Rio Tinto (RTP-N, RIO-L) has begun collecting a 50-tonne mini-bulk sample of the diamondiferous Cosmos 1 kimberlite on Vaaldiam Resources‘ (VAA-V) Pimenta Bueno diamond property in Rondonia state, Brazil.
A reverse-circulation drill rig is on its way to the 2.5-ha pipe situated on the northern edge of a cluster of nine kimberlite pipes currently being evaluated by Rio Tinto. The mini-bulk sample will involve the collection of kimberlite from different portions of the pipe.
The samples will be crushed and processed through one of Rio Tinto’s two 1-tonne-per-hour dense media separation plants to produce a diamond-bearing mineral concentrate. The diamonds will be manually recovered from the mineral concentrate in a secure environment.
Meanwhile, delineation drilling has wrapped up on the Pepper 3 and Pepper 1 pipes. Drilling results from three vertical holes on Pepper 3 were highlighted by hole no. 16, which yielded 148.3 metres of kimberlite, beginning 51.7 metres below surface. Hole no. 9, designed to test the northern margin of the pipe, failed to cut kimberlite.
Drilling and gravity surveying suggest the pipe has a surface area of around 17 ha.
At Pepper 1, two angled holes encountered kimberlite, with the best result being a 149-metre core length. Both holes were terminated while still in kimberlite. A third vertical hole missed the mark. A 500-kg sample of core from the holes will be subject to microdiamond analysis. Pepper 1 is estimated to measure 2 ha in surface area.
Delineation drilling is ongoing on the Cosmos 3 and Cosmos 4 pipes, 5km south of Cosmos 1. In all, Rio plans to test up to nine pipes, including the diamondiferous Pepper 4 and 13 pipes.
Previous drilling by Vaaldiam on Pepper 4 intersected 75 to 164 metres of tuffisitic kimberlite breccia. Five of seven holes encountered kimberlite. In all, 584 metres of kimberlite core, weighing an estimated 2.7 tonnes, was sampled. The pipe measures 5.5 ha., with only the eastern and southern boundaries defined by drilling.
About 100 metres to the northwest, two of three holes returned kimberlite from Pepper 13. Hole no. 1 yielded a 141.8-metre section of kimberlite. Both holes intersected diatreme facies olivine-rich tuffisitic kimberlite. Pepper 13 measures around 2 ha.
A portion of some 2,683 kg of kimberlite from Pepper 4 and 830 kg of core from Pepper 13 will be subject to caustic dissolution followed by micro- and macrodiamond recovery.
Rio Tinto can earn a 51% stake in the southern two-thirds of the property by funding US$5 million worth of exploration over three years. The major can also take a similar stake in the northern third of the property by spending US$7.5 million on exploration over three years.
So far, 33 kimberlite pipes have been discovered within the property area; 24 of those occur in a large cluster; 15 of the 33 pipes have been found to be diamondiferous on the basis of macro and micro diamond analyses.
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