term plans continues. Production The Williamson diamond mine is now characterized by low ore grade of about per hundred tons (12 mg/t) of ore. This is a dramatic decrease from its production in the mine's early life; during the first 25 years of operation, average ore grade was about per hundred tons (60 mg/t); in the first few years of full operation grades were as high as per hundred tons (124 mg/t), or 10 times the ore realized today. Production in the 1950s and 1960s was usually between 500,000 and 750,000 carats (100 and 150 kg) per year; the peak year of production was 1966, when 924,984 carats (185 kg) were produced. Today production levels for all Williamson mine diamond recovery activities is about 300,000 carats (60 kg) per year. Notable stones produced at the Williamson mine include the Williamson pink diamond which was presented to then-Princess Elizabeth and Prince Philip upon their wedding in 1947, and a diamond found in 1990. History The diamond industry of Tanzania in the 1930s was characterized by a scattering of very small mining operations that were insignificant in the economic makeup of the country. Dr. Williamson was hired by one of these operations, the Mabuki diamond mine, in 1938 and used it as his base for diamond prospecting in the region. In 1940 he discovered the Mwadui kimberlite pipe; over the next several years he developed the mine, although he was hindered by difficulty in procuring equipment and raising funds due to World War II. By the 1950s he had developed the Williamson diamond mine into the first significant diamond mine in Tanzania. The mine was visited in the early 1950s by the US author John Gunther who describes it in his book Inside Africa. The mine then employed 2,600 African workers, 110 Europeans and 60 Asians. The mine was noted for technical innovations in diamond mining which were developed under Williamson's watch. Williamson closely managed the mine until his death in 1958 at the age of 50. Williamson's heirs sold the mine for about £4 million GBP to an equal partnership between De Beers and the colonial government of Tanganyika on August 13, 1958. In 1971, a decade after Tanzania's independence, the government nationalized the mine. Although details are unknown, De Beers and other diamond industry players speculate that mine performance deteriorated significantly in the 1980s under government management. Suspected causes of