The Mwadui kimberlite was discovered by Canadian geologist Dr John Williamson in 1940. The kimberlite pipe covers 146 ha and ranked then as the largest economically exploitable pipe in the world – and indeed no other economic pipe of this size has been mined since. Dr Williamson developed Mwadui into one of the most famous diamond mines in the world. After his death in 1958, De Beers purchased fifty percent of the mine.
	Although it is often thought that Dr Williamson discovered Tanzania’s first diamonds, the Williamson mine was in fact preceded by several tiny operations, including the Mabuki mine which Williamson worked on and later owned. Williamson eked out a meagre living from Mabuki, which he used as the base for his prospecting operations in what was then known as Sukumaland. In 1940 in the Shinyanga area, around 160 km south of the town of Mwanza on Lake Victoria, he discovered the kimberlite, which would make his name world famous.  The site of the mine was named Mwadui – after a local chief – and in the years since the names “Mwadui” and “Williamson” have become virtually synonymous. With the Second World War in progress and with Williamson himself having few resources, development at Mwadui was initially slow but, by the 1950s, a formidable mine had emerged. The total staff and labour force numbered several thousand and included around 400 expatriates, mostly from the UK and South Africa. Williamson made his home at Mwadui and managed the operation very closely. Mining equipment included draglines and scrapers while a succession of treatment plants were built, the first being a pan plant running at a grade of 62 cpht. A notable innovation in the late 1950s was an HMS plant, which ranked as the first in the world in the diamond mining industry. Williamson died early. He contracted cancer and passed away in 1958 at Mwadui, aged 52. The mine passed into the hands of De Beers and the Government of Tanganyika on 13th August 1958 and was later, in 1971, nationalised by the Government of Tanzania (as Tanganyika had become after independence). Details of how the mine performed during the period of nationalization are sketchy, but it seems that in the 80s the mine’s health took a downward turn. The loss of expatriate skills, an inability to pare down a huge labour force, the declining grade of the ore body and a lack of maintenance or stay alive capital expenditure, all apparently contributed to a fall-off in performance. In the early 1990s, De Beers was invited back to manage the mine and today Williamson Diamonds Limited (WDL) is owned 75% by De Beers and 25% by the Government of Tanzania. The first Managing Director of the restructured company was John Acland, who arrived at Mwadui in 1993 and who retired earlier this year. Tony Guthrie, who has vast experience in the De Beers Group, and who now has the challenge of steering Williamson into the future, has succeeded him.