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a)
b)
Natural gamma
c)
d
Natural gamma
e)
f)
Natural gamma
(API)
Natural gamma
(API)
Natural gamma
(cps)
Natural gamma
(cps)
0 0 0
Lower
Higher
0
50
100
Lower
Higher
0
15000
30000
0
100
200
10
m
1
0
m
10
m
1
0
m
10
m
1
0
m
Quartzite
Calc-silicate
Massive slate
Mica schist
Slate with carbonate bands
Laminated slate
Sulphide mineralisation
Anhydrite
Halite
Limestone
Siltstone
Sandstone
Mudstone
Limestone
Coal
Red beds
Limestone
Halite
Anhydrite
Potash ore
Sandstone
Rhyolite
Graphitic
Amygdal' andesite
Dolerite
Andesite
Feldspathic rhyolite
Crystalline basement
Pyrite
Massive niccolite
Disseminated pitchblende
Massive uranium ore (pitchblende, coffinite)
Figure 4.28
Examples of
γ
-logs and their relationship to lithology from a range of mineralised geological environments. (a) Dugald River
-
-
Zn
Ag deposit, Queensland, Australia. The succession comprises various metasediments. Note the different responses from the sulphide
mineralisation, caused by variations in its shale content. Based on a diagram in Mutton (
1994
). (b) Herb River Member, Nova Scotia,
Canada. The discrimination between the different types of sedimentary rock is excellent, although the different types of evaporite cannot be
distinguished. Based on a diagram in Carter (
1989
). (c) Coal measure sequence, UK. The coal horizons have a typically low response. Based
on a diagram in Emery and Myers (
1996
). (d) Part of the Elk Point Group, including the Prairie Evaporite Formation, Saskatchewan,
Canada. Sylvite is responsible for the high
Pb
-response of the ore horizons. Based on a diagram in Klingspor (
1966
). (e) Cluff Lake area,
Saskatchewan, Canada. As expected, the U mineralisation is associated with extremely high readings. Based on a diagram in Mwenifumbo
et al.(
2004
). (f) Buchans Mine area, Newfoundland, Canada. The different igneous rock types are clearly distinguished, with higher
γ
cases they lack a discernible magnetic response. Ford et al.
(
1988
) present an excellent example of the Th channel
response from a carbonatite in Ontario, Canada. Also,
granitoids associated with tin
produce a U response. Iron pisolite deposits may also
exhibit similar responses.
tungsten mineralisation in
New South Wales, Australia, are shown by Yeates et al.
(
1982
) to be enriched in U, and sometimes exhibiting
anomalously high eU/eTh ratio. Host sequences for cal-
crete and sandstone-type uranium deposits may have dis-
formation normally has very low radioelement concentra-
tions. However, they can appear Th-rich in radiometric
data because of Th, liberated by weathering of other mater-
ials, becoming concentrated in iron oxides (see
Section
-
4.7.4
Example of geological mapping in a fold
and thrust belt: Flinders Ranges
The Flinders Ranges in eastern South Australia are an area
with signi
cant topographic relief and generally good
exposure. They are a succession of Neoproterozoic clastic
and carbonate sediments that form a fold and thrust belt,
and contain sediment-hosted base-metal mineralisation.
Outcrop is extensive in the west of the study area and this,
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