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concentrate.
The grease table is a sloping table coated with thick grease. The
concentrates from the jigs pass up in the greaser at one end and
everything passes off over the grease at the other end except the
diamond, pieces of metallic minerals and metals. This method has been
found to be very efficient. They are also enclosed to prevent theft.
(d) At
intervals the grease is removed to recover the diamonds from the
automatic sorters. After suitable treatment, the grease is used again.
The stones are cleaned by boiling in acids and alkalies. The stones are
sorted and weighed and made into packets ready for the market.
The
Premier is the largest known diamond mine with a surface area of 80
acres. The pipe mines used to supply most of the world's production but
latterly the alluvial deposits became more important. But recently all
the deep mines have been closed, and now the production is mostly from
alluvial deposits. The most important alluvial deposits of diamond are
located in the Belgian Congo, Gold Coast, Sierra Leone, Angola, Union
of South Africa and South-West Africa. Other areas include Brazil,
British Guiana, Borneo and India.
In
India, Central India is the only place where the diamond mining
industry is extant. The methods of diamond mining now at Panna are just
as primitive as those described by the early observers. The methods of
winning the diamond from the ore are also primitive. The workings
consist of three kinds: (i) deep workings, (ii) shallow workings, and
(iii) alluvial workings. The workings extend from 25 ft. to about 70
ft. The diamond occurs in a friable conglomerate 5-12 ft. below the
surface, and in alluvial workings there is no trace of conglomerate. In
one area at Majgawan an agglomeratic tuff was found resembling very
much the Kimberley ground (cf. Wajrakarur, mentioned ante).
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