Geoscience Reference
In-Depth Information
Fig. 13.3
Grade-Tonnage curves, 2001 Long-term (LT) and February 2002 Quarterly (QT) resource models. Note how the QT model has higher
grade and less tonnage than the LT model for most cutoffs
Fig. 13.4
Total copper grades by
Bench, 2001 Long-term (LT) and
February 2002 Quarterly (QT)
resource models
In general, sampling errors, estimation errors, limited in-
formation, and operational constraints result always in ore
loss and waste dilution, which in turn leads to economic loss-
es. These losses can be serious enough to make the operation
unprofitable.
One example was the Hartley platinum mine in Zimba-
bwe, which produced its first concentrate in 1997 and closed
in 1999 after what were deemed to be insoluble geologic
problems and low mine productivity (Matthey
2001
). Hart-
ley is located within the Great Dyke, a geological feature
running roughly north-south through the heart of Zimbabwe
for about 550 km. The platinum group minerals occur in a
layer known as the Main Sulphide Zone, which is typically
about 3 m thick. However, the economic mining width may
be as little as 1 m, depending on grade, metal prices and the
chosen mining method. The reef is difficult to mine because
it is not visible to the naked eye. This can lead to significant
unplanned dilution and ore loss, which reduces head grades.
