Page 306 - Handbook of Gold Exploration and Evaluation

Table 5.1 Geological criteria for selecting gold exploration areas (after Hodgson and Troop, 1988)
Feature Genetic significance

Rocks
Low- to medium-metamorphic-grade, deformed supracrustal Prograding arc-trench complex
sequence consisting of fault-bounded belts of volcanic and
sedimentary rocks intruded by major syn- to post-tectonic granitoid
batholiths
Mafic to ultramafic volcanic rocks Ultimate source of gold (?)
(in contact with)
Sedimentary rock belt Indicates fundamental fault in an accretionary geotectonic
environment
(especially if)
Molasse- or Timiskaming-type sedimentary rocks Indicates fault developed after the assembly of rocks by accretion;
on a smaller scale, sedimentary rocks occur along the part of this
fault that (i) has maximal throw, and therefore vertical dimensions,
to best tap deep fluid sources and (or) (ii) has dilated as a
consequence of trans-tensional oblique-slip movement and so is
favourably orientated to focus fluid flow
Major TTG or calc-alkaline batholiths Arc magmatism that has prograded over accretionary complex,
providing extra input of heat to drive devolatilisation of subcreted
oceanic crustal rocks
Alkalic or trondhjemitic felsic porphyry intrusions Like molasse, indicates a fault developed late in the geotectonic
development of the accretionary belt, a time favourable for
maximum fluid generation. On a smaller scale, intrusions are
localised at structural sites on faults characterised by high
permeability to magmas and ore-forming fluids