No. 2 Pipe

Background

No. 2 Pipe was sampled underground in 1967-1968 following the completion of the underground sampling of No. 1 Pipe. Further sampling and mining was carried out from 1968 to 1984, during which time and open pit to a depth of 33m had been established. After 1984, the pit was abandoned and allowed to fill up with water.

1966	Surface sampling of 10,653t of decomposed kimberlite from a depth below 3.5m yielded an average grade of 0.32ct/t.
1967 to 1968	Underground sampling at a depth of 38m yielded an average grade of 0.40ct/t from a selected (2,2728t) bulk sample comprising 51% of the total material extracted.
1968 to 1983?	The pipe was mined to a depth of 40m. No records exist as to total tonnage treated and recoveries.
1983 to 1984	Check sampling of benches in the depth range 27.6m to 33.0m. Seven bulk samples totalling 95,764t yielded grades in the range 0.14ct/t to 0.31ct/t, with an average of 0.23ct/t. Subsequently, sampling continued down to the 38m level, breaking into the underground development. 6,806t yielded 1,843.4 carats for a grade of 0.271 ct/t.
1984	Three boreholes confirmed the continuation in depth of the pipe to at least 250m from surface, without delineating the contacts.

Production

No. 2 Pipe was mined from May 2004 to May 2005, during which time the operation was hampered by mining and processing problems. The open pit was lowered by approximately 25m, with 64,886 carats being recovered from 230,251 tonnes and a grade of 0.28 ct/t. Although this grade is in line with reported historical grades, it is likely an underestimation of the global grade of the pipe for the following reasons. Apart from the fact that the plant grease table was not operational until August 2004, plant modifications in early 2005 resulted in significant losses in the smaller diamond size fractions. These diamond losses, as well as the unusually high internal and external waste component (30-40%) encountered during the period, severely impacted on the recovered grade for No. 2 Pipe. In light of the above, the production data was analysed and periods during which results were shown to be unrepresentative were omitted from the estimation process, suggesting a grade of approximately 0.34 carats per tonne for the period August 2004 to December 2005 during which 117,003 tonnes of ore yielded 39,817 carats.

Geological Model

Vertical section of No. 2 Pipe showing the resources delineated below the open pit.

Plan view of No. 2 Pipe showing the
extent of drillhole coverage

Two phases of drilling were completed on No. 2 Pipe in 2003 and 2007, with 20 drillholes totaling 5,507 metres. The geological model was based on these intersections, as well as the in-pit geological mapping. The resources extend from the current open pit floor at approximately 325m amsl (including remnants of the pipe above 325m amsl that were left behind in the ramp and sidewalls of the pit) to -165m bmsl, a depth of 490m.