Page 229 - Introduction to Mineral Exploration

212 M.K.G. WHATELEY & B. SCOTT

36.2 tonnes (80,000 lb)
bulk sample

18.1 tonnes for 18.1 tonnes
test work crushed to minus 32 mm
32 mm screen

ROTARY SPLITTER (4:1)

14.5 tonnes 3.6 tonnes
crushed to minus 10 mm
10 mm screen

SPLIT

3020 kg 580 kg

23 cm × 30 cm roll
crusher to minus 5 mm

SPLIT

Rejects 72 kg
446 kg

SPLIT (4:1) FIG. 10.6 Reduction of 36.2 tonne
(80,000 lb) bulk sample by
successive crushing and splitting.
This involves a concomitant
Four replicate reduction in grain size from +15 cm
18 kg samples to 0.5 cm. (After Springett 1983b.)

In order to provide an adequate number of and the broad range of gold particle size (i.e. d lib
increments, shovel capacity should be between in Gy’s formula) in the micrometer range,
one thirtieth to one fiftieth of the original devising an adequate subsampling plant was
sample mass to provide some 30–50 shovelfuls, difficult. The most problematical stage was
or increments, divided equally between the the reduction of the initial bulk of 36.2-tonne
two splits. In a final, fine-grained 100 g sample samples. This was effected by splitting each
the required asssay portion can be obtained such sample into two equal portions with one
by repeated alternative “shovelling” with a half (18.1 t) for sampling purposes and the other
spatula. for heap leaching gold tests (Fig. 10.6). Figure
An example of the reduction of a bulk sample 10.7 illustrates a flow sheet for reduction of
for chemical analysis is given in Figs 10.6 and 18 kg portions, which were treated in the same
10.7. The example is from a large, low grade, fashion as drilling samples, to four replicate
disseminated gold deposit with a grade of about samples each of 5 g at a grain size of 0.01 mm
−1
1gt . Due to the high specific gravity of gold (Springett 1983a,b).