Bellerophon-Nelson Gold Mine, St. Ives gold camp, Kambalda, Coolgardie Shire, Western Australia, Australiai

Regional Level Types
Bellerophon-Nelson Gold Mine	Mine
St. Ives gold camp	- not defined -
Kambalda	Town
Coolgardie Shire	Shire
Western Australia	State
Australia	Country

Newly discovered (2014) gold deposit showing the result of a high oxidised, tellurium rich hydrothermal fluid, with magmatic fluid and sulfidation causing the precipitation of gold. The telluride species also contain gold amounting to at least 15% of gold found at the deposit.

The host rocks are meta sedimentary of the lower Black Flag Group, and alkaline intrusions. There are 4 stages recognised, and from oldest to youngest are:
1. Quartz-carbonate veins
2. Quartz-albite-carbonate-pyrite veins and sericite-pyrite seams
3. Quartz-pyrite veins
4. Carbonate and chlorite veins.

Economic gold mineralisation is found in stages 2 and 3. The gold grains are strongly associated with pyrite. Intense albite and hematite alteration surround the veins, and trace amounts of gold have precipitated into these rocks. Thirteen species of telluride minerals and sulfosalts have been identified at the deposit in stages 2 and 3.

The deposit is located to the east of the Lefroy Mill, and existing deposits/mines to the east of the mill. Some of the study was done through microscopic examination of thin plates, and therefore some of the species may not be apparent in hand specimens. For example rucklidgerite (which has not been included in the species list) was found as only 1 grain.

The deposit is unusual. Significant combined telluride-native gold deposits are uncommon. In Western Australia only the Golden Mile and Sunrise Dam, could be considered significant, although minor tellurides have been found elsewhere including trace amounts at Victory in the St Ives area. Native gold and tellurium minerals are found in sheared sericite-pyrite seams. The seams can be found in quartz-pyrite veins as stringers.

Gold is found in the Black Flag Group of meta sedimentary and felsic volcaniclastic rocks, whereas other deposits in the area have been found in mafic-ultramafic rocks and felsic intrusions. Most other deposits in the area have a biotite alteration zone, whereas Bellerophon has alteration zones albite-hematite and muscovite. Another notable feature is the presence of Cl bearing minerals in the gold deposit, which has only previously been reported from the Kolar deposit in India, and Sunrise Dam deposit near Laverton Western Australia. At Bellerophon PbCl(OH) is mixed with Pb2Cl3(OH), and BiOCl is mixed with BiO(OH,Cl), and this combination has not been previously reported from a gold deposit.

The host rocks at the deposit are sandstone and siltstone interlayered with chert and volcaniclastic rocks. Monzonite and albite felsic intrudes supercrustal rocks, which also contain gold. Stage one veins are uncommon showing quartz-carbonate and rare apatite and pyrite. They are found at the contact between the regional metamorphic dark green rocks, and pale to brick red coloured mineralised zones. No native gold is found in the veins. The alteration zone is moderate to weak consisting of carbonate, quartz, sericite, pyrite.

Stage 2 shows quartz, albite, ankerite, and pyrite veins with an intense alteration zone around it. Fe dolomite is found as trace amounts and rare calcite. The veins can be several centimetres wide and up to 200 metres long. Pyrite cubes to 1 cm are found in the veins. Rutile, muscovite, apatite, anhydrite, chlorite, quartz and albite are accessory minerals. Chalcopyrite, galena, sphalerite, molybdenite are rarer. Barite, celestite, anhydrite co-exist with the pyrite. The veins change colour from dark green to pale brick red or yellow due to hematite or albite alteration. Haloes range from 2cm to 2 metres.

Stage 3 shows milky quartz and pyrite veins with locally small amounts of carbonate and albite. Common accessory minerals are barite, celestite, apatite, rutile, scheelite and tourmaline. There is also less than 5% cubic pyrite, anhydrite and chalcopyrite. The colour of the monzonite where is cuts the stage 3 veins changes from red to light grey or yellow due to albite alteration.

Stage 4 veins are carbonate-chlorite or simply carbonate. The composition of the veins tends to vary with some tourmaline-pyrite and others muscovite or magnetite altered to hematite. There are no alteration haloes around these veins.

Other Regions, Features and Areas containing this locality

References