PDF 51636.pdf | Request a copy Full text restricted Available under University of Tasmania Standard License.

Abstract

The early Palaeozoic Macquarie Arc, southeastern
Australia, hosts a variety of major late Ordovician
to earliest Silurian subduction-related deposits (e.g., Cadia
East, Ridgeway, Cadia Hill, Cowal and Northparkes).
However, there is uncertainty about whether coeval highsulfidation
epithermal deposits, which occur in intraoceanic
metallogenic belts elsewhere in the West Pacific,
(e.g., Lepanto and Chinkuashih), are also present in the
Macquarie Arc. This has led to suggestions that their
absence may be due to the poor preservation potential of
deposits that form at relatively shallow crustal levels in
ancient rocks. We present here an interpretation for
evolution of the Peak Hill Au–Cu deposit based on the
distribution of alteration facies, sulfur isotope data from
several textural forms of pyrite and barite, and an
assessment of the regional volcanic and sedimentary facies
architecture. These data show that the Peak Hill deposit
displays a distinct sub-vertical zoning with a pyrophyllite
and vuggy-quartz core, that today extends about 350 m
east–west and at least 550 m north–south, which grades out
through paragonite+muscovite, kaolinite to a chlorite+
epidote alteration zone at the margin. The alteration zoning
reflects both lower temperatures and neutralisation of acid
fluids with increasing distance from the core, which
represents the conduit along which hot acidic hydrothermal
fluids were channelled. Several temporally overlapping
events of silicification, bladed-quartz-pyrite veining,
brecciation and pyrite veining occurred during the last
stages of hydrothermal alteration, although most appear to
predate mineralisation. Au–Cu mineralisation was associated
with late quartz-pyrite-barite veins, and the highest
gold grades occur mainly in microcrystalline-quartz-altered
rocks in the paragonite+muscovite alteration zone, generally
within 50 m outward from the boundary of the
pyrophyllite and vuggy-quartz core. Sulfur- and leadisotope
data, and the characteristic zoning of ore minerals
and alteration assemblages support a magmatic source for
the hydrothermal fluids. Similarities in many of the
isotopic signatures between Peak Hill and deposits such
as Northparkes support generation of the high-sulfidation
mineralisation during the Late Ordovician to earliest
Silurian (possibly ca. 440 Ma) metallogenic event. The
Late Ordovician to Early Silurian volcanic and sedimentary
facies associations at Peak Hill are consistent with
alteration and mineralisation occurring in rocks deposited
in a submarine setting.

Item Type:	Article
Authors/Creators:	Squire, RJ and Herrmann, W and Pape, D and Chalmers, DI
Keywords:	Peak Hill . High sulfidation . Epithermal gold . Lachlan orogen . Australia
Journal or Publication Title:	Mineralium Deposita
ISSN:	0026-4598
DOI / ID Number:	https://doi.org/10.1007/s00126-006-0076-4
Additional Information:	The original publication is available at www.springerlink.com
Item Statistics:	View statistics for this item

Actions (login required)

Item Control Page