This page expands on that showing mineralisation throughout Tasmania (click here) to describe the Mount Read Volcanics in more detail as well as attempt to put a current value on selected mines and mineral deposits.
Geology of the Mount Read Volcanics
- Simplified geology of western Tasmania showing Mount Read Volcanics (green) and selected mineral deposits. Red square shows the approximate location of Paragon Resources’ exploration tenement in the southern MRV.
The most important metallogenic event in Tasmania coincided with the deposition of the Mount Read Volcanics (MRV). Mineralisation was concentrated in a short time interval in the late Middle Cambrian. Major alteration zones are dominantly of quartz-sericite mineralogy.
The main mineralised belt of the MRV between Mount Darwin and Hellyer is the Central Volcanic Complex (CVC), which is dominated by proximal volcanic rocks (rhyolitic to dacitic composition with rare basalt) deposited in a marine environment.
The CVC is flanked to the west by the coeval WesternVolcano-Sedimentary Sequence (WVS) of turbidite, mudstone, siltstone, shale with lesser intrusive (commonly andesitic) rocks and lavas.
The CVC and WVS are overlain by the Tyndall Group, a unit of quartz-bearing volcaniclastic sandstone and conglomerate of mixed felsic and andesitic provenance. Considerable erosion took place locally before deposition of the Tyndall Group. Clasts of granite and altered volcanic rocks occur in the basal Tyndall Group.
Flanking the CVC to the east and abutting the basement rocks of Tasmania is the Eastern Quartz-phyric Sequence (EQPS). The EQPS comprises quartz-feldspar-phyric lavas, intrusive porphyries and volcaniclastic sandstone, intruded by magnetite series granites. There is some controversy about the EQPS. Some consider that it is a time equivalent of the CVC, while others consider that it could be part of the Tyndall Group.
The geology of the MRV is complicated by varying degrees of rock alteration, folding and faulting.
The Henty Fault constitutes a fundamental tectonic divide within the MRV. To the northwest, polymetallic Zn-Pb-Au-Ag-Cu massive sulfide deposits dominate (Hellyer, Que River, Rosebery, Hercules) together with disseminated deposits with lower base metal, but relatively high Au and Ag tenor (Mount Charter, South Hercules). Southeast of the Henty Fault copper-gold and gold deposits dominate, exemplified by the Mount Lyell field and the Henty gold deposit. The most economically important deposits in the Mount Lyell field are disseminated chalcopyrite-pyrite orebodies in alteration assemblages dominated by quartz-sericite or quartz-chlorite-sericite.
Values of selected mineral deposits from the Mount Read Volcanics
Table 1. Estimated deposit size and pre-mining (in-ground) value (Based on metal prices current as of April 2012). Deposit data have been collected from a number of sources including company and government reports and should be treated as estimates only. Values are based on figures published in April 2012.
| Mt | Cu % | Au ppm | Ag ppm | Pb% | Zn% | Oz gold | $Am | |
| Mount Lyell field | 311 | 0.97 | 0.31 | 3,213,667 | $30,342 | |||
| Rosebery | 46.7 | 0.5 | 1.93 | 133 | 3.9 | 12.16 | 3,004,367 | $28,074 |
| Hercules | 3.33 | 0.4 | 2.8 | 171 | 5.5 | 17.3 | 310,800 | $2,703 |
| South Hercules | 0.56 | 0.11 | 3 | 157 | 1.9 | 3.7 | 56,000 | $251 |
| Hellyer | 16.5 | 0.38 | 2.55 | 169 | 0.38 | 13.9 | 1,402,500 | $10,346 |
| Helleyer tailings | 9.5 | 0.2 | 2.6 | 104 | 3 | 2.5 | 823,333 | $3,578 |
| Que River (historic) | 3.3 | 0.7 | 3.3 | 195 | 7.4 | 13.3 | 363,000 | $2,805 |
| Que River A | 0.36 | 2 | 0.3 | 63 | 1.3 | 3.4 | 3,600 | $123 |
| Que River B | 0.3 | 0.2 | 1.2 | 100 | 4 | 6.9 | 12,000 | $120 |
| Mt Charter | 6.1 | 1.2 | 36 | 244,000 | $632 | |||
| Fossey mine | 0.55 | 0.5 | 2.6 | 134 | 7.1 | 12.9 | 47,667 | $394 |
| Fossey East | 0.25 | 0.4 | 1.8 | 73 | 4.4 | 9.1 | 15,000 | $118 |
| Henty (historic) | 2.83 | 12.5 | 1,179,167 | $1,919 | ||||
| Henty | 2.08 | 4.9 | 339,733 | $553 | ||||
| Wart Hill | 0.55 | 0.5 | 94 | 3.4 | 7.2 | 9,167 | $184 | |
| Garfield | 13 | 0.3 | $325 | |||||
| Lakeside | 0.75 | 0.2 | 2.1 | 20 | 52,500 | $114 | ||
| Fire Tower | 3.6 | 0.8 | 96,000 | $156 | ||||
| 11,172,500 |