Lateritisation is associated with tropical climates and geomorphic conditions of peneplanation where hydromorphic processes of weathering predominate. Laterites are products of relative (residual) and absolute(chemical) accumulation after leaching of mobile constituents. Their major element chemistry is controlled by the aluminous character of bedrock and drainage. Bauxitisation is characterised by residual gibbsite neoformation and lateritisation, by both residual accumulation and hydromorphic precipitation of goethite controlled by the redox front at the water table. The laterite forms part of a weathering profile that is underlain by saprock, saprolite, the mottled zone and overlain by a soil horizon. The secondary gold in laterites has its source invariably with mineralised bedrock. The distribution of secondary gold is controlled by mechanical eluviation and hydromorphic processes governed by organic, thiosulphate and chloride complexing. The precipitation of secondary gold is controlled by pH conditions, stability of the complexing agent and ferrolysis. Gold-bearing laterites are Cainozoic in age and are best developed on stable Archean and Proterozoic cratons that have suffered epeirogenesis since lateritisation. Mechanical eluviation increases in influence at the expense of hydromorphic processes as a positive function of topographic slope and degradation rate. Gradients greater than 10⁰ are not conducive for lateritisation, with latosols forming instead. High vertical degradation rates may lead to the development of stone lines. In the Western Australian case, post-laterite aridification has controlled the redistribution of secondary gold at levels marked by stabilisation of the receding palaeowater table. Mineable reserves of lateritic ore are located at Boddington, Westonia and Gibson toward the south-west of the Yilgarn Block. A significant controlling variable appears to be the concentration of chloride in the regolith. Based on the Boddington model, the laterite concentrates the following elements from bedrock gold lodes: i) Mo, Sb, W, Hg, Bi and Au as mobile constituents. ii) As and Pb as immobile constituents. Geochemical sampling of ferruginous lag after bedrock and laterite has provided dispersed anomalies that are easily identifiable. "Chalcophile corridors" up to 150 km in length are defined broadly by As and Sb but contain more discrete anomalies of Bi, Mo, Ag, Sn, W, Se or Au, in the Yilgarn Block. The nature of the weathered bedrock, the tabular distribution of secondary gold ore deposition and the infrastructural environment lends the lateritic regolith to low cost, open-cut mining. The western Australian lateritic-gold model perhaps can be adapted and modified for use elsewhere in the world.

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.

The gold metallogeny of Australia is predominantly confined to the Archaean and Palaeozoic Provinces. The Archaean gold occurrences are predominantly hosted in ultramafic-mafic dominated greenstone belts, with less associated tofelsic-volcanic and sedimentary sequences. Most gold occurrences are confined to shear zones or faults, and adjacent discoveries of economic laterite-hosted deposits, host rocks. Recent are presently under investigation and will supply a significant proportion of production in the future. The Proterozoic gold deposits of Australia , are confined to geosyncinal sequences, commonly turbidites (eg: Telfer), with other hydrothermal deposits associated directly to granites. An important feature of the North Australian Craton deposits, is the spatial association of most deposits to granite bodies, although a genetic link has not been established conclusively. The Roxby Downs deposit in South Australia is a unique occurrence of gold in association to copper, uranium and R.E.E. This deposit is tentatively related to intraplate alkaline-magmatism, with further work necessary. The most significant recent discovery of gold mineralization in Australia is in the Drummond Basin in Queensland. This epithermal is tentatively related to mineralization within the Georgetown Inlier. The latter mineralization is Permo-Carboniferous, in a Proterozoic (and possibly Archaean) sequence of schists. It is tentatively suggested that all the gold mineralization in northern Queensland may be related to single tectonic event, a feature which requires further study . Other mineralization in the Phanerozoic includes the turbidite-hosted metamorphogenic deposits of Victoria, the rift related deposits in New South Wales and magmatic related deposits in Queensland. The gold deposits in Australia may in the future be classified in a tectonogeological framework, similiar to the layout of this dissertation, particularly once further data becomes available on recent discoveries.