Production
The Williamson diamond mine is now characterized by low ore grade of about 6 carats (1,200 mg) 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 30 carats (6.0 g) per hundred tons (60 mg/t); in the first few years of full operation grades were as high as 62 carats (12 g) 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 54.5 carats (10.9 g) Williamson pink diamond which was presented to then-Princess Elizabeth and Prince Philip upon their wedding in 1947, and a 388 carats (78 g) diamond found in 1990.
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