Page 76 - Introduction to Mineral Exploration

4: RECONNAISSANCE EXPLORATION 59

FIG. 4.4 Aeromagnetic map of western Canada showing the continuity of anomalies underneath sedimentary
cover. The edge of the sedimentary cover is the bold dashed line striking NW–SE . The belt containing the
Thompson nickel deposit runs NNE from 102°E, 52°N. Hudson Bay forms the northeast corner of the map.
(Reproduced with permission from Ross et al. 1991.)

the case that significant prospects have differ- Miocene accompanied by extensive volcanism
ent controls from weakly mineralized occur- and much current hot spring activity. In addi-
rences. The sort of economic information that tion a cursory glance at the Metallogenic Map
is useful are the grades and tonnages mined, of Europe shows that a number of gold occur-
recovery methods, and the reasons for stopping rences, as well as other elements, such as
mining. This can be obtained from journals or arsenic, antimony, and mercury which are
from company reports. often associated with epithermal activity, are
An example of a desk study is the recognition present (Fig. 4.5). The mineral map of Turkey
of target areas for epithermal gold deposits (Erseçen 1989) provides further information on
in western Turkey. Here mineral exploration reserves at several of these localities. The com-
increased significantly after 1985 due to the piler must test this information against the
reform of Turkish mining laws and the ability epithermal model in which gold is likely to be
of non-Turkish mining companies to obtain a associated with graben bounding faults or
majority shareholding in any discovery. West- volcanics. Most of the gold occurrences shown
ern Turkey is of interest as its geological setting in western Turkey are within high grade meta-
is similar to eastern Nevada (see section 16.4), morphic rocks and represent metamorphosed
with extension and graben formation in the quartz veins of little interest. However the gold