Dissertations / Theses on the topic 'Cu-Au mineralisation'

The Kansanshi Cu-Au deposit located in the Domes region of the North West province of Zambia is characterised by structurally controlled high angle veins and associated alteration halos. The northwest trending Kansanshi antiform flanks the Solwezi syncline to the north and hosts the Kansanshi deposit and consists of tillites and metasedimentary rocks. Mineralisation is associated with Neoproterozoic Pan African deformation events experienced during the formation of the Lufilian fold belt; however recent findings confirm that structures in the form of reverse and normal faults and drag folds are critical controls on mineralisation within the deposit, Main pit in particular. Low angle faults occurring below the current pit are believed to have served as major fluid pathways during mineralisation. Age dating data from the Kansanshi deposit suggest that mineralisation took place between 512 and 503 Ma indicating that the event was associated with metamorphism. Two types of alteration are dominant within the Main pit (Kansanshi deposit) with the type and intensity of alteration being largely controlled by lithological units. Albite alteration occurs dominantly in phyllites and schists whereas dolomitisation is prevalent in calcareous units. Alteration is associated with mineralisation, and therefore is used as a condition for predicting vein or disseminated mineralisation. The high Au tenor at Kansanshi can be attributed to gold grains occurring in association with melonite (NiTe₂) and microfractured pyrite intergrown with chalcopyrite in sulphide and quartz dominated veins and veinlets. Analysis of gold grade distribution within the Main pit shows a clear concentration of the element along the major north-south trending structures like the 4800 and 5400 zones, possibly through supergene enrichment in the oxide-transition-sulphide zones. It is imperative that exploration for Kansanshi-type deposits will require geochemical and geophysical studies, understanding of the geology of an area to identify the three lithostratigraphic units (red beds, evaporites and reducing strata).

This thesis investigates the tectonic and magmatic setting of a Copper-rich seafloor massive sulfide deposit. Integrated multi-scale data analysis produced a regional to deposit-scale framework to constrain how, why and where these types of mineral deposits form. Outcomes from this research advance our understanding of 1) regional tectonic evolution of the East Manus Basin, and 2) volcanic and magmatic processes conducive to seafloor massive sulfide deposit formation.

The genesis of the Minto copper-gold deposit, YT, Canada, has been variously interpreted since its discovery although no existing model accounts for ductile deformation as a control on mineralization. Results from this study show that Minto ore is hosted within ductiley deformed granitoid host rocks emplaced as multiple intrusions into an actively deforming environment, with the variably sheared host rocks separated by incipiently deformed granodiorites essentially barren of mineralisation. Contacts between deformed/mineralized rock and incipiently deformed/barren rock range from abrupt to gradational, and are the product of pre-existing igneous contacts, variably partitioned deformation, or a combination of these. Deformation of granitoids is interpreted to have controlled fluid flow, with associated alteration promoting further deformation and fluid flow. Potassic alteration, in the form of biotite-magnetite, is the dominant alteration associated with mineralisation, and analysis of alteration using isocon diagrams indicates that K, Fe, Si, Cu, Au, and Ag have been added during alteration, although mass has been lost overall due to a relative reduction in Na and Ca. Host rock intrusion, mineralization, and deformation are interpreted via geochronology and crosscutting relationships as ongoing over at least 5 m.a., from about 202 Ma until about 197 Ma, based on U-Pb SHRIMP geochronology of zircons in granitoids and Re-Os ICP-MS geochronology of molybdenite. The trend of mineralisation is now coincident with the strike of foliation on short steep limbs and of axial planes of folded foliation. This geometry may not be representative of original processes, but of remobilization of ore during continued deformation. The above observations, coupled with data from existing studies, strongly suggest Minto is representative of deposit generation within an arc subduction environment at depths not typically considered for copper-gold deposit formation.

The Masumbi Au-Cu deposit in the Ndori Greenstone Belt of western Kenya is hosted in dacitic volcanics of the Nyanzian Group (2710 ± 340 Ma) and dioritic to granodioritic felsic intrusives (2504 ± 48 Ma). The deposit is characterised by gold and copper mineralisation that is associated with quartz-sulphide veins and veinlets. The copper mineralisation typically occurs as chalcopyrite. Gold is closely associated with pyrite in mineralogy and its pathfinder elements silver, bismuth, tellurium and selenium in geochemistry. The gold occurs in two forms that may indicate two generations of precipitation: the equant and the elongate forms. Based on Au/Ag ratios, the equant gold grains can be classified as native gold as their gold content is greater than 90 wt%. The elongate gold grains can be classified as electrums as their silver content is greater than 38 wt%. While there is a strong Au-Ag association within individual gold grains supporting an orogenic model for the gold mineralisation, mineralisation at the Masumbi Prospect appears atypical of Archaean orogenic gold deposits because of the abundance of copper (up to 0.43%). The enrichment of silver, copper, bismuth and tellurium in ore assemblages is common in porphyry, VMS and epithermal systems, but their presence at Masumbi does not preclude the formation as an orogenic deposit. Assay results from three Masumbi diamond drill-holes show an apparent correlation between gold and copper. However, petrography and electron probe microanalyses results from this study indicate that chalcopyrite is an earlier phase than pyrite as it occasionally occurs as inclusions in pyrite. This petrogenetic relationship between pyrite and chalcopyrite suggests that there is no temporal relationship between gold and copper mineralisation. Statistical analysis of the assays shows no linear correlation between gold and copper thereby supporting the above findings. The gold and copper mineralisation have been interpreted as forming as two separate events with copper forming first followed by gold. These events are both related to the intrusion of the felsic rocks that are associated with the Aruan metamorphic event that has been responsible for the bulk of the gold mineralisation on the Tanzanian Craton. The common alteration assemblage in the Masumbi rocks comprises chlorite and epidote. This alteration assemblage is typical of regional greenschist metamorphic facies grading into amphibolite metamorphic facies in the Nyanzian Group of Kenya. However, these alteration minerals could possibly be products of propylitic alteration in the rock groundmass. Other alteration mineral assemblages, possibly of hydrothermal origin, comprise muscovite, sericite, quartz, carbonate, associated with the sulphides pyrite and chalcopyrite. Although the occurrence of gold appears to be controlled by the presence of pyrite, it is also associated with silicification. Exploration methods have been proposed to target undiscovered gold deposits in the Ndori Greenstone Belt that are similar to the Masumbi deposit. These methods could probably be applied to vein-type gold deposits in other granite-greenstone terranes in the Lake Victoria Goldfields.

Thesis (B. Sc.(Hons.))--University of Adelaide, Dept. of Geology and Geophysics, 1995?
National Grid Reference Maitland Sheet I-553/12 (1:250 000) Whyalla I-53/8 (1:250 000). Three folded maps in pocket inside back cover. Includes bibliographical references (leaves 74-78).

Continental magmatic arcs host economically important porphyry ore deposit types for copper, gold, and molybdenum, and, if preserved, epithermal high- to intermediate-sulfidation gold and silver deposits. These deposits are genetically and/or spatially associated with magmatism, so understanding the link between magmatism and mineralisation is seen as a crucial endeavor to assist knowledge of mineralisation processes and strategies for regional-scale mineral exploration. This thesis examines aspects of the mineralisation potential of continental arc magmatic rocks that are exposed as part of the Permo-Carboniferous Kennedy Igneous Association (KIA) from northeastern Queensland. This belt of upper crustal intermediate to felsic granitoids and associated volcanic rocks is recognised to host many economic ore deposits related to igneous activity. Using well-established analytical techniques to analyze whole-rock and mineral major- and trace element compositions combined with Sm-Nd isotopes, I investigate two different localities related by their occurrence in time and space, with the aim to better understand magma fertility, or more specifically the petrogenetic processes contributing to Permo-Carboniferous Cu-Au mineralisation in northeast Queensland. This work strives to improve the applicability of magma fertility concepts to confidently identify fertile igneous terranes potentially covering high grade Cu-Au deposits at depth. The first location investigated lies to the south of Townsville at the northern edges of the Bowen Basin, where the early Permian Lizzie Creek Volcanic Group (LCV) hosts the Mount Carlton high-sulfidation epithermal Au-Cu deposit. Established whole-rock geochemical parameters, e.g. Sr/Y, V/Sc, used to distinguish fertile porphyry Cu-Au hosting intrusive rocks from barren intrusions, were tested on the "fertile" LCV succession, hosting the Mt. Carlton deposit and compared to contemporary "barren" volcanic rocks of the same group. The results reveal that the key control on generating the fertile LCV sequence was a high magmatic water content, reflected by early fractionation of amphibole at the source level, whereas the barren sequence was comparably dry, and formed by typical fractionation of plagioclase and clinopyroxene. This outcome has major implications for the applicability of whole rock geochemistry as a magma fertility indicator. The here presented results suggest that for volcanic rocks, which tend to be affected by hydrothermal alteration; a) Sr/Y is not a reliable fertility proxy and; b) Rare earth element ratios (e.g. La/Yb, Dy/Yb), which are relatively resistant to alteration, can be used to reveal differences in magmatic evolution. This supports previous research on magma fertility, and provides strong evidence that fertile magmatic suites can be identified from volcanics sequences that evolved from basalt to rhyolite with a progressive increase in La/Yb, decreasing Dy/Yb, and consistent or slightly increasing V/Sc ratios, despite having experienced some degree of alteration. The second location investigated in this thesis is the Tuckers Igneous Complex (TIC); a calc-alkaline, I-type igneous complex which intruded the Ravenswood Batholith between ~300-290 Ma and formed within the same convergent margin as the LCV. The TIC is part of the KIA and its relevance for this project lies within its close association with the major early Permian, breccia-hosted Mt. Leyshon Au deposit. The TIC contains a sequence of intrusive rocks from gabbro to felsic granodiorite, and hence offers the opportunity to investigate geochemical evolution, particularly volatile element evolution, of arc magmas at upper crustal levels. Here, I build on previous geochemical and petrographic data for the complex using newly acquired whole-rock geochemistry and in-situ mineral analyses of the major rock forming minerals plagioclase-clinopyroxene-orthopyroxene, and the halogen-bearing minerals apatite and biotite (and amphibole) to monitor and track volatile evolution (Cl and F). As volatile element behavior is recognised to have a fundamental control on magma fertility, this study, offers new insights into the fertility of this Permo-Carboniferous arc, which can be applied to other arc worldwide. My new results show that the TIC formed through closed-system crystal fractionation from gabbro to mafic granodiorite varieties with only minor mixing and/or assimilation, and likely became an open system during cooling and crystallisation of the more felsic granodiorites. Based on apatite halogen contents, volatile saturation is suggested to have occurred at around ~63-65 wt.% bulk-rock SiO₂, up to which point estimated Cl melt contents steadily rise, and then suddenly drop from ~0.8 to 0.4 wt.%. This abrupt change likely relates to the exsolution of a Cl-rich volatile phase, and also marks important changes within the mineral assemblage from a dry Plag ± Px ± Fe-Ti oxide assemblage, towards a more hydrous and slightly more oxidised Plag ± Hbl ± Bt ± Mag assemblage. Fluorine enriches in the melt with fractionation, even once saturation in a volatile phase is reached, consistent with what is expected from experimental partitioning studies in the system apatite – melt – fluid. Local or temporal changes in the magma's fO₂ is indicated by a measurable increase in apatite S contents in evolved felsic granodiorite, as apatite preferentially incorporates S as its oxidised species S⁶⁺, which also coincides with the general observed changes in the rock forming mineral assemblages as described above. Indicated volatile exsolution, causing loss of significant proportions of Cl together with oxidising conditions at which the bulk of dissolved S may have been present and possibly degassed as S⁴⁺O₂ (and causing the presence of low amounts of available S²⁻ to precipitate base metals) from the TIC magma may have caused mineralization within overlying, but now eroded rocks. A second possibility may be that the TIC was never able to produce mineralising fluids due to early segregation of sulfides, scavenging ore forming metals (e.g. Cu, Au, and Ag) prior to the crystallisation of TIC gabbro, and thereby stripping the TIC of its ore-forming potential early on. However, an exsolved Cl-rich fluid is very capable of transporting ore metals, therefore the role and true nature of such fluid(s) originating from the TIC can be subject of further investigations. The here presented results help to understand Cu-Au fertility on a regional, magmatic arc terrane (both volcanic and intrusive) from initial lower crustal petrological processes to the surface, but also on a local scale; within confined individual igneous bodies, their respective mineral assemblages, and their potential role towards regionally present Cu-Au mineralisation. In particular the findings on volcanic rocks offer great potential as easily accessible first-order fertility assessment tool for magmatic-hydrothermal Cu-Au exploration worldwide.

Transported regolith has the capacity to mask underlying mineralisation by restricting the migration of most trace elements to the surface. Oxidation of sulphides generates highly mobile H+ which may migrate to surface, resulting in alteration of minerals and redistribution of elements within transported regolith cover. A detailed geochemical and geophysical study has been conducted at the Mandamah Cu-Au deposit in central-western New South Wales, where sub-economic mineralisation is covered by ~50 m of transported regolith and ~30 m of in situ regolith. A shallow-penetration electromagnetic survey was undertaken on nine transects and detailed mineralogical and selective extraction/ICP-MS geochemical analysis performed on regolith samples obtained from 107 soil cores and 16 pits spanning three extensive traverses across buried mineralisation. The selective extractions used were ammonium acetate, hydroxylamine.HCl and aqua regia. A distinct vertical zonation exists in the upper two metres of the transported regolith cover across the site and is related to soil mineralogy, soil pH, electrical conductivity and the amount of selectively extractable elements using the different geochemical extractions. The upper zone of near-neutral soil pH contains organic material but little carbonate; the intermediate high-pH zone has up to 2% Mg-calcite; the underlying low-pH zone displays Fe mottling. This zonation results from precipitation of salts due to evaporation, changes in redox potentials and accumulation of organic materials, in an otherwise relatively homogeneous quartz-clay alluvium. Ground conductivity measurements and selective extraction geochemistry display a strong response to parts of the underlying mineralisation. The principal signature is the depletion of Ca, S and Na, a reduction in the cation exchange capacity, the presence of non-carbonate alkalinity and a low electrical conductivity. A model to account for these patterns has been developed and involves a "prograde" stage of alteration of clay mineralogy and a redistribution of carbonates and various trace elements due to the development of an "acid chimney" above the oxidizing mineralisation during a period of elevated water tables and a "retrograde" stage involving a redistribution of some mobile elements back into the former acid chimney zone following the onset of more arid conditions. The results of this research demonstrate that the effects of sulphide mineralisation on the upper transported regolith at Mandamah can be detected using a combination of selective extraction geochemistry and shallow depth conductivity measurements. This technique has potential application in similar arid to semi-arid terrains.

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The Kanmantoo Cu-Au deposit has been in episodic operation since 1846, one decade after the capital city of Adelaide was established some 40 kilometres to the NW. Regionally and within the host stratigraphy there exists archetypal evidence of the Cambrian Delamerian Orogeny through a complex structural, metamorphic and intrusive history. Consequently, numerous theories exist within the literature regarding a syngenetic or epigenetic style of mineralisation and the debated contribution, if any, of magmatic hydrothermal fluids. This study has documented numerous felsic intrusive vein sets within the Kanmantoo Cu-Au deposit which have been utilised to constrain the role of igneous activity on mineralisation within a wider Delamerian context. Monazite U–Pb ages of felsic veins show that intrusion first occurred at syn-peak metamorphic, syn-orogenic conditions (495.11 ± 2.79 Ma), continuing periodically until post-peak metamorphic, extensional conditions (483.43 ± 2.52 Ma). Intrusions are coeval with mineralisation and are temporally and geochemically analogous to magmatic activity in the adjacent Monarto and Murray Bridge provinces. Analysis of trace elements in monazites identifies the Kanmantoo Cu-Au deposit as a syn- to post-peak metamorphic hydrothermal anomaly which, combined with the presence of felsic veins, indicates that mineralisation resulted partly from fluids generated by a pluton at depth. These findings broadly confirm the prospectivity of Delamerian-affected terranes throughout large parts of South Eastern Australia where pervasive intrusive geology exists.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2018

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The Palaeoproterozoic Poodla Granite within the Olary Domain, Curnamona Province, South Australia, has been suggested as a direct contributor to Cu-Au mineralisation within the region on the basis of age correlations. Alteration present within the Poodla Granite consists of four styles that have been interpreted as two events. The first event includes pervasive potassic alteration followed by pervasive Na-Ca alteration. Sm/Nd isotope analysis indicates fluids for this event were sourced from the Willyama Supergroup sediments. The second event consists of fracture-controlled sodic and Ca-Na-Si alteration with associated actinolite/clinopyroxene brecciation. Utilisation of magmatic major element trends obtained from a natural analogue (Mt Angelay Complex, Cloncurry District) has allowed greater accuracy in chemical characterisation of alteration. Fluid inclusion analysis has identified two distinct fluids involved in the later fracture-controlled sodic and Ca-Na-Si alteration event. Namely, a low salinity (18-26wt% NaCl equivalent) and a high salinity (35-45wt% NaCl equivalent) fluid. A later fluid mobilisation event related to the Palaeozoic Delamerian Orogeny is indicated by re-equilibration of the Rb/Sr isotopic system. New age constraints from other granites in the I-type suite, to which Poodla Granite belongs, suggest the Poodla Granite did not have direct hydrothermal input into regional Cu-Au mineralisation. Analysis of alteration chemistry suggests that Cu and Au mobilisation occurred during the first alteration event. These results offer evidence for previously untested Cu-Au mineralising models within the region and may encourage exploration for Cu-Au resources.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2003

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The world-class Boddington Cu-Au-Mo deposit has a complex genetic history. The relative importance of different ore-forming processes during the period 3.0 – 2.6 Ga is debated, particularly with respect to the role played by the 2611±3 Ma Wourahming granite. LA-ICP- MS analysis of trace element concentration in molybdenite represents a valuable new metallogenetic tool to track mineralising events in deposits with protracted geologic histories. The Re content and trace-element signatures in molybdenite from diorite and granite show three distinct populations, attributed to porphyry-style (hundreds of ppm) orogenic- and granite-related systems (<1 to a few ppm, respectively). Rhenium concentrations in molybdenite are highly variable on the deposit-scale. Economic concentrations of Re occur only at shallower levels in both Central Diorite and ABreccia. The Au content correlates with high-concentrations of chalcophile elements (CE). This is seen in the association of Au- minerals and Bi-(Pb)-tellurides present as inclusions in the molybdenite from diorite and is inferred from an LA-ICP-MS element map for molybdenite in granite. The FIB-SEM and TEM study show that visible telluride inclusions extend down to the nanoscale as coherent intergrowths with host molybdenite. Nanoporosity is accompanied by a whole range of structural defects and twinning. The telluride species identified include unnamed Bi4Pb7Te4S9. Analysis of stacking sequences show co-precipitation of Bi-tellurides and molybdenite under equilibrium conditions. In corroboration with EPMA data, this is the first confirmation that minerals from the aleksite series are characteristic components of the ore at Boddington. Molybdenite with high-concentration of chalcophile elements is present as the 2H polytype only, contrary to previous hypothesis that incorporation of trace elements is assisted by 3R structural modification. Instead, a new mechanism is presented in which coherent lattice-scale intergrowths between molybdenite and tellurides are reasons for the measured high CE concentrations. Knowing that Bi-(Pb)-tellurides are Au-carriers, this may also explain the observed, unusual Au-enrichment in molybdenite from Boddington. Nucleation of Au fine particles is inferred from element map correlations but further work is necessary to prove if Au nanoparticles are also present. Petrographic, mineralogical and geochemical evidence support a three-stage model for Boddington. An early porphyry event can account for the bulk of the Cu mineralisation, as well as some of the Au and Mo. A subsequent orogenic-Au event led to shearing and remobilisation of ore components. New constraints on metamorphic conditions are offered by chlorite and stannite-sphalerite geothermometry (200-420 °C) and the occurrence of two co- existing pyrrhotite species. The granite introduced some Au, Mo and other „granitic‟ elements, notably Bi leading to substantial upgrading of Au grades by Bi-melt scavenging. The study concludes however that hydrothermal activity associated with granite was not the most important concentrator of ore minerals.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Earth and Environmental Sciences, 2011

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Iron oxide copper gold (IOCG) systems display well-developed spatial zonation with respect to alteration assemblages, mineralogy and the distribution of rare earth elements (REE). The Middleback Ranges, South Australia, located in the Olympic Province, Gawler Craton, hosts anomalous Fe-oxide-bearing Cu-Au mineralisation, and are considered potentially prosperous for larger IOCG-style deposits. This study investigates whether the distribution of REE and other trace elements within selected minerals represents a potential exploration tool in the area. Iron-oxides (hematite and magnetite), potassium feldspar, albite and accessory minerals have been analysed by laser-ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) from two prospects (Moola and Princess) and in samples of the Myola Volcanics. The resultant multi-element datasets are compared to other IOCG systems. The results support the presence of sizeable and/or multiple IOCG alteration envelopes within the Middleback Ranges. Significant evolving hydrothermal events resulted in hydrolithic alteration and remobilisation of REE within the Moola Prospect and Myola Volcanics. Replacement of early magnetite by hematite (martitisation) in the Myola Volcanics is accompanied by an influx of REE visible on LA-ICP-MS element maps showing partial martitisation at the grain-scale. It is thus inferred the initial generation of magnetite must have pre-dated introduction of oxidised, REE-enriched hydrothermal fluids into the system. Sulphide assemblages observed within the Moola Prospect are complex and record sequential recrystallisation under evolving fS2 and fO2 conditions. Trace minerals, cycles of brecciation and replacement, and distributions of REE within minerals are similar to that observed in other IOCG domains. The Princess Prospect displays REE distributions in minerals which are dissimilar to the Moola Prospect, the Myola Volcanics and also those reported from other IOCG domains. This is interpreted as indicating that the Moola Prospect and Myola Volcanics in the south of the Middleback Ranges are more prospective IOCG targets.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Earth and Environmental Sciences, 2013

The Eastern Fold Belt (EFB) in north-west Queensland, Australia, is an extensively metasomatised terrain that contains a variety of Fe oxide (Cu-Au) and related deposits (IOCG). Most of these deposits formed after the peak of ca. 1600-1575 Ma regional metamorphism and exhibit a broad range of mineralogical and chemical associations. The origin of fluids associated with mineralisation is particularly controversial, whereby magmatic, non-magmatic and magmatic-evaporitic fluid-derived models have all been proposed. Several deposits in the district also exhibit different relations to ironstone (Fe oxide-rich rock) occurrences. These relations vary from early to pre-mineralisation Fe oxides (Starra and Osborne), syn-mineralisation Fe oxides (Ernest Henry) and examples where significant amounts of Fe oxide are distal to the site of mineralisation (Eloise). Fe oxide-rich rocks can form from a number of different processes (orthomagmatic, replacement, infill, sedimentary), and can be distinguished by textural observations and geochemical analysis. Sulphide mineralisation and Fe oxide-rich rocks within the Mount Fort Constantine (MFC) exploration lease (the main study area) are of particular interest due to their proximity to the Ernest Henry (Cu-Au) deposit. At the FC4NW and FC12 prospects in the MFC lease, sulphide mineralisation post-dates the formation of Fe oxide-rich rocks and is associated with amphibole-rich Na-Ca alteration. Fe oxide-rich rocks in the FC12 prospect were formed by orthomagmatic processes directly related to the formation of their tholeiitic gabbroic host. In contrast, Fe oxide-rich rocks in outcrop and at the FC4NW prospect were formed by hydrothermal processes. Fe oxide-rich rocks at the FC4NW prospect exhibit a close spatial and temporal association with an earlier clinopyroxene-rich Na-Ca alteration phase that predates sulphide mineralisation. The poor correlation between Fe oxide-rich occurrences and sulphide mineralisation at MFC differs from Ernest Henry, where Fe oxide and Cu-Au mineralisation are synchronous and post-date Na-Ca alteration. Na-Ca alteration at FC12 is associated with the enrichment of Fe, Mg, REE, Cu and S. In contrast, Fe is typically depleted and Mg, REE, Cu and S are variable in regional Na-Ca alteration throughout the Cloncurry District. Na was also found to be variable at FC12. These geochemical patterns suggest that the fluids at FC12 were cooler and more evolved than for regional Na-Ca alteration, and had previously undergone significant fluid-rock interaction prior to mineral precipitation. This is reflected in the low temperature mineral assemblage (chlorite, calcite, magnetite, hematite, pyrite, chalcopyrite) associated with these veins. Na-Ca alteration at FC4NW formed by a hypersaline (25 to 50 wt% NaClequiv) and CO2-bearing fluid at temperatures of around 260 to 442°C. These fluids cooled and became less saline with time, reflecting the transition from clinopyroxene-rich to amphibole-rich Na-Ca alteration. The chemistry of these fluids is similar to regional Na-Ca assemblages, containing elevated Mn, Zn, Cu, Fe, K, Cl, Ca, Ba and Pb. In contrast, they are distinctly different to fluids associated with Cu-Au mineralisation at Ernest Henry, Starra, and Lightning Creek in the EFB. In particular, Mn, Zn, Ba and Cu concentrations are significantly lower in Na-Ca assemblages from FC4NW. The lack of significant Cu-Au mineralisation at FC4NW may be attributed to the low Cu content in the fluid. The mineral chemistry of magnetite, hematite, pyrite and chalcopyrite can be used to discriminate between Cu-Au mineralised systems and systems which are weakly mineralised to barren. Magnetite associated with Cu-Au mineralisation contains a greater variety of elements including Mo, W, Th and U, which are typically low to below detection in other systems. In addition, Cu-Au mineralised systems are associated with higher Sc and Mn (magnetite), As and Co (pyrite), Bi, Sn, In and Ag (chalcopyrite) and As, Sb, Ga, and W (hematite). In contrast, Ti, V, Ga and Cr (magnetite) and Se and Ni (pyrite) are lower in Cu-Au mineralised systems. Fluid chemistry is interpreted to be the dominant control on the trace element content of magnetite, hematite, pyrite and chalcopyrite, however, other physicochemical factors including fO2 and temperature may also affect the relative concentration of elements including V, Cu and Se. These chemical signatures have the potential to be used as vectors towards geochemical haloes peripheral to Fe oxide (Cu-Au) mineralisation. The presence of granitic and pegmatitic dykes at FC12 and FC4NW suggests the presence of a nearby igneous intrusion. In contrast, no igneous intrusive phases are present at Ernest Henry. The felsic igneous rocks at FC4NW exhibit a close spatial and temporal relationship to clinopyroxene-rich Na-Ca alteration suggesting a genetic link. The presence of sulphide associated with the latter amphibole-rich Na-Ca phase at FC4NW, together with the low temperature mineral assemblage associated with Na-Ca alteration at FC12, suggests that mineralisation may have occurred due to a drop in temperature over time, irrespective of the specific mechanism responsible for the precipitation of sulphide. The paragenesis and fluid inclusion chemistry at MFC suggest that sulphide mineralisation is an earlier / unrelated event compared to the phase of Cu-Au mineralisation at Ernest Henry. Instead, sulphide mineralisation at MFC more closely resembles the early, weakly mineralised Na-Ca alteration phase and related hanging wall Fe oxide-rich rocks at Ernest Henry. The main ore genesis stage at Ernest Henry is noted by a more complex fluid chemistry, in addition to the presence of Au (absent at MFC) and K-Fe alteration, which suggest that at least one fluid associated with Cu-Au mineralisation at Ernest Henry was absent at MFC. However, the whole rock geochemistry of low temperature Na-Ca alteration at FC12 as well as the mineral chemistry of Fe oxides and Fe sulphides suggest that sulphide mineralisation at MFC and Ernest Henry may be more implicitly linked. In particular, magnetite associated with sulphide-bearing Na-Ca alteration at FC4NW and FC12 contain high Ni and anomalous W, Mo, Th and U, the latter of which are minor to absent in barren regional Na-Ca assemblages but highly enriched at Ernest Henry. One possibility is that Ernest Henry is part of an overlapping hydrothermal system, which supports the interpretation by Mark et al (1999) that more than one fluid was responsible for Cu-Au mineralisation. Fluids responsible for sulphide mineralisation at MFC may have either been diluted by another fluid, possibly of meteoric origin, or did not mix with a more chemically complex, S-bearing fluid. Thus, while a clear distinction can be made between sulphide mineralisation at MFC and Cu-Au mineralisation at Ernest Henry both chemically and paragenetically, MFC may represent a vector towards mineralisation at Ernest Henry, because a small amount of potentially ore-bearing Ernest Henry-style fluid appears to have contributed to the MFC magnetite geochemistry.

Major geophysical lineaments are commonly associated with active to ancient faults at a variety of scales. They may correlate with the edges of rifts, depositional basins, orogenic belts or plate boundaries, and they commonly represent corridors along which deformation, mineralisation, magmatism and intra-crustal heat flow is concentrated. In many instances, they encompass a number of these features. The Cloncurry Lineament, a major feature in wavelet processed magnetic and gravity potential field (worm) data over the Mount Isa Inlier Eastern Succession, displays several such characteristics. It is over 200 km long and inferred to extend to at least 30 km depth. It delineates a contact between two major Paleoproterozoic sedimentary sequences, implying that it originated as a normal fault during rifting and basin formation. Magnetic forward modelling results suggest it corresponds to the eastern margin of a 5-10 km wide deformation zone within the calc-silicate Doherty Formation; the Cloncurry Fault Zone. The Cloncurry Fault Zone encompasses a continuum of deformation from ~1.6 to1.5 Ga. While D₁-D₂ deformation is regionally dominant, D₃ is more significant in the fault zone itself as evidenced by much lower temperatures during mylonitisation (500- 350°C) and the superimposition of mylonitic fabrics on Maramungee aged (~1550 Ma) granites. Mapping and structural fabric analysis of the Cloncurry Fault Zone show that D₃ involved WSW shortening, sub-perpendicular to a pre-existing basin-bounding fault. D₃ created an anastomosing shear zone system displaying variable slip vectors with synchronous variably NNW or SSE plunging folds. Penetrative fabrics are attributed to strain partitioning in the D₃ event, rather than a more complex history of overprinting. During D₄-D₅ a sinistral Riedel strike-slip fault system formed, coincident with massive Na-Ca brecciation. Intrusive magmatism and IOCG, Cu, and Au mineralisation also occurred during the D₃-D₅ history of the Cloncurry Fault Zone, highlighting its importance as a magmatic and hydrothermal pathway. Sodic-calcic (Na-Ca) metasomatism, associated with Cu-Au mineralisation in the Mount Isa Eastern Succession, is widely recognised but heterogeneously distributed, and difficult to map regionally. Hence, a method to map Na-Ca alteration remotely was developed. ASTER Band ratios were ineffective for mapping amphiboles and carbonates as a proxy for sodic-calcic alteration due to numerous mineral species having similar absorption features in ASTER band 8. Therefore, the low Kradiometric and highly magnetic properties of Na-Ca alteration were integrated with ASTER band 8 to form a Sodic-Calcic Alteration Index. The Index highlights albiteactinolite- magnetite assemblages that are coincident copper with Cu-Au mineralisation in the Eastern Succession, and the Index is useful for regional exploration in the Mount Isa Inlier. Weights-of-evidence analysis identifies the Cloncurry Lineament as an important crustal-scale control on Au, Au-Cu, Cu-Au, and Cu mineralisation, and autocorrelation is used to identify local structural controls within the broad regional control. This integrated approach, using worms and weights-of-evidence and autocorrelation, may prove a useful exploration tool for mineralised terrains under Phanerozoic cover. Mineralisation along the Cloncurry Lineament appears to be facilitated by two main factors. Firstly, it is associated with long, deep-crustal structure lying above dynamic lower crust/mantle, which has concentrated magmatism and metasomatism. Secondly, the associated structures have been repeatedly reactivated; increasing the chances that dilation may coincide in space and time with upflow of mineralising fluids to form a mineral deposit. These two factors appear to be consistent in several of the world's major mineralised lineaments.

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The Moonta-Wallaroo area has been of economic, historical and scientific importance in South Australia's history for over 130 years. The nature of mineralisation in the area has long been a point of conjecture. This study looks at the nature of ore deposition and specifically its relationship to granitoids and pegmatites in the Moonta Subdomain. Using various analytical techniques the study has shown that granitoids in the region have distinctly different petrological, textural, structural, geochemical and isotopic characteristics. Two main granitoids were·recognised as the Tickera Granite and the Arthurton Granite. Geochemical studies suggest that magmatism in the Moonta Subdomain was a continuous process in the Mesoproterozoic. The older Tickera Granite, displays syn-collisional, more I-type characteristics and syn-collisional S-type characteristics (represented by a monzonite and a tonalite respectively). The younger Arthurton Granite shows A-type, anorogenic characteristics. A temporal shift from syn-collisional to anorogenic granites suggests a tectonic control on magma generation and emplacement during this period. Trace element characteristics of the Arthurton Granite are homogeneous over a wide spatial range, is suggesting that it may be part of an extensive batholith. Geochemistry of pegmatites implies that they were late stage fractionation products, related to these granite intrusions. A study of the Tickera Granite (Point Riley-Nth Beach) revealed a dominant structural fabric which suggested the granite was intruded into a tectonic regime in which shearing was prominent. Sediments intruded by the granite suggested deposition in a shallow intracratonic rift setting, followed by polyphase deformation during orogenic activity and subsequent shearing possibly related to the enigmatic Wartakan Event. Isotopic studies highlighted differences in the petrogenetic source regions of the Tickera Granite and the Arthurton Granite. The Tickera Granite (represented by monzonite) displayed more mantle like characteristics while the Arthurton Granite (represented by granite from Arthurton and adamellite from Moonta) displayed more crustal features, highlighting its A-type nature. Studies also showed that a pegmatite from the Wheal Hughes was most like the later of these two granites. Tourmaline studies of Wheal Hughes samples implicated derivation from a metapelite and calcsilicate precursor, a common feature of most tourmaline studied in the area. This may indicate remobilisation of boron rich fluids and metals from these sediments The close association of tourmaline with the ore in the Moonta Mines region implied a common source region. A tectonic setting and model for ore deposition is proposed on the basis of the study findings. The model proposed the remobilisation of metals which were initially deposited in a ensialic rift type environment (common to other Palaeoproterozoic metalliferous terrains) by the intrusion of the Tickera Granite, during regional shearing. And further concentration of metals by subsequent intrusions of the Arthurton Granite batholith.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Earth and Environmental Sciences, 1994

The Eastern Succession of the Proterozoic Mt Isa Block, including the Cloncurry District and the Mary Kathleen Fold Belt (MKFB), contains numerous examples of Fe-oxide-Cu-Au mineralisation. Most deposits, including Ernest Henry, Eloise, Starra and Mt Elliott formed after the peak of ca. 1600-1575 Ma upper greenschist to amphibolite facies metamorphism, and during the waning phases of the Isan Orogeny. Mineralisation was broadly synchronous with emplacement of voluminous phases of the Williams and Naraku batholiths (ca. 1550 - 1500 Ma) and widespread brecciation and accompanying metasomatism. Brecciation and metasomatism were best developed within Cover Sequence 2 stratigraphy, and in particular within calc-silicate rock and meta-siltstone stratigraphy of the Corella Formation, the predominant rocks of the Mary Kathleen Group. The geometry and distribution of brecciation in the Corella Formation was in part controlled by retrograde buckle folding imposed on a heterogeneous rock sequence that was fractured and boudinaged both pre- and syn-buckle folding. Brecciation is far more widespread in the Cloncurry District relative to the MKFB, reflecting in part a larger proportion of stratigraphy in the Cloncurry District that was at low angles to the shortening direction during the waning phases of the Isan Orogeny, favoring refolding and consequent fracturing. Variations in regional structural trends reflect strain partitioning around competent intrusive bodies, fault reactivation and refolding. Other contributing factors for brecciation include low temperature conditions during late deformation, and the proximity to voluminous intrusions, the emplacement of which likely resulted in transient elevated fluid pressure and strain rates, favoring fracturing and brecciation. The relative paucity of brecciation in most stratigraphic units outside of the Corella Formation reflects a high proportion of incompetent stratigraphy in these sequences (e.g. voluminous micaceous schists within the Soldiers Cap Group), which were able to• accommodate strain by plastic flow. The broad-scale geometry of the Cloncurry District reflects Cover Sequence 3 rocks overlying Cover Sequence 2 rocks, the two sequences being separated by early faults. Marbles within the Corella Formation, and schists in other stratigraphic sequences were not prone to brittle failure, and acted as low permeability barriers to fluid flow. These horizons allowed for the attainment of elevated fluid pressures within large volumes of brecciated rock. During the final stages of brecciation, these low competence marbles and schists were fractured and brecciated, predominantly within discrete fault zones. This shift from widespread brittle-ductile to purely brittle deformation likely reflects progressive cooling, as well as locally elevated fluid pressure and/or strain rate associated with pluton emplacement and degassing. A synchronous district-scale shift from compression to transtension facilitated the development of vertically continuous zones of dilation within faults, resulting in very large fluid pressure gradients and catastrophic fault valving. Brecciation was accompanied by widespread metasomatism that ranges from high temperature (400° - 600°C) Na-(Ca)-rich assemblages (e.g. albite ± actinolite, clinopyroxene, scapolite, magnetite, titanite, etc.) to retrograde (<400°C) chloritic assemblages. Interpretation of stable (0 and C) and radiogenic (Sr) isotopes and mineral chemistry is consistent with this spectrum of alteration assemblages reflecting metasomatic fluids of two predominant origins. The oxygen and carbon isotopic signature of carbonates from Na-(Ca) assemblages indicates that fluids responsible for this style of alteration were not simply equilibrated with magmatic rocks, but were exsolved from crystallizing plutons. Low temperature, low salinity fluids of inferred meteoric origin were introduced late in the paragenesis, and do not appear to have contributed significantly to the mass budgets of eu-Au ore systems in the district. Extensive fluid-wallrock interaction prior to mineralisation appears to have been important in the genesis of some deposits that record K- and Fe-rich alteration haloes, including for example the Ernest Henry deposit. However, the occurrence of skarn-like, intrusion-proximal mineralisation that lacks significant K- and Fe enrichment at for example Mt Elliott, indicates that fluid-wallrock interaction was not a necessary precursor for all styles of Cu-Au mineralisation in the Cloncurry District.