Page 14 - Handbook of Gold Exploration and Evaluation

Preface xiii

seabed features such as those that contain concentrations of gold in drowned
beach sand deposits at Nome, Alaska.
A statement of the laws of sampling is followed by a brief description of the
essential features of bench scale testwork required by mineral-processing
engineers to write down all of the quantitative data needed for the design of each
plant component. These data include all essential measurements of the gravel,
sand and clay contents of a particular alluvial-type ore and the processing
characteristics and percentages of gold grains in the different ore types involved.
The vexed question of sample reliability and representivity is examined in
relation to the methods employed in the computation of ore resource quantities.
Space is devoted to some of the many geological and geographic constraints that
may be encountered in the field.
Mine planning deals with various principles and factors involved in the
choice between wet and dry systems of surface mining, development access,
stripping and production requirements and environmental protection. Elements
of the design and operation of selected methods are discussed in sufficient detail
to make intelligent judgements of the most suitable types for any given case. In
land-based operations the nature of surface features, topography and ground
water, and the dimensions and location of pay horizons are of particular
relevance. Offshore dredging is concerned additionally with the need to
compensate for variable wind, wave and current conditions.
Determining the most effective recovery methods for specific ore types
during the mine-planning phase enables gold-processing plant to be designed
with a reasonable assumption of optimum performance within a designated
product size and range. Theoretical aspects of the transport mechanism in
natural stream channels are extended to examine the effects of sedimentation
under controlled conditions of shear flow in gravity concentrating plant.
Constraints to the recovery of finely divided gold particles in conventional
gravity plant are examined, and three different types of gravitationally enhanced
separators are compared in their respective abilities to recover micron size
particles of gold. An example is given of a typical chemical leaching process for
the treatment of lateritic gold ores. The carbon-in-leach process used in this
arrangement was selected from the results of continuous pilot plant testing of
batch samples of lateritic ore involving ancillary `Bond Mill' grindability
testing, thickening and carbon-stripping studies.
Ultimately the problems involved in the discovery of gold resources of the
required order of magnitude have financial as well as geological implications
and the process of evaluation is a necessary tool in the decision-making process.
Basic principles of economics apply to gold-mining projects of all types and the
full range of possible options is analysed to ensure that all costs and benefits are
considered. Three inter-related disciplines of investigation are considered as
being essential to any evaluation process: technical, economic and financial.
Risks inherent to each of these techniques are indicated by demonstrating the