Gem Breakdown

I want to know the production of rough diamonds from in Namibia (then called South West Africa) from 1950 to 1970, but particularly for the years 1960 to 1970. Nobody knows the number, or know of a source, preferably online, for the information?

I heard that out of Namibia for those years was 90% gem quality and only 10% industrial. Anyone able to confirm this or comment?

Any information on the jewel percent of industrial ventilation per cent for the same period in Angola, Sierra Leone and South Africa would also be appreciated.

860 million cubic tons.