Williamson Diamond Mine (also known as the Mwadui Mine) is a diamond mine 23 kilometers (14 mi) northeast of Shinyanga in Tanzania; It became known as the first large diamond mine outside of South Africa. The mine was established in 1940 by Dr. John Williamson, a Canadian geologist, and has been in continuous operation ever since, making it one of the oldest continuously operating diamond mines in the world. Over its lifetime, it has produced more than 19 million carats (3,800 kg) of diamonds. A report from The Guardian in 2020 said that high-quality pink diamonds from the mine can fetch up to $700,000 per carat.
The Williamson Mine was previously owned by the namesake Dr. Williamson and was later nationalized by the Government of Tanzania. Since February 2009, the mine is mostly owned by Petra Diamonds, 75%, and the remaining 25% is owned by the Government of Tanzania. In 2020, the mine came under scrutiny for alleged human rights violations.
The mine is located approximately 160 kilometers (99 miles) south of the city of Mwanza in the Kishabu District of the Shinyanga District. Dr. Williamson, discoverer of the site, and first owner and mine of the same name, named the site “Mwadui” after a local chieftain; “Williamson” and “Mwadui” are now almost synonymous in the world of diamond mining.
The most important geological feature of the Williamson Diamond Mine is the kimberlite tube on which it is located. At 146 hectares at surface level, it ranks as the largest economically exploitable diamond-bearing volcanic tube in the world. Recent exploratory drilling cores by De Beers have indicated that the tube is lava kimberlite, not hypabyssal kimberlite as previously suspected. This indicates that it may be possible to extend the existing 90-meter-deep open pit to a depth of up to 350 metres, continuing downward further with underground mining operations. However, mine operations and long-term plans continue to be reviewed.