Boogardie Goldfield, Mount Magnet, Mount Magnet Shire, Western Australia, Australiai

Regional Level Types
Boogardie Goldfield	Ore Field
Mount Magnet	Mountain
Mount Magnet Shire	Shire
Western Australia	State
Australia	Country

This is the area of gold mines directly west and south-west of the Mount Magnet townsite. Gold was discovered here in 1891, at the mis-named and now tourist sign-posted Poverty Flats, which can be seen next to the road about 2 kilometres west of the town, on the way to Checkers Mill. Boogardie was once a thriving gold rush town in its own right, but most of the historic remains have been swallowed up by modern mining.

A brochure can be obtained from the tourist bureau, detailing points of interest in the area, and containing a map naming the various open pits. There are at least 35 modern pits covering an area 5 kilometres east-west and the same distance north-south. The Lennonville Goldfield adjoins Boogardie to the north. Boogardie Station is several kilometres further west.

Some of the mines in this section are historic, some modern names. All are now encompassed by modern open pits created over the past few decades, over what was once historic workings from the 1890's. Mining is still active in the area.

Ore is strongly structured and stratigraphically controlled in a complex geological area. Gold is concentrated in banded iron formations found in a fold hinge zone, where the banded iron intersects vertical faults, at the intersections of faults, and lastly related to felsic porphyry intrusions.

The gold deposits are found in a slightly elongated north-south trending syncline greenstone belt of the Moyagee Formation. This contains metamorphosed mafic and ultramafic rocks, prominent banded iron formation interbeds, containing significant gold and minor metasediments.

The mafic rocks contain metamorphosed amygdaloidal and pillow basalt, metagabbro, metadolerite and fine grained amphibolite and hornblende schist. The ultramafic rock contains dunite, peridolite and tremolite schist. This is all intruded by fault filling porphyry dykes and sills.

The complex structure shows four phases of folding, the last accompanied by major faulting. The dominant structure is the Boogardie Synform, a shallowly south plunging, asymmetrical syncline, and the Boogardie Fault System, both produced in the last phase of a D4 deformation.

The units from the base are:
1. Morning Star Unit of komatiitic and high magnesium basalt, which hosts gold in mines like the Morning Star.
2. Warramboo Unit of banded chert, chert breccia, interlayered shale, felsic volcanics. Gold is hosted in chert-banded iron formation in structural sites, like at Water Tank Hill, St George and Galtee More mines.
3. Piedmont Unit of komatiitic basalt, and amphibolite in the core of the Boogardie Synform, with gold hosted in quartz veins.
4. Hill 60 Unit of banded iron formation, interlayered ultramafic lavas, dolerite, sandstone, shale, sediments, also in the core of the synform. Gold is hosted in stratabound chert-banded iron formation such as at the Hill 60 mine.
5. Windbag Unit of komatiitic peridolite lavas, dolerite, felsic intrusives, fine grained sediments, and minor thin interbedded banded iron formation.
6. Sirdar Unit of banded iron formation, interlayered felsic volcanics, ultramafic flows, and intrusives. Gold is hosted in major stratabound chert-banded iron formation, such as the Hill 50 mine.

More than twenty banded iron formation units are recognised, 1 to 7 metres thick and continuous. The largest is at Hill 50 at 45 metres thick, and hosts the gold deposit here.

The are three main styles of gold mineralisation:
1. Quartz vein fault infilling in the upper four units creating small but rich deposits. These occur on faults related to the Boogardie Fault System, or on minor fault zones.
2. Quartz veins and alteration haloes in altered pillow basalt of the Morning Star Unit as sulphide rich elliptical bodies.
3. Stratabound chert-banded iron formation in the Warramboo, Hill 60 and Sirdar units. Gold is found associated with Fe-sulphide rich zones as lenses and veinlets, in a complex geological zone with cross cutting faults.

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References