Abstract Volcanogenic massive sulfide deposits in Australia exhibit a range in average gold content from 0.2 to 4.75 ppm Au, with an overall mean of 1.6 ppm. The Mount Morgan Cu-Au deposit in eastern Queensland has been the major producer (237.5 metric tons of gold), followed by the deposits in the Mount Read Volcanics of western Tasmania (Rosebery, Hercules, Que River, Hellyer, and Mount Lyell) which together have a premining resource of 156.3 metric tons of gold. Two distinct spatial and mineralogical associations of gold mineralization have been defined for the eastern Australian volcanogenic massive sulfide deposits: (1) a gold-zinc association (with lead, silver, and barite), which typically occurs throughout the massive and layered ores with gold and barite concentrated toward the stratigraphic hanging wall of the deposit (e.g., Rosebery, Que River, and Hellyer), and (2) a gold-copper association, which typically occurs in the footwall stringer and lower massive zones of some deposits, particularly those with a high Cu/Zn ratio (e.g., Mount Chalmers, Mount Morgan, and Mount Lyell). This biparite gold association observed in the eastern Australian deposits is also displayed in other volcanogenic massive sulfide provinces, such as the kuroko district (Japan) and the Canadian Archean. Thermodynamic studies on the controls of gold transport and deposition indicate that the two gold associations described above may relate directly to the gold-transporting mechanism. The footwall gold-copper association reflects gold transport as the AuCl 2 complex by high-temperature (>300°C), low pH (<4.5), moderate to high f O2 , and high-salinity fluids (>seawater). The hanging-wall gold-zinc association reflects gold transport as the Au(HS) − 2 complex by lower temperature (150°-300°C), moderate pH (4.5-6), and moderate f o2 fluids. A process of gold refining where cooling hydrothermal solutions leach gold (plus zinc and lead) from the lower parts of the sulfide body and reprecipitate the gold at the top of the body, and which is associated with dropping temperature and increasing SO 4 /H 2 S ratio, is proposed as the mechanism which leads to gold enrichment at the top of zinc-rich deposits. This process is common in barite-rich Paleozoic deposits but less common in Archean deposits, due to lower SO 4 /H 2 S fluid ratios in the latter.

Abstract The stratiform and strata-bound ore deposits of the world include some of the most famous—for their size or richness, or both: the Rand, the Copperbelt of Zambia and Katanga, the Rio Tinto mines, the lead and zinc deposits of the middle United States, the Noranda field, the Sullivan mine, the iron ores, and the phosphates of the western United States. In Australia, ore deposits of this type include concentrations of Pb and Zn, Cu, Sn, W, Au, Ni, U, Fe, and phosphate. Most of the major Australian stratiform orebodies were found between 1870 and 1885. Significant gold discoveries had been made up to 25 years earlier, but an appreciation of the importance of gossans came later. Mount Morgan, Mount Lyell, Cobar, and Broken Hill all had prominent gossans, some of which had been well-known features of the landscape for up to 20 years before their metal content was realized. Mount Isa was found in 1923, 50 years after the development of the nearby Cloncurry copper field; no other discoveries of large, high-grade outcropping stratiform base-metal orebodies have been made since. All orebodies found later have been in fields which had been known and worked for many years.

Abstract Throughout his life, Lyell travelled extensively, always as a keen observer. He viewed the Earth's geological history as continuous with and subject to the same processes of change as at present. Leopold von Buch's theory of craters of elevation contradicted Lyell's view of Earth history. Thus Lyell travelled to Madeira and the Canary Islands in 1853 to see von Buch's evidence. Lyell found the islands formed by a long series of volcanic eruptions, not by the single explosive upheaval that von Buch had described. Nevertheless, Lyell still accepted Léonce Élie de Beaumont's claim that lava flows could not form compact rock on steep slopes. In 1855, Lyell learned from Eilhard Mitscherlich that on Stromboli contemporary steeply inclined lava flows were forming solid rock. In 1857, Lyell went to Sicily where unmistakable evidence contradicted Élie de Beaumont. In the walls of the Valle del Bove, steeply inclined layers of lava were intersected by dykes that pointed towards a former centre of eruption at Trifoglietto, later buried by volcanic rocks emitted from the present centre of eruption at the summit of Etna, proving that the Valle del Bove could not have originated as a crater of elevation.