Mobile Navigation

Our Mines

Our portfolio incorporates major underground pipe mines and a large high-volume open cast mine

 
  • Cullinan Mine

    The Cullinan Diamond Mine is one of the world’s most celebrated diamond mines and the source of the two largest diamonds in the British Crown Jewels

  • Cullinan Mine

    The Cullinan Diamond Mine is one of the world’s most celebrated diamond mines and the source of the two largest diamonds in the British Crown Jewels

Cullinan Mine

The Cullinan Mine 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.

The mine 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 the Cullinan Mine, and it continues to produce world-class diamonds under Petra’s stewardship.

The Cullinan Mine contains a world-class gross resource of 147.2 Mcts as at 30 June 2022, which suggests its mine life could be significantly longer than the current mine plan to 2030.

Recovered ROM grade was 36.2cpht in FY 2022, within guidance despite a decline towards the end of the Year due to a change in the composition of ore within the C-Cut block cave resulting in a higher proportion of lower-grade and greater-density ore. We are monitoring these changes together with options to mitigate the grade differential.

FY 2022 total production was 4.9 million tonnes, 1.8 Mcts. During FY 2022 the Board approved an extension project of CC1 East:

  • At the Cullinan Mine we will establish a CC1 East sub-level cave, on the same level as the current C-Cut operation, extending the mine plan to 2031. The capital investment is estimated at US$173 million over the life of the project and is expected to deliver a project internal rate of return (IRR) of more than 30% and incremental project NPV of more than US$70 million. Capital expenditure began during the Year and production is expected to begin in FY 2024, ramping up to a steady state in FY 2026.

+

Key Facts

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%
Total Resources
(inclusive of Reserves)
147.23 Mcts
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

Heritage

The Cullinan Mine’s 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 the ‘Cullinan Mine’ 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 2008, when it acquired Al Rajhi’s holding in the mine. Petra continues to mine the underground resource using block cave mining methods.

The Cullinan Mine 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.

The Cullinan Mine 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, the Cullinan Mine has produced the following important diamonds:

  • A 39.9 carat diamond which sold for US$8.8 million in 2008.
  • A 26.6 carat diamond which yielded a fancy vivid blue and internally flawless 7.0 carat polished stone known as the ‘Star of Josephine’ and sold for US$9.49 million at a Sotheby’s auction in 2009.
  • A 507.5 carat white diamond known as the ‘Cullinan Heritage’ which was sold in 2010 for US$35.3 million.
  • A 25.5 carat blue diamond which sold for US$16.9 million in 2013.
  • A 29.6 carat blue diamond which sold for US$25.6 million in February 2014 and was then cut and polished into the perfect 12 carat ‘Blue Moon’.
  • A 122.52 carat blue diamond which achieved a value of US$27.6 million in 2014.
  • A 232 carat white diamond which was sold for US$15.2 million in September 2014.
  • A 424.89 carat exceptional D colour Type IIa diamond which was sold for just under $15 million in May 2019.
  • The Letlapa Tala Collection of five blue diamonds of high quality and clarity sold in November 2020 for US$40.36 million.
  • A 299 carat white diamond sold for US$12.8 million in March 2021.
  • A 39.34ct blue diamond which sold for US$40.18 million in July 2021
  • A 342.92 carat Type IIa white diamond which sold for US$10 million in August 2021
  • A 295.8 carat white diamond which sold for US$13.9 million in December 2021
  • A 157.8ct white stone sold for US$5.5 million in March 2022
  • A 13.74ct blue stone sold for US$5.7 million in May 2022 into a partnership with Stargems (Pty) Ltd (“Stargems”), with Petra retaining a 50% interest in the profits of the resultant polished stones, net of costs (US$1.1 million)
  • Read more about our Diamond Heritage.

Other notable diamonds historically produced from the Cullinan Mine 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).

Reserves & Resources

Gross
Category Tonnes (millions) Grade (cpht) Contained Diamonds (Mcts)
Reserves
Proved
Probable 34.5 38.6 13.31
Sub-total 34.5 38.6 13.31
Diamond Resources per asset
Measured
Indicated 219.6 59.2 130.04
Inferred 169.5 10.1 17.19
Sub-total 389.1 37.8 147.23

1. Resource bottom cut-off: 1.0mm.
2. Reserve bottom cut-off: 1.0mm.

FY 2022 Results

Cullinan Mine – South Africa Unit FY 2022 FY 2021 Variance
Sales
Revenue US$m 322.4 250.6 +29%
Diamonds sold Carats 1,899,011 2,261,058 -16%
Average price per carat US$ 169 111 +52%
Total Production
Tonnes treated Tonnes 4,865,065 5,060,339 -4%
Diamonds produced Carats 1,814,975 1,943,942 -7%
Grade1
ROM Cpht 36.2 38.2 -5%
Tailings Cpht 49.6 41.0 +21%
Segment result2 (US$m) 154.4 76.8 +101.0
Costs and capex
On-mine cash cost per total tonne treated (ZAR/t) 312 260 +20%
Total capex (US$m) 35.0 16.8 +108%

Notes:

  1. Petra 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
  2. The segment result includes depreciation of US$52.5 million

At the Cullinan Mine we came in at the upper end of our production guidance ranges on all criteria except tailings. Diamonds produced were 7% below last year’s, largely as a result of the convergence in Tunnel 41 early in the Year, and the planned depletion of a mining block which had contributed to production in FY 2021. The convergence has now been effectively mitigated and factored into our guidance.

The Cullinan Mine’s revenue increased 29% to US$322.4 million due to a 52% increase in the average price achieved per carat and the US$75.2 million realised for Exceptional Stones. Together, these more than offset the 16% reduction in diamonds sold, which was mainly the result of a higher volume of sales in FY 2021 caused by the release of the inventory build-up during the COVID-19 crisis into the market. Additional revenue of US$1.1 million was generated from Petra’s 50% share of profit from the sale of polished stones cut from the 18.30ct Type II blue diamond sold as a partnership stone in August 2021.

The convergence of Tunnel 41 in the C-Cut impacted 18 of a total of 187 draw points. Remedial action was focused on arresting convergence by reinforcing the affected pillars and protecting the tunnel, so that access can be re-established once the area has been stabilised. We continue to monitor it to determine when we will be able to re-access this tunnel.

Grade was in line with guidance, notwithstanding the decline towards the end of the Year due to a change in the composition of ore within the C-Cut block cave resulting in a higher proportion of lower-grade and greater-density ore. We are monitoring these changes together with options to mitigate the grade differential.

During the Year, the efficiency of the X-Ray Luminescence technology (XRL), introduced in FY 2021, to reduce the risk of damage to larger stones in our processing circuit, was tested through the addition of a modular X-Ray Transmission (XRT) unit. This unit recovered only 11 additional diamonds of low value, validating the decision to use XRL technology in the recovery process.

The on-mine unit cash cost per total tonne treated increased to ZAR312/t due to inflationary increases, increased social expenditure and direct costs previously included under Group G&A costs. FY 2022 capex was US$35.0 million, the majority of which was spent on the commencement of the newly approved CC1 East mine extension project. The balance included spend on the projects already underway in the current mining area, development of a crusher, and improved long-term accessibility in an area of the C-Cut.

Mine Plan

At the Cullinan Mine we came in at the upper end of our production guidance ranges on all criteria except tailings. Diamonds produced were 7% below last year’s, largely as a result of the convergence in Tunnel 41 early in the Year, and the planned depletion of a mining block which had contributed to production in FY 2021. The convergence has now been effectively mitigated and factored into our guidance.

Life extension projects approved during FY 2022

As announced previously, the Board approved extension projects at our major South African mines, the Cullinan and Finsch Mines, during FY 2022 Year.

  • At the Cullinan Mine we will establish a CC1 East sub-level cave, on the same level as the current C-Cut operation, extending the mine plan to 2031. The capital investment is estimated at US$173 million over the life of the project and is expected to deliver a project internal rate of return (IRR) of more than 30% and incremental project NPV of more than US$70 million. Capital expenditure began during the Year and production is expected to begin in FY 2024, ramping up to a steady state in FY 2026.

The on-mine unit cash cost per total tonne treated increased to ZAR312/t due to inflationary increases, increased social expenditure and direct costs previously included under Group G&A costs. FY 2022 capex was US$35.0 million, the majority of which was spent on the commencement of the newly approved CC1 East mine extension project. The balance included spend on the projects already underway in the current mining area, development of a crusher, and improved long-term accessibility in an area of the C-Cut.

FY 2023 to FY 2025 production, cost and capex guidance for the Cullinan Mine remain unchanged.

  • Our production guidance for FY 2023 is between 4.1 and 4.3 Mt ROM material to be treated, and ROM grade of between 36.5 and 38.5cpht, including the ore from the portions of the current mining area, the C-Cut, that is lower grade and higher in density.
  • Tailings production is expected to increase to between 0.56 and 0.59 Mt material treated. ROM production will be prioritised, supplemented by low volumes of recovery tailings. The economic evaluation of the Cullinan Mine’s substantial tailings resource will be monitored continuously and could be included in future mine plans dependent on market conditions and the pricing of smaller diamonds.
  • The on-mine cash cost for FY 2023 guidance is between ZAR1,413 and ZAR1,486 million in real terms.
  • We are guiding FY 2023 capex of between US$72 and US$79 million. In addition to sustaining capex, it primarily relates to underground development of the new CC1 East production areas of our extension project, explained above.
  • We expect to commence mining from the higher grade CC1 East section from FY 2024.

Mining Right

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.

New Cullinan Mine Plant

In September 2017, Petra completed the construction and commissioning of a modern, fit-for-purpose processing plant at the Cullinan Mine, with a throughput capacity of 6 Mtpa.

This has replaced the previous plant at the Cullinan Mine, 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:

  • the number of conveyor belts used from 151 to 22 (from 15 km to just 3 km);
  • the number of water pumps used from 121 to 9; and
  • the number of electrical motors from 589 to only 84.

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.

 

New Cullinan Mine Plant Presentation

New Cullinan Mine Plant Press Release

Cullinan Mine Tours

Tours of the Cullinan Mine

To arrange a tour of the famous Cullinan Mine and learn more about its rich history and heritage, use this link.

Highlights

  • July 2008 Acquisition by Petra
  • 1.6m carats FY 2021 Production
  • 147.2 Mcts Total diamond resource

Map

Diamonds from the cullinan mine

The Letlapa Tala Collection of five blue diamonds of high quality and clarity sold in November 2020 for US$40.36 million

A 39.34ct blue diamond which sold for US$40.18 million in July 2021