The Tolukuma Gold Deposit is hosted by metamorphic and volcanic
rocks, and igneous intrusions. Dilatant structures for the main veining
appear to be provided by post-metamorphic flexure/faulting;
syn-mineralisation tectonics is recognised from the en-echelon patterns of
much of the veining. A SSE trending structure containing high grade
mineralisation has acted as a major dilational zone within or at the
contacts of porphyry intrusions. An ESE trend has controlled numerous
dilational structures splaying eastward from the SSE vein structure and
containing medium grade mineralisation.
Early hydrothermal activity (Stage I) is represented by unmineralised,
pyrite-rich brecciation and fracturing. Associated chloritic veining is
indicative of single phase neutral-chloride fluids upwelling in relatively
low fracture controlled nenneahility