Our Mines

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

 
  • Williamson

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

  • Williamson

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

  • Williamson

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

Williamson

Williamson is Tanzania’s only important diamond producer. The mine is an open pit operation based upon the 146 hectare Mwadui kimberlite pipe, which is the world’s largest economic kimberlite to have seen continuous mining.

Despite having been in operation since 1940, the pit is only 95 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.

Petra’s expansion plan at Williamson will see tonnage throughput ramp up to ca. 5 Mtpa from FY 2018, which, at a grade of ca. 7 cpht, is expected to deliver ca. 350,000 ctpa. Petra’s current mine plan for Williamson has a life extending to 2033, but given that the Mwadui kimberlite hosts a major resource of 40.4 Mcts, there is potential to extend the LOM considerably.  

ROM throughput is planned at 4.6 Mt at a grade of ca. 6 cpht during FY 2017, in line with previous guidance, as the enhancements being made to the plant (introduction of an additional crusher circuit and two autogenous mills) are expected to come into effect during FY 2017.

Throughput is expected to increase to ca. 5 Mtpa by FY 2018 at a grade of ca. 7 cpht, resulting in a 7 – 10% increase in revenue per tonne compared to the FY 2017 guided level of 6 cpht.

 

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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)
40.39 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

Heritage

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

Gross
Category Tonnes (millions) Grade (cpht) Contained Diamonds (Mcts)
Reserves
Proved
Probable
Sub-total
Resources
Measured
Indicated 84.9 5.0 4.21
Inferred 993.9 3.6 36.18
Sub-total 1,078.8 3.7 40.39

1. Resource bottom cut-off: 1.15mm.
2. Updated Resource model in line with in-pit exploration drilling and production sampling.

FY 2016 Results

Unit FY 2016 FY 2015 Variance
Sales
Revenue US$M 78.9 62.1 +27%
Diamonds sold Carats 205,548 208,351 -1%
Average price per carat US$ 384 298 +29%
ROM Production
Tonnes treated Tonnes 4,003,180 4,056,638 -1%
Diamonds produced Carats 199,796 194,048 +3%
Grade Cpht 5.0 4.8 +4%
Alluvial Production
Tonnes treated Tonnes 417,452 369,406 +13%
Diamonds produced Carats 13,073 8,216 +59%
Grade Cpht 3.1 2.2 +41
Total Production
Tonnes treated Tonnes 4,420,632 4,426,044 0%
Diamonds produced Carats 212,869 202,265 +5%
Costs
On-mine cash cost per tonne treated US$ 11 12 -8%
Capex
Expansion Capex US$M 23.0 8.3 +177%
Sustaining Capex US$M 1.4 7.9 -81%
Total Capex US$M 24.4 16.2 +51%

Production increased 5% to 212,869 carats (FY 2015: 202,265), mainly due to an increase in both the ROM and alluvial grade of the tonnes treated for the Year.

Additional waste stripping during the Year has yielded a more flexible mining plan.

Mine Plan

Our expansion plan at Williamson will see tonnage throughput ramp up to ca. 5 Mtpa from FY 2018, which, at a grade of ca. 7 cpht, is expected to deliver ca. 350,000 ctpa. Petra’s current mine plan for Williamson has a life extending to 2033, but given that the Mwadui kimberlite hosts a major resource of 40.4 Mcts, there is potential to extend the LOM considerably. 

ROM throughput is planned at 4.6 Mt at a grade of ca. 6 cpht during FY 2017, in line with previous guidance, as the enhancements being made to the plant (introduction of an additional crusher circuit and two autogenous mills) are expected to come into effect during FY 2017.

Throughput is expected to increase to ca. 5 Mtpa by FY 2018 at a grade of ca. 7 cpht, resulting in a 7 – 10% increase in revenue per tonne compared to the FY 2017 guided level of 6 cpht.

Click on schematic to enlarge.

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.

Highlights

  • February 2009 Acquisition by Petra
  • 212,869 carats FY 2016 Production
  • 40.4m carats Total diamond resource

Map

Williamson Diamonds

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