EARLY THEORIES AND PRACTICALITIES ON GOLD OCCURRENCE IN AUSTRALIA

The discovery of gold in Australia forced many changes to theory on the occurrence and origin of gold deposits. Initial discoveries appeared to confirm existing ideas on the global distribution of gold-bearing terrains. Later discoveries and research would show that this confirmation was largely coincidental, but nevertheless helpful in early prospecting. Prior to the first Australian gold rush, theoretical predictions of payable gold were made by Sir Roderick Murchison and Rev. W. B. Clarke based on knowledge of accidental gold finds and geological analogy with known areas of significant gold occurrence, particularly the Ural region in Russia. These predictions were overwhelmed when Edward Hargraves, realised he might be able to spark a gold rush that would prove the existence of payable gold. Hargraves travelled to the Bathurst region of New South Wales where numerous gold finds had already been made and with local guides, prospected Lewis Ponds Creek and the Macquarie River. He demonstrated the methods of alluvial mining, to John Lister and William and James Tom enabling them to find sufficient alluvial gold to initiate a gold rush. The crowd of attracted diggers demonstrated the existence of a payable goldfield. The unstoppable first rush resulted in the pragmatic introduction of government regulation and administration to allow alluvial gold mining. Other discoveries of payable goldfields quickly followed. As the local scientific expert on gold, W. B. Clarke was commissioned to conduct two extensive surveys of the goldfields between 1851 and 1853. Clarke also drew on his geological knowledge to provide practical advice to the thousands of prospecting gold diggers. Gold-bearing quartz reefs and lodes were discovered, but it was predicted that these could not be mined economically. Theory also predicted that the reef gold would not continue to depth. Practical observations and mining experience from the numerous discoveries led to revision of the widely held dicta on gold occurrence. Alluvial gold was found in a range of settings, including the recent drainage and ancient and buried leads. A wider variety of rock types was recognised as favourable for gold. Different styles of reef gold were identified and found to be economically mineable to great depth. Evolving ideas on the origin of gold deposits were widely discussed, tested, and refined. Of the many players involved in the early discovery of gold in Australia, Clarke, Hargraves and Murchison probably had the greatest overall influence in terms of theoretical predication and practical outcomes that initiated the Australian gold-mining industry.

Physical and mechanical properties of placers and rocks in the Rakovsky and Bolotny stream channels in the Vedugin gold occurrence area

The information on the rock mass behavior in the course of mineral mining is of vital necessity for exploration and mining companies. In engineering decision-making as well as for the prevention of possible difficulties, it is required to have the most comprehensive data on physical and mechanical properties of rock masses. The aim of this study is determination of physical and mechanical properties of placer rocks in the Rakovsky and Bolotny stream channels in the Vedugin gold occurrence area, as well as assessment of elasticity and brittleness of ore and rocks to define their susceptibility to rockbursting. It is found that bedding rocks in Rakovsky and Bolotny placers down to a depth of 87 m below ground surface are rockburst-non-hazardous. The research findings are usable in elaboration of project documentation for mining Rakovsky and Bolotny placers, as well as in selection of technologies for supporting rock mass and for actual mining of placer reserves. In the latter case, it is possible to make reasonable decisions on support design and geotechnology parameters so that to combine mining safety with the quality of mineral extraction as early as the project design. It is recommended that Burkandya company undertakes continuous monitoring and prediction of rockburst hazard as mining is advanced to deeper levels.

The Mustajärvi orogenic gold occurrence, Central Lapland Greenstone Belt, Finland: a telluride-dominant mineral system

The Mustajärvi gold occurrence lies in the southern part of the Paleoproterozoic Central Lapland Greenstone Belt, in proximity to the first-order transcrustal Venejoki thrust fault system. The gold occurrence is structurally controlled by the second-order Mustajärvi shear zone, which is located at the contact between siliciclastic metasedimentary and mafic to ultramafic metavolcanic rocks. The main mineralization comprises a set of parallel veins and sulfidized rocks that are slightly oblique to the shear zone and are hosted by third-order structures likely representing Riedel R-type shears. The gold-mineralized rock at Mustajärvi is associated with pyrite that is present in 0.15- to 1-m-wide quartz-pyrite-tourmaline veins and in zones of massive pyrite in the host rocks with thicknesses ranging from 1.15 to 2 m. In unweathered rock, hypogene gold is hosted by Au- and Au-Bi-telluride micro-inclusions in pyrite, whereas strong weathering at near surface levels has caused a remobilization of gold, resulting in free gold deposited mainly in the cracks of oxidized pyrite. The geochemistry of both mineralization styles is typical of orogenic gold systems with strong enrichments comprising Au, B, Bi, CO2, Te, and Se; and less consistent anomalous amounts of Ag, As, Sb, and W. Unusual for orogenic gold deposits is the strong enrichment of Ni and Co, which leads to the classification of Mustajärvi as orogenic gold occurrence with atypical metal association.