Page 303 - Handbook of Gold Exploration and Evaluation

5

Gold exploration

Exploration is a search for the unknown, and challenging aspects of gold explora-
tion are to find new deposits in hitherto unexplored areas and to re-examine
previously explored areas that may have been rejected because of inefficient
technology, faulty or inadequate geological investigations, or geographical con-
straints. Because some prospective areas have been looked at and rejected by others
does not necessarily preclude them from further consideration. Radical new ideas
and improved technologies have emerged during the past few decades, and more
will emerge in the future. Theories of plate tectonics have had an enormous impact
upon such traditional problems as the origin of folded mountains, effects of certain
types of igneous intrusion on the creation of gold source rocks, and tectonic and
climatic controls on the functioning of the fluvial system. Improved age dating
techniques have been developed for placing the geological events of Earth history
in sequence according to age. Control of deposit size and mineral content has been
established as a function of the geological setting. Some mountain ranges are still
in the process of formation, e.g. the Andes of South America and Rocky Mountains
of the USA. Older systems, exposed to weathering and erosion for long periods of
geological time, now exist only as remnants of palaeo-zones, represented by
specific rock types, e.g. intermediate to acid intrusives and andesite volcanoes.
The scope of modern exploration programmes has been expanded by the
deployment of remote-control systems such as thermal I.R., radar and high-
resolution photography on spacecraft, and increasingly high-resolution (spectral
and spatial) satellite imagery. Thanks to modern technology, exotic remote
sensing and geophysical methods can indicate the potential of deposits that are
now masked by profuse vegetation, or by a cover of later sediments or volcanics.
With the general acceptance of seafloor tectonic and hydrothermal processes as
being either analogous to or integral parts of geological processes operating in
the continental crust, proposals postulating a seafloor origin for many land-based
metallic deposits seem plausible. Giant mapping projects are being carried out
into previously uncharted waters, piecing together previously unknown
geological features in an under-sea landscape that has been developed by plate
tectonic processes over millions of years.