Page 62 - Introduction to Mineral Exploration

3: MINERAL DEPOSIT GEOLOGY AND MODELS 45

exports, which inhibited uranium exploration.
Lake Unconformity The importance of recognizing the elements
Athabasca
associated with this type of deposit became
obvious in the late 1980s with the discovery
McClean
Cluff Lake Athabasca Lake of the Coronation Hill gold–palladium deposit
Formation in the Northern Territory and similar prospects
Cigar Lake in Saskatchewan. Unfortunately for the com-
Rabbit
McArthur Lake pany concerned Coronation Hill is on the edge
300m depth
River of the Kakadu National Park and will not be
mined in the foreseeable future.
0 100 km
Key Lake The application of a particular deposit model
will depend on the quality of the database and
should not be regarded as a panacea for the ex-
FIG. 3.13 Outline of the Athabasca Basin and ploration geologist. Some deposit types such as
distribution of the associated uranium deposits.
(Modified after Clark et al. 1982.) placer gold are easy to understand and have
well-developed models, whereas others such as
Besshi-style massive sulfides or the Olympic
A). At roughly the same time a small Canadian Dam models are not well developed and may be
company explored the eastern edge of the basin represented by a single deposit on which infor-
knowing that they had an aircraft available and mation is difficult to obtain.
that the sandstones might be prospective by The major pitfalls of using models are ably
comparison with the much younger Western illustrated in cartoon form by Hodgson (1989).
US deposits (Reeves & Beck 1982). They also He identifies a number of problems which he
discovered glacial boulders which led them likens to religious cults:
back to the deposit (Rabbit Lake). At roughly 1 The cult of the fad or fashion. An obsession
the same time (1969) in Australia airborne sur- with being up to date and in possession of the
veys in the East Alligator Valley detected major newest model.
anomalies at Ranger, Koongarra, and Narbalek. 2 The cult of the panacea. The attitude that
The area selection was initially based on the one model is the ultimate and will end all
similarity of the geology with known produc- controversy.
ing areas in South Alligator Valley, with acid 3 The cult of the classicists. All new ideas are
volcanics as the postulated source rock, and rejected as they have been generated in the hot
by a re-interpretation of granites, that were pre- house research environment.
viously thought to be intrusive, as basement 4 The cult of the corporate iconoclasts. Only
gneiss domes (Dunn et al. 1990b). When drill- models generated within an organization are
ing started it became clear that the miner- valid, all outside models are wrong.
alisation was closely associated with the 5 The cult of the specialist. In which only one
unconformity. Thus the overlying sandstones, aspect of the model is tested and usually not in
rather than being responsible for the erosion of the field.
the deposits or being a barren cover, became a The onus is thus on the exploration geologist
target. In Canada the Key Lake and Midwest to ensure that a model is correctly applied and
Lake deposits were discovered as a result of this not to exclude deviations from the norm. Other
change in model (Gatzweiler et al. 1981, Scott examples of the application of models are given
1981). The exploration model has been further in Chapters 12–17.
developed in Canada, to the point at which
deposits with no surface expression (blind
deposits), such as Cigar Lake and McArthur 3.4 FURTHER READING
River, have been found by deep drilling of elec-
tromagnetic conductors caused by graphitic Longer discussions of the subjects forming the
schists (McMullan et al. 1989). Similar devel- main sections of this chapter can be found in
opments could have been anticipated in Aus- Robb Introduction to Ore-Forming Processes
tralia but for government control on uranium (2004). Kesler’s Mineral Resources, Economics,