Cover Sequence Research Articles

Micron- to nanoscale characterisation and U-Pb geochronology of zircon from granites of the Samphire Pluton, South Australia

Zircons from three distinct granites within the Samphire Pluton, South Australia, are characterised at the micron- to nanoscale. Sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon dating generated 207Pb/206Pb weighted average ages of 1586 ± 9.3 Ma, 1583.2 ± 8.5 Ma and 1578 ± 9.5 Ma, respectively. Although zircons from all three granites display evidence of hydrothermal overprinting, this is most strongly expressed in a distinct, red-colored granite referred to here as Granite C. Alteration is expressed as variation in the concentrations of HREE + Y, Th and Pb, whereby grain margins are relatively enriched in these elements and both Zr and Si are depleted. Altered zircon cores have high U contents relative to grain margins, which are appreciably poorer in this element, whereas Th is strongly enriched within crosscutting microfractures. Coupled with the relative enrichment in non-formula elements and marked disturbance of U-Th-Pb isotope ratios, the nanoscale observations of Pb-bearing nanoparticles (galena?) implying mobility of Pb and other elements, nanofractures and structural defects demonstrate that zircon in Granite C has undergone multi-stage alteration impacting upon accurate dating. Importantly, and with implications for analogous systems elsewhere, our results confirm nanoscale open system U-Pb behaviour in Hiltaba Suite zircon. SHRIMP U-Pb zircon geochronology cannot confidently resolve any statistical differences in the age of the three granites, despite their distinct appearance suggesting they might represent temporally distinct phases of a larger magmatic system. Zircons within the most altered Granite (C), directly underlying the Blackbush uranium prospect contain convincing micron- to nanoscale evidence for an alteration event that triggered a remobilisation of uranium from granite into the cover sequence.

Locally Derived, Meteoric Fluid Infiltration Was Responsible for Widespread Late Paleozoic Illite Authigenesis in the Appalachian Basin

AbstractIsotopic and geochronologic investigation of authigenic, K‐bearing clays in the Appalachian Plateau of the northeastern U.S. Midcontinent yields new insights about the tectonic and diagenetic history of the North American sedimentary cover sequence. In situ texture analysis by High Resolution X‐ray Texture Goniometry indicates preservation of bedding‐parallel diagenetic fabrics with burial depths of 2–5 km, and illite mineralization temperatures are spatially variable, ranging from 80 to 190 °C, correlating to similar depths of 3–6 km. The mineralizing geofluid is surface derived, with δD values ranging from −48‰ to −72‰ (in the range of predicted Pangea meteoric fluid). In addition, we find that mineralizing fluid δD values increase away from the orogenic front, consistent with a rain shadow effect from the high elevation Appalachian orogen. The age of authigenic illite is constrained by 40Ar/39Ar geochronology to 308–318 Ma, reflecting Upper Carboniferous diagenesis. We postulate that far‐field stress transmission from continent‐continent collision created regional permeability pathways for surface fluids, altering the hydrologic architecture of the brittle crust and allowing meteoric fluid infiltration into upper crustal rocks. This interpretation challenges the popular view of tectonically forced, lateral fluid flow from the Appalachian orogen (squeegee hypothesis).

Terrestrial kaolin deposits trapped in Miocene karstic sinkholes on planation surface remnants, Transdanubian Range, Pannonian Basin (Hungary)

AbstractIn the Transdanubian Range, Pannonian Basin, Hungary, karstic sinkholes on a planation surface of Triassic carbonates are filled by grey clayey–silty kaolin deposits. The provenance and accumulation age of these strongly altered terrestrial karst-filling sediments are constrained by X-ray powder diffraction, heavy mineral analysis and zircon U–Pb dating. The heavy minerals of the Southern Bakony Mountains samples are dominated by the ultra-stable zircon–rutile–tourmaline association. Zircon U–Pb data indicate accumulation between 20 and 16 Ma. Furthermore, Archaean to Palaeogene grains were also determined, reflecting the principally fluvial recycling of Eocene bauxites and their cover sequences. In contrast, the sample from the Keszthely Hills consists almost exclusively of airborne material including zircons of 18–14 Ma, reflecting a dominant contribution from the Carpathian–Pannonian Neogene volcanism. The shift in the Miocene age components is inferred to have been caused by the landscape evolution and burial history of the planation surface remnants controlled by local block tectonics.

Interpretation of buried basement in the southwestern Athabasca Basin, Canada, from integrated geophysical and geological datasets

Recent discoveries of basement-hosted uranium deposits in the Patterson Lake corridor in the southwestern Athabasca Basin of Canada have brought vigorous exploration interest to the region. New lithostratigraphic constraints, geochronology and airborne geophysical surveys have dramatically improved the understanding of the host basement geology, warranting a re-examination of the remote predictive mapping and geophysical responses of the buried basement rocks. This study took a two-step approach to examine the regional basement geology and architecture. First, a mosaic of the long-wavelength response of potential field (gravity and magnetic) datasets was examined to divide the basement into regional domains based on bulk physical property variations. The interpretive geological model was then refined using textural and lineament analysis of new airborne gravity and magnetic datasets, geological drill hole logs and magnetic susceptibility measurements. The new basement map identifies and updates major features including a crustal-scale structure that separates the southern Tantato Domain from the newly defined eastern Taltson Domain. This structure may have played a role in localizing fluid flow in the Patterson Lake corridor, defining the spatial extents of structurally controlled buried felsic intrusions, and redefines the boundaries of the Taltson, Clearwater and Tantato Domains. In addition, the potential field enhancements delineated significant regional faults that controlled the geometry of Paleoproterozoic cover sequences and have implications for understanding the crustal architecture of the southern Rae Province. These new interpretations shed light on the tectonic history of the region to support on-going exploration activities and delineate regionally prospective areas in this understudied area of the Canadian Shield. Thematic collection: This article is part of the Uranium Fluid Pathways collection available at: https://www.lyellcollection.org/cc/uranium-fluid-pathways

A Mineralisation Age for the Sediment-Hosted Blackbush Uranium Prospect, North-Eastern Eyre Peninsula, South Australia

The Blackbush uranium prospect (~12,580 tonnes U at 85 ppm cut-off) is located on the Eyre Peninsula of South Australia. Blackbush was discovered in 2007 and is currently the single example of sediment-hosted uranium mineralisation investigated in any detail in the Gawler Craton. Uranium is hosted within Eocene sandstones of the Kanaka Beds and, subordinately, within a massive saprolite derived from the subjacent Hiltaba-aged (~1585 Ma) granites, affiliated with the Samphire Pluton. Uranium is mainly present as coffinite in different lithologies, mineralisation styles and mineral associations. In the sandstone and saprolite, coffinite occurs intergrown with framboidal Fe-sulphides and lignite, as well as coatings around, and filling fractures within, grains of quartz. Microprobe U–Pb dating of coffinite hosted in sedimentary units yielded a narrow age range, with a weighted average of 16.98 ± 0.16 Ma (343 individual analyses), strongly indicating a single coffinite-forming event at that time. Coffinite in subjacent saprolite generated a broader age range from 28 Ma to 20 Ma. Vein-hosted coffinite yielded similar ages (from 12 to 25 Ma), albeit with a greater range. Uraninite in the vein is distinctly older (42 to 38 Ma). The 17 ± 0.16 Ma age for sandstone-hosted mineralisation roughly coincides with tectonic movement as indicated by the presence of horst and graben structures in the Eocene sedimentary rocks hosting uranium mineralisation but not in stratigraphically younger sedimentary rocks. The new ages for hydrothermal minerals support a conceptual genetic model in which uranium was initially sourced from granite bedrock, then pre-concentrated into veins within that granite, and is subsequently dissolved and reprecipitated as coffinite in younger sediments as a result of low-temperature hydrothermal activity associated with tectonic events during the Tertiary. The ages obtained here for uranium minerals within the different lithologies in the Blackbush prospect support a conceptual genetic model in which tectonic movement along the reactivated Roopena Fault, which triggered the flow of U-rich fluids into the cover sequence. The timing of mineralisation provides information that can help optimise exploration programs for analogous uranium resources within shallow buried sediments across the region. The model presented here can be predicted to apply to sediment-hosted U-mineralisation in cratons elsewhere.

New paleontological evidence for complex middle Paleozoic tectonic evolution in the Appalachian western Blue Ridge

Abstract Reconstructing the tectonic evolution of the southern Appalachian metamorphic internides is hampered by the relative paucity of accurate geochronologic constraints and the apparent rarity or absence of Paleozoic cover sequences. At the orogen’s greatest width, near the junction of Georgia, North Carolina, and Tennessee, the western Blue Ridge is a composite metamorphic allochthon of three major thrust sheets: (A) a basal sheet above the Great Smoky fault overlying rocks of the foreland thrust belt composed of the Lower Cambrian Chilhowee Group and underlying Sandsuck Formation of the Neoproterozoic Walden Creek Group; (B) an intermediate sheet above the Maggies Mill–Citico fault composed of the middle Paleozoic Maggies Mill Formation; and (C) the main mass of the western Blue Ridge above the Alaculsy Valley–Miller Cove fault composed of the Neoproterozoic Ocoee Supergroup, and younger overlying sequences in the Epperson and Murphy synclinoria. The age of peak deformation and metamorphism in all of these sequences has historically been assigned to the Ordovician Taconic orogeny, but recent paleontologic discoveries suggest these events are significantly younger. In addition to the middle Paleozoic fauna recently reported from the Maggies Mill Formation in the intermediate thrust sheet, Silurian-Devonian conodonts have been found in units formerly correlated with the Walden Creek Group in the Epperson synclinorium. These discoveries suggest that widespread middle Paleozoic successor basin sequences unconformably overlie the Neoproterozoic-Cambrian drift-facies of the Chilhowee Group (and equivalents) and underlying rift-facies of the Ocoee Supergroup, and require modifications to existing models for the timing of the region’s stratigraphic framework and tectono-metamorphic evolution.

Mineralogy as a proxy to characterise geochemical dispersion processes: A study from the Eromanga Basin over the Prominent Hill IOCG deposit, South Australia

The Early Cretaceous interbedded sandstone, siltstone and mudstone of the Cadna-owie Formation and the reduced mudstone of the Bulldog Shale overlying the Prominent Hill IOCG deposit in South Australia (total tonnage: 140 Mt. @ 1.2% Cu and 0.5 g/t Au; OZ Minerals Limited 2017) are shown to preserve Cu concentrations up to 5043 ppm Cu. These cover sequence materials are approximately 100 m thick over the basement rocks that host the deposit. This study investigates the source of elevated Cu in the cover material by assessing the Cu deportment in these formations and focuses on understanding element migration processes resulting in development of elevated Cu concentrations. Petrographic and QEMSCAN® analysis show that Cu resides within sulphides including high-temperature Cu-sulphides (e.g. bornite) in the Cadna-owie Formation. The Cu-sulphides are associated with Fe-oxides (magnetite) and minerals including pyroxene, amphibole, garnet, chlorite and plagioclase that are interpreted to be detrital and are likely to be of metamorphic origin. Based on these observations, lateral physical processes driven by sedimentary dynamics are interpreted to be the main processes responsible for elevated Cu concentrations in the Cadna-owie Formation in the Prominent Hill area. Chemical migration processes likely had only localised influence and resulted in minor Cu redistribution. QEMSCAN® data collected on samples from the weathering profile of the Bulldog Shale shows that weathering processes (e.g. pyrite oxidation, serpentinisation and feldspar hydrolysis) mostly affect the upper Bulldog Shale and that Eh-pH conditions gradually change with depth from the oxidised and acidic upper Bulldog Shale to the reduced and slightly acidic lower Bulldog Shale. Copper speciation and Eh-pH conditions are used to interpret downward chemical migration of Cu due to weathering as the main process for development of elevated Cu concentrations within the weathered Bulldog Shale in the Prominent Hill area. Upward chemical and lateral physical migration processes may have influenced Cu concentrations within the unweathered Bulldog Shale, however the degree of influence is yet to be determined. Overall this study shows that elevated Cu concentrations in the Early Cretaceous cover sequences overlying the Prominent Hill deposit can be linked back to mineralisation itself and that processes resulting in elevated Cu concentrations include chemical and physical migration.

Utilising geochemical data for the identification and characterisation of mineral exploration sample media within cover sequence materials

A first pass workflow for placing cover sequence materials into four broad lithological groups using A–CNK–FM (Al2O3–CaO + Na2O + K2O–Fe2O3+MgO) and A–CN–K (Al2O3–CaO + Na2O–K2O) ternary diagrams in conjunction with the SiO2 vs Al2O3, Fe2O3 and CaO plus the Ca versus Sr XY diagrams has been derived from lithological logging and laboratory whole-rock geochemistry of 2346 samples. These lithological groups include siliciclastics (quartz sands and clays), weathered material, carbonate lithologies (marine limestone, pedogenic carbonate and compositions intermediate between the two end members) and ferruginous lithologies (including ferricrete and ferruginous sediments). Depositional, weathering and groundwater processes influence sample geochemistry during or after the formation of the material and will influence where the sample will plot on the geochemical diagrams used in this study. Geochemical data for discrete lithologies targeted during sampling (e.g. carbonate lithologies) clusters on diagrams used in the geochemical workflow, whereas data from targeted stratigraphic horizons (e.g. basement–cover interface) are more variable. The ability to characterise rock types that are texturally defined using the geochemical workflow is limited. For instance, the geochemistry of diamictite/conglomerate samples is dependent on the matrix versus clast content and composition as well as the source rock and catchment area. This workflow has the potential to be applied in a mineral exploration environment for rapid interpretation of real-time geochemical (e.g. portable XRF) data to gain an understanding of background geochemistry and geochemical signatures that may be related to underlying mineralisation. Key points A workflow for broad lithogeochemcial characterisation of cover sequence materials has been developed. Uses commonly collected major element plus strontium data acquired by laboratory or portable techniques. Categorises materials into siliciclastics, weathered material, carbonate lithologies and ferruginous lithologies. Applications include a mineral exploration environment for interpretation of large geochemical datasets to understand geology and mineralisation vectors.

Integrating hyperspectral and radiometric remote sensing, spatial topographic analysis and surface geochemistry to assist mineral exploration

Exploration and mining companies in Australia are faced with the challenge of locating deep ore deposits potentially buried under hundreds of metres of cover sequence materials. This research aims ...

Geochemical dispersion processes in deep cover and neotectonics in Coompana, Nullarbor Plain, South Australia

SummaryMineral exploration in regions under thick cover is challenging. This study looked into vertical geochemical dispersion processes through ~550 m of cover in the Coompana Province, South Australia. We collected new data from CDP008 drill hole (~680 m), which contains the most complete record of the cover sequence in this region including: (1) mafic volcanic basement; (2) ~140 m of undifferentiated fluvial sediments (Phanerozoic); (3) overlain by ~230 m of fluvio-lacustrine to marine Mesozoic deposits; and (4) followed by ~200 m of Cenozoic carbonates. Our study revealed that REE patterns in the basalts and the overlying sandstone package show similarities. Yet, no geochemical similarities existed with the Mesozoic units and the upper stratigraphic units. Regolith mapping of this area revealed intricate landscape patterns. These include numerous linear scarps, which trend NW-SE to N-S to NE-SW and experienced <10 m of displacement. When coupled with magnetic data, this scarp trend correlates with basement structural trends at depth and hence these scarps are interpreted as neotectonic features. Based on the geochemistry we concluded that: (1) the lower sandstone package contains a geochemical footprint of the basement rocks produced by vertical and lateral geochemical dispersion; (2) the Mesozoic sediments do not record vertical dispersion related to the underlying basement; (3) the top limestone units are a chemical barrier for vertical geochemical dispersion due to lack of permeability. They are an efficient stratigraphic boundary to produce redox gradients and therefore differential geochemical horizons; and (4) basement features identified from magnetic data are mimicked by linear surface landscape features. We pose that neotectonic surface features may record vertical geochemical dispersion from lower stratigraphic units. The relation between neotectonic structures and landscape geochemistry could have critical implications in mineral exploration under cover in Australia and in other similar landscape settings in the world.

Geophysical and geological interpretation of the Vienna Basin pre-Neogene basement (Slovak part of the Vienna Basin)

Abstract The Vienna Basin is situated at the contact of the Bohemian Massif, Western Carpathians, and Eastern Alps. Deep borehole data and an existing magnetotelluric profile were used in density modelling of the pre-Neogene basement in the Slovak part of the Vienna Basin. Density modelling was carried out along a profile oriented in a NW–SE direction, across the expected contacts of the main geological structures. From bottom to top, four structural floors have been defined. Bohemian Massif crystalline basement with the autochthonous Mesozoic sedimentary cover sequence. The accretionary sedimentary wedge of the Flysch Belt above the Bohemian Massif rocks sequences. The Mesozoic sediments considered to be part of the Carpathian Klippen Belt together with Mesozoic cover nappes of Alpine and Carpathian provenance are thrust over the Flysch Belt creating the third structural floor. The Neogene sediments form the highest structural floor overlying tectonic contacts of the Flysch sediments and Klippen Belt as well as the Klippen Belt and the Alpine/Carpathians nappe structures.

Numerical Simulation Based Targeting of the Magushan Skarn Cu–Mo Deposit, Middle-Lower Yangtze Metallogenic Belt, China

The Magushan Cu–Mo deposit is a skarn deposit within the Nanling–Xuancheng mining district of the Middle-Lower Yangtze River Metallogenic Belt (MLYRMB), China. This study presents the results of a new numerical simulation that models the ore-forming processes that generated the Magushan deposit and enables the identification of unexplored areas that have significant exploration potential under areas covered by thick sedimentary sequences that cannot be easily explored using traditional methods. This study outlines the practical value of numerical simulation in determining the processes that operate during mineral deposit formation and how this knowledge can be used to enhance exploration targeting in areas of known mineralization. Our simulation also links multiple subdisciplines such as heat transfer, pressure, fluid flow, chemical reactions, and material migration. Our simulation allows the modeling of the formation and distribution of garnet, a gangue mineral commonly found within skarn deposits (including within the Magushan deposit). The modeled distribution of garnet matches the distribution of known mineralization as well as delineating areas that may well contain high garnet abundances within and around a concealed intrusion, indicating this area should be considered a prospective target during future mineral exploration. Overall, our study indicates that this type of numerical simulation-based approach to prospectivity modeling is both effective and economical and should be considered an additional tool for future mineral exploration to reduce exploration risks when targeting mineralization in areas with thick and unprospective sedimentary cover sequences.

Structural evolution of the active Waimea-Flaxmore Fault System in the Nelson-Richmond urban area, South Island, New Zealand

ABSTRACTThe Waimea-Flaxmore Fault System (W-FFS) comprises NE-striking, SE-dipping reverse faults superposing Eastern Province terranes on Cenozoic sedimentary units of the Moutere Depression. We present a revised geological map and cross sections of the W-FFS in the Nelson-Richmond urban area, aimed at reconstructing the structural evolution during multiple phases of reactivation. Our data and structural interpretations depict the inversion of the W-FFS from an inherited system of Late Cretaceous-Eocene normal faults to multiple reverse fault splays that propagated through the cover sequence over the last 10 Ma. Fault tip propagation with folding of the cover sequence persisted during the Quaternary, with breaching of the Waimea and Flaxmore faults to the surface and propagation of a splay thrust (Tahunanui Fault) still concealed beneath Quaternary deposits. Ongoing crustal shortening associated with the Pacific-Australian plate boundary in the northern South Island creates favourable conditions for reactivation of the long-lived W-FFS in the contemporary stress field.

Tectonic evolution of the hinterland of the Zagros Orogen revealed from the deformation of the Golpaygan Metamorphic Complex, Iran

In the southwestern part of the Central Iran zone, the Golpaygan Metamorphic Complex (GMC) was evolved during the Zagros orogeny. This complex is composed of different metamorphic rocks including schist, marble, slate, gneiss and amphibolite. The metamorphic complex is overlain by a cover sequence including Permian carbonates, Jurassic clastic rocks, Cretaceous carbonates and Eocene clastic rocks. The internal structure of the GMC is characterized by four deformational stages. The first stage (D1) developed contemporaneously with the prograde regional metamorphism and resulted in formation of the first generation folds and prevailing axial plane foliation. The second stage of deformation (D2) was accompanied by deformation partitioning and formation of contractional shear zones. These structures were overprinted by different scale folds of the third stage (D3). The fourth stage of deformation (D4) is characterized by generation of the extensional shear zones which gradually transformed into normal faults. D1 and accompanied metamorphism may have resulted from steep subduction of the Neotethys Ocean beneath the active margin of the Central Iran zone during Jurassic times. D2–D3 structures and retrograde metamorphism may have been formed by a regional shortening and transpression deformation event which resulted in exposure of the metamorphic rocks in shallower levels during Cretaceous flat slab subduction. This condition lasted until Paleocene time when the slab roll-back caused extension and thinning of the overriding Central Iran plate. The subsequent decompression and regional extension resulted in intrusion of magmatic rocks and generation of D4 which formed the GMC and related magmatism in Paleocene-Eocene time.

Use of immobile trace elements in gold exploration in the Neoarchean Sandstone Greenstone Belt, Yilgarn Block, Western Australia

Exploration in the Sandstone Greenstone Belt (SSGB), with its widespread complex regolith cover, is extremely difficult as targeted orogenic gold deposits have no consistent parameters that allow direct geophysical detection, and gold and ore-metal surface geochemistry reflects variations from in situ to highly transported responses. Based on aeromagnetic interpretations, the gold deposits of the SSGB can be viewed within broad litho-structural frameworks, and NNW-NW and NNE-NE–trending domains, with more favourable orientation with respect to the inferred principal maximum stress during the time of gold mineralisation, can be defined. Fault jogs and high-angle corridors of cross faults further constrain more-prospective zones. However, the aeromagnetic data cannot identify relatively small volumes of critical host rocks which can localize ore-fluid flux and fluid-rock reactions that control the deposition of gold mineralisation. In the SSGB, these critical host rocks include thin granodiorite intrusions within ultramafic schists or specific mafic bodies in mafic-ultramafic sequences. A reconnaissance study using the immobile trace elements, Ti and Zr, demonstrates that these critical rock types can be readily recognized at surface and in drill chips. In particular, Ti–Zr geochemistry identifies previously unknown 20-km-long differentiated dolerite units with granophyric zones that localize gold mineralisation. A combination of aeromagnetic interpretation of structures and major Domains, plus the location of critical host units using Ti–Zr geochemistry, allows production of an exploration targeting map for this district with definition of priority targets based on a mineral system approach. Thus, in the SSGB, for gold exploration under regolith cover that represents in situ weathering of those host rocks, rather than later cover sequences, immobile trace element geochemistry provides an effective, low-cost methodology, as an adjunct to conventional ore-metal geochemistry, and should be used in other orogenic gold provinces worldwide.

Delimiting geochemical anomalies in the exploration of covered deposits with multifractal methods and using stream sediment data from the Iberian Pyrite Belt, Southwest Iberia

The Iberian Pyrite Belt (IPB) is a world-class province of Upper Paleozoic age for volcanic- and shale-hosted massive sulfides that includes 5 of the 10 supergiant (>150 Mt) deposits of their kind in the World. The volcano-sedimentary sequences hosting the ores are locally exposed, commonly covered by flysch-type successions of variable thickness (the Baixo Alentejo Flysch Group, BAFG) as a result of primary (sedimentary) features and superimposed effects due to Variscan folding and tectonic stacking. In addition and when affected by late-developed geomorphic depressions, the exhumed Paleozoic basement is also capped by Meso-Cenozoic sediments. The total thickness of cover sequences on top of the litho-stratigraphic sequence of interest can reach 100′s of meters, creating problems for mineral exploration.A large stream sediment (multi-element) geochemical database for the IPB was done in the 90′s during a wide-ranging regional survey. This database was reassessed by means of multifractal methods in view of their faculty to enhance the detection of faint geochemical anomalies and provide geochemical indicators to deep buried ore systems. Several anomalies were detected, namely for Cu, Zn, and Co along NW-SE to WNW-ESE trends. The main anomalous geochemical trends identified include zones that: (i) extend along the Mira Formation of BAFG, opening for the first time two non-traditional areas for further exploration studies; (ii) run along the boundary between the Mira and Mértola Formations of BAFG, probably related to different geochemical signatures and late-developed, fault-controlled, epigenetic ore systems; and (iii) overlap windows of volcanic-sedimentary sequences within the Cenozoic detrital cover and the site below which the deep buried deposit of Lagoa Salgada is located.

Metal-Bearing Nanoparticles Observed in Soils and Fault Gouges over the Shenjiayao Gold Deposit and Their Significance

Mineral deposits concealed by thick cover sequences present special problems for geochemical exploration. A variety of penetrating geochemical methods have been developed in the last few decades to explore for buried deposits. The theoretical basis of the mechanism by which metals migrate upward from buried deposits through the cover to the surface is still not fully understood. One hypothesis is that metal particles or metal elements could be carried onto bubbles or micro-flow of geogas and migrate upward to the surface. After years of study, nano-scale metal-bearing particles have been widely observed in geogas samples from different kinds of concealed deposits. However, the occurrence of these metal-bearing particles carried by geogases in near-surface media, such as soil, has not been studied in detail. In this study, metal-bearing nanoparticles were observed in samples from soils and fault gouges over the Shenjiayao gold deposit. The results indicate that (1) the ore-forming elements in soils can only come from deep-seated ore bodies and they occur in nanoparticles in the study area; (2) there is an obvious relationship between metal nanoparticles in fault gouges and soils; (3) the metallic nanoparticles in fault gouges represent a transitional phase along the whole vertical migration process. In addition, the observation results show that the metal-bearing nanoparticles tend to be adsorbed on the surface of clay minerals, which provide theoretical support for using fine fraction soils as sampling media to carry out geochemical exploration in sediment-covered terrains. Based on the results and discussion, a simple migration model was built in this paper.

The Olympic Cu-Au Province, Gawler Craton: A Review of the Lithospheric Architecture, Geodynamic Setting, Alteration Systems, Cover Successions and Prospectivity

The Olympic Cu-Au Province is a metallogenic province in South Australia that contains one of the world’s most significant Cu-Au-U resources in the Olympic Dam deposit. The Olympic Cu-Au Province also hosts a range of other iron oxide-copper-gold (IOCG) deposits including Prominent Hill and Carrapateena. This paper reviews the geology of the Olympic Cu-Au Province by investigating the lithospheric architecture, geodynamic setting and alteration systematics. In addition, since the province is almost entirely buried by post-mineral cover, the sedimentary cover sequences are also reviewed. The Olympic Cu-Au Province formed during the early Mesoproterozoic, ca. 1.6 Ga and is co-located with a fundamental lithospheric boundary in the eastern Gawler Craton. This metallogenic event was driven in part by melting of a fertile, metasomatized sub-continental lithospheric mantle during a major regional tectonothermal event. Fluid evolution and multiple fluid mixing resulted in alteration assemblages that range from albite, magnetite and other higher temperature minerals to lower temperature assemblages such as hematite, sericite and chlorite. IOCG mineralisation is associated with both high and low temperature assemblages, however, hematite-rich IOCGs are the most economically significant. Burial by Mesoproterzoic and Neoproterozoic-Cambrian sedimentary successions preserved the Olympic Cu-Au Province from erosion, while also providing a challenge for mineral exploration in the region. Mineral potential modelling identifies regions within the Olympic Cu-Au Province and adjacent Curnamona Province that have high prospects for future IOCG discoveries. Exploration success will rely on improvements in existing potential field and geochemical data, and be bolstered by new 3D magnetotelluric surveys. However, drilling remains the final method for discovery of new mineral resources.

Provenance evolution of the Paleoproterozoic metasedimentary cover sequences in northern Fennoscandia: Age distribution, geochemistry, and zircon morphology

The metasedimentary basin-fill successions of the Central Lapland belt, Peräpohja belt, and Kuusamo belt form an important part of the northern Fennoscandia Shield. They each record ca. 600 Ma (2.5–1.9 Ga) of sedimentation history and tectonic evolution, providing important information about past depositional conditions and tectonic settings. Detrital zircon geochronology shows that Archean age populations between 3.00 and 2.70 Ga have provenances from the surrounding basement complexes of granitoid/TTG rocks, whereas the Paleoproterozoic age populations (≤2.25–1.86 Ga) can be linked to the surrounding granitoids in northern Finland and Sweden. Zircon morphology studies indicate that basin sedimentation and/or provenance area(s) were likely influenced by eolian processes ca. 2.3–2.1 (or possible earlier). Major and trace element geochemistry indicates minor to moderate weathering trends, closely resembling Archean-Proterozoic sandstones and shales. Provenance signatures of tectonic settings vary from rift to arc and collisional. We propose five basin evolution stages for the Central Lapland belt, Peräpohja belt, and Kuusamo belt: a rifting stage from 2.5 to 2.1 Ga including (i) initial rifting/early syn-rift, (ii) syn-rift, and (iii) syn-rift to early post-rift; (iv) a passive margin (post-rift) stage from 2.1 to 1.94–1.92 Ga; and (v) a foreland basin system 1.94–1.92 to 1.88 Ga. The rifting stage includes bimodal subaerial to subaqueous volcanism with continental to marine sedimentation, and the initial accumulation of carbonate and evaporate successions, indicating later local tectonic stability and restricted hydrological circulation. The early development of an epeiric sea setting was followed by a passive margin stage and the development of aulacogens, controlled by cyclic sea-level fluctuations superimposed on long-term thermal subsidence. This stage was characterized by the accumulation of hemipelagic deposits together with gravity-driven sandstone deposits and associated subaqueous volcanism. The foreland basin system comprises an initial compressional stage with the development of forebulge and foredeep depozones and magmatic arc collision. This was followed by the main compressional stage, where basin inversion resulted in a foreland fold-thrust belt. The foreland basin system includes syn- and post-orogenic deposystems and a transition from underfilled marine sedimentation to overfilled non-marine deposits.

Evolution of the Palaeotethys in the Eastern Mediterranean: a multi-method approach to unravel the age, provenance and tectonic setting of the Upper Palaeozoic Konya Complex and its Mesozoic cover sequence (south-central Turkey)

ABSTRACTSiliciclastic sediments from the Upper Palaeozoic Konya Complex and its Mesozoic cover were studied by a multi-method approach combining thin-section petrography, bulk-rock geochemistry, mineral chemistry of rutile, and U–Pb geochronology of detrital zircons. Provenance sensitive data of samples from the Upper Palaeozoic Halıcı Formation indicate sediment supply from mainly low- to medium-grade metamorphosed sedimentary rocks of felsic character, while the contribution from volcanic rocks was rare. The detrital zircon record of sediments from the Halıcı Formation documents sediment supply from different sources and excludes a similar provenance. Some samples show great similarities with Palaeozoic sandstones from the cover sequence of the Saharan Metacraton and the Arabian–Nubian Shield, while the other samples indicate a provenance that must be sought in units with a southern Eurasian affinity. The upper limit for sediment deposition in the Halıcı Formation is mostly constrained by Early Palaeozoic zircon populations; however, sediment accumulation in Pennsylvanian–Cisuralian time is more likely, contemporaneously with the Upper Palaeozoic succession on the Karaburun Peninsula (western Turkey). The provenance of sediments from the Upper Triassic Ardıçlı Formation remains enigmatic, but the source should be sought nonetheless in units close to the depositional site. In any case, detrital zircon age spectra and compositional data exclude recycling of underlying rock units (i.e. Halıcı Formation). Overall, our new provenance data reveal great similarities between the Konya Complex and comparable units (Chios, Karaburun) but also highlight distinct differences in terms of sediment composition and provenance.