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Conference Proceedings

2001 AusIMM New Zealand Branch Annual Conference

Conference Proceedings

2001 AusIMM New Zealand Branch Annual Conference

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Low-Sulfidation Epithermal Veins at the Gladstone Hill Prospect, Waihi, New Zealand

The
Gladstone Hill area hosts epithermal veins similar to those at Martha Hill,
which is less than one kilometre away. There are several vein types in the
Gladstone Hill area including (1) pyrite-marcasite, (2) quartz, (3) base metal
sulfide, and (4) calcite. Pyrite veinlets formed first, whereas the quartz and
carbonate veins formed later. The base metal sulfide vein occurs at depth and is
predominantly comprised of quartz and chlorite intimately intergrown with
pyrite, sphalerite, galena, and rare chalcopyrite. Platy calcite and massive
calcite veinlets were the last vein types to form. Several vein textures occur
in the Gladstone Hill area, including colloform and crustiform banding,
lattice-bladed, zonal, comb, massive and feathery textures. Crustiform banded
veins are the dominant texture and contain variable gold-silver grades.
Colloform banded veins consist of ubiquitous quartz and minor chalcedony with
gold grades as high as 60 g/t. The lattice-bladed texture forms from the
deposition of calcite, which has been replaced in many samples by quartz,
indicating that boiling and later cooling has taken place. Unreplaced platy
calcite only occurs at deeper levels (>300 m). Zonal and comb textures are
preserved in quartz and late-stage amethyst veins. Feathery textures within
quartz are commonly associated with breccias and some colloform banding, and
with significant Au-Ag grades.

The
homogenisation temperatures (Th) of primary and secondary inclusions in quartz,
amethyst and platy calcite range from 166 to 274C, with salinities <1.3 wt%>
NaCI equiv. The presence of vapor-dominated inclusions and primary fluid
inclusions in platy calcite suggests that boiling occurred intermittently
throughout deposition. The veins formed under a relatively flat lying paleowater
table that occurred 280 - 300 m above sea level. The fluids involved in vein
formation were alkali chloride in composition and low in
CO2.
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  • Published: 2001
  • PDF Size: 1.172 Mb.
  • Unique ID: P200107018

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