2013 – COM 2013, Montreal, Canada


Clay minerals can cause nightmares with mineral processing. These clay minerals typically
form in near surface geological environments due to weathering, particularly above the
natural water table, sedimentation and digenesis and are common in hydrothermally altered
rocks. Clay minerals associated with alteration is referred to as Argillic alteration. The
extremely small particle size, usually <2 microns (sometimes coarser or finer) and with the
very high specific surface area, these clay minerals are highly reactive and respond to
changes in the processing environment. Understanding the geology, mineralogy and correctly
selecting representative samples of the ore to be processed is critical in getting the mineral
processing right. Clays have the potential, if not recognised, to destroy project economics.
Testing at an early stage of representative ore samples is critical.
The presence of clays in hard rock comes as a surprise if not fully understood. Similarly
waste dilution from country rock containing clay can adversely affect the process. There are
some solutions which assist in processing high clay ores but do not negate all of the
The presence of clays has a major influence on the process selection and equipment used in
the final flowsheet. The industry has paid a heavy price on a number of projects where the
clay was not recognised or the process plant was based on a hard rock design which later
proved to be totally unsuitable. Trying to mitigate the impact of clay on the process, if the
percentage of clay in the feed cannot be controlled, is a mineral processing challenge.

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