Productive Brazilian diamond deposits are all secondary. They are usually small, and some are of low grade, so mines typically operate for short periods. Primary diamond pipes exist but are generally uneconomic, suggesting that erosion has stripped away the richest portions from them. In 1890 and 1901, secondary diamond deposits were discovered in Guyana and eastern Venezuela, adjacent to deposits in Brazil's northern state of Rora’ma. Since 1890, Guyana and Venezuela have produced a total of about 4.5 and 14 million carats, respectively.
Total: 55 million carats
Old annual: 50,000 to 300,000 carats; 1730s to 1861
Today: 1.5 million carats
No comments:
Post a Comment