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.

1. Resource bottom cut-off: 1.15mm.
2. Changes to Resource figures due to mining depletions and the removal of Shale and Mudstone from Resource.
3.US$/ct values of 215-225 for ROM guided for FY 2018, based on sales values and production size frequency distributions.

• Excluding Exceptional Diamonds, the average value for FY 2017 was US$235 (FY 2016: US$238).

Production increased 6% to 225,202 carats (FY 2016: 212,869 carats), mainly due to a 16% increase in ROM grades (as a result of improved liberation associated with the new milling section of the plant), partially offset by throughput constraints experienced during the commissioning of the new milling section plant during H2 FY 2017.

Petra’s expansion plan at Williamson is expected to see production rise from ca. 225,000 carats in FY 2017 to ca. 337,500 ctpa by FY 2019. The current mine plan has a life extending to 2033, but given that the Mwadui kimberlite hosts a major resource of 39.0 Mcts, there is potential to extend the LOM considerably.

ROM throughput is planned at ca. 4.6 Mt at a grade of ca. 6.75 cpht during FY 2018, before ramping up to steady state of ca. 5 Mt by FY 2019 onwards at a grade of 6.5 – 7 cpht.

Click on schematic to enlarge.

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.