User:Graeme Bartlett/Great Serpentine Belt

The Great Serpentine Belt or Great Serpentinite Belt also termed the Weraerai terrane is a band of altered ultramafic rocks found along the Peel Fault on the west side of the southern part of the New England Orogen. The belt is several kilimeters wide and 350 km long. When used originally the term referred to the whole region of the Serpentinite outcrops, and was named by William Noel Benson in 1913. The belt forms a rough line between the Tamworth Belt (a forearc basin from the Carboniferous) and the Tablelands Complex or Woolomin Terrane. The Serpentinite is not only found along the Peel Fault, but also outcrops on either side. On the southeast side faults have cut up the belt and displace it during Triassic times.

The rocks actually are from a variety of sources. One source is ophiolite, originally gabbro and dolerite from a Cambrian oceanic crust. Serpentinite melange includes broken up mafic rocks metamorphosed at a variety of conditions. The high pressure blocks of serpentinite is found at Attunga, Gleneden, at the top of the Barnard River, Glenrock, Pigna Barney River, and at Port Macquarie. The melange includes eclogite, actinolite-chlorite rock. Blueschist is found at Glenrock and Pigna Barney.

The ophiolite rocks form bands and lenses from 100 m to 5 km wide. Ultramafic rocks in these are in the form of bands only tens of meters wide. The ophiolite rocks have been brought to the surface from deep down via tectonic processes such as faulting and nappes.

Two different kinds of deposits of chromitite have been formed within harzbugite in the ultramafic rocks. Banded chromitite contains base metal sulfides like pentlandite and chalcopyrite, and palladium group metals including potarite (PdHg), and NiFePtPd alloy. Fractures in this banded chromitite may be hydrothermally altered. Minerals formed here include porous OsIr or RuOs grains, PdHgCu alloy, PdSbCu, PdCu alloys and PtAs2. Podiform chromitite include minerals such as laurite RuS2, OsIrRu alloy, irarsite(IrAsS) hollingsworthite RhAsS, and (OsIrRu)2S3. The metals only melt at temperatures over 2000°C and so must have come from extremely hot magma. In parts hydrothermal activity of the serpentinite has convert it to quartz-carbnite rock. This rock contains iron rich magnesite, and quartz. Also found is fuchsite, chlorite, dolomite and sulfide minerals. The fluid that converted this was from a magmatic or metamorphic source and was rich in CO2 Barium, Strontium, Arsenic, Antimony, Mercury, and Gold. The fluid reduced ferric to ferrous ions, was low salt, and slightly acid at 200 to 300°. The Peel Fault provided a path for the fluid to flow from deep in the crust to high levels. The fluid conversion happened near the end of the Permian. The same fluid was responsible for forming gold and Antimony deposits in the New England Orogen.

Related serpentinites
Another large outcrop of serpentinite is near Baryulgil. It is 32 km long extended in the north south direction. This is known as Gordonbrook Serpentinite, Baryulgil Serpentinite, the Eastern Serpentinite Belt or Bundjalung Terrane. The rock is serpentinised harzburgite, with some dunite and pyroxenite. It also contains dykes of boninite.

Economics
Mineral deposits include the Woodsreef asbestos deposit, and nephrite The serpentinite,  via Carbon dioxide sequestration has the capacity to absorb up to 300 years of New South Wales carbon dioxide emissions.