No.1 Pipe Background

After the discovery of the No. 1 Pipe and No. 2 Pipe in 1948, the kimberlites were sampled, drilled and mined, first by SLST in the period 1953 to 1967, and then by NDMC between 1978 and 1984. Several feasibility studies were also undertaken.

1953 to 1961	Sampled (mined?) to a depth of 7.3m. A total of 23,362t yielded 14,080 carats, for an average grade of 0.60ct/t, with a largest stone of 60.67ct.
1962 to 1966	Presumably mined in the depth range 7.3m to 17.8m. A bulk sample of 3,558t yielded 2,649.6 carats and a grade of 0.74ct/t.
1965 to 1966	K-shaft sunk to a depth of 91.4m. Some 3,540t yielded grades of 0.75ct/t and 0.78ct/t from two different sampling periods, an assumed average grade of 0.765ct/t.
Unknown	Core drilling. Three inclined boreholes were drilled from surface designed to map kimberlite facies and to prove continuity of the kimberlite with depth.
1966?	Nine horizontal core boreholes were drilled from the development on the 91.4m level, designed to delineate the pipe contacts with the country rock, and thus the area at that level.
1967 to 1968	Sampling continued in the depth range 17.8m to 23.7m, indicating an average grade of 0.556ct/t.
1978 to 1979	Total extraction of the 100ft level from the pit gave ten bulk samples totalling 633,867t, which yielded 411,167ct, for an average grade of 0.64ct/t.
1978 to 1982	Mining in the depth range 17.8m to 41m. Tonnage treated reported to be 138,300t at an average grade of 0.522ct/t. This grade was subsequently recalculated by NDMC/Outokumpu to be 0.552ct/t. This is compatible with 100% extraction.