The satisfactory testing and characterisation of mineralisation amenable
to heap leaching, is of prime importance to successful operation of a
project. This paper outlines a methodology for assessing material
suitability. A general model is used for classing material types for suitability for
treatment and for economic analysis. The four levels of these are
overburden, oxide, transitional and unoxidised materials. During exploration, reverse circulation (RC) drilling can be used
effectively to define these zones by a combination of logging, analysis
and provision of cuttings for column leach and bottle roll trials. RC
cuttings can he used effectively for column leach trials, when calibrated
against conventional processing-sized samples, obtained from surface.
Tbis allows metallurgical testing to depth and definition of transitional
ore types and the base of oxidation, accurately and economically with an
acceptable density of samples. The accurate prediction of base of oxidation and variations in recovery
with depth and ore types can be used to develop 'economic' pit designs
with zones of variable recovery. Petrological studies of leaching results and examination of
mineralisation types carried out on concentrates, provide information on
gold distribution and physical and chemical constraints. The examination
of concentrates can be particularly useful for types of mineralisation when
overall gold content is frequently at or below one pan per million. Explanation of anomalous recovery of gold grains in dense goethite
and solution-robbing by carbonaceous material can be identified by use of
petrological and scanning electron microscope. An understanding of the role of the host rock in leaching characteristics
can also he provided by petrology where siliceous or clayey materials can
require significantly different treatment.