Tungsten Hill (Tungsten Trench), Mount Mulgine, Perenjori Shire, Western Australia, Australiai

Regional Level Types
Tungsten Hill (Tungsten Trench)	Hill
Mount Mulgine	Mountain
Perenjori Shire	Shire
Western Australia	State
Australia	Country

An Mo-W deposit.

Located 70 km west of Paynes Find in the Yalgoo Mining District.
Latitude: -29.18115
Longitude: 116.9763
Coordinates: 497696mE, 6771944mN.

The Tungsten Trench deposit is 1.5 kilometres south-east of the Mulgine Hill deposit, both north of Mt Mulgine. Tungsten Trench is a large low grade W-Mo deposit with a resource of 83 million tonnes of 0.14% Wo. It was discovered during a geochemical survey in 1982. Its strike length is 200 metres and is 100-170 metres thick. Drilling at the deposit has been extensive, and a 'library' of drill cores exists for the deposit. The reference used for this article examined only drill cores, and no matrix specimens or mineralization in-situ.

Mineralization was formed at, or soon after the metamorphism peak and overlaps a period of retrograde metamorphism, and the minerals are genetically related to the Mulgine Granite host. Mineralization is found in a scheelite and molybdenum bearing quartz stockwork vein system
in a sequence of meta basalts and banded iron formations forming a large and low grade W-Mo deposit in an Archaean greenstone belt. There are two main sets of quartz veins, the dominant set dips 35-40 degrees north-west the same as the host rock, and the second set 50-60 degrees north-west. Scheelite and molybdenum also occur in greisenized sills, and the intrusive granites.

Mineralization at Tungsten Trench formed over a wide range of temperatures (500-260 degrees) from fluids dominated by CaCl2. Fractures formed during the intrusion of the granite providing pathways for the fluids and sites for its deposition. The Mulgine Granite is composed of small ovoid leucocratic granite, with cross-cutting porphyritic biotite adamellite, intruded into the core of a north north-west plunging anticline in the eastern part of the Warriedar Fold Belt.

The host rocks are a sequence of ultramafic to felsic meta-volcanics with banded iron formations at its base. It dips 35-40 degrees north-west, and intruded by aplites, microgranites, quartz porphyry and greisenized sills. The original tholeiitic basalts have undergone deformation, metamorphism, retrograde metamorphism and extensive hydrothermal alteration.

Scheelite occurs as coarse grains and aggregates to quartz veins exceeding 1cm within the veins. It fluoresces a whitish blue, suggesting it contains little Mo. Huebnerite is rare as coarse grains partially replaced by scheelite. Molybdenite is interleaved with muscovite, and is also found as margins to the quartz veins and within fractures in the veins. Sometimes it is found within fractures in scheelite.

Pyrite is the most abundant mineral in the deposit and is found in a variety of forms. It is found as veins, sometimes found in veins of quartz or fluorite, and sometimes as veins of pyrite within quartz veins. Euhedral crystals may contain granular intergrowths or include other minerals such as magnetite, chalcopyrite, pyrrhotite, epidote, sphene, tetrahedrite and fluorite. Pyrite enclosed by epidote is common. Pyrrhotite is associated with chalcopyrite as inclusions within sphalerite. Marcasite is only found as late stage replacement of pyrrhotite.

Chalcopyrite is minor and the only Cu mineral found at Tungsten Trench, and forms granular intergrowths with pyrite and pyrrhotite, and more commonly as fine inclusions in other minerals including sphalerite, tetrahedrite, pyrrhotite, pyrite, sphene, epidote, fluorite, or in fractures in pyrite and pyrrhotite.

Tetrahedrite is a common minor constituent as fine grains associated with pyrite, arsenopyrite and chalcopyrite, partially replacing these minerals. Only one sample of pyrargyrite was found and was in an assemblage of chalcopyrite, pyrite and bismuth.

Pentlandite, gersdorffite and ullmannite are rare and found in a matrix of chlorite and phlogopite. The pentlandite is partially replaced by chalcopyrite, and the gersdorffite is found as inclusions within pyrite. Thorian brannerite was rare.

Arsenopyrite is a common minor constituent as isolated euhedral crystals or aggregates of crystals, and as arsenopyrite-pyrite or pyrrhotite intergrowths. Sphalerite is also a common minor constituent as granular intergrowths with other sulphides or as narrow veins. Larger grains include chalcopyrite and/or pyrite and pyrrhotite randomly distributed or as veinlets.

Rutile, magnetite, ilmenite and chromite are all found in the non-mineralised host rocks. Rutile is the most common as either minor constituents or abundant fine grains or clusters of grains within, and partially replaced by sphene. Rutile has also undergone replacement by ilmenite and brannerite, and is also found as inclusions in pyrrhotite. Chromite is rare. Magnetite contains inclusions of ilmenite and chromite. The magnetite has partially replaced stilbite, antimony and tintinaite. Stilbite is uncommon, but as crystals several centimetres across intergrown with arsenopyrite, tremolite and chert, and as inclusions in pyrrhotite. It also occurs as fractures in quartz and sometimes shows twinning. Antimony and tintinaite was only found in one sample replacing chalcopyrite and tetrahedrite. The tintinaite occured as an intergrowth with tetrahedrite enclosed by scheelite.

Galena and bismuth was found in only two samples as an assemblage with pyrite, tetrahedrite and antimony, and with pyrite and fine inclusions of bismuth.

Gangue minerals are quartz, epidote, chert, adularia, apatite, tremolite, stilbite, fluorite, carbonates, sphene and chlorite. Quartz dominates the stockwork veins and is also found as lenticular patches. Chert is uncommon, while epidote is common both as alteration products of feldspar and amphibole in the host rock, and associated with scheelite and sulphide minerals in veins. Carbonate is common in hydrothermally altered rocks, in veins, and as replacement of scheelite. Carbonate minerals are calcite, ankerite and Ca-Mn carbonate, possibly kutnohorite. Stilbite is rare, in vughs associated with ankerite. Apatite is very rare in carbonate veins. Tremolite, adularia, fluorite, chlorite and sphene forms microscopic veins.

Other Regions, Features and Areas containing this locality

References