An overview of vis-nir-swir field spectroscopy - Spectral International

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from magmatic volatiles venting from intrusive sources at depth (Corbett and
Leach, 1998). These alteration zones are characterized by high temperature
minerals such as pyrophyllite-diaspore, zunyite, topaz, locally including
corundum and andalusite. Silica characteristically occurs as a massive form
rather than vuggy silica, typical of mineralized high sulphidation deposits.
Examples include Lookout Rocks, Horse Ivaal at Frieda River, Vuda, and Alum
Mountain. Lithocaps (Sillitoe (1995, 1999) may extend to higher crustal levels,
include additional lower temperature argillic alteration, and are interpreted
(Sillitoe, op cit) to locally conceal epithermal or porphyry mineralization.
Shoulders and lithocaps crop out as variably dipping bodies termed ledges
developed by the exploitation of permeable lithologies (typically flat dipping), or
dilatant structures (typically steep dipping). These alteration zones are
distinguished from mineralized high sulphidation systems in the field by the lack
of vuggy silica and generally coarse grained and higher temperature layered
silicates (e.g., alunite, pyrophyllite, dickite). The presence of high temperature
alteration minerals such as alunite or corundum is distinctive. PIMA, Terraspec
and XRD studies are therefore useful for the delineation of alteration zonation
and provision of vectors towards where mineralization should occur in ore
systems.
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