School of Earth Sciences - Theses
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ItemThe platinum-group element geochemistry and petrogenesis of the Heazlewood River mafic-ultramafic complex, Tasmania( 1990)The Heazlewood River mafic-ultramafic complex (HRC) comprises well-layered olivine- and orthopyroxene-rich cumulates, gabbronorite dykes, tonalites and low-Ti tholeiitic basalt and boninite lavas. The complex was emplaced as part of a large, low-angle thrust sheet during the middle Cambrian and subsequently deformed during the Devonian, so that the original stratigraphical relationships are obscured. The cumulate succession incorporates two distinct blocks, viz. the western HRC, comprising primitive adcumulates, and the eastern HRC, consisting of more evolved orthocumulates and mesocumulates. These two cumulate blocks are interpreted to represent stratigraphically equivalent parts of a single magma chamber. In this scenario, the western HRC represents an axial part of the intrusion where high heat flows, due to repeated injections of primitive magma, promoted the development of a compositionally zoned magma chamber. In contrast, the eastern HRC is believed to constitute a marginal facies of the intrusion, where sidewall cooling caused rapid crystallisation of successive magma additions and inhibited adcumulate growth and the formation of a compositionally stratified liquid column. Results from a detailed study of the mineral compositions and whole-rock geochemistry of the HRC suggest that all of the cumulates and most of the dykes and tonalites were derived from boninitic parental magmas. This hypothesis is substantiated by empirical models which were calculated using both major and trace element approaches. The models also show that the low-Ti basalts (second-stage melts) and boninites (third-stage melts) were probably derived from component-induced progressive partial melting of a MORB-depleted spinel lherzolite source. Partial melting of the refractory mantle source was initiated and sustained by the continued influx of slab-derived Si02-, LREE-, Zr-enriched hydrous fluids. The proposed petrogenetic model for the HRC is most consistent with an island arc setting for the complex, with melting occurring in MORB-depleted forearc lithosphere overlying a subduction zone. The HRC is not an ophiolite sensu stricto, despite the fact that it is more similar to the upper portions of the so-called 'island-arc ophiolites' (eg. Troodos) than to any other type of ultramafic intrusion. It is best perceived as a high-level boninitic magma chamber which developed immediately beneath a platform of genetically-related submarine lavas. The composition of the boninitic parental magmas was the principal control on the PGE geochemistry of the cumulate sequences. Despite representing PGE-enriched, S-undersaturated second-stage melts similar to the parental (U-type) magmas for the ultramafic portions of the Bushveld complex, the boninites were unable to form a Merensky-reef type PGE deposit because they did not come into contact with S-saturated (A-type) magmas. In the absence of cumulus sulphides, the PPGE (Pt, Pd, Rh) were partitioned into the residual liquids, whereas the IPGE (Os, Ir, Ru) were strongly fractionated into early-formed olivine-chromite cumulates. These features are highlighted by the extremely low IPGE tenor of the boninites, and the relatively high IPGE tenor of the dunites in comparison to the more evolved cumulates. Three types of chromitites are recognised in the HRC. Type I and type II chromitites occur as magmatic schlieren which probably formed during replenishment events. Type III chromitites occur as layers, pods and irregular patches developed in an unusual xenolith-bearing plagioclase peridotite. It is interpreted to have formed due to mixing between ascending xenolith-bearing, hydrous intercumulus liquids and resident ultramafic magma along the floor of the magma chamber. Chromitite occurrences in the HRC are enriched in PGE by up to two orders of magnitude relative to their ultramafic host rocks, and most strongly-enriched in Ru and/or Pt and Rh. Their PGE tenor reflects the early crystallisation of laurite, followed by Pt and Rh sulpharsenides, in response to increasing S and As activities which developed primarily due to magma mixing. The low Os and Ir abundances in the chromitites is believed to reflect their formation from Os- and Ir-depleted boninitic magmas. The HRC and the Adamsfield complex were the world's major suppliers of Os-Ir-Ru alloys during the early part of this century. The alloys occur in alluvial deposits that are spatially associated with primitive olivine-rich cumulate sequences. The latter are commonly suspected to represent the source for the alloys, but recent exploration programs have yet to define a bedrock occurrence of Os-Ir-Ru alloys in Tasmania. The results from the present study provide important constraints on the genesis of these alloys. Silicate inclusions found in the alloys suggest that they formed at mantle temperatures and pressures and were transported to crustal magma chambers by boninitic magmas. The alloys may have crystallised during ascent, or alternatively, represent residual mantle phases which became incorporated into the boninites during partial melting. Most of the observations pertaining to the Os and Ir geochemistry of the HRC suggest that the alloys probably occur in thin magmatic concentrations that were deposited along the base of the intrusion from the most primitive of the boninitic magmas involved in the generation of the cumulate sequences. Future exploration should focus on delineating the cumulate products of these primitive magmas and specifically, in defining the horizons which demarcate fresh influxes of these liquids.
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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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ItemAustralian lineament tectonics: with an emphasis on northwestern Australia( 1994-08)Australia is transected by a network of systematic continental-scale lineaments that are considered to be zones of concentrated, aligned tectonic activity which have apparent continuity over vast distances. The influence of lineaments on the rock record can be identified in many types of data-sets, and existing data reveals previously undescribed basement influences. Several continental-scale lineaments can be traced offshore with apparent continuity for hundreds to thousands of kilometres, two of which are seen to cross the Tasman Sea in offshore eastern Australia. Geological and chronological evidence demonstrates that many of the lineaments have been zones of reactivation since at least the Early Proterozoic (- 1880 Ma) and that they appear to cross major terrane boundaries. Alternative models for their origin are a) a pre-existing lineament network maintained in an ancient basement underlying the entire continent; b) lateral propagation of crustal-scale structures; c) alignment of genetically unrelated lineaments giving the appearance of continuity. Australian deep-seismic profiles show that continental-scale lineaments are zones of crustal-scale structure which in some cases transect the crust-mantle boundary. Lineaments demonstrate many faulting styles, e.g. listric extensional (G3), planar moderate-angle thrusts (G2 l), and sub-vertical thrusts (G 17). In some cases the structural style varies laterally along the length of the lineament. (For complete abstract open document)
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ItemRecent glacier and climate change in the New Zealand Alps( 1995-07)The sensitivity of glaciers in the Southern Alps of New Zealand is evaluated to identify the nature of recent climate change. Past glaciological observations are compiled and to these are added 4 summer field seasons on the Tasman (including Hochstetter), Dart, Fox and Franz Josef Glaciers. The field data are an important aspect in the calibration and verification of glacier modelling. The detailed studies of these glaciers provides the basis for assessing the glacier and climatic changes over the whole glacierized region. (For complete abstract open document)
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ItemThe Permian glacial sediments of central Victoria and the Murray Basin: their sedimentology and geochemistry( 1986)This study investigates the sedimentology and geochemistry of Permian glacial sediments cropping out in the Bacchus Marsh and Derrinal areas in central Victoria and in the subsurface beneath the Cainozoic Murray Basin in Victoria, New South Wales and South Australia. Facies analysis of the Bacchus Marsh Formation, based on a critical review of literature on glacial sedimentary processes and environments, identifies the following major facies groups: 1. Subglacial tillites deposited beneath wet-based ice. Some of these tillites exhibit structures indicative of a number of subglacial processes such as frictional lodgement of large clasts, subglacial bed deformation, subglacial meltwater flow and subglacial size sorting of clasts. Other subglacial tillites are essentially structureless. 2. Bedded diamictites to sandstones deposited predominantly by ice-rafting of debris into standing water. 3. Fluvial outwash sandstone and conglomerate facies that are finer-grained than typical proglacial outwash facies. 4. Deltas and subaqueous outwash fans vary from sandy sediments deposited by proglacial and subglacial streams to coarse, poorly sorted complexes deposited as debris aprons close to the ice front. Abundant underflow deposits suggest that less than normal marine salinities prevailed in these water bodies, even if they were arms of the sea. 5. Supraglacial tillites consisting of sandy diamictites to pebble conglomerates. Facies in the thickest sequence in the Bacchus Marsh area suggests that the area was covered by a major ice mass at least 8 times. Minor glacial advances took place during predominantly ice-free periods. The Derrinal Formation consists of a basal unit of predominantly subglacial tillite deposited in shallow glacially excavated valleys overlain by a complex of subglacial and supraglacial facies deposited by about 8 minor advances of a small ice tongue. Facies relationships in this part of the sequence are confused by intense deformation of the sediment pile during the melting of buried ice and dewatering of saturated diamictons. A major ice advance then overwhelmed the area depositing thick subglacial tillite. The Urana Formation, beneath the Murray Basin, is dominated by marine ice-rafted diamictite and mudstone. Rhythmically bedded siltstone and claystone, sediment gravity-flow deposits, traction-current deposits, and, possibly, subglacial tillites are also present. Facies assemblages in some drill holes indicate areas that were never covered by grounded glacial ice. Sedimentological and palaeontological evidence suggests that the Urana Formation was deposited towards the end of the glaciation. Ice motion indicators and ice sheet limits inferred from the facies assemblages in the Urana Formation are used to estimate the thickness of the ice over central Victoria during glacial maxima. These estimates support the conclusion drawn from the facies analysis that the ice was a large ice sheet. Comparisons of ice movement directions for central Victoria and formerly adjacent parts of Gondwana suggest that a large ice sheet was centred in North Victorialand. Major and some trace elements analyses of the clay component of marine and non-marine diamictites were used to test a number of methods of distinguishing marine from nonmarine glacial diamictites. None of the methods were clearly successful because sediment detrital mineralogy dominates the geochemical composition though V/Cr ratios may be useful in some circumstances.
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ItemVolatile and precious metal geochemistry of the Mount Isa ores and their host rocks( 1986)Geochemical and petrographic investigations of Pb-Zn-Ag mineralization (12 orebody) and Cu-Co mineralization (1100 orebody) from Mount Isa were undertaken. Over one hundred and twenty carefully selected samples were analyzed for major and minor elements and for some or all of the following volatile metals: Au, Ag, Cd, As, Sb, Se, Bi, Co and Tl. A strong Tl enrichment is observed in (pyritic) unmineralized lateral equivalents of 12 orebody for several kilometers to the north of the mine sequence. The Se and As contents, S/Se ratios and S isotope relationships in the Pb-Zn ores and their host pyritic shales preclude a magmatic or deep-seated hydrothermal S Source. The data suggest that sulfide S in the Urquhart Shales was derived from reduction of a “seawater”/evaporitic/pore water sulfate source. Lateral variations in the thickness of mineralized intervals, the nature of the sulfide-gangue textures in the ores, the pervasive K and Tl enrichment in the host rocks and other chemical features of the Pb-Zn ores indicate that much of the Mount Isa mineralization formed epigenetically within the unconsolidated Urquhart Shales. The Pb-Zn-Ag ores contain very little Au and it is argued that this feature is best explained by the hydrothermal solutions that formed the Pb-Zn ores being cool (<<200°C) and moderately oxidized. The “silica dolomite” (the host to all the Mount Isa Cu mineralization) formed from “normal” Urquhart Shale as a result of intense fault-related hydrothermal activity (Perkins, 1984). The alteration has silicified the shales adjacent to the fault, and dolomite, phyllosilicates and “immobile” elements liberated during the silicification have been re-deposited at higher levels up-dip in the silica dolomite bodies. For the most part primary sulfide textures have not been preserved. It is argued that the distribution of several elements (notably Co, Bi, As, Fe and S) in 1100 orebody and its location down-dip from a strongly pyritic section of Urquhart shale are good evidence that stratiform Co (and Cu) mineralization was present in pyritic Urquhart Shales prior to formation of the silica dolomite. Chemical and isotopic evidence suggest that the Cu mineralization had a similar S-source and formed from similar solutions to the Pb-Zn-Ag ores. A new co-genetic model for the Mount Isa Cu and Pb-Zn-Ag deposits in which the mineralization formed from cool oxidized solutions in the upper few meters of the unconsolidated Urquhart Shales is presented. The metal-bearing solutions were expelled from their source rocks (oxidized clastic sediments lower in the Moust Isa Group) during the course of normal basin compaction and dewatering. Base metal sulfides were fixed by sulfate reduction processes occurring in the diagenetic environment of the Urquhart Shales. Weathered mafic volcanic detritus may have been and important component of the source.
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ItemGeochemistry and mineralisation of primary and secondary platinum-group elements in the ultramafic "Alaskan-type" Owendale complex and laterites in the Fifield Region, New South Wales, Australia( 1995)The Owendale Complex belongs to a family of ultramafic-mafic intrusions that is characterised by a zonal, nonstratiform arrangement of the principal ultramafic units. The ultramafic rocks of the Owendale Complex are virtually identical to many of the Alaskan-type intrusions, however the associated gabbroic rocks (wehrlites) are K-rich and Si-undersaturated, in contrast to the tholeiitic gabbroic rocks of the Alaskan examples. The intrusion history of the Owendale Complex is thought to have involved emplacement of a gabbroic intrusion that was invaded by an ultrabasic magma, possibly while the former was still only partly solidified. Emplacement of both magmas probably occurred during Late Devonian tectonism and deformation synchronous with emplacement and crystallisation is necessary to explain the present non-stratiform arrangement of the rock units. The most obvious linkage factor between the two proposed parent magmas (gabbroic and ultrabasic) of the Owendale suites is their mutual affinity with tholeiitic basalt magmas and the similarities of their products with intrusions of alkalic basalt derivation. This suggests the possibility that the Owendale Complex rocks and those of other tholeiitic intrusions of the regions are comagmatic products of an ancestral magma that may have also produced the widespread assemblage of complexes. Viewed from this perspective, the ultramafic rocks of Owendale Complex would thus represent a very minor product of a period of regional magmatic activity. Most alloys, erlichmanite, cooperite and some grains with exclusion texture of Pt-Os-Ir-Pd-Rh are considered to represent a primary high-temperature paragenesis. Concentration of PGE in pegmatoidal units of dunite-wehrlite is explained by the accumulation of platinum-rich alloys that segregated directly from the melt at an early stage in the evolution of the complex. The high-temperature PGM segregate directly from a silicate melt and were not generated by exsolution from spinels or magmatic sulphides. These suggest that fS2 was generally low (subordinate sulphide formation) and, after some influence at the beginning, has given way to rising fO2 (chromite, olivine and Pt-Fe-Cu-Ni alloys formation). After lithification, the ultramafic rocks become subject to "reducing" conditions, i.e., conditions of lower O2 and S2 activities. Ni-Fe alloys, native Fe and Bi formed in cracks which filled the serpentine matrixes. The former PGM (erlichmanite, cooperite and Pt-Fe alloys) were exposed to the reducing conditions via cracks were desulphurated to form porous cooperite with Pt-Fe alloys and multiphase textural Os-Ir-Ni, Pt-Ir aggregates. It is plausible that the veinlets and aggregates of unnamed Rh-Sb-S, (Pt, Ir)2(Fc, Cu)3(S, Sb, AS)3 in the dunites may also have been formed by reduction of Ni-rich sulphides and erlichmanite, Pt-Fe alloys or cooperite. Late PGM are dominated by sperrylite-geversite solid solution resulting from the reaction of early PGM with a fluid phase. A hydrothermal origin is also indicated for native Fe, native Bi and awaruite (NiFe) and the base-metal sulphides (pentlandite, chalcopyrite, sphalerite, arsenopyrite, pyrite, pyrrhotite, and some Ni-Co-Fe sulfide). The cause of the reducing conditions may have been related to H2 production accompanying hydrous alteration of the dunites and clinopyroxenites. The laterites overlying the ultramafic complexes in the Fifield region are exceptionally well-developed and well-preserved weathering profiles. Field, textural and geochemical data all support a chemical weathering origin for the profiles and compatible with meteoric and ground water origins. Meteoric water with intermediate Eh and pH and negligible dissolved species sinks into the laterite where these parameters are modified. The Eh rises and pH decreases to the conditions typical of lateritic soils and the concentration of dissolved species increases. In this state the water is able to take PGE and Au into solution from a finely disseminated form in the bedrock as a part of the process of lateritisation. When the soil solution transports the PGE and Au towards a transitional interface must exist between the ferruginous and saprolite zones with lower Eh, neutral pH and lower concentration of dissolved salts. At this transitional region, deposition of the PGE and Au occurred. The presence of magnetic Pt-Fe-Cu-Ni alloys suggests that hydrothermal solutions play a later role in the Fifield region, and the alloys have grown in situ in a lateritic soil by a process involving laterite water solution in the high Eh, low pH conditions prevalent in such soil, followed by deposition when the conditions become less extreme. Some examples of the Pt-Fe alloys from such an environment become frequently strongly magnetic with larger size. It is assumed that the temperature of the hydrothermal solution is in the range of 300° - 500° C (Bowles, 1990). PGE mineralisation in the primary rocks and laterite in this region has demonstrated a good example of multi-stage process mineralisation including primary high temperature magmatic formation; low temperature postmagmatic hydrothermal alteration and residual lateritic enrichment.
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ItemLate Paleozoic glaciations of Eastern Australia( 1959)In a re-analysis of the Late Paleozoic glaciations of Eastern Australia, close review of elements of paleogeography results in many new interpretations. New data appear from field studies of the details (including till fabric analyses in the Heathcote District of Victoria) of glacial stratigraphy in drift sequences of Victoria and South Australia. Analysis of sedimentary volumes in Tasmania and analysis of sedimentation during the Upper Carboniferous and Permian of New South Wales and Queensland adds more new information. Field reviews of sequences in the Finke District of the Northern Territory, Tasmania, New South Wales, and Queensland aid in understanding the effects of glaciations in those regions. All data known to the writer from extensive field examinations and review of published data may be incorporated into a unified history of the glacial times. Many lacunae exist, but analogy with studies of Pleistocene glacial drifts helps to bridge some gaps. Principally during the Middle and Upper parts of the Upper Carboniferous and in the Early Permian, highland centers in the northwest of Tasmania (the Macquarie Mountains) and in northeast New South Wales (the Clarencetown Mountains, a volcanic range) became loci for glacial formation and spread. From the former, glaciers spread east, north, and northwest. Upon advancing northwest, the Mt. Lofty-Kangaroo Island Ranges were encountered. These were breached with the establishment of glacial corridors, and a glacial lobe subsequently pushed about 600 miles further north-north-west. In that region, this glacial [?] [?] [?] joined a sheet from Western Australia. Also, in pushing north from the Macquarie Mountains, the glaciers apparently advanced 900+ miles to the Springsure District of Queensland. From the Clarencetown Mountains, piedmont glaciers radiated east (to the sea near Mt. George, Booral, and Limeburner’s Creek), south, and west to fill subsiding basins with glacial deposits and some volcanic effusions. Additionally, some glaciers spread east from the epi-Kanimblan mountains of New South Wales. Thick drift sequences left by these spreading glaciers have been preserved in favourable sites. Fluvial and lacustrine deposits in the drifts demonstrate the presence of interstadial and interglacial conditions, but the entire interval may be considered a single glacial epoch much resembling the Pleistocene, although that of the Late Paleozoic probably was much longer. After wastage of the glaciers, cold weather (at least during winters) persisted, for many phenomena found in the Permian sediments seem best related to climates which were cold at least part of the year. Notable among these are the erratics so widely distributed through the marine Permian sediments of eastern Australia. Such erratics seem best explained as phenomena resulting from the transport by winter ice floes of material eroded from glacial drift left on the land by earlier glaciations.
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ItemGenesis of volcanogenic epithermal gold-silver mineralization, Budawang Rift, New South Wales, Australia( 1988)The genesis of four volcanogenic epithermal Au-Ag deposits located within the Budawang Rift of South Coastal New South Wales, Australia have been investigated. Co-genetic pyrophyllite deposits have also been studied. Mineralization is hosted within peraluminous rhyolites which comprise approximately 50% of the bi-modal (rhyolites and tholeiitic basalts) Budawang Volcanic Complex. All mineralization occurs within the confines of the Budawang Rift of early Late Devonian age, with which mineralization is temporally related. Based upon geochemical, isotopic, structural, and lithologic investigations, the former division of the intra-rift volcanic rocks into three units (Boyd, Comerong, and Yalwal Volcanics) has been abandoned, with the adoption of a new name to include all three co-magmatic rocks; the Budawang Volcanic Complex. The name Eden-Comerong-Yalwal Rift has also been abandoned, and the new name Budawang Rift applied. The Pambula, Wolumla, Grassy Gully, and Yalwal deposits are each located along the margins of separate rhyolite flow domes, located within cumulo flow dome complexes. All four deposits plus co-genetic pyrophyllite deposits occur along N-S trending faults of similar orientation and are probably genetically related to rift graben faults. The Pambula and Wolumla deposits, plus at least two proximally located pyrophyllite deposits are situated adjacent to E-W trending cross graben block faults which predate rifting but which were re-activated by that event. Fluid inclusion studies yield temperatures of mineralization of between 320° C and 380 ° C for the Au-Ag deposits, and 290 ° C for the pyrophyllite deposits. System fluids were highly saline, ranging from 12 to 17 wt. % NaCI equiv. for the Au-Ag deposits, to 9% for the pyrophyllite deposits. Salt species are NaCI dominant with variable amounts of CaC!. No carbon dioxide was documented in fluid inclusions. Depth calculations for mineralization using the salinity corrected critical path of boiling fluids (most of the intra-rift deposits display evidence of phase separation) yield depths of: Pyrophyllite deposits 800-1,000 m, Pambula 1,200 m, Yalwal 1,300 m, Grassy Gully 1,450 m, and Wolumla > 1,600 m. Ore mineralogy is dominated by electrum which displays a distinct Au:Ag compositional ratio for each deposit, and which conforms to a temperature-depth profile for the suite of deposits, with increasing Ag in the higher temperature deposits. At Wolumla, other Ag minerals identified include native Ag, acanthite, stephantite, antimonpearceite, arsenpolybasite, pearceite, and proustite. cerargyrite, and the very rare selenide minerals naumannite and aguilarite. At Grassy Gully, trace amounts of the telluride minerals hessite and petzite were also identified. Ore associate mineral assemblages include chalcopyrite, galena, sphalerite, chalcocite, chalcostibite, tetrahedrite, tennantite, and arsenopyrite. The bulk of these minerals are co-depositional to electrum. Multiple episodes of pyrite have been identified in all goldfields, and always occur post-brecciation and shearing, but pre-electrum and pre-electrum associate mineral deposition. Some pyrites display As as well as optical zonation patterns. The chemical composition and paragenetic sequence of all mineral species identified have been documented. The levels of Se substitution of S in the Ag sulphosalts, and composi tion of naumannite and aguilarite are also discussed in detail. Ore geochemistry yields a vertical metal zonation pattern among the deposits, with the deepest and highest temperature deposit containing higher concentrations of base metals, Se, and Ag. In the shallower deposits, correlation coefficients and metal ratios indicate a decoupling of base and precious metals, and a previously un-recognized behavioural aspect of Sand Se in boiling epithermal systems.......