The pyroclastic-filled Voorspoed kimberlite pipe has a low grade due to significant internal dilution which translates to a marginal business case. The site, with excavations, tailings dumps and buildings remnant of mining from 1906 to 1912 is to become De Beers' benchmark mine in South Africa. In a climate of skills shortages and lean structures, a geological service to optimise exploitation of this complex resource was established._x000D_
As historical mining removed the higher-grade centre of the pipe, initial production was in the weathered upper benches along brecciated pipe margins._x000D_
Trenching and blasthole logging before blasts helped to mitigate the effects of the drastic contact deviations that occur when working with an inferred geological model. However, identification of unfamiliar weathered kimberlite and delineation of unmodelled internal waste posed challenges. Efficient grade control by demarcation and allocation of individual truck loads will be vital to continue profitable mining at Voorspoed._x000D_
Further challenges arose across disciplines. The first year's planned production of mostly weathered kimberlite was processed through a plant designed for Voorspoed's unusually competent ore. The high clay content of the weathered material led to clogged chutes and overloaded fines disposal, hampering efforts to commission the plant. Resolving this problem involved mining out of plan' to provide a blend of fresh and weathered kimberlite._x000D_
The calculation of an accurate mine call factor was hindered by a lack of haul truck monitoring, process stoppages and stockpiling in the plant during commissioning._x000D_
Updating of the geological model to incorporate the contact changes observed in the pit was slowed by the need to first understand how 40 years of exploration data was integrated to create the model._x000D_
A plan, involving focused mine geology practices, is in place to upgrade a portion of the resource from Inferred to Indicated level of confidence._x000D_
These challenges are not limited to new mines but will be ongoing as new information is constantly gained at Voorspoed and many mining operations._x000D_
FORMAL CITATION:Lindsell-Stewart, K, 2009. Voorspoed Diamond Mine - challenges of re-opening a historical mine with an inferred resource, in Proceedings Seventh International Mining Geology Conference 2009, pp 223-230 (The Australasian Institute of Mining and Metallurgy: Melbourne).