Academic literature on the topic 'Lachlan Orogen'

AbstractThe classical S–I–A-type granites from the Lachlan Orogen, SE Australia, formed as a tectonic end-member of the accretionary orogenic spectrum, the Paleozoic Tasmanides. The sequence of S- to I- to A-type granite is repeated at least three times. All the granites are syn-extensional, formed in a dominantly back-arc setting behind a single, stepwise-retreating arc system between 530 and 230 Ma. Peralkaline granites are rare. Systematic S–I–A progressions indicate the progressive dilution of an old crustal component as magmatism evolved from arc (S-type) to proximal back-arc (I-type) to distal back-arc (A-type) magmatism. The alkaline and peralkaline A-type Younger granites of Nigeria were generally hotter and drier than the Lachlan A-type granites and were emplaced into an anhydrous Precambrian basement during intermittent intracontinental rifting. This geodynamic environment contrasts with the distal back-arc setting of the Lachlan A-type granites, where magmatism migrated rapidly across the orogen. Tectonic discrimination diagrams are inappropriate for the Lachlan granites, placing them in the wrong settings. Only the peralkaline Narraburra suite of the Lachlan Orogen fits the genuine ‘within-plate’ setting of the Nigerian A-type granites. Such discrimination diagrams require re-evaluation in the light of an improved modern understanding of tectonic processes, particularly the role of extensional tectonism and its geodynamic drivers.

Abstract The Reward mine at Hill End hosts structurally controlled orogenic gold mineralization in moderately S plunging, high-grade gold shoots located at the intersection between a late, steeply W dipping reverse fault zone and E-dipping, bedding-parallel, laminated quartz veins (the Paxton’s vein system). The mineralized bedding-parallel veins are contained within the middle Silurian to Middle Devonian age, turbidite-dominated Hill End trough forming part of the Lachlan orogen in New South Wales. The Hill End trough was deformed in the Middle Devonian (Tabberabberan orogeny), forming tight, N-S–trending, macroscopic D2 folds (Hill End anticline) with S2 slaty cleavage and associated bedding-parallel veins. Structural analysis indicates that the D2 flexural-slip folding mechanism formed bedding-parallel movement zones that contained flexural-slip duplexes, bedding-parallel veins, and saddle reefs in the fold hinges. Bedding-parallel veins are concentrated in weak, narrow shale beds between competent sandstones with dip angles up to 70° indicating that the flexural slip along bedding occurred on unfavorably oriented planes until fold lockup. Gold was precipitated during folding, with fluid-flow concentrated along bedding, as fold limbs rotated, and hosted by bedding-parallel veins and associated structures. However, the gold is sporadically developed, often with subeconomic grades, and is associated with quartz, muscovite, chlorite, carbonates, pyrrhotite, and pyrite. East-west shortening of the Hill End trough resumed during the Late Devonian to early Carboniferous (Kanimblan orogeny), producing a series of steeply W dipping reverse faults that crosscut the eastern limb of the Hill End anticline. Where W-dipping reverse faults intersected major E-dipping bedding-parallel veins, gold (now associated with galena and sphalerite) was precipitated in a network of brittle fractures contained within the veins, forming moderately S plunging, high-grade gold shoots. Only where major bedding-parallel veins were intersected, displaced, and fractured by late W-dipping reverse faults is there a potential for localization of high-grade gold shoots (>10 g/t). A revised structural history for the Hill End area not only explains the location of gold shoots in the Reward mine but allows previous geochemical, dating, and isotope studies to be better understood, with the discordant W-dipping reverse faults likely acting as feeder structures introducing gold-bearing fluids sourced within deeply buried Ordovician volcanic units below the Hill End trough. A comparison is made between gold mineralization, structural style, and timing at Hill End in the eastern Lachlan orogen with the gold deposits of Victoria, in the western Lachlan orogen. Structural styles are similar where gold mineralization is formed during folding and reverse faulting during periods of regional east-west shortening. However, at Hill End, flexural-slip folding-related weakly mineralized bedding-parallel veins are reactivated to a lesser degree once folds lock up (cf. the Bendigo zone deposits in Victoria) due to the earlier effects of fold-related flattening and boudinage. The second stage of gold mineralization was formed by an array of crosscutting, steeply W dipping reverse faults fracturing preexisting bedding-parallel veins that developed high-grade gold shoots. Deformation and gold mineralization in the western Lachlan orogen started in the Late Ordovician to middle Silurian Benambran orogeny and continued with more deposits forming in the Bindian (Early Devonian) and Tabberabberan (late Early-Middle Devonian) orogenies. This differs from the Hill End trough in the eastern Lachlan orogen, where deformation and mineralization started in the Tabberabberan orogeny and culminated with the formation of high-grade gold shoots at Hill End during renewed compression in the early Carboniferous Kanimblan orogeny.

Non-collisional, convergent margin orogens are generally called accretionary orogens, although there may not have been horizontal accretion across the plate boundary. We revive the term non-collisional orogen and use a Gondwanaland perspective to discuss different types. On the northern margin of the Australian Plate, the New Guinea non-collisional, accretionary orogen was formed by large-scale terrane accretion across an advancing plate margin. On the eastern margin, the Southwest Pacific Orogen is a non-collisional and non-accretionary orogen, involving virtually no horizontal transfer of material across its eastward-retreating plate boundary. In the Tasmanides, the Lachlan Orogen, commonly described as an accretionary orogen, is another non-collisional, non-accretionary orogen developed behind the plate margin after major Cambrian rollback, with resultant backarc basins filled mainly by quartz-rich turbidites subsequently recycled. The outboard New England Orogen is a non-collisional but accretionary orogen, marked by the frontal accretion of continental margin arc detritus, subsequently recycled into younger arcs. The Permian to Cretaceous Rangitata Orogen of New Zealand is an ?oblique non-collisional, accretionary orogen in which Permian–Triassic sediments of the accretionary wedge have no link with inboard (near) arc terranes. Late Jurassic to Cretaceous parts were sourced by a combination of first cycle volcanogenic detritus passing through the forearc basin together with recycling of the exhumed parts of the wedge. All non-collisional orogens involve continental growth, but only the New England Orogen and to a lesser extent the New Guinea Orogen involve significant crustal growth.

Abstract. The New England Orogen, eastern Australia, was established as an outboard extension of the Lachlan Orogen through the migration of magmatism into forearc basin and accretionary prism sediments. Widespread S-type granitic rocks of the Hillgrove and Bundarra supersuites represent the first pulse of magmatism, followed by I- and A-types typical of circum-Pacific extensional accretionary orogens. Associated with the former are a number of small tholeiite–gabbroic to intermediate bodies of the Bakers Creek Suite, which sample the heat source for production of granitic magmas and are potential tectonic markers indicating why magmatism moved into the forearc and accretionary complexes rather than rifting the old Lachlan Orogen arc. The Bakers Creek Suite gabbros capture an early ( ∼ 305 Ma) forearc basalt-like component with low Th ∕ Nb and with high Y ∕ Zr and Ba ∕ La, recording melting in the mantle wedge with little involvement of a slab flux and indicating forearc rifting. Subsequently, arc–back-arc like gabbroic magmas (305–304 Ma) were emplaced, followed by compositionally diverse magmatism leading up to the main S-type granitic intrusion ( ∼ 290 Ma). This trend in magmatic evolution implicates forearc and other mantle wedge melts in the heating and melting of fertile accretion complex sediments and relatively long ( ∼ 10 Myr) timescales for such melting.

AbstractThe Ross Sea is bordered by the Late Precambrian–Cambrian Ross–Delamerian Orogen of East Antarctica and the more Pacific-ward Ordovician–Silurian Lachlan–Tuhua–Robertson Bay–Swanson Orogen. A calcsilicate gneiss from Deep Sea Drilling Project 270 drill hole in the central Ross Sea, Antarctica, gives a U-Pb titanite age of 437 ± 6 Ma (2σ). This age of high-grade metamorphism is too young for typical Ross Orogen. Based on this age, and on lithology, we propose a provisional correlation with the Early Palaeozoic Lachlan–Tuhua–Robertson Bay–Swanson Orogen, and possibly the Bowers Terrane of northern Victoria Land. A metamorphosed porphyritic rhyolite dredged from the Iselin Bank, northern Ross Sea, gives a U-Pb zircon age of 545 ± 32 Ma (2σ). The U-Pb age, petrochemistry, Ar-Ar K-feldspar dating, and Sr and Nd isotopic ratios indicate a correlation with Late Proterozoic–Cambrian igneous protoliths of the Ross Orogen. If the Iselin Bank rhyolite is not ice-rafted debris, then it represents a further intriguing occurrence of Ross basement found outside the main Ross–Delamerian Orogen.

This project investigated an ancient volcanic field in southern NSW to further understand the geological formation of eastern Australia. It examined the timing, chemistry and paleoenvironment of the Comerong Volcanic Complex, situated in the Budawang National Park, NSW. The project used field mapping to record the physical volcanology and to collect representative samples. The samples were then tested for their chemistry by using X-Ray Fluorescence spectrometry and dated using U-Pb isotopic age dating techniques. This study showed the volcanism occurred in the Middle Devonian and was erupted as lava flows and pyroclastic density currents into an intraplate rift setting.

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A geophysical study utilising the method of magnetotellurics (MT) was carried out across southwestern Victoria, Australia, imaging the electrical resistivity structure of the lithosphere beneath the Delamerian and Lachlan Orogens. Broadband MT (0.001-1000 Hz) data were collected along a 160 km west-southwest to east-northeast transect adjacent to crustal seismic profiling. Phase tensor analyses from MT responses reveal a distinct change in electrical resistivity structure and continuation further southwards of the Glenelg and Grampians-Stavely geological zones defined by the Yarramyljup Fault, marking the western limit of exploration interest for the Stavely Copper Porphyries. The Stawell and Bendigo Zones also show change across the Moyston and Avoca faults, respectively. Results of 2D modelling reveal a more conductive lower crust (10-30 Ωm) and upper mantle beneath the Lachlan Orogen compared to the Delamerian Orogen. This significant resistivity gradient coincides with the Mortlake discontinuity and location of the Moyston fault. Broad-scale fluid alteration zones were observed through joint analysis with seismic profiling, leaving behind a signature of low-reflectivity, correlating to higher conductivities of the altered host rocks. Isotopic analysis of xenoliths from western Victoria reveal the lithospheric mantle has undergone discrete episodes of modal metasomatism. This may relate to near-surface Devonian granite intrusions constrained to the Lachlan Orogen where we attribute the mid to lower crustal conductivity anomaly (below the Stawell Zone) as fossil metasomatised ascent paths of these granitic melts. This conductivity enhancement may have served to overprint an already conductive lithosphere, enriched in hydrogen from subduction related processes during the Cambrian. A predominately reflective upper crust exhibits high resistivity owing to turbidite and metasedimentary rock sequences of the Lachlan Orogen, representative of low porosity and permeability. Conductive sediments of the Otway Basin have also been imaged down to 3 km depth southwest of Hamilton.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2016

Masters Research - Master of Philosophy (MPhil)
Recent tectonic evolution models for the Lachlan Orogen are evaluated by examining a key region located at the boundary between the central and eastern provinces; the Tumut trough and western boundary, the Gilmore Fault Zone (GFZ). This distinct structural boundary separates the Ordovician Macquarie Arc volcanics and Silurian-Devonian Tumut trough of the eastern province from Ordovician meta-sediments and ~430 Ma old S-type granites of the Wagga Omeo Metamorphic Belt (WOMB) in the western province. The research focuses on the timing of movement of the GFZ, and the tectonic controls on the dynamics of the Tumut trough, by U-Pb zircon age determination of key stratigraphic and magmatic units in the region. This is augmented with 40Ar/39Ar age determination of synkinematic minerals within high-strain deformation zones, where the kinematic evolution had been determined. The initial focus of the research was to develop a new regional basement map, which was achieved by merging and revising current available regional geology maps and reconstructing associated time-space plots. This map provided the regional tectono-stratigraphic context to choose appropriate samples for age determinations. The major results from this thesis are as follows: (1) Conglomerates and associated shear zones, including the Yiddah and Manna Formation (conglomerates), cannot be correlated without U-Pb age constraints from detrital zircons; (2) The deep marine meta-sedimentary rock of the Trigalong Formation are Early Devonian, not Late Ordovician, which requires the Tumut trough was a deep water basin at this stage; (3) the Bumbolee Formation is Early Devonian, unconformably overlying deformed Silurian sediments - not Ordovician as previously assumed; (4) the Blowering Formation is Early Devonian, not middle Silurian as assumed; (5) the GFZ has a protracted history of sinistral re-activation, from ~415 Ma to 360 Ma, with significant E-W shortening at ~400 Ma; (6) Repeated extension-contraction events (tectonic switching) occurred from Ordovician to Carboniferous. At broadest scale, the orocline model for the Lachlan Orogen appears to be consistent with the information presented, but the geological history is more complex than proposed in that model. In particular, the Tumut Trough appeared to have had two distinct phases of opening, in the middle-Silurian and Early Devonian, separated by a period of intense deformation associated with the Bindian orogeny at ~420 Ma. Also, repeated periods of extension and contraction are evident along the Gilmore Fault, beginning at ~430 Ma with dextral opening of the Tumut trough, but followed by repeated periods of contraction associated with sinistral strike slip deformation at ~415 Ma, 400 Ma, 390 Ma and 360 Ma. Periods of dextral extension are inferred to occur at ~430 Ma, 420-415 Ma, and ~370 Ma, associated with distinct phases of magmatic activity. These periods of repeated extension and contraction are consistent with a tectonic switching model for Lachlan fold belt tectonic evolution.

This study focuses on facies analysis, geochemistry, geochronology and tectonic significance of the Ural Volcanics (UV) and Mount Hope Volcanics (MEV) in the Central Lachlan Orogen in New South Wales. The UV and MHV overlie non-volcanic sedimentary, below wave base, submarine facies within two intracontinental rift basins, the Rast and Mount Hope Troughs. The UV and MHV consist primarily of felsic, coherent facies and associated felsic monomictic breccia facies. These volcanic facies are interpreted to represent submarine lava-sill complexes, which define intrabasinal, effusive, volcanic and shallow intrusive centres. The lTV include at least 35 separate lava or sill emplacement units that amount to ~10 km3 In the MHY, at least 18 lavas and sills are present, and have thicknesses up to ~120 m. The combined volume of the two largest MHV units is estimated to be <1.5 km3 In the Uv, siltstone-matrix monomictic breccia facies is characterised by continuously laminated siltstone matrix between monomictic, non-vesicular, felsic clasts. This facies is interpreted to form from water-settled sediment deposited between lava clasts, and must therefore occur on the upper margin of a lava. The presence of conformable, continuous laminae helps to distinguish this facies from peperite. Hence, correct identification of the siltstone-matrix monomictic breccia facies is critical in distinguishing lavas from sills. The autoclastic facies in the UV and MHV account for up to 10% of single emplacement units. In most cases, the clasts have blocky or slab by shapes and are flow-banded, implying that auto brecciation was the main fragmentation mechanism. Neither in situ or resedimented hyaloclstite are recognised in the UV or MHY, in contrast to other submarine felsic lavas and domes elsewhere. Pumice-rich volcaniclastic facies in the UV and MHV are less voluminous than the coherent and monomictic breccia facies. The UV pumice-rich facies are interpreted to represent felsic pyroclastic facies erupted in a single, open-vent explosive eruption from a local vent and transported in, and deposited from, submarine gravity currents (pumice-rich facies association), and settled from suspension in the water column (fiamme-siltstone breccia facies). Similar syneruptive pyroclastic facies occur in the MHv, but their source has not been identified. Fiamme-bearing facies occur in both the UV and MHv, in fiamme-bearing pyroclastic facies and as pseudoclastic textures. Fiamme textures can also be formed in a variety of other ways. The common genetic use of the term fiamme for textures produced by welding compaction is easily misinterpreted. 'Fiamme' would be better used descriptively to mean elongate lenses or domains of the same mineralogy, texture or composition, which define a pre-tectonic foliation, and are separated by domains of different mineralogy, texture or composition. Results from LA-ICPMS U/Pb dating of zircons indicate that the UV and the MHV were roughly coeval and erupted in the Late Silurian-Early Devonian, within the time period ~420- 410 Ma. Both successions consist of dacites and rhyolites and have A-type to transitional I-type geochemical affinities. High-level, felsic, A-type plutons with myrmekitic and/ or granophyric texture occur in both study areas. Geochemistry suggests they are comagmatic with the volcanic facies. Cross-cutting mafic to intermediate dykes and small intrusions are not co magmatic with the felsic coherent facies. A modern analogue for the UV and lvlHV felsic has not been recognised. The closest analogue is the Late Devonian-Early Carboniferous Iberian Pyrite Belt (IPB). Parts of the IPB contain similar felsic coherent, monomictic breccia facies, and syn-eruptive pyroclastic facies as the UV and MHV The IPB volcanic rocks are also A-type in composition. The numerous similarities of the IPB to the UV and MHV suggest the Australian successions have great potential for hosting volcanic-hosted massive sulfide (VI-IMS) deposits, however, neither previous exploration nor mapping during this study have uncovered any VHMS-related altered zones or prospects.

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A combination of magnetotelluric and geomagnetic depth sounding data were used to attempt to image the electrical resistivity structure of southeast Australia, to investigate the physical state of the crust and upper mantle. A 3D forward model of southeast Australia comprised of regional sets of broadband and long-period magnetotelluric and geomagnetic depth sounding data, over an area of 440 x 300 km2, was used to map broad-scale lithospheric properties. Model results show an order of magnitude decrease in resistivity from the depleted continental mantle lithosphere of the Delamerian Orogen in the west, to the more conducting oceanic mantle of the Lachlan Orogen in the east. The decrease in resistivity in conjunction with a 0.1 km/s decrease in P-wave velocity at depths of 50-250 km, suggest a change in temperature (_T_200_C) due to lithospheric thinning toward the east as the likely cause, in conjuction with a change in geochemistry and/or hydration. A high resolution two-dimensional inversion using data from 37 new and 39 existing broadband magnetotelluric stations mapped crustal heterogeneity beneath the Delamerian Orogen in much greater detail. Lateral changes in resistivity from 10-10 000 m occur over the space of a few kilometres. Low resistivity (_10 m) regions occur at depths of 10-40 km. Narrow paths of low resistivity extend to the surface, coinciding with locations of crustal faults from seismic interpretations. Movement of mantle up these faults, during periods of extension prior to the Delamerian Orogen, may have produced a carbon-rich, low resistivity lower crust, leaving a resistive upper mantle, depleted of volatiles.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Earth and Environmental Sciences, 2012

The Oberon region is dominated by two major lithological successions: The quartzrich turbidite succession is represented by the Adaminaby Group comprising mainly medium- to thick-bedded sandstone, siltstone, shale, and thinly bedded chert with a minimum thickness of 750 m. The Adaminaby Group was deposited on the eastern Gondwana margin in a distal submarine fan. The other succession faulted against the Adaminaby Group is the Rockley-Gulgong Volcanic Belt of the Ordovician Macquarie Arc, which is represented by the Budhang Chert, the Triangle Formation, the Rockley Volcanics, the Fish River Breccia, and the Swatchfield Monzonite. The Budhang Chert is characterized by moderately to highly deformed dark thinbedded chert interbedded with siliceous mudstone ranging between Early to early Late Ordovician (Bendigonian-Gisbornian). The Middle to Late Ordovician Triangle Formation conformably overlies the Budhang Chert and comprises thin- to medium-bedded mafic volcaniclastic fine-grained sandstone and minor conglomerate with common greenschist facies. The Triangle Formation is overlain by Late Ordovician Rockley Volcanics. The Rockley Volcanics are composed of pyroxene-phyric mafic to ultramafic breccia, lava, and volcaniclastic conglomerate and sandstone. The Triangle Formation and the Rockley Volcanics are unconformably overlain by the Fish River Breccia. This is a new unit proposed in this study to describe pyroxene-plagioclase-rich mafic to intermediate volcaniclastic pebbly siltstone breccia occurring near the Fish River 5 km to the east of Oberon. This youngest unit contains minor quartz-rich sandstone clasts which indicate mixing between the Adaminaby Group and the Rockley-Gulgong Volcanic Belt. Comparisons of the overall stratigraphy of the Macquarie Arc rocks in Oberon with the central Molong Volcanic Belt shows that the rocks around Oberon tend to be finergrained and more distal to the volcanic centers that were active in the Ordovicia. Whole-rock geochemistry of the volcaniclastic and volcanic rocks was characterized as shoshonitic to high-K calc-alkalic with the Triangle Formation possibly correlated with Phase 2 magmatism of the Macquarie Arc and the Rockley Volcanics correlated to Phase 4 magmatism. The Fish River Breccia are correlated with the coarse conglomerates at the base of the Waugoola Group. Detrital zircon U-Pb age determination from several quartz-rich sandstones in the Oberon and Black Springs region indicate maximum depositional ages in the Early to Late Ordovician. However, a slightly different provenance in the source of zircons was detected between the Oberon and Black Springs quartz-rich sandstones with a much larger 500 Ma peak in the sandstones from Oberon. The Fish River Breccia contains detrital zircons that are uncommon in volcanic/volcaniclastic rocks of the Macquarie Arc with old continental-derived zircons recorded both in mineral separates and in situ in polished rock mounts suggesting that this unit is post-collisional deposit formed during the Silurian to Early Devonian. U-Pb zircon age determinations and whole-rock geochemistry of intrusive igneous rocks in the Oberon region shows that the Swatchfield Monzonite is a Late Ordovician intrusion that may be made up of several intrusive bodies. The Greenslope Porphyry and Racecourse Porphyry were determined as Early to Middle Silurian and are unrelated to the intrusive suites of the Macquarie Arc. The whole-rock geochemistry, U-Pb age dating, and stratigraphy demonstrate that the Ordovician volcanic rocks of the Oberon region formed in a distal zone relative to the main volcanic centers and are less likely to host Cu-Au mineralization.

Research Doctorate - Doctor of Philosophy (PhD)
Sulfur- and lead-isotope signatures for 64 deposits/systems located in the Central and Easternn Subprovinces of the Lachlan Orogen in eastern New South Wales were characterised in the present study. Here are presented four new ⁴⁰Ar/³⁹Ar dates, 644 new sulfur- and 105 new leadisotope analyses, plus a collation of 386 unpublished and 277 published sulfur isotope and over 560 unpublished and published lead isotope analyses for middle Silurian to Early Carboniferous mineralisation. Measured δ³⁴S values for 22 VHMS deposits range between -7.4‰ to 38.3‰. S-isotope values for Currawang East, Lewis Ponds, Mount Bulga, Belara and Accost (Group 1) range from - 1.7‰ to 5.9‰ with the ore-forming fluids for this group of deposits likely to have been reducing and sulfur derived largely from magmatic sources. By contrast, S-isotope signatures for sulfides from Black Springs, Calula, Captains Flat, Commonwealth, Cordillera, Gurrundah, Kempfield, Peelwood mine, Sunny Corner, The Glen, Wet Lagoon and Woodlawn (Group 2) have average δ³⁴S values between 5.4‰ and 8.1‰. These deposits appear to have formed from ore fluids that were more oxidising than those for Group 1 deposits, representing a mixed contribution of sulfur derived from partial reduction of seawater sulfate, in addition to sulfur from other sources. Four deposits, Elsinora, John Fardy, Mount Costigan and Stringers, have heavier average δ³⁴S signatures (10.1‰ to 13.2‰) than Group 2 deposits, suggesting that these deposits included a greater component of sulfur of seawater origin. The S-isotope data for barite from Black Springs, Commonwealth, Stringers, Gurrundah, Kempfield and Woodlawn range from 12.6‰ to 38.3‰. Over 80% of the δ³⁴S values are between 23.4‰ and 30.9‰, close to the previously published estimates for the composition of seawater sulfate during Late Silurian to earliest Devonian times, providing supporting evidence that these deposits formed concurrently with a Late Silurian volcanic event. New Pb isotope data for eleven VHMS deposits included in the present study support earlier Pb-isotope studies which indicate that lead was largely sourced from the host sequence. However, the data for Black Springs, Elsinora and Commonwealth indicate that some lead, included in these deposits, was sourced from units forming basement to the Silurian troughs. Sulfur isotope values for thirteen orogenic gold systems range between -7.5‰ and 16.1‰ (excluding outliers). The Wyoming One–Myall United system has an average δ³⁴S value of -5.5‰ and a primitive mantle-derived lead isotope signature implying that sulfur and gold were sourced from a fractionated mantle-derived intrusion. The δ-isotope data for Adelong, Bodangora, Calarie, Hargraves, Hill End, London–Victoria, Sebastopol, Sofala–Wattle Flat and Stuart Town are all very similar with average δ³⁴S values close to 0‰ (range -2.8 to 3.4‰). Sulfur in these deposits was derived from reduced fluids, sources from magmatic reservoirs either as a direct input or through dissolution and recycling of rock sulfide. For deposits hosted by the northern HET it is suggested that sulfur and gold were sourced from mantle-derived units located beneath the HET rather than the siliclastic fill of the trough itself. Windeyer and Napoleon Reefs have heavier S-isotope signatures suggesting a greater contribution of sulfur derived from reduced seawater sulfate reservoirs. Springfield, located adjacent to the northern HET, has the heaviest S-isotope signature (15.4 δ³⁴S‰) for orogenic gold deposits included in the present study. For this deposit it is suggested that HET-derived basinal fluids containing reduced seawater sulfate migrated along faults and leached gold from Ordovician mantle-derived units forming basement to that area. Seven sulfide-rich orogenic base metal deposits were included in the present study. Average δ³⁴S values for Currawang South, Frogmore, Montrose, Ruby Creek, Wallah Wallah vary between 3.5‰ and 6.0‰ (Group 1), with Kangiara, and Lucky Hit–Merrilla, having heavier average δ³⁴S values (10.0‰ and 8.2‰ respectively — Group 2). Group 1 deposits are small, and S-isotope signatures suggest significant sulfur was sourced from magmatic reservoirs; whereas, Group 2 deposits are larger and δ³⁴S signatures indicate a larger component of sulfur was derived from reduced seawater sulfate reservoirs. The Pb-isotope data for these deposits suggest that the majority of the lead was derived from older Ordovician and Silurian crustal reservoirs. The data for Mount Werong and Merrilla support a Middle Devonian Pb-model age; whereas, those for Wallah Wallah point to an Early Carboniferous Pb-model age. Browns Reef, in the Central Subprovince, is now interpreted to be a syn-deformational orogenic base metal deposit, for which the S-isotope data are similar to Group 2 orogenic base metal deposits and Pb-isotope data suggest lead was sourced from the fill of the Rast Trough. Five epithermal systems were included in the present study. Bauloora, Bowdens and those in the Yerranderie district are intermediate-sulfidation epithermal systems; whereas, Yalwal and Pambula are low sulfidation epithermal systems. Yerranderie, Yalwal, Pambula and Bauloora have δ³⁴S values close to 0‰. Sulfur in these deposits was derived largely from a magmatic reservoir. The Yerranderie system is zoned with respect to S-isotope distribution and shows mineralogical zonation along the Yerranderie Fault. Yalwal is zoned with 0‰ S-isotope values correlating with sericitic alteration assemblages and heavier S-isotope values (up to 17.9 δ³⁴S‰) correlating with assemblages that include minerals characteristic of argillic alteration. Sixteen middle Silurian to Early Devonian intrusion-related deposits were included in the present study. Collector, Dargues Reef, Mayfield, Ryans, Tallawang, Whipstick and Yambulla are located east of the I–S granite line, with Dargues Reef, Majors Creek, Mayfield, Whipstick and Yambulla hosted by or adjacent to their causative intrusion. These deposits have S-isotope signatures close to 0‰ (range -3.6‰ to 3.0‰) similar to that for granites east of the I–S line (range -1.5‰ to 4.9‰). The Pb-isotope data for these deposits includes both crustal- and mantle-derived lead. Deposits distal to their causative intrusions (Collector and Ryans) have heavier S-isotope signatures (7.7‰ and 4.3‰ respectively) indicating that some sulfur was probably sourced from the host sequence. The majority of lead, for these deposits, was sourced from the host sequence and/or older reservoirs. The S-isotope data for Tallawang suggest that the sulfur was largely sourced from the host sequence. Eight deposits are located to the west of the I–S line. Nasdaq, Phoenix, Tara, Rye Park and Mineral Hill have heavier S-isotope signatures (range: 2.6‰ to 7.3‰) which overlap with the range of values typical of granites located to the west of the I–S line (1.9 to 9.6‰) supporting the interpretation that the majority of sulfur was derived from the causative intrusion. The Pb-isotope data for Nasdaq, Mineral Hill and Tara suggest that lead originated from the host sequence or from older lead reservoirs; whereas, at Rye Park and Phoenix lead was probably sourced from the causative intrusion. Ardlethan and Browns Creek deposits have near 0‰ S-isotope signatures, lower than the range of δ³⁴S values for granites west of the I–S line which is accounted for by mantle-derived volatiles and a possible biogenic sulfur component. The Pb-isotope data for these two deposits are consistent with a lead sourced largely from the causative intrusion; although, some mantlederived lead is probably present. Red Hill has the highest S-isotope signature (13.7‰) indicating that the majority of sulfur was sourced from a seawater sulfate reservoir. ⁴⁰Ar/³⁹Ar dating showed that intrusion-related mineralisation at Tara formed at 420 ± 2 Ma; VHMS-related mineralisation at The Glen (Glen E deposit) formed at 418.2 ± 2.2 Ma; and that the Yerranderie and Bauloora intermediate sulfidation epithermal systems formed at 372.1 ± 1.9 Ma and 371 ± 13 Ma (respectively). New dating plus a review of timing constraints to Tabberabberan and Kanimblan cycle-related mineralisation highlighted metallogenic events at ~430 Ma (intrusion-related), ~420 Ma (intrusion- and VHMS-related) and a mid Devonian epithermal event. The timing of orogenic-related mineralisation is diachronous across the study area with the majority of orogenic gold systems in the west forming during the Middle Devonian Tabberabberan Orogeny; whereas, similar mineralisation in the northern HET formed during the Early Carboniferous Kanimblan Orogeny.

Southeastern Australia, part of the Phanerozoic Tasmanides, is a unique region where large amounts of granite (~30% of the surface rocks) with a very wide range of compositions (S-, I- and A-types) were intruded in the Ordovician to Triassic. The distinctive Carboniferous granites in the Lachlan Fold Belt (LFB) are transitional in time and space between the major magmatic episodes of the LFB and New England Orogen (NEO). There was a contemporaneous continental-arc developed in the NEO, products of which became the dominant source for the NEO Early Permian S-type granites. The Carboniferous granites in the LFB have characteristic compositions (K, Sr and LILE-enrichment and Y-depletion) similar to the Late Permian I-type granites (and to the S-type granites in part) in the NEO. The in situ microanalyses of zircon (both melt-precipitated and inherited; over 1280 grains analysed from 31 samples) from those granites, using SIMS and LA-MC-ICPMS, show that the Carboniferous magmatism in the LFB was closely related to the tectonic movement of the NEO, and that the granites with similar compositions which transect the two contrasting orogens had similar source compositions. From the isotopic compositions of zircon from the Carboniferous granites in the LFB, it is evident that the granites are distributed in zones of different ages and Hf and O isotopic compositions. The zones are approximately parallel to the NEO boundary. It is likely that tectonic activity related to the NEO triggered the production of the Carboniferous magmas and their source rocks. The new data demonstrate, however, that the Carboniferous granites were not directly related to the contemporaneous arc volcanism in the NEO. The source rocks of the Carboniferous granites in each zone consisted of different mixtures between a mantle-like underplate and relatively mature pre-existing lower crust during the Devonian. The distinctive O isotopic compositions of inherited zircon from the NEO S-type granites demonstrate that the source rock of the granites was a Carboniferous arc-related volcanogenic sedimentary pile which included increased amounts of Devonian volcanogenic sediments with time. The age difference between the inherited and melt-precipitated zircon indicates rapid crustal recycling to produce the peraluminous magmas within 15 Ma of source rock deposition. The I-type Moonbi Supersuite granites were generated from the underplate with a minor crustal contribution. As all the studied NEO granites have remarkably similar initial Hf isotopic compositions, the components comprising most of the NEO, including sediments, are similarly radiogenic, probably due to the geologic processes operating in the young accretionary orogen. Combining all the results of U-Pb dating and Hf and O isotopic analyses of zircon from the Carboniferous granites in the LFB and the Permian I- and S-type granites in the NEO, it is also inferred that the source rocks of the studied granites had similar isotopic compositions. This suggests a potential petrogenetic link between the granites across the two orogens. From a source composition similar to that of the most primitive LCG, three igneous components have evolved in different ways depending on the nature of the crustal materials incorporated into each component.