Characterisation of Folded Rocks in the Context of Exploration and Mining

Introduction of Folded Rocks

Mineralisation is commonly hosted in rocks that have undergone one or more stages of deformation. Consequently, the formation of mineral deposits commonly shows a close spatial and temporal relationship to folds in the host rocks.  In many cases the mineralisation also defines fold geometries, from the scale of large deposits down to the microscale.



Consequently,

Primary and Tectonic Folds in the Context of Exploration and Mining

Folds are the most familiar, and commonly the most spectacular, manifestation of bulk heterogeneous deformation in rocks. They occur at all scales from the microscopic to the scale of the whole lithosphere. Folds form under a range of conditions in igneous, sedimentary and metamorphic rocks.



A necessity for identification of folds is the presence of some planar layering that can define the

Types of Nickel Laterite Deposits

Nickel laterite deposits that are exploited for the extraction of nickel, cobalt and related metals generally fall into three distinct types as described below. At places, all three types of deposits may be associated with a single weathering profile occupying different horizons. At most locations, a saprolite zone may underlie an oxide zone.



Oxide Deposits

Consisting essentially of

Limonite and Goethite in the Laterite Profile

Limonite

Limonite is a non-crystalline mineral colloid. It can be found as stalactitic botryoidal or mammillary forms, but most commonly in laterite areas simply as an earthy mass. The colour in its earthy form is brownish yellow to ochre brown.

The term “Limonite” for a specific mineral species is no longer acceptable. At present the term “Limonite” designates various iron hydroxides that

Silicification in the Laterite Profile

Generally speaking, silica is associated with the laterite profile in two distinct ways : a) As massive silica; forming thick silica cap or silcrete, and b) As boxwork; silica sheets and lenses that are emplaced within limonite, saprolite or clay zones.

Massive silica cap or silcrete is generally present in “fossil” laterite deposits that have developed over ultramafic rocks of Precambrian age.