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Our Mines

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

  • Williamson

    Williamson is Tanzania’s only significant diamond producer and is based upon the 146 hectare Mwadui kimberlite pipe

  • Williamson

    Williamson is Tanzania’s only significant diamond producer and is based upon the 146 hectare Mwadui kimberlite pipe

  • Williamson

    Williamson is Tanzania’s only significant diamond producer and is based upon the 146 hectare Mwadui kimberlite pipe


In Tanzania, Petra’s partner is the Government of the United Republic of Tanzania and Taifa Mining and Civils Limited.

The Williamson mine is Tanzania’s only important diamond producer. The mine is an open pit operation based upon the 146 hectare Mwadui kimberlite pipe, which is one of the world’s largest economic kimberlites.

Despite having been in operation since 1940, the pit is only 120 metres at its deepest point due to the large size of the deposit. The low grade of the deposit is countered by the high value of its diamonds and lends itself well to high volume, bulk mining methods.

Williamson is renowned for beautifully rounded white goods and ‘bubblegum’ pink diamonds, including the 23 carat Williamson Pink (54 carat rough stone), which is considered to be one of the finest pink diamonds ever recovered, not to mention the exceptionally rare Williamson Pink Star, an 11.15 carat internally flawless Fancy Vivid Pink polished diamond that fetched US$57.7 million at auction in October 2022 – the second most valuable jewel or gemstone ever sold at auction. Following the closure of the Argyle mine in Australia, the world’s primary source, of pink diamonds in late 2020, Williamson is considered to be one of the few remaining sources of pink diamonds.

The Company’s expansion plan at Williamson has involved major pit reshaping and plant rehabilitation work in order to take the mine to a 5 Mtpa operation. In FY 2019 the Company achieved the highest level of production at the mine in over forty years, with 399,615 carats produced.

The Company’s current mine plan for Williamson has a life to 2030, but given that the Mwadui kimberlite hosts a major resource of 37.7 Mcts, there is potential to substantially extend the LOM.

Production at Williamson is currently temporarily suspended – following the breach of one of its Tailing Storage Facilities on 7 November 2022. For more information please see here: Williamson Tailings Storage Facility Breach


Key Facts

Location Shinyanga Province, Tanzania
Size of kimberlite pipe 146ha
Mine start date 1940
Acquisition by Petra Diamonds February 2009
Acquisition cost US$10m
Ownership* Petra Diamonds: 75%
Government of the United Republic of Tanzania: 25%
Total Resources
(inclusive of Reserves)
37.69 Mcts
Current depth of Resources 580m
Mining Method Open pit
Depth of current mining 55m average; 95m at deepest point
Mine Plan To 2033
Potential Mine Life +50 years

* Note 1: As announced on 31 May 2023, upon completion of a Framework Agreement with the Government of Tanzania and receipt of regulatory approvals for a transaction entered into with Taifa Mining and Civils Ltd, ownership will become: Government of Tanzania (37%), Taifa (31.5%) and Petra (31.5%). Petra will retain control and continue to consolidate Williamson in it’s accounts.


The Williamson mine was discovered in 1940 by Dr John Williamson, a Canadian Geologist, and is the largest economic primary diamond deposit to be in continuous production. Williamson has been successfully mined for over 70 consecutive years, and as such holds the record for the world’s longest running uninterrupted diamond mining operation.

By the 1950s the mine had developed into a successful operation with equipment that was state-of-the-art for its time and a labour force of several thousand. The mine was closely managed by Dr. Williamson until his death in 1958. During this period production was predominantly from near-surface eluvial deposits that had undergone significant secondary diamond concentration, with grades that ranged from 30 cpht to 100 cpht and an annual production approaching 1 Mcts.

In 1958, the mine was sold to an equal partnership between De Beers and the colonial Government of Tanganyika. De Beers operated the mine until 1973. Tonnages and carats produced increased dramatically during this period, but grades dropped to well below 30 cpht as the open pit entered primary RVK (link to glossary) material underneath the near-surface zone of eluvial enrichment.

From 1974 to 1993, the mine was operated by STAMICO (the Tanzanian State Mining Organisation). Grades varied between 5 and 12 cpht and diamond output fell dramatically relative to the previous 15 years to approximately 70,000 carats per annum. In 1993 De Beers returned to Williamson as operators, together with a recapitalisation and ownership restructuring. Production increased to approximately 195,000 carats per annum to 2005. De Beers announced it would be selling its 75% interest to Petra in November 2008, and the acquisition of Williamson in February 2009.

Williamson is renowned for ‘bubblegum’ pink diamonds, including the Williamson Pink, which is considered one of the finest pink diamonds ever discovered. It was found in October 1947 weighing 54 carats in the rough. The mine, then owned by the Canadian geologist and royalist Dr John Williamson, gave the diamond to Princess Elizabeth in 1947 as a wedding present. It was cut into a 23 carat round brilliant and set as the centre of a brooch in the form of a jonquil flower, designed and set by Cartier in 1953 – see our Diamond Heritage.

The mine also produces beautifully rounded white diamonds of high quality.

Reserves & Resources

Category Tonnes (millions) Grade (cpht) Contained Diamonds (Mcts)
Diamond Reserves per asset
Probable 42.8 7.2 3.09
Sub-total 42.8 7.2 3.09
Diamond Resources per asset
Indicated 61.2 4.9 2.98
Inferred 956.8 3.6 34.71
Sub-total 1018.0 3.7 37.69

1. Resource bottom cut-off: 1.15mm.
2. Reserve bottom cut-off: 1.15mm.

FY 2022 Results

Williamson – Tanzania Unit FY 2022 FY 2021
Revenue US$M 75.9 4.6
Diamonds sold US$M 197,756 30,339
Average price per carat US$ 384 150
Total production
Tonnes treated Tonnes 3,591,099 0
Grade Cpht 6.4 0
Diamonds produced Carats 228,070 0
Segment result2 US$M 22.2 (14.3)
Costs and capex
On-mine cash cost per total tonne treated US$/t 13.9 0
Total capex US$M 3.3 0.3

Note 1: Williamson was on care and maintenance during FY 2021

2 The segment result includes depreciation of US$5.0 million

Operations at Williamson recommenced in August 2021, having been on care and maintenance from April 2020. FY 2022 was a year of improving the performance of the mine after this 17-month period of shutdown and the operations are now fully ramped up.

Williamson’s production and grade were in line with guidance. Revenue was US$75.9 million, compared with US$4.6 million in FY 2021 when the only diamond sales were the final parcel recovered prior to the mine being placed on care and maintenance. We benefitted from the recovery of an exceptional 32.32 carat pink diamond which was sold for US$13.8 million in the December 2021 tender.

The on-mine cash unit cost of US$13.9/t was in line with guidance. FY 2022 capex was US$3.3 million, which included the costs of preparing the mine for reopening and sustaining the operations.

Mine Plan

The Company’s current mine plan for Williamson has a life to 2030, but given that the Mwadui kimberlite hosts a major resource of 37.9 Mcts, there is potential to substantially extend the LOM.

FY 2022 capex was US$3.3 million, which included the costs of preparing the mine for reopening and sustaining the operations.

The focus will be the continued stabilisation of operations following the period of care and maintenance, including increasing throughput and diamond recovery, while ensuring waste-stripping is undertaken at the required rate.


FY 2023 to FY 2025 production, cost and capex guidance remain unchanged for Williamson.

  • We are guiding between 5.2 and 5.5 Mt of ROM material to be treated during FY 2023 which reflects the fully ramped up production.
  • The total on-mine cash cost for FY 2023 is guided at between US$66 and US$69 million in real terms.
  • Capex guidance for FY 2023 is approximately US$9 million and relates to sustaining capital largely associated with waste stripping and fines-residue infrastructure.

Mining Licence

Williamson Diamonds Limited (“WDL”) holds a valid and unencumbered special mining licence number 216/ 2005 dated 25 May 2005 in respect of property described by co-ordinates in the special mining licence located in the Mwadui area in the Shinyanga region.

The special mining licence confers on WDL the exclusive right to mine for diamonds in relation to the licence areas until 24 May 2030. The special mining licence may be renewed for a further period, not exceeding the estimated life of the remaining orebody, on the basis more fully set out in the Tanzania Mining Act 14 of 2010 (“the Mining Act”).

In terms of section 87 (1) (b) of the Mining Act, a royalty of 5% is payable on the sale of diamonds recovered by WDL.

In addition, corporate tax at the rate of 30% is payable in terms of section 4 and other relevant sections of the Tanzania Income Tax Act, 2014 together with an export levy of 0.3% of diamond sales.


  • February 2009 Acquisition by Petra
  • 228,070 carats FY 2022 Production
  • 37.69m carats Total diamond resource


Williamson Diamonds

32 carat pink diamond – November 2021

Petradiam_0005423.16 carat pink diamond – November 2015

16.39 carat pink Williamson diamond - September 2014 low res16.39 carat pink diamond – September 2014

Beautifully rounded white diamonds of high quality Beautifully rounded white diamonds of high quality