Alluvial Basin-Fill Dynamics and Gold-Bearing Aspect of Early Proterozoic Strike-Slip Basins in French Guiana
- M. Marzo and
- C. Puigdefábregas
Published Online: 14 APR 2009
Copyright © 1993 The International Association of Sedimentologists
How to Cite
Manier, E., Mercier, D. and Ledru, P. (1993) Alluvial Basin-Fill Dynamics and Gold-Bearing Aspect of Early Proterozoic Strike-Slip Basins in French Guiana, in Alluvial Sedimentation (eds M. Marzo and C. Puigdefábregas), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444303995.ch35
- Published Online: 14 APR 2009
- Published Print: 16 SEP 1993
Print ISBN: 9780632035458
Online ISBN: 9781444303995
- pattern of infilling and alluvial facies;
- the Paramaca Formation;
- Arouany Formation and Tortue Formation;
- gold particles occur in the matrix of debris-flow conglomerates;
- considerable variation in chemical composition of gold particles could be explained by several hydrothermal fluid pulses
As a consequence of the Trans-Amazonian collisional orogeny (2.2–2.0 Ga BP), the North Guyana Fault Zone developed as a major sinistral wrench-fault lineament with associated en échelon continental sedimentary basins. The pattern of infilling and the alluvial facies of these strike-slip basins show significant differences. The Mana Basin was formed as a graben-like feature along a relatively straight–linear segment of the strike-slip fault zone. There are no major escarpments at the basin margins, and the fluvial sedimentation apparently kept pace with semicontinuous basin-floor subsidence. The basin-fill alluvium (Arouany Formation), comprised of sandy braided stream deposits, is more than 5000 m thick. It shows no obvious cyclic organization due to tectonic pulses and contains no ‘proximal’ (fault scarp-derived) conglomeratic facies. The Régina Basin was formed along a curvilinear, southeastern segment of the strike-slip fault zone. The transpressional tectonic regime here created a fault escarpment along one of the basin margins. From there coarse debris-flow dominated alluvial fans repeatedly prograded into the fluvial basin's interior. The basin-fill alluvium (Tortue Formation) is 2000–3000 m thick, markedly conglomeratic along the faulted margin and shows cyclic organization (CU–TU sequences; 15–50 m thick) attributable to spasmodic rejuvenation of the fault escarpment due to transpressional stress build-up and release. Backward thrusting along the faulted margin supports this interpretation.
The ‘proximal’ (fault scarp-derived) conglomeratic alluvium in the Régina Basin contains gold, whose particles appear to be associated with the unsorted sandy matrix of clast-supported debris-flow conglomerates. The chemical composition and morphoscopic characteristics of gold particles are not consistent with a simple detrital origin. It is suggested that the gold, if originally of detrital provenance, has been remobilized and redistributed by hydrothermal processes, or was hydrothermally derived from external sources altogether. This notion is supported by the gold-bearing mineral paragenesis (quartz veins with pyrite, chlorite and tourmaline), which suggests hydrothermal derivation of both Fe–Ti oxides and the gold.
The study calls for a reassessment of the origin of gold occurrences in other, analogous Proterozoic deposits, such as those in West Africa and in other parts of South America, where a detrital (‘placer’) genesis has so far been adopted rather uncritically.