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Summary: Cliffmont: High Sulphidation Epithermal Project
This suite of 16 polished thin sections is comprised almost exclusively of hydrothermally altered volcanic and
volcaniclastic rocks and is typical of, but not a text-book example of, high sulphidation epithermal
mineralization, based primarily upon rock type, alteration, and ore minerals (Simmons et al., 2005). Some of the
supplied samples have varying levels of clay alteration, but some samples still maintain some relict volcanogenic
minerals and textures. The sample offcuts were also studied to aid in defining alteration minerals. All the offcuts in this suite were stained for potassic feldspar. In most cases there was not a great abundance of potassic
feldspar present. This is somewhat consistent with the level of alteration within the suite, and we interpret the
lack of stain to indicate that all potassic feldspar that may have been present in the original rocks has been
altered to sericite or to clay. The individual thin sections are described separately and the general approach was
to describe the mineralization, rock types, veining and alteration. Oriented features such as veins are described
relative to a hypothetical North at the top of the thin section for any sample. Mineral abbreviations for the
common rock forming and silicate minerals are from Kretz (1983) and abbreviations for the common rock
forming minerals are from Marshall et al (2011).
The clay alteration for the most part would best be characterised as intermediate argillic to epithermal, but
simple classification of these samples within the epithermal deposit class is difficult. The major clays identified
were smectite, kaolinite and illite. The typical high sulphidation indicator mineral alunite, a hydrated potassium
sulphate mineral, was not identified, but this may be attributed to the depth of the epithermal mineralization,
as alunite tends to occur closer to the surface in epithermal systems. Also alunite in thin section and hand
specimen is very similar to the clay minerals identified in this suite. In thin section alunite tends to have higher
birefringence than clays, and this was not observed. PIMA or X-ray analyses would remove any doubt as to the
presence of alunite. However the lead sulphate anglesite was identified in minor amounts in this suite and that
is also indicative of high-sulphidation fluids. In addition to clay alteration the suite has undergone a few different
types of alteration: these are sericitization, silicification, and carbonate alteration. There is also extensive
silicification within the suite and the clay alteration, sericitization, and silicification are somewhat
contemporaneous as the alteration types are observed to overprint each other, indicating that the alteration of
these rocks was a prolonged and variable event, probably over a range of temperatures and depths.
Most of the deformation in the suite of samples is expressed as brittle deformation seen as fractures or veining.
The most prevalent vein type is quartz veining, but some samples have carbonate and clay vein infill as well.
Sulphides are abundant within a number of specimens within the suite. Generally, the most abundant sulphide
is pyrite, with lesser amounts of low-iron sphalerite, galena, chalcopyrite, covellite, chalcocite, pyrrhotite, and
possibly trace amounts of digenite, all in varying quantities and ratios.
Gold was identified in seven of the sixteen polished thin section in the suite. The gold displays varying levels or
reflectivity and this is in general an indication of silver concentrations. Of special note is that the gold in some
samples has reflectivity and colour very similar to chalcopyrite. I’ve confirmed the gold via SEM/EDS in these
instances. The gold is generally associated with the sulphides commonly occurring as inclusions in pyrite and
more rarely sphalerite. However, the timing of the gold seems to postdate sulphides and gold is associated with
Summary: Cliffmont Resources
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clay and silica (±carbonate alteration). Polished thin section SLD-01-01P hosts the most gold. The gold in this
sample is infilling fractures in pyrite and quartz and is interpreted to be contemporaneous with a clay and a later
silicic alteration. It is not always clear which alteration events or gangue minerals are associated with gold, but
there does seem to be an association with the breakdown of sulphides, such as in sections SLD-01-01P and SLD08-02P.
Daniel Marshall, D.Sc., M.Sc., B.Sc.
Professor of Economic Geology and Geochemistry
Peter Steele Mustard, Ph.D., M.Sc., B.Sc., P.Geo.
Mustard Geologic Consulting
References:
Kretz R. (1983). Symbols for rock forming minerals. American Mineralogist. v. 68, 277-279.
Marshall D., Anglin C. and Mumim H. (2011) Ore Mineral Atlas: 2nd Edition, Geological Association of Canada,
Mineral Deposits Division ISBN 978-0-86491-318-0, 112 p.
Simmons S., White N., and John D. (2005) Geological characteristics of epithermal precious and base metal
deposits. Economic Geology 100th Anniversary Volume. 485-522.
Summary: Cliffmont Resources
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