Gold-bearing volcanic breccia complexes related to carboniferous-permian magmatism, North Queensland, Australia
- Authors: Mujdrica, Stefan
- Date: 1994
- Subjects: Gold mines and mining -- Australia -- Queensland , Gold ores -- Geology -- Australia -- Queensland
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4965 , http://hdl.handle.net/10962/d1005577 , Gold mines and mining -- Australia -- Queensland , Gold ores -- Geology -- Australia -- Queensland
- Description: Gold-bearing volcanic breccia complexes are the major sources of gold in the Tasman Fold Belt System in north Queensland. The Tasman Fold Belt System represents the site of continental accretion as a series of island-arcs and intra-arc basins with accompanying thick sedimentation, volcanism, plutonism, tectonism and mineralisation. In north Queensland, the fold belt system comprises the Hodgkinson-Broken River Fold Belt, Thomson Fold Belt, New England Fold Belt and the Georgetown Inlier. The most numerous ore deposits are associated with calc-alkaline volcanics and granitoid intrusivesof the transitional tectonic stage of the fold belt system. The formation and subsequent gold mineralisation of volcanic breccia complexes are related to Permo-Carboniferous magmatism within the Thomson Fold Belt and Georgetown Inlier. The two most important producing areas are at Mount Leyshon and Kidston mines, which are high tonnage, low-grade gold deposits. The Mount Leyshon breccia complex was emplaced along the contact between CambroOrdovician metasedimentary and metavolcanic rocks, and Ordovician-Devonian I-type granitoids of the Lolworth-Ravenswood Block. The Kidston breccia complex is located on a major lithological contact between the Early to Middle Proterozoic . Einasleigh Metamorphics and the Silurian-Devonian Oak River Granodiorite. The principal hosts to the gold mineralisation at the Mount Leyshon and Kidston deposits, are breccia pipes associated with several episodes of porphyry intrusives. The goldbearing magmatic-hydrothermal and phreatomagmatic breccias post-date the development of a porphyry-type protore. The magmatic-hydrothermal breccias were initially emplaced without the involvement of meteoric-hydrothermal fluids, within a closed system. Later magma impulses reached higher levels in the cooled upper magma chamber, where meteoric water invaded the fracture system. This produced an explosive emplacement of phreatomagmatic breccias, as seen at Mount Leyshon. Widespread sericitisation and pyrite mineralisation are common, with cavity fill, disseminated and fracturelveincontrolled gold and base metal sulphides. The Kidston and Mount Leyshon breccia complexes have hydrothermal alteration and mineralisation characteristics of the 'Lowell-Guilbert Model'. However, the argillic zone is generally not well defined. The gold travelled as chloride complexes with the hydrothermal fluids before being deposited into cavities and fractures of the breccias. Later stage epithermal deposits formed at the top of the breccia complexes that were dominantly quartz-adularia-sericite-type. The erosion, collapse and further intrusion of later porphyry phases allowed the upper parts of the breccia complexes to mix with the lower hydrothermal systems. Exploration for gold-related volcanic breccia complexes is directed at identifying hydrothermal alteration. This is followed by detailed ground studies including geological, mineralogical, petrological and geochemical work, with the idea of constructing a 'model' that can be tested with subsequent subsurface work (e.g. drilling). Geomorphology, remote sensing, geochemistry, geophysics, petrology, isotopes and fluid inclusions are recommended exploration techniques for the search of gold-bearing volcanic breccia complexes. Spectral remote sensing has especially become an important tool for the detection of hydrothermal alteration. Clay and iron minerals of the altered rock, within the breccia complexes, have distinctive spectral characteristics that can be recognisable in multispectral images from the Landsat thematic mapper. The best combination of bands, when using TM remote sensing for hydrothermally altered rock, are 3/5/7 or 4/5/7. The breccia complexes have exploration signatures represented as topographic highs, emplaced within major structural weaknesses, associated I-type granitic batholiths, early potassic alteration with overprint of sericitic alteration, and an associated radiometric high and magnetic low. The exploration for gold-bearing volcanic breccia complex deposits cannot be disregarded, because of the numerous occurrences that are now the major gold producers in north Queensland.
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- Date Issued: 1994
Pollution caused by mine dumps and its control
- Authors: Chikusa, Chimwemwe Mainsfield
- Date: 1994
- Subjects: Pollution , Pollution -- Law and legislation -- South Africa , Mineral industries -- Waste disposal , Slimes (Mining)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4991 , http://hdl.handle.net/10962/d1005603 , Pollution , Pollution -- Law and legislation -- South Africa , Mineral industries -- Waste disposal , Slimes (Mining)
- Description: All mine dumps are a point source of either physical, chemical or both forms of pollution. Physical pollution includes the physical site coverage of the dump, slumping of parts of the dams and dust that may originate from it (air pollution). Chemical pollution from, or related to the mine dumps include the dominant acid drainage (which contains heavy metals), radioactivity, electromagnetic radiation, noise and chemicals released from the mineral processing stage. In one way or the other, exposure to these pollution forms is detrimental to the human health and his environment. It is this fact that urges the public, government and the responsible mining companies to find ways of monitoring the pollution and stopping it, preferably at the source. Where it can not be stopped, techniques of reducing it, or containing it have been, and are still being developed. Personal protection is the priority. Pollution exposure to the general public is minimised as much as possible. Pollution control techniques that employ less expensive, natural, self-sustaining elements suitable for the environment such as wetlands and vegetation are recommended. The artificial short term and often expensive alternatives are of secondary priority. However, choice of which technique to use is based on the merit of each problem, knowing that chemicals act faster but are effective for a short period as compared to the natural systems. Pollution management is the critical part of the whole process. This involves decision making on courses of action and financial allocation on the part of both the polluter and the monitoring department/agent. The ability to effectively manage pollution programmes is achieved these days with the aid of computers. It is emphasised that pollution control should be handled in an integrated, multi-disciplinary approach manner. This is because pollution is a question of life and death, hence every individual remains accountable to it. Keeping the public and the concerned parties educated, informed and welcoming their concerns on the environmental issues related to the mine dumps generated in a mining venture is essential in the modern days of environmental public awareness, or otherwise face the public lath.
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- Date Issued: 1994
Surficial placer gold deposits
- Authors: Mann, P L
- Date: 1994
- Subjects: Gold mines and mining , Gold ores -- Geology , Placer deposits
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5088 , http://hdl.handle.net/10962/d1018245
- Description: This review summarises the factors which control the formation and distribution of surficial gold placer deposits. Regional tectonic and climatic conditions as well as gold source are considered. The characteristics of eluvial, alluvial, marine, glacial and fluvioglacial gold placer deposits are described. Particular attention is paid to the gold grains within these placers. These gold grains have a distinctive morphology and chemical composition which reflect the manner in which they were transported, deposited and concentrated within the placers. The knowledge of the processes which lead to the formation and location of surficial gold placers is then used to guide exploration and target potential deposits, which can then be evaluated.
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- Date Issued: 1994
The petrography, mineral chemistry and isotope geochemistry of a mantle xenolith suite from the Letlhakane DK 1 and DK 2 kimberlite pipes, Botswana
- Authors: Stiefenhofer, Johann
- Date: 1994
- Subjects: Geochemistry Isotope geology Kimberlite Kimberlite -- Botswana
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4988 , http://hdl.handle.net/10962/d1005600
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- Date Issued: 1994
The porphyry copper system and the precious metal-gold potential
- Authors: Gendall, Ian Richard
- Date: 1994
- Subjects: Copper ores , Porphyry , Gold ores -- Geology , Prospecting
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4992 , http://hdl.handle.net/10962/d1005604 , Copper ores , Porphyry , Gold ores -- Geology , Prospecting
- Description: It has been established that porphyry copper/copper-gold deposits have formed from I Ma to 2 Ga ago. Generally, they are related to the Mesozoic-Cenozoic interval with few reported occurrences from the Palaeozoic or Precambrian. A reason cited is the erosion of these deposits which are often related to convergent plate margins and orogenic belts. Observations of the alteration and mineralisation within and around porphyry copper/copper-gold systems have been included in numerous idealised models. These alteration and mineralisation patterns are dependent on the phases of intrusion, the tectonic setting and rock type, depth of emplacement and relationship to coeval volcanics, physiochemical conditions operative within and surrounding the intrusive and many other mechanical and geochemical conditions. Island arc and cratonic arc/margin deposits are generally considered to be richer in gold than their molybdenum-rich, intra-cratonic counterparts. Metal zonation may occur around these copper/copper-gold deposits, e.g. copper in the core moving out to silver, lead, zinc and gold. This zonation is not always present and gold may occur in the core, intermediate or distal zones. Examples of gold-rich porphyry deposits from British Columbia, Chile and the SW Pacific Island regions suggest gold is closely associated with the potassic-rich zones. Generally these gold-rich zones have greater than 2% magnetite and a high oxygen fugacity is considered to be an important control for gold deposition. High Cl contents within the magma are necessary for gold mobility within the host intrusive centres. Beyond this zone HS₂ becomes an important transporting ligand. Exploration for porphyry copper-gold deposits includes an integrated geological, geophysical and geochemical approach. Petrographic work through to Landsat imagery may be used to determine the chemical conditions of the system, ore association, favourable structural zones and alteration patterns, in order to focus exploration activities.
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- Date Issued: 1994