Page 9 - Geochemical Remote Sensing of The Sub-Surface

VIII Preface

reacts with carbonate minerals to generate carbon dioxide. In other cases, gases from
depth are simply carriers of trace quantities of metals collected as the gases pass through
a mineral deposit. On the other hand, gases are not involved if such trace quantities of
metals are transported upward by means of geoelectrochemical potentials.
This volume sets out to document the techniques for geochemical remote sensing of
the subsurface, to present case-history evidence of their successes and limitations, and to
consider their further potential. The chapters in Part I focus on the mechanisms and
models of dispersion that give rise to the patterns we attempt to detect. Those in Part II
deal with the detection of dispersion pattems that owe their origins to processes (such as
leakage) that are allied to resource emplacement. Those in Part III describe the detection
of dispersion pattems that are generated by processes (such as radiodecay and oxidation)
taking place in deposits after their emplacement. If I generalise, the particular strength
and attraction of the techniques that are presented is their potential to detect a chemical
signature at surface genetically-related to a parent petroleum or mineral resource in the
subsurface. Their weakness is poor signal reproducibility due to a plethora of chemical,
biological and meteorological factors at play in the near-surface environment. The
obstacle to their wider application has been this poor signal reproducibility coupled with
the lack of a universally-accepted migration model. Nevertheless, every chapter brings a
fresh perspective. Radon has met with much success in uranium exploration, whilst
thorough research studies on helium and mercury lead to conclusions that tend to
discourage use of these gases in mineral exploration. The case for light hydrocarbons is
one of compelling simplicity whilst elaborate mathematical and electrochemical models
are advanced for metal migration.
The volume has taken an inexcusably long time to assemble and I must register here
an apology to those contributors who had quite reasonably expected earlier publication
of their work. Most have shown unending patience and have even been kind enough to
update their reviews; two withdrew and their work, though a loss to this volume, has
appeared elsewhere. The other side of this coin has been the opportunity to include
recently-drafted chapters on geoelectrochemistry. This subject has experienced
something of a resurgence of interest in recent years and it gives me particular pleasure
to be able to include it in this volume as a compliment to the much earlier work of the
series editor. I thank, of course, the contributors and note that they represent expertise
from Australia, Canada, China, the Netherlands, Russia and the USA. I thank the
Intemational Institute for Aerospace Survey and Earth Sciences for resources and many
individuals for assistance. In particular I thank my graduate students, John Carranza,
Asadi Haroni and Alok Porwal, for helping me with the not inconsiderable task of
producing the first camera-ready volume of the Handbook of Exploration Geochemistry.

MARTIN HALE, Delft
October 1999