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The geology and geochemistry of the Naringla Monzodiorite, and the mineralization and alteration of the associated Porphyry Copper Deposits, Yeoval, Central-Western N.S.W.

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Cooke, DR (1985) The geology and geochemistry of the Naringla Monzodiorite, and the mineralization and alteration of the associated Porphyry Copper Deposits, Yeoval, Central-Western N.S.W. Honours thesis, La Trobe University.

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Abstract

A study of the petrology, geochemistry and field relationships of
sedimentary, volcanic and plutonic rocks from the Yeoval district has
revealed a complex and varied geological history. Volcanics derived from
the nearby Molong Volcanic Rise were deposited with marine sediments in the
Middle to Late Silurian. They were then deformed during the Bowning
Orogeny.
Intrusion of the Naringla Monzodiorite occurred in the Early Devonian.
This is a heterogeneous body ranging in composition from pyroxenite
cumulates to microgranodiorite and dacite porphyry. The latter two rock
types are
Co-genetic
prior to
pyroxene
formed by
the host to disseminated porphyry copper style mineralisation.
basaltic andesites were erupted above the monzodiorite body
final crystallization of the monzodiorite. The pyroxenites,
bearing basaltic andesites and pyroxene
crystal fractionation of augite from
bearing monzodiorites
a primitive magma of
basaltic andesite composition. The chemical variations in the Naringla
Monzodiorite (apart from the low-Si rocks) is thought to have been derived
by chemical fractionation of hornblende, plagioclase and possibly biotite,
although magma mixing and restite unmixing cannot be ruled out as formation
processes.
Hydrothermal alteration associated with the porpyritic intrusions has
produced propylitic mineral assemblages in most of the rocks of the
Naringla Monzodiorite. Alteration is most intense around the copper
deposits, and occasional albitic alteration is developed. Alteration is of
a weak and patch nature, and lateration zones are generally not developed.
A small body of gabbro that outcrops adjacent to the Naringla
Monzodiorite is probably unrelated due to chemical inconsistencies between
the two units.
The Ohley Adamellite intruded during the Middle Devonian, and contact
metamorphosed the gabbro and a body of quartz-hornblende-diorite. The
intrusion of rhyolite dykes into the Naringla Monzodiorite may have been
related to the emplacement of the adamellite.The final geological event in the area was the emplacement of small
basic dykes along east-west joints in the Naringla Monzodiorite.
dykes are of probable Tertiary age.

Item Type: Thesis (Honours)
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Date Deposited: 12 Aug 2011 02:20
Last Modified: 15 Sep 2017 01:06
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