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The Pico Machay high sulphidation alteration system is hosted within
lower Miocene volcaniclastics of the Castrovirrenya Group, which is
equivalent to the Upper Calipuy of northern Peru in age and composition
(NB. Both Yanacocha and Pierina are hosted within the felsic volcanics
of the Upper Calipuy).
Several
felsic volcanic units, which have the potential to host significant
alteration and mineralization, occur within the stratigraphy at Pico
Machay and are up to 100 meters thick. These felsic units occur within
the 300m thick host volcaniclastics which have been altered varyingly
to residual silica, silica alunite and silica kaolinite. The residual
silica units form porous horizons within the greater volcanic package.
The thickness of these porous felsic units indicates, that there is
considerable potential to discover large zones of mineralization at
Pico Machay.
The
volcaniclastics are sandwiched between andesitic flows. The andesitic
flows are extremely hard and impermeable and play host to
mineralization along narrow structures and breccias. Seven hundred
meters north east of the main zone of vuggy silica occurs in a zone of
highly altered andesitic volcanics.
Regionally
the volcanics strike northwest and dip at 25 degrees to the southwest.
Within the zone of mineralization, bedding had been rotated to 80
degrees and the dip has steepened to about 50 degrees to the south.
Topographically
the mineralized horizons outcrop on a main east-west trending ridge at
the centre of the property. The residual silica units outcrop on the
main ridge over a strike length of about 1km. Over the remainder of the
approximately 2km strike length of the mineralization and alteration,
residual silica is found as subcrop and scree on the south dipping
slope of the main east-west ridge.
A
drill program carried out by Newcrest in 1996 – 97 consisted of 8 holes, which were collared on the
north side of the main ridge and angled to the south. Newcrest’s drill
holes were collared in the silica alunite / silica kaolinite alteration
located between the residual silica units, were drilled sub parallel to
bedding and failed to intersect the residual silica units. Hole No.1
which was drilled underneath the main residual silica outcrop still
managed to intersect 62m @ 0.8 g/t Au. This drill hole failed to test
the main felsic volcanic unit, which hosts the vuggy silica and dips to
the south.
Pico
Machay has excellent size potential. Disseminated mineralization can be
found over a strike length of 2km, a thickness of 300m and a down dip
extension of somewhere between 300 to 400m.
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