructure deployed, including a reduction in:
In efficiency terms, these changes will give effect to improvements of 12% in electricity consumption (as expressed in kWh/t) and a staggering 65% in water consumption (0.17 m3/t to 0.06 m3/t).
This is a good example of how Petra has applied the integrated environmental management principle of ‘Cradle to Grave’ planning for a new project as it has embedded environmental efficiency into the process.
The optimisation of the plant was ongoing in FY 2019, with the recovered ROM grade improving from 35.9 cpht in FY 2018 to 38.6 cpht for FY 2019. ROM grade is expected to remain in the 38-42 cpht range for FY 2020.
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