Page 142 - Geochemical Remote Sensing of The Sub-Surface

Spontaneous potentials and electrochemical cells 119

9 Conductive sulphide mineralisation.
9 Non-conductive but oxidisable sulphide mineralisation (e.g., sphalerite).
9 Ultramafic dikes, diatremes and flows, including komatiites, kimberlites and
lamprophyres.
9 Geological contacts between two units with strong redox contrast, such as
carbonatite and granite.
9 Shear-zones containing fault gouge.
9 Graphitic-hosted gold mineralisation.
9 Bitumen, coal and natural gas seeps.

There are, however, a considerable number of sources of reducing agents that are of
no economic significance. These include the following.

9 Barren sulphide mineralisation.
9 Geological contacts between two units with strong redox contrast, such as diabase
and granite
9 Minor barren graphite horizons.
9 Methane pockets in shale or overburden.
9 Gas hydrates.

The study of electrochemical cell processes that result in surface geochemical
anomalies is still in its infancy. Many apparently unrelated geochemical processes and
phenomena occurring over chemically-reduced geological features may prove to be
directly or indirectly related to electrochemical processes. Although electro-geochemical
techniques have enormous potential, a great deal of additional work must be done if
geochemical mapping over deeply buried features is to be a reliable technique yielding
easily interpretable data. The most pressing issues are to determine mass transport rates
from bedrock, whether a near-surface signature due to bedrock is possible within the age
period of young deposits, and whether the replacement of charge carriers between
bedrock and ground surface results in spurious overburden-related anomalies. Another
important issue is the understanding of the specifics of mass and charge transfer from the
reduced source to the groundwater environment.