Page 78 - Introduction to Mineral Exploration

4: RECONNAISSANCE EXPLORATION 61

occurrences within volcanics to the south of and to generate other, previously unknown,
Çanakkale and to the northwest of Izmir targets preferably without taking out licenses.
(points A and B, Figs 4.5, 4.6) remain of interest, In areas of reasonable outcrop the first stage
as do the mercury and antimony occurrences will be to check the geology by driving along
along the graben bounding faults (points C, D, roads or from the air if ground access is impos-
E). The area south of Çanakkale was mined by sible. A considerable number of disseminated
a British company until the outbreak of the gold prospects have been found by helicopter
1914–18 World War and has lain nearly dor- follow-up of Landsat data processed to high-
mant since then. The first company to appreci- light argillic alteration and siliceous caps in
ate the potential of this area has defined a arid areas, particularly in Chile. Airborne geo-
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resource of 9 Mt at 1.25 g t Au within one of logy can be extremely effective in solving
the areas of brecciated volcanics and a number major questions quickly, but it is expensive,
of other targets have been identified in the US$500 per hour, and is best undertaken by
vicinity. The area near Izmir has been mined experienced geologists with specific problems
since Roman times but the gold mineralisation to solve. In any case a preliminary visit to the
is largely confined to a vein structure. Recent field should be made as soon as practicable to
exploration by the Turkish geological survey check the accessibility of the area, examine on
(MTA) who hold the license has defined a the ground some of the data emerging from the
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further resource of 1.4 Mt at 1.3 g t Au. The desk study, and check on competitor activity.
mercury and antimony deposits are largely the Reconnaissance techniques can be divided
concessions of the state mining group, Etibank, into those which enable a geologist to locate
but at least one exploration company was able mineral prospects directly and those which
to agree a joint venture and found significant, provide background information to reduce the
although subeconomic, gold grades at the search area.
Emirli Antimony Mine (point C, Figs 4.5, 4.6). Airborne geophysics and stream or lake sedi-
The most significant gold discovery in the area, ment geochemistry are the principal tools for
Ovacik (point F), is not shown on either map, directly detecting mineralisation. Perhaps the
although a number of veins in the area had, at most successful of these has been the use of
least in part, been mined by ancient workers. airborne electromagnetic techniques in the
The Ovacik deposit was discovered during a search for massive sulfide deposits within the
regional reconnaissance of favorable volcanic glaciated areas of the Canadian Shield. This has
areas using stream sediment geochemistry and led to the discovery of a number of deposits,
prospecting. Larson (1989) provides a further such as Kidd Creek (see section 15.3.2), by
overview of the potential of the area including drilling the airborne anomalies after very little
much on logistics. Since the Ovacik discovery ground work. However, each method has draw-
exploration has been much reduced as the backs. In the case of airborne electromagnetic
company (originally Eurogold, a joint venture techniques it is the inability to distinguish
beteeen Australian and Euopean interests) was base-metal-rich sulfides from pyrite and graph-
unable to get permission to mine even though ite and interferences from conductive over-
it had constructed all the facilities. The mine burden. Airborne radiometrics have been very
was, however, brought into production in 2001 successful in finding uranium deposits in
after local opposition had been overcome. The nonglaciated areas and led to the discovery of
limited exploration in west Turkey since 1990 deposits such as Ranger 1 and Yeelirrie in
has also identified a major porphyry sytem at Australia (Dunn et al. 1990a,b). In glaciated
Kisladag (point G) which contains a reserve areas radiometric surveys have found a number
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of 5M ounces of gold at 1.1 g t Au (Eldorado of boulder trains which have led indirectly to
Gold 2003). deposits. In areas of residual overburden and
active weathering stream sediment sampling
has directly located a number of deposits, such
4.2.2 Reconnaissance
as Bougainville in Papua New Guinea, but it
The aim of reconnaissance is to evaluate areas is more likely to highlight areas for ground
of interest highlighted in the desk study rapidly follow-up and licensing.