Page 48 - Handbook of Gold Exploration and Evaluation

Nature and history of gold 29

1.10 Simplified classification scheme for ore deposits showing the broad
categories of processes and some of the associated elements (modified from
McQueen, 1997).

elements. The geological requirements of hydrothermal systems are linked
together through processes and associated elements that link placer and residual
minerals including gold with partial melting, metamorphism, weathering and
erosion. An understanding of these linkages is fundamental to gaining a full
understanding of ore deposition as a whole. Conceptual models of primary gold
ore deposition (see Chapter 2, Section 2.3) are based upon a variety of
classification schemes and may be related to:

· a source for the primary ore components (ligands and metals) and of energy
to drive the system
· a transport mechanism that controls the flow of fluid between the source and
discharge regimes and allows the appropriate concentration
· the chemistry of the fluid phase and a depositional mechanism to distribute
the components in the orebody as ore minerals and associated gangue.

Assignment of residual and placer gold types to specific groups within one
particular system of classification is fraught with much greater difficulty. Most
classifications tend either to represent specific research interests or be more
practically orientated as a result of field experience in different geological and
climatic environments. Problems of interpretation arise due to the uncertainty of
many of the processes and source parameters needed to complete the cycle.
Included amongst these are:
· the wide spectrum of sediments generated by the activities of glaciers, rivers,
wind and marine agencies (Chapter 3)