Page 260 - Introduction to Mineral Exploration

10: EVALUATION TECHNIQUES 243

FIG. 10.25 Plot of the simulated sulfur variable, used for predicting life-of-mine (LOM) coal feed.

From 100 simulations the probability dis- phase of a project. The engineers must decide
tribution of a grade variable can be derived. whether it is feasible to mine the potential ore,
Prediction of grade variability is then possible. as this information is required for the financial
analyses which may follow (see Chapter 11).
Geotechnical investigations essentially
10.5 GEOTECHNICAL DATA cover three aspects: soil, rock, and subsurface
water. A good field guide for the description of
During the sampling and evaluation of a min- these is given by West (1991). Soil refers to the
eral deposit, the exploration geologist is in uncemented material at or near the surface,
an ideal position to initiate the geotechnical and can include weathered or broken rock. Soil
investigation of that deposit. Usually, geotech- is mainly investigated for civil engineering pur-
nical and mining engineers are invited on to poses such as foundations of buildings. Rock is
the investigating team after the initial drilling the solid material which is excavated during
is complete. They will need to know some of mining to reach and extract the ore. Subsurface
the properties of the rocks, such as strength, water is part of the soil and the rock, and is
degree of weathering, and the nature of the found in the pore spaces and in joints, fractures
discontinuities within the rock, in order to and fissures.
begin designing the rock-related components There are two forms in which the data can be
of the engineering scheme (haulages, under- collected: (i) mainly subjective data obtained
ground chambers, pit slopes). It is important to by logging core and the sides of excavations
investigate some of the geotechnical properties (Table 10.8), and (ii) quantitative data obtained
of the overburden and of the rocks in which the by measuring rock and joint strengths and also
mineralisation is found during the exploration virgin rock stress, etc., either in the laboratory