School of Earth Sciences - Theses
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ItemThe geology, petrology and geochemistry of the granitic rocks of Victoria(University of Melbourne, 1973)In the field the granitic rocks of Victoria show a wide variety of characteristics but chemically all are related and are the result of similar processes that occurred cyclically during the Palaeozoic. The granites may be divided into two groups on the basis of whether or not primary hornblende is present in the more basic members of the suite. Rocks of the hornblende-free series concentrate mainly in central Victoria and usually contain biotite that is red-brown in colour. In the granites of the hornblende-bearing group green-brown biotite is generally present. The two different colours appear to indicate unlike oxygen fugacities in the magmas from which the micas crystallized. The rocks of the hornblende-bearing and hornblende-free provinces also vary slightly in chemistry - the most important difference being that the basic members of the first group contain slightly more Ca than those of the second having comparable silica content. The compositions of the Victorian granites is consistent with their derivation by anatexis of a mixture of basic igneous rocks and sedimentary material. The conclusion is drawn that a combination of Cambrian basalts and dolerites and Cambro-Ordovician sediments constitute the source. The explanation of the fact that two chemical trends are observed in the granites may lie in the possible existence of two chemically distinct groups in the Cambrian igneous rocks - the one having lower Ca predominating under central Victoria.
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ItemStudies in Victorian Tertiary foraminifera neogene planktonic faunas( 1977)Planktonic foraminiferal faunas are described for the interval late Early Miocene to the Pleistocene, in the Tertiary basins along the southern margin of Victoria, including the Otway Basin, the Port Phillip Embayment, and the Gippsland Basin. Ninety-two foraminiferal taxa are identified. The faunas are dominated in the Early Miocene by globigerinid and globigerinoidid species, by unkeeled globorotalids in the Middle Miocene, and by keeled globorotalids for most of the Late Miocene. Unkeeled globorotalids are again important in the Early Pliocene, but keeled species again reappear in the Late Pliocene and the Early Pleistocene. One Pleistocene, two Pliocene, two Late Miocene, and two Middle Miocene planktonic foraminiferal zones are recognised on the first appearance of the following species: Orbulina suturalis, Globorotalia mayeri, Globorotalia acostaensis, Globorotalia conomiozea, Globorotalia puncticulata, Globorotalia viola, Globorotalia truncatulinoides. Subzones are identified by the extinction of Globorotalia peripheroronda, and by the appearance of Globigerina nepenthes and Globorotalia plesiotumida. Foraminiferal datum levels are used to correlate the Victorian sections with the Italian stratotype sections, the New Zealand late Tertiary, and the N-zonation of Blow, and hence into the palaeomagnetic and radiometric time scales. In the Tertiary basins, the maximum extent of marine deposition occurred in the Early Miocene, and despite subsequent sea level falls, continuous marine deposition is found through the Middle Miocene and most of the Late Miocene in the Otway Basin and the Port Phillip Embayment. Shallowing within the Middle Miocene is reflected by breaks in the Gippsland Basin sections, and lithological changes in other basins. A major sea withdrawal occurred near the top of the Miocene. Small scattered Pliocene deposits indicate short high sea level phases at the base of the Pliocene, in the middle of the Pliocene, and about the Pliocene - Pleistocene boundary.
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ItemMineralogy, geochemistry and origin of the Kalgoorlie gold deposits, Western Australia( 1978)Rich gold-telluride lodes (steeply dipping and flatly dipping) and minor gold-quartz stockwork mineralization characterize the Kalgoorlie gold-field. The origin of these gold deposits, the relationship between deposits and then nature of the host rocks are the major problems considered in this thesis. Extensive diamond drilling at the essentially unmineralized southern end of the field provided excellent material for stratigraphic studies and for country rock analysis whilst ore samples were obtained from both mines and drill core.
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ItemGeology of the Dookie District (Part I) & Trace element distributions within some major stratiform orebodies (Part II)( 1973)Part I: The Cambrian rocks outcropping in the Dookie district consist of a series of altered igneous rocks (diabases), a variety of pyroclastic rocks and cherts. The igneous rocks are thought to have been originally tholeiitic, having undergone low grade burial metamorphism, hydrothermal alteration and possibly contact metamorphism. Field evidence indicates that at least one of the igneous bodies is intrusive, probably a sill. The relation between these rocks and Cambrian rocks elsewhere in Victoria is discussed. The lithology and structure of an area of folded Ordovician and Silurian — L. Devonian sediments outcropping to the south of the main Cambrian massif is reviewed. Part II: Trace elements Tl, Ag and Au abundances in whole rock samples from a number of important stratiform basemetal orebodies have been determined by neutron activation analysis. Suites of samples were taken from the HYC Zn-Pb-Ag deposit at McArthur River, N.T., the Cu-Pb-Zn deposit of Rosebery, Tasmania and a Karoko type orebody from Shakanai, Japan. While the distribution of Au and Ag in the three deposits were found to closely follow those of Cu and Pb respectively, a higher Ag/Au ratio is apparent in the HYC deposit. In the other deposits, probably formed at temperatures greater than 200°, high concentrations of Au are explainable in terms of high temperature transport via chloride or thiocomplexing, while in the HYC deposit, formed below 150°, hydrothermal transport of comparable amounts of Au is considered unlikely. In response to lower temperature, strongly reducing conditions and restricted circulation, Tl concentrations in the HYC deposit are markedly greater than those in the remaining deposits. At McArthur River, significant enrichments in Tl occur up to, 250 metres stratigraphically above the main ore shales, and the geochemical significance and practical value of such metal haloes about stratiform orebodies are discussed.
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ItemGeology of the Wood's Point dyke swarm( 1974)The wood’s Point dyke swarm, Victoria, consists of a set of abundant subparallel narrow dykes with occasional elliptical expansions (“bulges”) intruded into strongly folded Lower Palaeozoic sediments. The swarm represents a hisly differentiated calc-alkaline rock series derived by fractional crystallization of a single parent magma, possibly of periodotitic composition. The rock types present include both high and low Cr-Ni periodotites, pyroxenite, hornblendite, hornblende diorite and monzonite, biotite leucodiorite, and minor residual granophyre. Apart from this hornblende-bearing rock series, a few hornblende-free basaltic dykes of related chemical composition but intruded later, are petrographically and mineralogically distinct, displaying tholeiitic tendencies. The latter dykes appear to be genetically related to volcanics underlying the Upper Devonian Acheron and Cerberean cauldron subsidences. Fractional crystallization, flowage differentiation, crystal accumulation and chilling were important factors in the development of the members of the dyke swarm, whilst assimilation in situ was not. The dykes are zonod, ultramafic types having more basic interiors (“cores”) whereas basic to intermediate composition bulges have more basic margins (“rims”). Magmalic copper-nickel sulphides rich in precious metals (Pt, Pd, Au) occur in dyke bulges of all compositions, especially close to margins where they accumulated by gravitational settling or were trapped by chilling. The sulphides have high Cu/Ni (and Co/Ni) ratios indicative of a highly evolved magma and, along with Au, Pd and Ir are fractionated between dykes of different silicate compositions. The base metal contents of silicates and sulphides vary sympathetically. The dykes have undergone pervasive hydrothermal alteration during which sulphides were largely recrystallised and Au was leached from some copper-nickel sulphides. A zonal arrangement of increasing intensity of alteration inwards was observed in one ultramefic dyke bulge. Later the dykes were deformed and the basic to intermediate composition dykes were fractured and veined, and major gold deposits formed. The veins have associated wall rock alteration which may be mineralogically subdivided into inner and out zones. Dyke bulges, ultramafic rocks, copper nickel sulphides and Au mineralization are all concentrated along two main lineations paralleling the fold axes of the sedimentary trough. The eastern and more important trend (at the centre of the trough) marks the eastern limit of the dyke swarm except at its northern end. These lineations may represent deep-seated fractures which controlled the later upward migration of Au-bearing hydrothermal solutions from depth. The source of the Au could have been various rock types present at depth, including copper-nickel sulphides and Lower Palaeozoic sediments.