Chemostratigraphic analyses of the Yeneena Basin (Australia) offshore marine succession reveal a prominent similar to 12 parts per thousand negative carbon-isotope excursion within the Tonian strata. Integrated chemostratigraphic and geochronological data from the Yeneena, Amadeus, Officer basins and the Adelaide Rift Complex (Centralian Superbasin) demonstrate that this anomaly, herein defined as the BRISA event (Broadhurst-Isdell Anomaly), is regionally extensive and stratigraphically well constrained. Specifically, the BRISA forms one of two distinct negative Tonian delta C-13 excursions within the Centralian Superbasin. The BRISA excursion occurs in an interval with a maximum depositional age of similar to 960 Ma and a minimum of 837 +/- 6 Ma (sill intrusions). The second excursion occurs in overlying Tonian strata in the Officer Basin, where both anomalies are present, and terminated prior to similar to 752 Ma (basalt). In the Adelaide Rift Complex, indirect stratigraphic correlation suggests a potential age between similar to 827 Ma (by Gairdner-related magmatism) and similar to 788 Ma (tuff horizons). The revised chronostratigraphic framework suggests that the Bitter Springs Anomaly (BSA; similar to 811-788 Ma) in the Amadeus Basin is older (>similar to 837 Ma) than previously interpreted as it correlates with the BRISA. This creates a naming conundrum as the BSA was named after the Amadeus Basin stratigraphy and a proposed name change toward Werji-Assem-Tsedia Excursion (WATE), based on its dated occurrence in Ethiopia is presented. Together, these results demonstrate that Australian Tonian successions record two temporally distinct and stratigraphically separable negative C-isotope excursions that are separated by millions of years (>10 Ma) and consistently expressed across the Centralian Superbasin.

Carbonaceous shales and carbonates within the Neoproterozoic Yeneena Basin in the Paterson Orogen, Western Australia are prospective for sulphide mineralisation, as exemplified by the Nifty copper deposit. However, the tectonic setting of basin formation, its present-day structural architecture, and the kinematic evolution associated with basin inversion remain ill-constrained due to limited exposure. We address this issue by integrating published geological and geophysical datasets with new structural measurements from drill cores, performing subsidence analysis, and constructing four regional-scale balanced cross-sections. Subsidence analysis of the Throssell Range Group reveals an initial phase of rapid subsidence consistent with syn-rift extension, followed by a progressive decrease in subsidence rates indicative of the sag phase. Basin inversion produced folds with predominantly NW-SE trending hinge lines, and systematic variations in bedding-cleavage angles relative to fold geometry indicate that folding occurred via buckling by the flexural shear mechanism. Structural relationships suggest that deformation initiated in the northeastern part of the basin, where sedimentary rocks and underlying basement were folded first, followed by the reactivation of basement normal faults as reverse faults that transected these folded structures. Deformation subsequently propagated southwestward across the basin. Restoration indicates the presence of horsts that segmented the basin into smaller subbasins. We estimated a minimum shortening of similar to 11-21 km (19-30%) from the study area. Forward modelling demonstrates that folding was the dominant mechanism for accommodating shortening rather than reverse faulting. This study presents the first basin-scale structural reconstruction of the Yeneena Basin and offers new insights into its kinematic evolution.

The Stuart Shelf is part of the Adelaide Superbasin overlying the Gawler Craton and Cariewerloo Basin in South Australia. The basin is of interest for sediment-hosted copper mineralisation known to be hosted in numerous stratigraphic intervals across the region. Therefore, facies analysis and understanding of spatial distribution of host units are essential for exploration targeting and mineral systems research. Our study presents improved and new definitions of Cryogenian and Ediacaran Stuart Shelf stratigraphy, and a detailed, regional-scale sequence stratigraphic analysis. The Cryogenian non-glacial interlude was of particular interest, as it includes the Tapley Hill Formation, a known host for copper mineralisation. The succession of Tapley Hill Formation (including Sturtian cap carbonates), Brighton Limestone and Angepena Formation represents a third-order depositional cycle, an equivalent to the lowermost cycle of the Cryogenian non-glacial interlude in the adjacent Adelaide Rift Complex. The Ediacaran post-glacial succession includes the Nuccaleena Formation and Tent Hill Formation and is interpreted as a second-order depositional cycle. The Sturtian and Marinoan cap carbonates form regional stratigraphic marker horizons and were deposited in a transgressive systems tract. Variations in facies and thickness can be linked to development of localised depocentres and topographic highs, such as the Pernatty High. Modelling of 3D surfaces reveals a shift in the basin orientation between the Cryogenian and Ediacaran sedimentation from an NNW-SSE axis towards a N-S axis. The Stuart Shelf sequence stratigraphic framework provides new insights in the basin sedimentology and evolution, which aids sediment-hosted mineral systems analysis and improves the understanding of Cryogenian and Ediacaran basin evolution in Australia. KEY POINTS 1.The Cryogenian non-glacial interlude on the Stuart Shelf represents a third-order depositional cycle. 2.The Pernatty High develops during deposition of the Cryogenian successions. 3.The Stuart Shelf basin orientation shifts from NNW-SSE during the Cryogenian towards N-S in the Ediacaran. 4.3D stratigraphic surfaces aids copper exploration targeting in sediment-hosted mineral systems.

The ca 1640 Ma Barney Creek Formation is a mostly fine-grained silicicastic unit of the McArthur Group in the southern McArthur Basin of northern Australia. It is one of the most prospective units for clastic-dominated (CD-type) Zn-Pb deposits in the world, hosting the giant McArthur River Zn-Pb-Ag and the Teena Zn-Pb deposits. The Barney Creek Formation records deposition of dominantly dolomitic siltstone turbidite facies at or below storm wave base. These strata were deposited in a series of sub-basins and on submerged paleohighs that formed in response to roughly north-south extension during early Barney Creek times. A detailed, regional-scale sequence stratigraphic analysis based on 20 wells indicates that the middle McArthur Group (Emmerugga Dolostone to Lynott Formation) comprises six third-order depositional sequences, of which the Barney Creek Formation includes two (named B1 and B2). These two sequences and the overlying sequence L1 (Reward Dolostone and lower Lynott Formation) record significant lateral facies and thickness changes across the southern McArthur Basin. These variations can be explained by a geographical shift in the depocentre during structural re-organisation of the basin. The depocentre migrated from the south, where accommodation was mostly created during deposition of sequence B1, towards the north during deposition of sequence B2.

The Granites-Tanami Orogen (GTO) is a lower-greenschist to amphibolite facies succession of >1840 Ma backarc basalts and volcaniclastic-sedimentary rocks that was metamorphosed (similar to 1850-1840 Ma), and later intruded by granites and granodiorites (similar to 1825-1791 Ma) during assembly of the Kimberley Craton, proto-Northern Australia Craton, and the Arunta Region. The data presented here show geochronological, sedimentological, petrographic, and geochemical evidence for the existence of a volcanic arc ('Tanami Arc') in the GTO at similar to 1912 Ma. Furthermore, the combination of volcanic structures, including fiamme and hyaloclastites, and a mafic HFSE geochemical signature of the pyroclastic and volcaniclastic-sedimentary turbidite successions suggests a syndepositional volcanic front within an oceanic arc-backarc system during deposition of the Dead Bullock Formation (and equivalents). Geochemical vectors applied to existing stratigraphic interpretations indicate a trend towards more felsic composition with younging, providing an alternative proxy for relative stratigraphy and a tool for exploration and correlation across the GTO. The localisation of the volcanic arc within the N-NNE dipping arc-continent collision zone has important implications for the debated Palaeoproterozoic amalgamation of the North Australia Craton.

The Bigrlyi deposit is a tabular, sandstone-hosted, uranium–vanadium deposit of Carboniferous age located in the Ngalia Basin of central Australia. The deposit is similar to the continental, fluvial Saltwash-type of sandstone-hosted U-V deposits which are well known from the Colorado Plateau, USA. Most mineralization at Bigrlyi occurs as thin, multiple-stacked, stratiform lenses at the base of fluvial channels near the contact between a grey sandstone succession and a hematitic, purple–red sandstone succession. A larger halo of lower grade vanadium mineralization extends beyond the main U-V-mineralized zone. The host is an immature, feldspathic sandstone, grading into arkose and lithic-rich variants. Lithic ‘rip-up’ clasts of clay-rich sediments are common in the basal parts of fluvial channels, and are frequently the focus of, and have acted as sites for, U-V mineralization. Coffinite and uraninite are the main uranium minerals, with the former dominant. Vanadium is mainly hosted by Fe-V-bearing clays and chlorite, including roscoelite, grading into vanadian illite, the interlayer mineral corrensite, and altered detrital biotite. The V-Fe–oxyhydroxide minerals montroseite, haggite and doloresite, and altered detrital Fe-Ti oxides, are minor V-hosts. Mineralized zones correlate with enrichments in Se, Li, Ba, Be, Mo, Mg and Fe, and elevated Se/S ratios are characteristic of U-mineralized zones. Petrographic studies show that a heterogeneous mixture of variably mineralized lithic clasts is present; in the same rock, some clasts are Fe-rich and only weakly U-V-mineralized, while other clasts are strongly V- and/or U-mineralized. These observations point to mineralization processes that did not take place in-situ in the host sandstone at the site of deposition as required by conventional groundwater models. Lead isotope results provide evidence of the open-system mobility of radiogenic elements in parts of the deposit. In V-bearing zones, radiogenic Pb contents were found to be unsupported by current U levels, suggesting that over time U has been mobilized from these zones and redistributed, resulting in U-enrichment in other parts of the deposit. Mobility pathways were likely open over time from early in the history of the Bigrlyi deposit. A hybrid mineralization model, involving an interplay between solution-precipitation processes, detrital transport and post-depositional U remobilization, is proposed for Bigrlyi. Ferrous-ion-bearing clay minerals and pyrite are considered to be the most likely primary reductants/adsorbents, while the deposit is lacking carbonaceous matter.

The Palaeoproterozoic Granites-Tanami Orogen in central Australia is an important orogenic gold province. Gold mineralisation is hosted by structurally-controlled epigenetic quartz veins with a suggested mineralisation age of ~1805 and ~1795 Ma associated with granitic intrusions. The quartz veins are emplaced in the Tanami Group, which consists of mostly lower-greenschist metamorphic grade volcaniclastic-sedimentary rocks and basalts. The Tanami Group depositional age is between ~1900 and 1850 Ma, and was deposited in an oceanic back-arc basin setting. Due to lack of exposure and the complex structural setting, the stratigraphic evolution of this basin is poorly understood, and regional stratigraphic correlations are difficult. In this presentation, we present sedimentological interpretations together with newly developed geochemical tools for regional-scale correlation. High field strength elements (HFSE) were used to classify basalts in different study areas and are interpreted to be geochemically affiliated with either backarc basin (Supplejack area) or volcanic arc (Capstan and Bluebush areas). Massive pyroclastic flow deposits and interflow sedimentary rocks have a mafic geochemical signature close to a basaltic composition of intermittent basalt flows. In contrast, thinly bedded to laminated volcaniclastic-sedimentary rocks have an increasingly more andesitic to dacitic composition and are overlying the massive mafic-derived successions. It is interpreted that the change in composition is related to changing igneous composition in a maturing volcanic arc. Therefore, we can use the geochemical composition for the volcaniclastic-sedimentary rocks of this succession as relative age and depositional environment indicator in a deformed, partly preserved oceanic basin succession that is poorly exposed and lacks drill core data.

© Northern Territory of Australia (NT Geological Survey) 2019. With the exception of logos and where otherwise noted, all material in this publication is provided under a Creative Commons Attribution 4.0 International licence (https://creativecommons.org/licenses/by/4.0/legalcode). 1 CSIRO Mineral Resources, CSIRO Mineral Resources, 26 Dick Perry Avenue, Kensington WA 6151, Australia 2 Email: heather.sheldon@csiro.au 3 Northern Territory Geological Survey, GPO Box 4550, Darwin NT 0801, Australia Introduction

Early Cambrian black shales of the Niutitang Formation are found across the Yangtze Platform in a 1600-km belt extending across south China. A thin organic matter-rich layer in the lowermost part of this formation contains exceptional concentrations in Mo, Ni, Se, Re, Os, As, Hg, Sb, Ag, Au, Pt, Pd, and Ag. Due to their extreme metal enrichment, these black shales provide a rare opportunity to study the interface between semi-metals, metals and biogenic material. We report the first detailed μm-scale investigation of metal distributions and associations in samples from two sites, Zunyi and Sancha, located hundreds of km apart, using a combination of analytical techniques including X-ray fluorescence (XRF) mapping, scanning electron microscopy (SEM), Synchrotron-based XRF mapping, electron probe micro-analyser (EPMA), particle induced x-ray emission (PIXE) probe and x-ray absorption near-edge structures (XANES) imaging. Strong μm-scale variations in metal and semi-metal distributions were highlighted by Synchrotron-based XRF mapping of samples from both sites. At both locations, U is present within phosphorite nodules. Arsenic, Mo and Se are particularly abundant in the organic-rich matrix, showing strong associations with organic matter. Nickel, however, shows different distributions between the two sites. It is mainly present in association with the organic matter at the Sancha site while it is found in abundance in millerite at the Zunyi site, suggesting slightly different local conditions at Zunyi favouring Ni-S associations over Ni-organic matter. At both sites, biogenic structures were re-mineralised with laminations dominated by different metals, indicating a likely control of organic matter over metal distributions. In addition, the XANES imaging highlighted different redox states of As over μm-scale areas. While As−1 appears to be mainly present in pyrite, As+3 was mainly detected in association within the carbon and MoS2 mixed layer phase (MoSC). Overall, the present results emphasize the complexity of metal associations in this mineralised layer, the significant role of organic matter in the accumulation and precipitation of metals and semi-metals in these metalliferous shales and highlight how biogenic activity can induce μm-scale variations in redox conditions in sediments.

The McArthur Basin is part of a Proterozoic basin system on the North Australian Craton that represents a world.class Zn-Pb province. Ore bodies are typically stratiform and hosted by pyritic, organic-rich, and dolomitic siltstones deposited in local depocenters and sub-basins. The mineralization is characterized by syngenetic and/ or diagenetic textures. These characteristics highlight the need to understand the sedimentological and structural evolution of the basin for mineral exploration. Here we report a facies analysis of the middle McArthur Group (Tooganinie to Lynott formations) in the southern McArthur Basin, distinguishing four facies associations and 19 lithofacies. Depositional environments range from slope and deep subtidal settings to supratidal sabkhas. The middle McArthur Group records a systematic similar to 3.5 parts per thousand shift in the carbon isotope ratio of carbonates (delta(13) C-carb) that can likely be used for basin-wide or even global correlation. The Barney Creek Formation, the main Zn-Pb host unit, was mostly deposited under deep subtidal to slope conditions, although shoaling to shallow subtidal environments locally occurred on paleohighs. Together with the overlying Reward Dolostone, it comprises two 3rd-order transgressive-regressive sequences, which distinguishes it from the younger and less prospective but lithologically similar Caranbirini Member, which only comprises one incomplete sequence. The HYC Pyritic Shale Member of the lower Barney Creek Formation, which hosts most of the known mineralization, is lithologically similar across the studied area, and reflects significant deepening of the entire basin. A maximum flooding surface in the HYC Pyritic Shale Member represents the most pyritic and organic-rich interval and can be developed as a black shale in sub-basin depocenters. It represents an ideal chemical trap for base metals in syngenetic models for mineralization; however, lithification and compaction would convert this black shale interval into a physical trap in diagenetic models. Regardless of the preferred model, sequence stratigraphy integrated with facies maps can be used for targeting.

Lower Cambrian (Tommotian) black shales of the Niutitang Formation, South China, host a thin accumulation (5-20 cm) of Ni, Mo, platinum group elements (PGE)-Au, Ni, As, Zn, Cu, V and rare earth elements (REE). Of all known deposits, the late Devonian Ni-Mo-PGE sulphide horizon in black shales of the Nick deposit, Selwyn Basin in Canadian Yukon, presents the strongest similarity with the Niutitang Formation polymetallic layer. In the present study, samples of the mineralised layer and host shales in South China from two mine sites (Zunyi and Sancha) were investigated in order to further characterise the prevailing redox conditions and mechanisms involved in the metal concentration process at both sites. Additional comparison with the Nick deposit mineralised layer was also undertaken. Bulk geochemical analysis (including PGE analysis) were conducted on all samples, along with pm-scale investigation of metal distributions and associations by X-ray fluorescence (XRF) mapping and Synchrotron XRF mapping. The comparison of the two sites from South China highlights strong similarities in metal enrichment factors. PGE and REE distribution patterns are also highly similar and suggest a source from seawater. Strong variations in elemental distributions at m-scale were observed at both sites, most likely related to intense variations in redox conditions in the sediment. The comparison with the Nick deposit highlights a stronger enrichment in Ni and Zn in the Nick deposit and a greater variety of minerals in the Niutitang shales. The PGE and REE distributions of both the Nick deposit and the Niutitang shales, however, present highly similar patterns, and support an origin from seawater. The present study provides further insight into mineralisation style and processes in these mineralised black shales, highlighting the importance of redox conditions and re-emphasizing the role of organic matter in the formation of these mineralised layers.

The Cambrian Paibian sedimentary succession of the central Australian Amadeus Basin contains a sequence of supratidal to subtidal shallow marine siliciclastic and oolitic, stromatolitic limestones and dolostones. Basin wide sequence stratigraphy in combination with biostratigraphy revealed the G. stolidotus Zone within a 3rd order transgressive systems tract (TST). The westward transgression caused changes from a fluvial-dominated depositional environment towards a shallow-marine oolitic carbonate shoal environment. The eastern succession is dominated by stromatolitic, oolitic carbonate rocks with 2- to 5-m 5th-order shoaling upward cycles with several 4th-order cycles. The change from TST to HST (highstand systems tract) is marked by a maximum flooding surface within the Goyder Formation, which coincides with the peak of the Steptoean Positive Carbon Isotope Excursion (SPICE). The SPICE shows a facies-independent, synchronous positive delta C-13 excursion of 5 parts per thousand in a 130 m interval in 8 sections across a similar to 460 km transect. The SPICE peak is lowest in the nearshore successions (+ 0.4 parts per thousand delta C-13), and highest in the platform succession (+ 4.9 parts per thousand delta C-13) and is interpreted to be related to the chemical gradient of seawater and mixing of the DIC with atmospheric CO2-derived (i.e. terrestrial) bicarbonate. The recovery from SPICE is recorded by 4th-order shoaling upward cycles that compose the 3rd-order HST. This is the first time that sequence stratigraphy and biostratigraphy has been combined with carbon isotope chemostratigraphy across the nearshore to subtidal Cambrian basin succession in Australia.

The Caranbirini sediment-hosted Zn-Pb-Ag prospect is located west of the Emu Fault, ~20 km north of McArthur River Mine (formally HYC), within the Batten Fault Zone of the McArthur Basin (Northern Territory). The Caranbirini area exposes stratigraphy from McArthur Group and shows some structural complexity with post-depositional folding and faulting. In order to better characterize the subsurface basin architecture we combine structural, sedimentological, and stratigraphic interpretations with 3D gravity inversion, and a 1D airborne electromagnetic inversion. Results are integrated to build a 3D model of the subsurface basin architecture, and identify prospective stratigraphy such as the Barney Creek Formation. 3D gravity inversions were performed using a preliminary 3D geological model of the project area as a reference model for a constrained property inversion. The gravity inversion identified an anomalous density zone immediately west of the Emu Fault. Interpretation of the inverted AEM data provided stratigraphic constraint for the geological model by defining the depth and geometry of the Barney Creek Formation. They also indicated the presence of several N-S trending faults to the west of the Emu Fault coincident with the western boundary of the anomalous density zone. The interpretation suggests that the depth to the Barney Creek Formation increases westwards of the Emu Fault. We interpret the increase in depth to the Barney Creek Formation, in combination with the zone of increased density as a fault-bounded sub-basin, bounded in the west by a paleo-high. Recognition of the sub-basin and controlling faults has implications for targeting Zn-Pb-Ag mineralization.

The sedimentary succession of the central Australian Amadeus Basin consists of Neoproterozoic to Carboniferous sedimentary rocks and contains shallow marine, subtidal carbonates of Middle to Late (Series 2 to Furongian) Cambrian age. A combination of sequence stratigraphy, geochemistry and mineralogy shows a transgressive 2nd order cyclicity deposited between ~511–490Ma and a change from arid, low energy to humid, high energy depositional environments. This is reflected in an initially evaporitic sequence with upward decreasing halite and anhydrite abundance and transition from oxygenated to anoxic conditions, reflected by the Fe mineral species change from hematite to pyrite during transgression. Sequence boundaries of several 3rd order cycles consisting of HST carbonate rocks and LST siltstones, correlate with globally recognised sequence boundaries linked to the inferred eustatic sea level record for the upper two series of the Cambrian System. The carbon isotope record for this ~1400m thick succession in combination with biostratigraphic age correlation allowed the identification of the globally recognised Steptoean Positive Carbon Isotope Excursion (SPICE), Drumian Carbon Isotope Excursion (DICE) and Redlichiid-Olenellid Extinction Carbon Isotope Excursion (ROECE).

The Neoproterozoic sedimentary succession of the Amadeus Basin, Central Australia, includes potential hydrocarbon source and reservoir rocks with maturity indicators in the oil to dry-gas window. However, petroleum well distribution across the basin is sparse and a general lack of organic geochemical data encourages the use of whole-rock inorganic geochemistry and mineralogy as proxy for the evaluation of the hydrocarbon-generating potential. The present study provides a detailed investigation of the geochemistry and mineralogy of the majority of Neoproterozoic strata across the Amadeus Basin and suggests that the Pertatataka and Aralka formations are the most favourable potential source rocks. A decreasing K/Rb ratio in these units is interpreted as higher degree of illitisation and therefore increased maturity. Sulphide versus sulphate abundance show that the Pertatataka and Aralka formations are the only units of significant stratigraphic thickness deposited under dominantly anoxic conditions. However, low concentrations of the redox-sensitive trace elements Mo, U and V, and low organic matter abundance suggest that these units were deposited under anoxic-ferruginous, not anoxic-sulphidic (euxinic) conditions. We interpret this to reflect an overall low hydrocarbon-generating potential. The present study highlights the benefit of using a multi-proxy approach for large-scale evaluation of the hydrocarbon potential in sedimentary successions, especially when organic geochemical data are sparse.

The Amadeus Basin displays subtle magnetic anomalies that trace strata for considerable distance, highlighting complex folding patterns. Magnetic modelling techniques can be utilised on these stratiform anomalies to extrapolate the near-surface structure of the basin. However, because of the mathematical trade-off between the dip and magnetisation of bodies, the dips of the bodies cannot be known unless the magnetisation is also known. Normally it would be optimal to measure the magnetisation, but this is not always possible or feasible. In this study, we investigate the relationships between dip and magnetisation using an approach that would generally be considered a little backward, i.e. constraining magnetisation direction using geological data. Three study areas were chosen to investigate a number of stratigraphic horizons, the Waterhouse Range, Glen Helen and Ross River areas. Modelling results suggest that some layers primarily retain induced magnetisation, remanence is dominant in others, but both are present in most. Remanence is mainly associated with relatively oxidised units that contain only hematite (e.g. Arumbera Sandstone), and we have demonstrated that these magnetisations predate folding of the Ross River Syncline. In some cases, the anomalies represent redox zonation within units, e.g. the Pertatataka Formation near Glen Helen, where discrete magnetic layers correspond to thin grey (reduced, magnetite-rich) horizons interbedded with more prevalent red (oxidised, hematite-rich) horizons. We also found that where magnetised units are relatively thin and occur near the surface, their magnetic response is sharp, and in aeromagnetic data such adjacent anomalies commonly overlap to form a single anomaly, thus misrepresenting the magnetic field, and mis-mapping the actual magnetic horizons. While the magnetic properties of the causative bodies are variable, we have demonstrated that a better understanding of the magnetic properties of these magnetised horizons can be used to provide insights into the structure and tectonic history of the Amadeus Basin.

The Paleoproterozoic McArthur Basin (McArthur Group) of northern Australia hosts world-class sedimentary 'exhalative' (SEDEX) McArthur type Zn-Pb deposits, which are largely hosted within a sequence of 1.64 Ga pyritic carbonaceous shales deposited in an extensional rift setting. A well-known example of these is McArthur River (or Here's Your Chance [HYC] Zn-Pb-Ag deposit). The similar to 1.78 Ga McDermott and similar to 1.73 Ga. Wollogorang formations (Tawallah Group) both contain carbonaceous shales deposited in similar environments. Our observations suggest the carbonaceous fades of the Wollogorang Formation were deposited under mostly euxinic conditions, with periodically-high concentrations of sedimentary pyrite deposition. The carbonaceous shales in the older McDermott Formation contain considerably less early pyrite, reflecting a mostly sulfide-poor, anoxic depositional environment. Localized fault-bound sub-basins likely facilitated lateral fades variations, which is evident from synsedimentary breccias.The presence of evaporitic oxidized facies within the McDermott and Wollogorang formations, alongside evidence for synsedimentary brecciation in reduced shales are favourable criteria for SEDEX-style base metal deposition. Both formations overlie volcanic units, which could have been sources of base metals. Detailed X-ray petrography, new geochemical data and sulfur isotope data from historical drill cores indicate multiple horizons of stratiform and sediment breccia-hosted base metal sulfide within carbonaceous shale units, with high-grade Zn concentrations. A close association between sphalerite and ferromanganean dolomite alteration draws comparisons with younger SEDEX mineralization at HYC. Additionally, SEDEX alteration indices, used demonstrably as a vector to the younger orebodies, indicate the sedimentary rocks analyzed in this study are marginally below the ore window when compared to the overlying mineralized stratigraphy.Our data imply that localized active circulation of metalliferous brines occurred in the Tawallah Group basin. High-grade sulfide deposition in reduced facies alteration may represent distal expressions of larger SEDEX-style deposits. Furthermore, abundant pyrite and high molybdenum in the Wollogorang Formation suggest the global oceanic sulfate concentration was sufficient by-1.73 Ga to engender intermittent but strong bottom-water euxinia during shale deposition, thus providing a robust chemical trap for base metal sulfide mineralization. (C) 2016 Elsevier B.V. All rights reserved.

The Cambrian Drumian carbon isotope excursion (DICE) event is a negative carbon isotope (δ13C) excursion. It is associated with the first appearance datum (FAD) of the agnostoid arthropod Ptychagnostus atavus, whose first appearance in the Global boundary Stratotype Section and Point (GSSP) defines the base of the Cambrian Series 3 Drumian Stage. Although this isotopic event has been clearly identified in the Great Basin, USA, it has not been consistently reported in other areas of the world. Here, we report a study integrating isotopic and geochemical data from middle Cambrian (Series 3) sections from the northeastern Georgina Basin, Australia, to investigate the occurrence of the DICE event in Australia and the paleoenvironmental conditions associated with this event. The similarity between the isotopic excursions observed in the Georgina Basin (−2‰ to −3.2‰ δ13C excursion) and that observed in the Great Basin (−2‰ to −3.6‰ δ13C excursion) highlighted the presence of the DICE in Australia and emphasized the potential use of this event for refining global isotopic correlations. The multi-proxy correlation used in this study also showed a pulse of euxinia in association with the DICE, suggesting strongly euxinic conditions near the base of the Drumian Stage.