Page 138 - Handbook of Gold Exploration and Evaluation

Geology of gold ore deposits 117

This is demonstrated by the pattern of gold distribution in source rocks of the
Gros Rosabel Alluvial Gold Concession Area, Suriname, South America
(Macdonald and Wright, 1984). The control mechanism at Royal Hill (Fig. 2.22)
was apparently built up around the thrusting of the diapur together with some
strike fault development with normal movement at about 60ë to 70ë to the north.
Gash veins were opened up at about 90ë to the strike faults, probably in areas
prestressed by the folding. These veins flattened and tightened as they extended
away from the initial break. The openings so produced provided channels for the
passage of hydrothermal fluids containing quartz, potash, iron sulphide,
tourmaline, gold and other minerals. Flat-lying gash veins filled with quartz
veins containing gold and pyrite make up 95% of the productive veins in the
Royal Hill area.
Individual mesothermal gold deposits may comprise economically important
parts of large-scale fluid flow systems in the crust. Provenances for major
alluvial gold fields in Victoria and NSW, Australia (e.g., Ballarat, Ararat,
Beechworth) in zones in the Lachland fold belt (Fig. 2.23), which comprised
parts of larger deformation zones in which the faults acted as major fluid
conduits (Woodall, 1990). In the Lucknow gold field of NSW, quartz veins were
developed along a main fissure for about 900 m. A feature of deposits in this
field is the invariable association of rich veins with calcite and its occurrence in

2.22 Zoning of a gold-bearing system around a diapur at Royal Hill, Suriname.