Page 117 - Handbook of Gold Exploration and Evaluation

Geology of gold ore deposits 97

2.17 Components of a mineral system (Huston, 1997, as modified from Knox-
Robinson and Wybourn, 1997).

of sediment-hosted Pb-Zn and Cu minerals during the formation of Pangaea
(400±200 mya) are interpreted to have developed in either epi-continental or
foreland settings of the Caledonian-Appalachian Orogen (e.g. Duane and DeWit,
1998). From 200 mya to present, i.e., following the break-up of Pangaea, most
types of gold deposits, including volcanic hosted massive sulphides, podiform
chromite porphyry style Cu and Mo mineralisation occur in island arcs and
basins along Pacific margins (Sawkins, 1990).
Important factors controlling the geometry and chemical behaviour of large-
scale flow of hydrothermal fluids within the crust are illustrated in Fig. 2.17. The
ore deposit-ligand source is suggested as an essential basis for all hydrothermal
system models. Linkages between the various independent factors that control
the overall geometry and the physical and chemical behaviour of large-scale
flow of hydrothermal fluid in the crust are of fundamental importance; possibly
more so than a detailed understanding of any one of them (Heinrich et al.,
1989b).
It is generally recognised that periods of major hydrothermal fluid flow and
hence mineralisation are related to movement of the controlling faults and
opening of dilatational structures within such fault systems. The controlling
structures remain either weakly or non-mineralised and auriferous vein deposits
are commonly found in normal or strike-slip systems perpendicular to the fault
slip vector (Sibson, 1987). Amongst the best known are the shear zone deposits
of Yellow Knife (N.W.T), Golden Mile, Kalgoorlie, Australia and the Mother
Lode, California.