Page 243 - Introduction to Mineral Exploration

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

1
253.66 m Sample

2
40° Fragment missing
15 cm
Slate
3 Chlorite and
5 cm core loss ore minerals
15 cm
hanging–wall
Chlorite and quartz

4
31 cm

Lode zone
5
15 cm
Chlorite and feldspar

23 cm
254.65 m
Core intersection angle average 40°
Slate footwall
Sample Depth Recovery True width %Sn cm%
number from(m) to(m) (m) (%) (cm)
1 253.66 253.81 0.15 100 12 0.03 0.36
2 253.81 253.96 0.15 100 12 0.56 6.72
3 253.96 254.27 0.25 81 20 4.75 95.00
4 254.27 254.42 0.15 100 12 1.27 15.24
5 254.42 254.65 0.23 100 18 NIL –
FIG. 10.12 Typical intersection of a
Weighted average lode value = 116.96cm% = 2.66%Sn tin-bearing vein showing sampling
intervals and the uncertainty
44cm (true thickness)
introduced by incomplete core
at a weighted average core recovery of 91% recovery. (After Walsham 1967.)
half is returned to the core box for record pur- affect the measurement of relative density of
poses. Obviously structural features have to be the core (Preston & Sander 1993) or alter the
recorded before splitting and a good practice is nature of the material.
to photograph wet core, box by box, before log- Rock chips and dust (“sludge”) can be col-
ging it, to produce a permanent photographic lected during core drilling; they represent the
record (Fig. 13.10). rock cut away by the diamond drill bit. Drill-
When core from coal seams is to be sampled ing with air circulation in relatively shallow
or the samples are to be collected for geotech- holes (as in most percussion drilling) delivers
nical analysis, the core should be sealed as soon cuttings to the surface within a minute or
as the core leaves the core barrel. This is to so. However, with core drilling, water circula-
prevent loss of moisture, which can adversely tion, and longer holes, there is an appreciable