Henty Mine, Tyndall Valley, West Coast municipality, Tasmania, Australiai

Regional Level Types
Henty Mine	Mine (Active)
Tyndall Valley	Valley
West Coast municipality	Municipality
Tasmania	State
Australia	Country

The Henty Mine is a gold mine located between Queenstown and Rosebery in western Tasmania. It is unusual in being associated with massive sulphides in altered Cambrian Mount Read Volcanics, and is probably genetically related to the VHMS deposits in the Mt Read Volcanics, including the Mt Lyell, Rosebery and Hellyer mines. There is structural alteration and remobilisation, which may include some Devonian overprinting.

Description: Complex hybrid Au system with possibly exhalative top, located near the CVC - Tyndall Group boundary
Resource:
Date Total Production Pre-Mining Grade
30/06/2015 264,041 Tonnes 5,700,000 Tonnes 8.4g/t Au

The Mount Julia-Henty gold deposits are a series of small tonnage (< 500,000 t), high-grade (10-30 g/t Au) sheet-like lenses hosted in an extensive package (> 20 Mt) of quartz-sericite altered volcanics. The alteration system is hosted in Cambrian submarine volcaniclastic and hyaloclastic dacites associated with interbedded carbonates and calcareous volcaniclastic samdstones located at the Tyndall Group-Central Volcanic Complex boundary. The alteration zone forms a subvertically dipping tabular sheet over 3 km in length and between 10 and 100 m in width. Although this zone is broadly strata bound in the north, it crosscuts stratigraphy and is hosted 50 to 300 in deeper to the south, well below the Central Volcanic Complex-Tyndall Group contact. The alteration zone is bound updip by the South Henty fault and downdip has abruptly decreasing alteration intensity. Mineralization is confined to quartz-rich lenses within the subvertically dipping alteration zone. The alteration zone is strongly deformed due to reactivation of the South Henty fault. The sericitic alteration assemblage is strongly foliated and mylonitized and the orebody is now located on the steeply west dipping, overturned limb of a broad, shallowly south plunging syncline..

Mineralization consists of pyrite and chalcopyrite with lesser galena and sphalerite and with minor gold, electrum, galenobismutite, and native bismuth. Gold, copper, and bismuth are mainly confined to the massive quartz and quartz-sericite alteration zones, whereas the outer quartz-sericite-chlorite alteration halo is dominated by pyrite.

The Au-Cu-Bi-Ag association and alteration zonation suggests that the Henty-Mount Julia system formed from an evolving submarine Cambrian hydrothermal system, with some low-sulfidation epithermal characteristics.

The Henty-Mount Julia alteration system possibly represents a gold-rich end member of a large, regional, submarine magmatic copper-gold hydrothermal event. This mineralizing event is probably responsible for most of the deposits found on the southeastern side of the Henty fault, including the Mount Lyell deposits.

Gangue: dolomite-ankerite, quartz, albite, Chlorite, Pyrite, Sericite, fluorite

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