Scotia Central Gold Mine, Norseman, Dundas Shire, Western Australia, Australiai

Regional Level Types
Scotia Central Gold Mine	Mine
Norseman	Town
Dundas Shire	Shire
Western Australia	State
Australia	Country

Brodie, Kirtley and Devine (surnames) discovered the Scotia deposit in June 1893, only seven months after the original discovery of gold in the Dundas area. The mine is about 2 kilometres south of the old Dundas townsite (marked now only with an information sign), on the western shores of the Lake Dundas salt-pan.

Lease 25 acres. The lease was sold to an Adelaide syndicate in 1896, who spent a lot of money erecting machinery, before running out of funds nine months later. The company asked an expert from the Norseman Crushing Company to inspect the deposit. It was determined there were no defined lodes, with gold found in 'floating blocks' of dark coloured glassy rock. At a depth of 40 feet, the rock type changes, and lodes pinch out. It was stated at the time, the amount of gold found was uneconomic. The company was voluntarily wound up.

As the full purchase price of 2500 pounds had not been fully paid to the original prospectors, litigation followed, and Brodie et al retook possession of the mine.

A local Albany-Norseman syndicate then went into partnership with them to develop the mine. The old mine was located on top of a hill overlooking the lake. The reef strikes north-south, and dips east. By 1898 there were four shafts on the property. The north shaft was down to 45 feet on a 2 foot 6 inch wide reef. The south shaft was down to 65 feet on a reef the same width as in the north shaft. The Adelaide company had sunk a further two shafts, both 60 feet down.

Modern geology investigations at the site, state it consists of north-south striking quartz veins, the ore lode dipping east, within a shear zone. The quartz veins plunge 20 degrees north-east.

Scotia has been mined periodically from the 1890's by open cut and underground. The geologist was not impressed, stating the strike length, thickness and attitude of the ore zones were highly variable.

Further detailed geology information was found for the mine. Due to space limitations here, we focus mainly on the species found.

Ore bodies at Scotia are hosted by a shear zone that transects the Woolyeenyer Formation, with various types of intruding dykes. The rocks differ from that at Norseman, in that Scotia rocks were formed at higher metamorphic grades, and at a higher temperature for alteration minerals. Primary gold is structurally controlled by closely spaced brittle faults of varying orientations. Gold mineralisation is hosted by a D3 ductile shear zone striking north north-west and north, dipping east. Within the mine workings this follows a north striking, east dipping grabbroic dyke. Most of the ore is found in 5 lenses, of a short strike, the lense consisting of quartz-diopside-calcite veins within the shear zone. The ore bodies are cross-cut by porphyry dykes, in turn cross-cut by pegmatites with a quartz-plagioclase-muscovite-biotite-garnet assemblage. D4 and D6 brittle faults abruptly off-set the ore bodies, with dextral and reverse faults also cross-cutting, with smaller scale west north-west faults, in a complex geology zone.

The metabasalt rocks at Scotia contain varying proportions of amphibolite and plagioclase, with minor quartz, Mg-chlorite, ilmenite, and accessory apaite and titanite. The amphibolite-plagioclase is cross-cut by zoisite-actinolite-calcite veinlets. Late stage prehnite-albite veinlets also cross-cut.

The discontinuous and variably deformed veins are banded, with alternating bands of quartz, clinopyroxene, calcite, amphibolite, biotite and microcline. This banded nature produces complex overlapping alteration envelopes, with an inner zone of hornblende-plagioclase-epidote-ilmenite alteration, to an outer zone of biotite-hornblende-plagioclase. This in turn is progressively replaced closer to the veins by actinolite, then diopside-clinopyroxene-calcite-microcline, and less commonly quartz-amphibolite-zoisite-microcline. Ilmenite is partly altered to titanite and pyrrhotite throughout the shear zone.

At the microscopic level, loellingite is rimmed by gold, bismuth and arsenopyrite. The Au, Bi, and (un-named) tellurides are intergrown with quartz, amphibolite and microcline.

Pyrrhotite is the dominant sulphide in the veins, associated with chalcopyrite. Fractures within clinopyroxene, and quartz is infilled with actinolite-pyrrhotite-chalcopyrite. Diopside bearing veins outside the mineralised zone is gold barren, but contain garnet, but lack biotite alteration, and may represent a separate forming event.

Since the above was written, modern open pit mining has taken place at the location likely to have destroyed anything historic that was at the site.

References

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