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“Invisible gold” refers to gold (Au) occurring either within the lattice of a host sulfide or as discrete nanoparticles (NPs, 50% of pyrites contain measurable Au and As, and plot below the Au-As solubility curve. Au and As are geochemically associated with Te, Bi, Pb, Ag, and Sn. Primary oscillatory zoning patterns in pyrite defined by As-Co-Ni are reshaped by processes of dissolution-reprecipitation, including new nanoscale growth and rhythmical misorientation structures. Low-angle slip dislocations, twist-wall boundaries and deformation-dipole nanostructures are associated with Te-Bi-Pb-enrichment and host Au-Ag-telluride nanoparticles (NPs). Electrum NPs occur associated with pores coated by Bi-Ag-tellurides or within chalcopyrite particles. Bi-Pb-sulfotellurides, petzite, and sylvanite were identified by atomic-scale scanning transmission electron microscopy. The data support trace element (re)mobilization during pyrite deformation at the brittle to ductile transition (0.5–1 kbar, 300–400 °C) during brecciation. Au-NP formation is decoupled from initial As incorporation in pyrite and instead fingerprints formation of strain-induced, chalcogen-enriched nanoscale structures. Pore-attached NPs suggest scavenging of Au by Bi-bearing melts with higher rates of fluid percolation. Similar scenarios are predictable for pyrite-hosted “invisible Au” in pyrite from other deposits that experienced multiple overprints. Unveiling the cloak of invisibility using contemporary micro- to nano-analytical techniques reveals new layers of complexity with respect to the trace/minor element incorporation in mineral matrices and their subsequent release during overprinting.

The Mount Weld rare earth element (REE) deposit, Western Australia, is one of the largest of its type on Earth. Current mining exploits the high-grade weathered goethite-bearing resource that lies above, and which represents the weathering product of a subjacent carbonatite. The mineralogy, petrography, deportment of lanthanides among the different components, and variation in mineral speciation, textures, and chemistry are examined. Microanalysis, involving scanning electron microscope (SEM) imaging, electron probe microanalysis (EPMA) and laser ablation inductively coupled-plasma mass spectrometry (LA-ICP-MS), was conducted on sized fractions of three crushed and ground laterite ore samples from current and planned production, and a representative sample from the underlying carbonatite. High-magnification imaging of particles in laterite samples show that individual REE-bearing phases are fine-grained and extend in size well below the micron-scale. Nanoscale inclusions of REE-phosphates are observed in apatite, Fe-(Mn)-(hydr)oxides, and quartz, among others. These have the appearance, particularly in fluorapatite, of pervasive, ultrafine dusty domains. Apart from the discrete REE minerals and abundant nano- to micron-scale inclusions in gangue, all ore components analysed by LA-ICP-MS contain trace to minor levels of REEs within their structures. This includes apatite, where low levels of REE are confirmed in preserved igneous apatite, but also Fe- and Mn-(hydr)oxides in which concentrations of hundreds, even thousands of ppm are measured. This is significant given that Fe-(Mn)-(hydr)oxides are the most abundant component of the laterite and points to extensive mobility and redistribution of REEs, and especially HREE, during progressive lateritisation. Late-formed minerals, notably tiny grains of cerianite, reflect a shift to oxidising conditions. REE-fluorocarbonates are the main host for REEs in carbonatite and are systematically replaced by hydrated, Ca-bearing REE-phosphates (largely rhabdophane). The latter displays varied compositions but is characteristically enriched in HREE relative to monazite in the same sample. Fine-grained, compositionally heterogeneous rhabdophane is accompanied by minor amounts of other paragenetically late, hydrated phosphates with enhanced MREE/HREE relative to LREE (although still LREE-dominant). Minor, relict xenotime and zircon are significant HREE carriers. Ilmenite and pyrochlore group members contain REE but contribute only negligibly to the overall REE budget. Although the proportions of individual mineral species differ, the chemistry of key ore components are similar in different laterite samples from the current resource. Mineral signatures are, however, subtly different in the lower grade southeastern part of the deposit, including higher concentrations of HREE relative to LREE in monazite, rhabdophane, florencite and Fe-(Mn)-(hydr)oxides.

Silician magnetite within ~1.85 Ga lithologies hosting the ~1.6 Ga Wirrda Well iron oxide copper gold (IOCG) prospect, South Australia, was examined at the nanoscale. The magnetite is oscillatory-zoned with respect to the density and orientation of nanometer-scale inclusions, among which Si-Fe-nanorods and Al-rich amphibole (as much as hundreds of nanometers long and tens of nanometers wide) form swarms along directions in magnetite. The amphibole is identified as ferro-tschermakite (Ftsk) with the crystal-chemical formula: A(K0.06Na0.01)0.07B(Ca1.65Na0.35)2C(Fe2.072+Al1.64Mg1.15Ti0.06Fe0.043+Mn0.04)5T(Si6.48Al1.52)8O22W(OH)2. This contains single and double rows of a triple-chain silicate attributed to clinojimthompsonite (Cjt) as coherently intergrown (010) zippers along the entire length of the grains. High-angle annular dark-field scanning transmission electron microscopy (HAADF STEM) imaging and simulation of Ftsk and Cjt on the [001] zone axis provide direct visualization of crystal structures. These are defined by the 7- and 10-atom octahedron strips (B+C sites) and flanked by double- and triple-pairs of Si atoms (T sites). Remarkably, the sites for light cations and/or vacancies are clearly imaged as single and double, darkest, diamond-shaped motifs separating the octahedron strips showing that A cavities known in amphibole are readily depicted in the wider-chain silicate. I-beam models show that nanoscale intergrowths among the two silicates are coherent along zigzag chains of cations at the edges of the octahedron strips, with single and double rows of the triple-chain silicate corresponding to 1 and 1.5 unit cells of Cjt (27 and 41 Å intervals along the b axis). This type of polysomatic chain-width disorder is widely reported in Mg-rich pyriboles but is shown here in an Al-Fe-rich amphibole. The lack of planar defects and/or reaction fronts at mutual contacts between three-chain zippers and host amphibole indicates primary co-crystallization growth, promoted by the formation of the Si-Fe-nanorods. Co-crystallizing plagioclase is also preserved in close vicinity to the amphibole hosted by magnetite (from a few nanometers to micrometers apart). In contrast, the replacement of amphibole by phyllosilicates is recognizable as irregular swells along the (010) zippers and results in extensive chloritization of the amphibole during an overprinting event. Pressures of ~11.5 kbar are estimated using Al-in-hornblende nano-geobarometry and calculated Al content in Ftsk (3.16 apfu). Assuming the amphibole-plagioclase association buffered by host magnetite fulfills the textural equilibration criteria required for application of this barometer, we interpret the Ftsk nanoinclusions in magnetite as preserved evidence for amphibolite facies metamorphism affecting host lithologies at Wirrda Well with subsequent retrograde alteration during the ~1.6 Ga IOCG mineralizing event. Magnetite records petrogenetic processes by accommodating variable ranges of nanomineral inclusions and preserving them over geological time scales. HAADF STEM imaging is ideally suited to the depiction of crystal-structural modularity and also provides insights into the evolution of geological terranes with protracted histories.

The accelerated pace of transition to green energy technologies has led to increased demand for rare-earth elements (REEs). Fluorocarbonates from the bastnäsite [REE(CO3)F]—synchysite [CaREE(CO3)2F] group are abundant in nature and the dominant REE minerals in the >10 billion ton Olympic Dam Cu–U–Au–Ag deposit, South Australia. Intergrowths of bastnäsite and synchysite slabs at the nanometer to micron scales are the rule rather than the exception and account for structural and compositional changes between the two endmembers. This article reviews REE-fluorocarbonate mineralogy at Olympic Dam with emphasis on the significance of intergrowths among bastnäsite and synchysite for achievement of thermodynamic equilibrium. Imaging by high-angle annular dark-field scanning transmission electron microscopy (HAADF STEM) allows visualization of atomic-scale periodicity and structural modularity in REE fluorocarbonates and, in turn, determination of domain compositions, which are otherwise below the spatial resolution of microbeam methods. Despite highly irregular, such domains featuring atomic-scale intergrowths can approach the compositions of the next intermediate member phase within each host, implying formation in a system close to thermodynamic equilibrium. Graphic Abstract

Texturally complex minerals can provide critical information on dynamic hydrothermal processes. This study combines cathodoluminescence (CL), laser ablation-inductively coupled plasma-mass spectrometry (LA–ICP–MS), and high-resolution femtosecond laser ablation multi-collector inductively coupled plasma mass spectrometry (fs–LA–MC–ICP–MS) analyses to document textures, in situ Sr-Nd isotope systematics, and trace element compositions of texturally complex scheelite from the Yangjiashan W deposit, South China. The major motivation for this contribution was to reveal the correlation between CL response, textures, and trace element concentrations; document the origin of various REE fractionation patterns; and characterize grain-scale in situ variability of Sr-Nd isotopes of scheelite. Five sub-types of scheelite from both stages, including Sch1 and Sch2 from Stage 1, and Sch3 to Sch5 from Stage 2, are identified. CL images feature complex oscillatory, patchy, and evidence for coupled dissolution-reprecipitation reaction. These scheelites precipitated from reduced fluids and are close to end-member in composition, with Mo concentrations below 46 ppm. Concentrations of other elements vary, e.g., Sr (36–1025 ppm), Nd (8–351 ppm), and Na (7–300 ppm). LA–ICP–MS element maps reveal a large variability in REE concentrations among oscillatory zones and no consistent behavior between REE, Sr and Mo concentration, and CL intensity. Four distinct chondrite-normalized REE fractionation patterns are recognized: LREE-enriched, MREE-enriched, HREE-enriched, and flat patterns. Complex Eu anomalies (δEu = 0.2 to 20.7) are recognized among the five sub-types and are commonly observed within individual grains. Fluid compositions, different substitution mechanisms (i.e., Ca2+ + W6+ = REE3+ + Nb5+, and 2Ca2+ = REE3+ + Na+, 3Ca2+ = 2REE3++ ☐Ca, where ☐Ca is a Ca-site vacancy), primary-secondary processes (i.e., oscillatory and dissolution-reprecipitation, respectively), all contribute to the variation in REE fractionation patterns. Local fluctuation in fluid pH is responsible for the complex Eu anomalies. In situ Sr and Nd isotope signatures for the five sub-types of scheelite show relatively large ranges, i.e., the initial 87Sr/86Sr ratios range from 0.71336 to 0.72617, and the initial εNd values ranging from –24.9 to –7.7, suggesting a source derived from a mixture of magmatic-hydrothermal fluids and the Neoproterozoic slate. Decreasing 87Sr/86Sr ratios from Sch2 to Sch5 record decreasing fluid-rock interaction intensity. Large variation of εNd(t) values (–24.9 to –7.7) of scheelite with oscillatory zoning textures may relate to changes of Sm/Nd ratio of scheelite and contamination from wall rock with inhomogeneous Nd isotope composition. This study highlights the importance of performing coupled LA–ICP–MS mapping and in situ Sr-Nd isotope analyses on sample material that has been characterized in detail at the micrometer scale.

Magnetite is the dominant Fe-oxide at the Acropolis IOCG prospect, Olympic Dam district, South Australia. Complementary microbeam techniques, including scanning transmission electron microscopy (STEM), are used to characterize titanomagnetite from veins in volcanic rocks and Ti-poor magnetite from a granite body with uplifted position in the volcanic sequence. A temperature of 670 ± 50 °C is estimated for Ti-poor magnetite using XMg-in-magnetite thermometry. Titanomagnetite, typified by Ti-rich trellis lamellae of ilmenite in magnetite, also displays sub-micrometer inclusions forming densely mottled and orbicular subtypes of titanomagnetite with increasing degree of overprinting. STEM analysis shows nanoparticles (NPs) of spinels and TiO2 polymorphs, anatase, and rutile. These vary as dense, finest-scale, monophase-NPs of spinel sensu stricto in Ti-poor magnetite; two-phase, ulvöspinelhercynite NPs in primary titanomagnetite; and coarser clusters of NPs (hercynite±gahnite+TiO2-polymorphs), in mottled and orbicular subtypes. Nano-thermobarometry using ilmenite-magnetite pairs gives temperatures in the range ~510–570 (±50) °C, with mineral-pair re-equilibration from primary to orbicular titanomagnetite constrained by changes in fO2 from ilmenite-stable to magnetite+hematite-stable conditions. Epitaxial relationships between spinel and Fe-Ti-oxides along trellis lamellae and among phases forming the NPs support exsolution from magnetitess, followed by replacement via mineral-buffered reactions. Lattice-scale intergrowths between ulvöspinel and ilmenite within NPs are interpreted as exsolution recording cooling under O2-conserving conditions, whereas the presence of both TiO2-polymorphs displaying variable order-disorder phenomena is evidence for subtly fO2-buffered reactions from anatase (reducing) to rutile (more oxidizing) stabilities. Transient formation of O-deficient phases is retained during replacement of ilmenite by anatase displaying crystallographic-shear planes. Development of dense inclusion mottling and orbicular textures are associated with NP coarsening and clustering during vein re-opening. Fluid-assisted replacement locally recycles trace elements, forming gahnite NPs or discrete Sc-Ti-phases. Hydrothermal titanomagnetite from Acropolis is comparable with magmatic magnetite in granites across the district and typifies early, alkali-calcic alteration. Open-fracture circulation, inhibiting additional supply of Si, Ca, K, and so on during magnetite precipitation, prohibits formation of silician magnetite hosting calc-silicate NPs, as known from IOCG systems characterized by rock-buffered alteration of host lithologies. Obliteration of trellis textures during subsequent overprinting could explain the scarcity of this type of hydrothermal magnetite in other IOCG systems.

Trace/minor element variation in pyrite is a feature that has proved invaluable for reconstructing a wide range of geological processes. Routine reflectance observations commonly fail to constrain this variation due to the typically subtle and barely perceptible change in reflectance brought about by deviation from ideal stoichiometry. Such differences may be difficult or impossible to observe in conventional polished sections using standard optical microscopes, at least without oil immersion. Chemical etching and staining, although widely used, are destructive, hazardous, or both, and the etching process is not completely reproducible. Here we use the g correction method to enhance optical digital signal differences obtained in reflected light to constrain compositional heterogeneity in pyrite from a representative hydrothermal ore deposit in eastern China. The g-enhanced images show significant reflectance variation caused by compositional heterogeneity, confirmed by quantitative electron microprobe analysis and qualitative imaging. Higher reflectance domains in g-enhanced images correspond to increases in the effective number of free electrons, whereas darker domains are attributed to the decrease of these free electrons by trace/minor element substitution in pyrite (e.g., As). Gamma correction provides a rapid, effective, non-destructive method to constrain compositional heterogeneity of pyrite through enhancement of reflectance variation. Used alone, this method is unable to determine the chemical composition due to simultaneous substitutions, causing a disparate increase or decrease of reflectance, in most ore minerals. Nevertheless, γ correction may be sufficient to predict the substitution of trace/minor elements under the optical microscope prior to scanning electron microscope imaging and quantitative investigation of mineral composition and may help constrain links between textures and compositions of pyrite in evolving ore systems, which could also be applied to other ore minerals with negligible bireflectance.

Micrometer- to submicrometer-scale indium-rich domains are preserved within sphalerite included in hornfels-hosted pyrrhotite from the Dulong polymetallic skarn, Yunnan, China. The nano-mineralogy of the ZnS-bearing blebs was investigated using scanning transmission electron microscopy on thinned foils extracted in situ from pyrrhotite. Indium incorporation in sphalerite occurs via the coupled substitution 2Zn2+ ↔ Cu+ + In3+; the results thus allow insights into phase relationships in the system ZnS-CuInS2 in which solubility limits are debated with respect to a cubic to tetragonal phase transition. The highest concentrations of In are measured in basket-weave domains from the smallest ZnS blebs or from un-patterned areas in coarser, irregular ZnS inclusions in pyrrhotite. Indium-rich domains contain 17–49 mol% CuInS2, whereas In-poor sphalerite contains

The halogens Cl and Br are sensitive indicators for the origin of ore-forming fluids. Here, we use a combination of microchemical and microscopic methods to show that measurable concentrations of these elements commonly occur as atomic-scale substitutions in hydrothermal sphalerite. Furthermore, the Cl/Br ratios of halogen-rich sphalerites are indistinguishable from those of the corresponding ore-forming fluids. Thus, they record fluid compositions, which in turn record fluid origin. Given the abundance of sphalerite in hydrothermal base-metal deposits, as well as the relative ease of conducting in situ microchemical analyses, the halogen signature of sphalerite has the potential to become a sensitive proxy to distinguish between different ore-forming environments.

The Pefka Cu-Au-Te-In-Se and nearby St Philippos Pb-Zn-Bi-Sn-Ge-Ga-In vein- and breccia-type deposits in western Thrace, Greece, display strong similarities, but also differences in terms of mineralization style, ore mineralogy, and chemistry, and host rock compositions. The Pefka mineralization consists of two crosscutting vein systems with high sulfidation (HS)- and intermediate-sulfidation (IS) assemblages hosted by andesitic lavas and is unusually enriched in In (up to 700 ppm), Te (>1000 ppm), Se (>100 ppm), and Cu (>1 wt%). The main In-carriers are roquesite (CuInS2) and In-bearing “tennantite-(Cu)” and Cu-rich “tennantite-(In)” which contains up to 6.5 wt% In, substituting into the C site. Roquesite is associated with enargite and arsenosulvanite/colusite, as part of the HS assemblage at Pefka. Selenium-bearing galena and a large suite of tellurides including calaverite, sylvanite, petzite, hessite, kostovite, empressite, tellurantimony, and coloradoite, in addition to native tellurium, account for the marked tellurium and selenium enrichment in the ores from Pefka. Tellurides and native gold at Pefka accompany the precipitation of Te-bearing minerals of the tetrahedrite group, such as “stibiogoldfieldite” and “arsenogoldfieldite”, and Cu-excess varieties of tetrahedrite and tennantite. However, the bulk of telluride deposition is associated with normal, fully substituted tetrahedrite-tennantite varieties. The St Philippos deposit is associated with a brecciated fault zone hosted by Eocene sandstones and Oligocene quartz-feldspar porphyry dikes. It is enriched in a large suite of incompatible elements, including Bi (>2000 ppm), Sn (>100 ppm), U (up to 200 ppm), Pb (>1 wt%), Zn (>1 wt%), Mo (up to 62 ppm), Ge (>100 ppm), Ga (up to 466 ppm) and In (up to 222 ppm), contrasting with the element suite defining the nearby Pefka deposit. The main carrier of In, Ga, and Ge is sphalerite (and wurtzite) with In-rich zones in sphalerite containing up to 6.1. wt% In. Germanium and Ga in sphalerite reach concentrations of up to 0.27 and 0.32 wt%, respectively. Sphalerite from the St Philippos deposit is extremely Fe-poor (300 °C) and HS fluid conditions, followed by IS assemblages as temperatures waned. Rhyolitic oxidized magmas are considered to be the sources of metals in the St Philippos deposit; however, their anomalous W, Sn, U, and Bi contents suggest a contamination by crustal rocks. The Cu-Au-Te signature of the Pefka deposit is compatible with a genetic relationship to less fractionated andesitic magmas, although a possible contribution of In from rhyolitic magmas could explain the high In contents of the ore. However, other factors, as for example different metal-deposition mechanisms resulting in metal zonation around causative porphyry centers at depth, may also account for the observed metal endowment in these two deposits. The Sn-Te-In-(Ge-Ga) element association at Pefka and St Philippos is unusual in that it has been previously reported from only a few other places in the world (e.g., Capillitas deposit, Argentina, and the Kawazu deposit, Japan). We conclude based on this exotic mineralization-style that the northeastern part of Greece represents an area of great potential for the exploitation of critical metals and metalloids.

Bi8Te3 is a member of the tetradymite homologous series, previously shown to be compositionally and structurally distinct from hedleyite, Bi7Te3, yet inadequately characterized structurally. The phase is identified in a sample from the Hedley district, British Columbia, Canada. Compositions are documented by electron probe microanalysis and structures are directly imaged using high-angle annular dark field (HAADF) scanning transmission electron microscopy (STEM). Results confirm that Bi8Te3 has an 11-atom layer structure, in which three Bi-Bi pairs are placed adjacent to the five-atom sequence (Te-Bi-Te-Bi-Te). Bi8Te3 has trigonal symmetry (space group R3¯m) with unit cell dimensions of a = ~4.4 Å and c = ~63 Å calculated from measurements on representative electron diffraction patterns. The model is assessed by STEM simulations and EDS mapping, all displaying good agreement with the HAADF STEM imaging. Lattice-scale intergrowths are documented in phases replacing Bi8Te3, accounting for the rarity of this phase in nature. These results support prior predictions of crystal structures in the tetradymite homologous series from theoretical modeling and indicate that other phases are likely to exist for future discovery. Tetradymite homologues are mixed-layer compounds derived as one-dimensional superstructures of a basic rhombohedral sub-cell. Each member of the series has a discrete stoichiometric composition and unique crystal structure.

We used high-angle annular dark field scanning transmission electron microscopy (HAADF STEM) to image the crystal structures of four minerals in the Bi4X3 isoseries (X = Te, Se, S), a subgroup of the tetradymite homologous series: ikunolite (Bi4S3), laitakarite (Bi4Se2S), joséite-B (Bi4Te2S), and joséite-A (Bi4TeS2). The four minerals are isostructural and interpretable in terms of regular stacking of seven-atom packages: [Bi–S–Bi–S–Bi–S–Bi], [Bi–Se–Bi–S–Bi–Se–Bi], [Bi–Te–Bi–S–Bi–Te–Bi], and [Bi–S–Bi–Te–Bi–S–Bi], respectively. The four phases are mixed-layer structures representing the Bi2kTe3 (k = 2) module within the tetradymite series. Diffraction patterns confirm they are seven-fold superstructures of a rhombohedral subcell with c/3 = d~1.89–1.93 Å. Modulation along the d* interval matches calculations of reflection intensity using the fractional shift method for Bi4X3. Internal structures can be discerned by high-resolution HAADF STEM imaging and mapping. Paired bismuth atoms are positioned at the outside of each seven-atom layer, giving the minerals a modular structure that can also be considered as being composed of five-atom (X–Bi–X–Bi–X) and two-atom (Bi–Bi) sub-modules. The presence of mixed sites for substituting cations is shown, particularly for Pb. Moreover, Pb may be important in understanding the incorporation of Ag and Au in Bi–chalcogenides. Visualisation of crystal structures by HAADF STEM contributes to understanding relationships between phases in the tetradymite homologous series and will play an invaluable role in the characterization of potential additional members of the series.

Aluminum-phosphate-sulfate (APS) minerals of the alunite supergroup are minor components of uranium-bearing copper ores from the Olympic Dam deposit, South Australia. They typically represent a family of paragenetically late replacement phases after pre-existing REE-bearing phosphates (fluorapatite, monazite, and xenotime). Characterization with respect to textures and composition allows two groups to be distinguished: Ca-Sr-dominant APS minerals that fall within the woodhouseite and svanbergite compositional fields; and a second REE- and phosphate-dominant group closer to florencite in composition. All phases nevertheless display extensive solid solution among end-members in the broader APS clan and show extensive compositional zoning at the grain-scale. Samples representative of the deposit (flotation concentrate and tailings), as well as those that have been chemically altered during the processing cycle (acid leached concentrate), were studied for comparison. NanoSIMS isotope mapping provides evidence that the APS minerals preferentially scavenge and incorporate daughter radionuclides of the 238U decay chain, notably 226Ra and 210Pb, both over geological time within the deposit and during ore processing. These data highlight the role played by minor phases as hosts for geologically mobile deleterious components in ores as well as during mineral processing. Moreover, Sr-Ca-dominant APS minerals exhibit preferential sorption of Pb from fluid sources, in the form of both common Pb and 210Pb, for the first time revealing potential pathways for 210Pb elimination and reduction from ore processing streams.

The Acropolis prospect is a vein-style magnetite (±apatite ±hematite) system located ~20 km southwest from the giant Olympic Dam iron-oxide copper gold (IOCG) deposit, South Australia. A whole rock...

The Zhengguang gold deposit, a typical intermediate-sulfidation epithermal deposit, is located in the southeastern part of the Duobaoshan orefield, west of the Hegenshan-Heihe suture zone, in the eastern part of the Central Asian Orogenic Belt. The deposit comprises five ore zones with total Au reserves exceeding 35 tonnes, with potential additional resources at depth. All vein-type orebodies are hosted by Paleozoic volcanic rocks and comprise multiple vein sets 1–100 cm in thickness. Although gold generally occurs in native form, or as electrum in epithermal deposits like Zhengguang, both pyrite and sphalerite are known to accommodate modest concentrations of invisible gold. This study employs a combination of petrography and sulfide chemistry to determine the role of invisible gold in the Zhengguang ores and the mechanisms of gold incorporation into epithermal sulfides. Three sulfide stages are identified: an early quartz + pyrite (Py1a, Py1b) ± chalcopyrite (Ccp1) stage; a subsequent quartz + sphalerite (Sph2a, Sph2b) + pyrite (Py2a, Py2b, Py2c, Py2d) + chalcopyrite (Ccp2a, Ccp2b) ± galena ± calcite stage; and a late stage containing deformed quartz + pyrite (Py3a, Py3b) ± sphalerite. Petrography and sulfide chemistry allow three groups of pyrite (Au-poor, Au-rich, and a distinct Sb-rich group) to be distinguished, alongside three groups of chalcopyrite (Bi-rich, intermediate-Bi, and Bi-poor), and two groups of sphalerite (Au-poor, Au-rich). A potential porphyry system is indicated beneath the epithermal system by the appearance of Au-poor pyrite and Bi-poor chalcopyrite. After precipitation of early Au-poor sulfides, inflow of relatively low temperature epithermal fluids led to alteration and replacement of early porphyry-related sulfides, and to precipitation of Au-rich pyrite, Bi-rich and intermediate-Bi chalcopyrite, and sphalerite. Gold-rich pyrite contains up to 140 ppm Au, interpreted as both as lattice-scale substitution (Au1+) and as included particles of native gold (Au0). Epithermal chalcopyrite is an important silver carrier but, although Au is measurable, it is a not a good carrier for gold. A strong positive correlation between Au and Cu in pyrite from the first two stages indicate that gold and other metals were likely sourced from magma-derived hydrothermal fluids. The deposit was formed in the Early Paleozoic but some gold ores appear deformed and partially destroyed by a later metamorphic event during which a distinct Sb-rich pyrite crystallized. This study should catalyze exploration in the orefield as it provides further support for an as-yet undiscovered porphyry system close to the Zhengguang deposit.

The Olympic Dam Cu-U-Au-Ag deposit is dominantly composed of mineralised hematite-breccias and occurs entirely within the Roxby Downs Granite. Multivariate statistical analysis of a large whole-rock, 15 m-interval geochemical dataset (10,565 samples) was undertaken to identify geochemical signatures characteristic of iron-oxide copper gold (IOCG)-style mineralization and constrain the conspicuous lithogeochemical zonation observed at Olympic Dam. Statistical analyses include principal component analysis on centred logratio (clr)-transformed data coupled with hierarchical clustering. Certain groups of elements that can be interpreted in terms of an evolving hydrothermal system relative to host lithologies are derived from data analysis: granitophile (U-W-Sn-Mo); siderophile (Ni-Co); chalcophile (Ag-Bi) and related elements (As-Sb and Au-Te). The distributions of elements within each group are investigated through three vertical cross-sections and are compared with known lithological and Cu-(Fe)-sulphide zonation. Throughout the Olympic Dam Breccia Complex, the IOCG signature is defined by multi-element combinations of the commodity metals Cu, U, Au, and Ag, coupled with a range of trace elements. Overall, the IOCG signature overlaps well with Fe-metasomatism despite mismatch which is likely due to discrete styles of mineralisation found only on the margins of the deposit and also to the presence of mineralised domains within Fe-poor zones. The IOCG signature is composed of two geochemical associations, which exhibit distinct spatial distributions. The first group, Cu-U3O8-Se-S, shows concentric zonation whereas the second group, Au-W-Mo-Sb-As, forms a vertical ∼1800 m deep corridor in the southeastern lobe of the deposit. The specific Au-W-Mo-As-Sb signature could potentially be generic within IOCG systems across the Olympic Cu-Au province and if so, would provide a proxy model for near-mine exploration.

This experimental study explored the potential of oral zinc sulfate to protect the gut mucosa from 5-fluorouracil (5-FU)-induced degenerative lesions in Wistar rats.Female Wistar rats were used and divided into 2 interventional groups (Z with 6 animals and F with 5 animals) and one control group (M with 5 rats). After 2 hours of fasting, group Z received via oral gavage 1.5 ml of solution, corresponding to 15 mg zinc sulfate for 9 consecutive days. Groups F and M received only the vehicles. On day 3, 400 mg/kg of 5-FU was administered intraperitoneally to groups Z and F. Tissue samples were collected from the duodenum, jejunum, colon and liver. Histological assessment for each gastrointestinal tract segment was determined semi-quantitatively by rating 11 histological features from normal (0) to severe (3). The independent groups were analyzed using the Kruskal-Wallis test and the Mann-Whitney U-test, with a Bonferroni correction for alpha (p ≤ 0.016).In group F the jejunum was the most affected area with a mean histological score of 27 (25-32). In the Z group, significantly lower histological scores were obtained compared with group F (duodenum Z vs. F: U = 0, p = 0.004; jejunum Z vs. F: U = 0, p = 0.006 and colon: Z vs. F: U = 0, p = 0.005). Graded liver necro-inflammatory lesions were significantly lower in group Z compared with group F (U = 0, p = 0.004), suggesting fewer bacterial intestinal translocation processes.Zinc sulfate has a beneficial role, decreasing the severity of gut mucosal injuries induced by 5-FU in Wistar rats.

Background Neopterin and RNA-ase are markers of inflammation with low disclosed role in diagnosis and prognosis of either STEMI or NSTEMI, although inflammation is well documented as a leader pathogenic mechanism in these pathologies. Aim Evaluation of serum admission levels of neopterin and ARN-ase in pts with STEMI and NSTEMI and their prediction value concerning the risk of MACE in 1 year of follow up period. Material and methods The admission serum concentration of neopterin and ARN-ase was determined by ELISA in 94 pts with STEMI and 92 pts with NSTEMI which was compared with normal markers appreciated in 32 healthy persons. Likewise, the rate of MACE in both groups was estimated during 1 year of post-infarction period. Diagnostic worth and MACE prediction power of markers have been established using respectively ROC curve and odds ratio. Results In patients with STEMI the serum level of neopterin was significantly increased compared with normal index by 3,5 times (11,6±3,4 vs 3,3±1,4 nM/L), but RNA-ase was significantly decreased by 43,4% (24,1±3,2 vs 42,6±5,2 nM/ml). In pts with NSTEMI neopterin level was lesser than STEMI, but significantly elevated by 39% (4,6±2,5 vs 3,3±1,4 nM/L) vs normal marker. RNA-ase level didn't significantly differ from normal level. However, adjusted to diabetes mellitus established in 19 pts, RNA-ase significantly diminished (36,4±3,9 vs 42,6±5,2 nM/ml), and its diagnostic value of NSTEMI according to ROC was 69,6% (RNA-ase level indicates inversely inflammation response, such as it breaks down extracellular RNA which has proinflammatory ability). Both markers in pts with NSTEMI and diabetes mellitus demonstrated a diagnostic value of 77,6%. In pts with STEMI highest tertile level of neopterin and lowest tertile level of ARN-ase had 2,8fold (adds ratio=2,8; CI=1,98–4,62; p Conclusions 1. In STEMI both neopterin and RNA-ase could be as diagnostic markers, due to their significant change. In NSTEMI neopterin significantly elevated, but RNA-ase didn't shift from normal. In diabetic pts with NSTEMI, however, their combination demonstrated in ROC estimation a diagnostic value of 77,6%. 2. Prediction value of markers combination regarding MACE risk in pts with NSTEMI is significant and close to each marker in partly prediction of MACE for pts with STEMI. Funding Acknowledgement Type of funding source: Public Institution(s). Main funding source(s): Research Institute of Cardiology, Moldova Republic of

Proximal and distal garnets from skarns at Jiaduobule, Tibet, are used to demonstrate how variation in the fluid composition and parameters such as salinity, pH, fO2, and $${\text{X}}_{{\rm CO}_{2}}$$ will impact on rare earth element (REE) distribution in garnets, and also to constrain skarn evolution across the orefield from proximal (Fe mineralization) to distal (Cu mineralization). These garnets display a diversity from proximal to distal skarn which is expressed in mineral assemblages, textures, major to trace element contents, and particularly, chondrite-normalized REE fractionation trends. The empirical variation among REE fractionation trends, determined from laser ablation inductively coupled-plasma mass spectrometry data, can be numerically modelled in terms of variable fluid compositions and physicochemical parameters, among which the key determining factors are salinity, pH, $${\text{X}}_{{{\text{CO}}_{{2}} }}$$ and Ca content buffered from the rock-fluid reaction with carbonate rocks. Modelling REE trends in skarn garnet is shown to be valuable for constraining conditions during garnet formation and a useful tool for monitoring the evolution of complex skarn deposits.

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&ndash, Pb dating of coffinite hosted in sedimentary units yielded a narrow age range, with a weighted average of 16.98 &plusmn, 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 &plusmn, 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.

Nanoscale characterization (TEM on FIB-SEM-prepared foils) was undertaken on feldspars undergoing transformation from early post-magmatic (deuteric) to hydrothermal stages in granites hosting the Olympic Dam Cu-U-Au-Ag deposit, and from the Cu-Au skarn at Hillside within the same iron-oxide copper-gold (IOCG) province, South Australia. These include complex perthitic textures, anomalously Ba-, Fe-, or REE-rich compositions, and REE-flourocarbonate + molybdenite assemblages which pseudomorph pre-existing feldspars. Epitaxial orientations between cryptoperthite (magmatic), patch perthite (dueteric) and replacive albite (hydrothermal) within vein perthite support interface-mediated reactions between pre-existing alkali-feldspars and pervading fluid, irrespective of micro-scale crystal morphology. Such observations are consistent with a coupled dissolution-reprecipitation reaction mechanism, which assists in grain-scale element remobilization via the generation of transient interconnected microporosity. Micro-scale aggregates of hydrothermal hyalophane (Ba-rich K-feldspar), crystallizing within previously albitized areas of andesine, reveal a complex assemblage of calc-silicate, As-bearing fluorapatite and Fe oxides along reaction boundaries in the enclosing albite-sericite assemblage typical of deuteric alteration. Such inclusions are good REE repositories and their presence supports REE remobilization at the grain-scale during early hydrothermal alteration. Iron-metasomatism is recognized by nanoscale maghemite inclusions within ‘red-stained’ orthoclase, as well as by hematite in REE-fluorocarbonates, which reflect broader-scale zonation patterns typical for IOCG systems. Potassium-feldspar from the contact between alkali-granite and skarn at Hillside is characterized by 100–1000 ppm REE, attributable to pervasive nanoscale inclusions of calc-silicates, concentrated along microfractures, or pore-attached. Feldspar replacement by REE-fluorcarbonates at Olympic Dam and nanoscale calc-silicate inclusions in feldspar at Hillside are both strong evidence for the role of feldspars in concentrating REE during intense metasomatism. Differences in mineralogical expression are due to the availability of associated elements. Lattice-scale intergrowths of assemblages indicative of Fe-metasomatism, REE-enrichment and sulfide deposition at Olympic Dam are evidence for a spatial and temporal relationship between these processes.

The Middleback Ranges is a major iron ore belt in the southeastern region of the Gawler Craton, South Australia, interpreted to be of BIF origin. Iron ore deposits are hosted within ∼2550 Ma metasedimentary rocks of the Middleback Group and occur as a series of N-S trending hills, forming a ∼60 km-long magnetic anomaly. A petrographic-geochemical study of iron-oxides from BIFs and iron ores was undertaken on samples from thirteen locations spanning the strike of the belt. Iron-oxides are texturally diverse due to multiple processes accompanying and postdating ore formation. Primary magnetite features preserved in the southern segment of the belt display distinct overprinting features (e.g., increased porosity, reworked grain boundaries) and multiple generations of growth associated with deposition of trace minerals, including native gold. Northwards along strike, this overprint is expressed by the pseudomorphic replacement of magnetite by hematite (martite) and is locally associated with brecciation, the presence of rare earth element (REE)-minerals, and replacement by iron-hydroxides. Whereas evidence of microplaty hematite accompanying martitization and predating iron-hydroxides is observed throughout the belt, distinct iron-oxide generations postdating the iron-hydroxides are inferred based on compositional zoning with respect to Si and intimate relationships between iron-oxides and -hydroxides. Chondrite-normalized fractionation trends obtained from the various iron-oxides and from different BIF types generally display LREE-enrichment and distinct positive Eu- and Y-anomalies. An increasing ΣREY- and LREE-trend accompanies martitization. The presence of specific element groups, e.g., granitophile elements (U, W, Sn, Mo), or transition metals (Cr, Mn, Co, Ni, Ti, V, Nb) within the lattice of iron-oxides suggests their formation in evolving environments associated with the emplacement of felsic and mafic lithologies, respectively. The impact of local setting on iron-oxide formation is highlighted by complex trace element signatures of iron-oxides; the northern segment of the belt is relatively enriched in As and Sb, while the southern segment is enriched in granitophile elements and REY. Further complexity is shown in the local variation of Mn and Zn in iron-oxides in the southern segment of the belt, where the Iron Magnet deposit shows the strongest correlation between the two elements. Various depositional settings for BIFs are inferred based upon Post-Archean Australian Shale-normalized REY fractionation trends of iron-oxides and various water types. These settings include environments where iron-minerals precipitate from mixtures of 1) anoxic seawater and high-temperature hydrothermal fluids, 2) anoxic seawater and low-temperature hydrothermal fluids, and 3) oxygen-richer seawater and low-temperature hydrothermal fluids. A genetic model for ore formation is proposed based upon textural and compositional variations observed in iron-oxides throughout the belt and includes formation resulting from supergene fluids rich in elements leached from local granites penetrating BIF, interaction with granite-derived hydrothermal fluids, and heat generated during emplacement of younger dikes. Recognition of petrographic features linked to changes in composition demonstrates the utility of iron-oxides to trace iron ore formation in a temporal and spatial context, with implications for ore genesis and models of mineral exploration.

Cu-Fe-sulphide mineral assemblages from the Olympic Dam (OD) Fe-oxide Cu-U-Au-Ag deposit, South Australia, are studied down to the nanoscale to explore the potential these minerals have for understanding genetic processes such as primary deposit zonation. Cu-Fe-sulphide pairs: ‘brown’ bornite associated with chalcopyrite (bornite-chalcopyrite zone); and symplectites of ‘purple’ bornite with species from the chalcocite group, Cu2 − xS (bornite-chalcocite zone), co-define an upwards and inwards deposit-scale zonation at OD. In the bornite-chalcocite zone, there is also an increase in the proportion of chalcocite relative to bornite within the symplectites towards upper levels. In this case, two-phase Cu2 − xS assemblages are also present, as anisotropic, hexagonal chalcocite (CcH) with lamellar exsolutions of digenite, distinguishable at the μm-scale. Using compositional data (electron microprobe) combined with Transmission Electron Microscopy (TEM) study of foils prepared in–situ via Focused Ion Beam (FIB)-SEM, we show that Cu-Fe-sulphides from different ore zones feature nanoscale intergrowths, lattice defects, superstructure domains (na) and antiphase boundary domains (APBs) that can be interpreted as due to exsolution, coarsening and phase transformation during cooling from high-T solid solutions in the system Cu-Fe-S and sub-systems according to published phase diagrams. ‘Brown’ bornite [(Cu + Fe)/S > 5] contains pervasive lamellae of chalcopyrite which extend down to the nanoscale; such specimens appear homogeneous at the μm-scale. ‘Purple bornite’ [(Cu + Fe)/S 300 °C (high-T phases, Cu-poor digenite), followed by cooling along distinct paths down to

The textural relationships and geochemistry of feldspars from least-altered to sericite-hematite altered and mineralised ~ 1.595 Ga Roxby Downs Granite (RDG) at Olympic Dam, South Australia, were examined. The sample suite is representative of RDG both distal (> 5 km) and proximal ( 27–34 ) is recognised, along with a more abundant, less-calcic plagioclase (~ An 12–20 ) both displaying rapakivi and anti-rapakivi textures with alkali feldspar. Alkali feldspars (~ Or 55 Ab 43 An 2 ) record post-magmatic evolution from cryptoperthite to patch perthite. Subsequent patch perthite is overprinted by highly porous, near end-member albite and K-feldspar, while plagioclase undergoes replacement by albite + sericite ± Ba-rich K-feldspar. In sericite-hematite altered and mineralised RDG along the margin of the ODBC, sericite replaces all plagioclase, whereas red-stained, Fe-rich K-feldspar persists. Sulphide-uranium-rare earth element mineralisation is observed in association with hydrothermal feldspars, and increases in abundance with proximity to the orebody. Petrographic observations and whole-rock geochemistry illustrate the transformation of plagioclase and alkali feldspar from igneous to hydrothermal processes, and indicate that hydrothermal albite and K-feldspar formed within the RDG without the need for an external source of alkalis. Feldspar geothermometry indicates a minimum crystallisation temperature of 765 °C at 2.2 kbar for alkali feldspar (pressure estimate obtained using plagioclase-amphibole geobarometry) followed by a range of lower temperature transformations. Late-stage magma mixing/contamination is postulated from supportive temperature and pressure estimates along with feldspar and mafic mineral relationships.

Minerals form in all types of chemical and physical environments [...]

Titanite textures and chemistry have been investigated from the Roxby Downs Granite, host to the Olympic Dam Cu–U–Au–Ag deposit, South Australia. Three textural subtypes of titanite are documented: primary magmatic (cores and rims); deuteric; and hydrothermal (low T recrystallisation). Magmatic cores are defined by enrichment in LREE (~ 3 wt%), Nb (up to 1 wt%) and Zr relative to rims, which typically contain

Metal nanoparticles (NP) in minerals are an emerging field of research. Development of advanced analytical techniques such as Z-contrast imaging and mapping using high-angle annular dark field scanning transmission electron microscopy (HAADF STEM) allows unparalleled insights at the nanoscale. Moreover, the technique provides a link between micron-scale textures and chemical patterns if the sample is extracted in situ from a location of petrogenetic interest. Here we use HAADF STEM imaging and energy-dispersive X-ray spectrometry (EDX) mapping/spot analysis on focused ion beam prepared foils to characterise atypical Cu-As-zoned and weave-twinned hematite from the Olympic Dam deposit, South Australia. We aim to determine the role of solid-solution versus the presence of discrete included NPs in the observed zoning and to understand Cu-As-enrichment processes. Relative to the grain surface, the Cu-As bands extend in depth as (sub)vertical trails of opposite orientation, with Si-bearing hematite NP inclusions on one side and coarser cavities (up to hundreds of nm) on the other. The latter host Cu and Cu-As NPs, contain mappable K, Cl, and C, and display internal voids with rounded morphologies. Aside from STEM-EDX mapping, the agglomeration of native copper NPs was also assessed by high-resolution imaging. Collectively, such characteristics, corroborated with the geometrical outlines and negative crystal shapes of the cavities, infer that these are opened fluid inclusions with NPs attached to inclusion walls. Hematite along the trails features distinct nanoscale domains with lattice defects (twins, 2-fold superstructuring) relative to hematite outside the trails, indicating this is a nanoprecipitate formed during replacement processes, i.e., coupled dissolution and reprecipitation reactions (CDRR). Transient porosity intrinsically developed during CDRR can trap fluids and metals. Needle-shaped and platelet Cu-As NPs are also observed along (sub)horizontal bands along which Si, Al and K is traceable along the margins. The same signature is depicted along nm-wide planes crosscutting at 60&deg, and offsetting (012)-twins in weave-twinned hematite. High-resolution imaging shows linear and planar defects, kink deformation along the twin planes, misorientation and lattice dilation around duplexes of Si-Al-K-planes. Such defects are evidence of strain, induced during fluid percolation along channels that become wider and host sericite platelets, as well as Cl-K-bearing inclusions, comparable with those from the Cu-As-zoned hematite, although without metal NPs. The Cu-As-bands mapped in hematite correspond to discrete NPs formed during interaction with fluids that changed in composition from alkali-silicic to Cl- and metal-bearing brines, and to fluid rates that evolved from slow infiltration to erratic inflow controlled by fault-valve mechanism pumping. This explains the presence of Cu-As NPs hosted either along Si-Al-K-planes (fluid supersaturation), or in fluid inclusions (phase separation during depressurisation) as well as the common signatures observed in hematite with variable degrees of fluid-mineral interaction. The invoked fluids are typical of hydrolytic alteration and the fluid pumping mechanism is feasible via fault (re)activation. Using a nanoscale approach, we show that fluid-mineral interaction can be fingerprinted at the (atomic) scale at which element exchange occurs.

The petrography and geochemistry of zircon offers an exciting opportunity to better understand the genesis of, as well as identify pathfinders for, large magmatic&ndash, hydrothermal ore systems. Electron probe microanalysis, laser ablation inductively coupled plasma mass spectrometry, high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) imaging, and energy-dispersive X-ray spectrometry STEM mapping/spot analysis were combined to characterize Proterozoic granitic zircon in the eastern Gawler Craton, South Australia. Granites from the ~1.85 Ga Donington Suite and ~1.6 Ga Hiltaba Suite were selected from locations that are either mineralized or not, with the same style of iron-oxide copper gold (IOCG) mineralization. Although Donington Suite granites are host to mineralization in several prospects, only Hiltaba Suite granites are considered &ldquo, fertile&rdquo, in that their emplacement at ~1.6 Ga is associated with generation of one of the best metal-endowed IOCG provinces on Earth. Crystal oscillatory zoning with respect to non-formula elements, notably Fe and Cl, are textural and chemical features preserved in zircon, with no evidence for U or Pb accumulation relating to amorphization effects. Bands with Fe and Ca show mottling with respect to chloro&ndash, hydroxy&ndash, zircon nanoprecipitates. Lattice defects occur along fractures crosscutting such nanoprecipitates indicating fluid infiltration post-mottling. Lattice stretching and screw dislocations leading to expansion of the zircon structure are the only nanoscale structures attributable to self-induced irradiation damage. These features increase in abundance in zircons from granites hosting IOCG mineralization, including from the world-class Olympic Dam Cu&ndash, U&ndash, Au&ndash, Ag deposit. The nano- to micron-scale features documented reflect interaction between magmatic zircon and corrosive Fe&ndash, Cl-bearing fluids in an initial metasomatic event that follows magmatic crystallization and immediately precedes deposition of IOCG mineralization. Quantification of &alpha, decay damage that could relate zircon alteration to the first percolation point in zircon gives ~100 Ma, a time interval that cannot be reconciled with the 2&ndash, 4 Ma period between magmatic crystallization and onset of hydrothermal fluid flow. Crystal oscillatory zoning and nanoprecipitate mottling in zircon intensify with proximity to mineralization and represent a potential pathfinder to locate fertile granites associated with Cu&ndash, Au mineralization.

Scheelite (CaWO4) and powellite (CaMoO4) are isostructural minerals considered as a non-ideal solid solution series. Micron- to nanoscale investigation of a specimen of skarnoid from Zhibula, Gangdese Belt, Tibet, China, was carried out to assess the identity of the phases within a broad scheelite-powellite (Sch-Pow) compositional range, and to place additional constraints on redox changes during ore formation. An electron probe microanalysis shows that Mo-rich domains within complex oscillatory-zoned single crystals, and as thin sliver-like domains, have a compositional range from 20 mol.% to 80 mol.% Pow. These occur within a matrix of unzoned, close-to-end-member scheelite aggregates (87 mol.%&ndash, 95 mol.% Sch). Laser-ablation inductively coupled plasma mass spectrometry spot analysis and element mapping reveal systematic partitioning behaviour of trace elements in skarn minerals (grossular50, diopside80, anorthite, and retrograde clinozoisite) and scheelite-powellite aggregates. The Mo-rich domains feature higher concentrations of As, Nb, and light rare earth elements LREE, whereas W-rich domains are comparatively enriched in Y and Sr. Transmission electron microscopy (TEM) was carried out on focused-ion-beam-prepared foils extracted in situ from domains with oscillatory zoning occurring as slivers of 20 mol.%&ndash, 40 mol.% Pow and 48 mol.%&ndash, 80 mol.% Pow composition within an unzoned low-Mo matrix (20 mol.% Pow). Electron diffractions, high-angular annular dark field (HAADF) scanning-TEM (STEM) imaging, and energy-dispersive spectroscopy STEM mapping show chemical oscillatory zoning with interfaces that have continuity in crystal orientation throughout each defined structure, zoned grain or sliver. Non-linear thermodynamics likely govern the patterning and presence of compositionally and texturally distinct domains, in agreement with a non-ideal solid solution. We show that the sharpest compositional contrasts are also recognisable by variation in growth direction. Atomic-scale resolution imaging and STEM simulation confirm the presence of scheelite-powellite within the analysed range (20 mol.%&ndash, 80 mol.% Pow). Xenotime-(Y) inclusions occur as nm-wide needles with epitaxial orientation to the host scheelite-powellite matrix throughout both types of patterns, but no discrete Mo- or W-bearing inclusions are observed. The observed geochemical and petrographic features can be reconciled with a redox model involving prograde deposition of a scheelite+molybdenite assemblage (reduced), followed by interaction with low-T fluids, leading to molybdenite dissolution and reprecipitation of Mo as powellite-rich domains (retrograde stage, oxidised). The observation of nanoscale inclusions of xenotime-(Y) within scheelite carries implications for the meaningful interpretation of petrogenesis based on rare earth element (REE) concentrations and fractionation patterns. This research demonstrates that HAADF-STEM is a versatile technique to address issues of solid solution and compositional heterogeneity.

Many analytical techniques for trace element analysis are available to the geochemist and geometallurgist to understand and, ideally, quantify the distribution of trace and minor components in a mineral deposit. Bulk trace element data are useful, but do not provide information regarding specific host minerals&mdash, or lack thereof, in cases of surface adherence or fracture fill&mdash, for each element. The CAMECA nanoscale secondary ion mass spectrometer (nanoSIMS) 50 and 50L instruments feature ultra-low minimum detection limits (to parts-per-billion) and sub-micron spatial resolution, a combination not found in any other analytical platform. Using ore and copper concentrate samples from the Olympic Dam mining-processing operation, South Australia, we demonstrate the application of nanoSIMS to understand the mineralogical distribution of potential by-product and detrimental elements. Results show previously undetected mineral host assemblages and elemental associations, providing geochemists with insight into mineral formation and elemental remobilization&mdash, and metallurgists with critical information necessary for optimizing ore processing techniques. Gold and Te may be seen associated with brannerite, and Ag prefers chalcocite over bornite. Rare earth elements may be found in trace quantities in fluorapatite and fluorite, which may report to final concentrates as entrained liberated or gangue-sulfide composite particles. Selenium, As, and Te reside in sulfides, commonly in association with Pb, Bi, Ag, and Au. Radionuclide daughters of the 238U decay chain may be located using nanoSIMS, providing critical information on these trace components that is unavailable using other microanalytical techniques. These radionuclides are observed in many minerals but seem particularly enriched in uranium minerals, some phosphates and sulfates, and within high surface area minerals. The nanoSIMS has proven a valuable tool in determining the spatial distribution of trace elements and isotopes in fine-grained copper ore, providing researchers with crucial evidence needed to answer questions of ore formation, ore alteration, and ore processing.

Compositionally zoned uraninite from the Olympic Dam iron oxide-copper-gold deposit is rarely preserved, but represents an early product of in situ transformation of primary uraninite. Electron backscatter diffraction data (inverse pole figure, image quality, and grain reference orientation deviation mapping) reveal formation of zoned uraninite to be the result of a sequence of superimposed effects rather than from primary growth mechanisms alone. This is the first known microstructural analysis of uraninite showing crystal-plastic deformation of uraninite via formation and migration of defects and dislocations into tilt boundaries. Defining grain-scale characteristics and microstructural features in radiogenically modified minerals like uraninite carries implications in better understanding the processes involved in their formation, highlights limitations in the use of uraninite for U-Pb chemical ages, as well as for constraining the incorporation and release of daughter radioisotopes, especially where zoning, porosity, fractures, and microstructures are present.

There is an abundance of published trace element data for sphalerite, galena and chalcopyrite in natural systems, yet for a co-crystallized assemblage comprising these base metal sulphides, there is no detailed understanding of the preferred host of many trace elements. Laser-ablation inductively-coupled plasma mass spectrometry trace element maps and spot analyses were generated on 17 assemblages containing co-crystallized sphalerite and/or galena and/or chalcopyrite from 9 different ore deposits. These deposits are representative of different ore types, geologic environments and physiochemical conditions of ore formation, as well as superimposed syn-metamorphic remobilisation and recrystallization. The primary factors that control the preferred base metal sulphide host of Mn, Fe, Co, Cu, Zn, Ga, As, Se, Ag, Cd, In, Sb, Te, Tl and Bi are element oxidation state, ionic radius of the substituting element, element availability and the maximum trace element budget that a given sulphide mineral can accommodate. Temperature, pressure, redox conditions at time of crystallization and metal source, do not generally appear to influence the preferred base metal sulphide host of all the trace elements. Exceptions are Ga, In and Sn recrystallized at high metamorphic grades, when the preferred host of Ga and Sn usually becomes chalcopyrite. In more typical lower temperature ores, the preferred host of Ga is sphalerite. Indium concentrations also increase in chalcopyrite during recrystallization. At lower temperatures the partitioning behaviour of Sn remains poorly constrained and shows little predictable pattern among the data here. The results obtained may be used as a tool to assess co-crystallization. If trace element distributions in a given base metal sulphide assemblage match those reported here, and assuming those distributions have not been significantly altered post (re-) crystallization, then it may be suggestive of a co-crystallized assemblage. Such information provides a foundation for novel attempts to develop trace element-in-sulphide geothermometers.

The Olympic Dam IOCG-U-Ag deposit, South Australia, the world’s largest known uranium (U) resource, contains three main U-minerals: uraninite, coffinite, and brannerite. Four main classes of uraninite have been identified. Uraninite occurring as single grains is characterized by high-Pb and ΣREE+Y (ΣREY) but based on textures can be classified into three of these classes, typically present in the same sample. Primary uraninite (Class 1) is smallest (10–50 μm), displays a cubic-euhedral habit, and both oscillatory and sectorial zoning. “Zoned” uraninite (Class 2) is coarser, sub-euhedral, and combines different styles of zonation in the same grain. “Cobweb” uraninite (Class 3) is coarser still, up to several hundred micrometers, has variable hexagonal-octagonal morphologies, varying degrees of rounding, and features rhythmic intergrowths with sulfide minerals. In contrast, the highest-grade U in the deposit is found as micrometer-sized grains to aphanitic varieties of uraninite that form larger aggregates (up to millimeter) and vein-fillings (massive, Class 4) and have lower Pb and ΣREY, but higher Ca. Nanoscale characterization of primary and cobweb uraninite shows these have defect-free fluorite structure. Both contain lattice-bound Pb+ΣREY, which for primary uraninite is concentrated within zones, and for cobweb uraninite is within high-Pb+ΣREY domains. Micro-fractured low-Pb+ΣREY domains, sometimes with different crystal orientation to the high-Pb+ΣREY domains in the same cobweb grain, contain nanoscale inclusions of galena, Cu-Fe-sulfides, and REY-minerals. The observed Pb zonation and presence of inclusions indicates solid-state trace-element mobility during the healing of radiogenic damage, and subsequent inclusion-nucleation + recrystallization during ![Formula][1] -driven percolation of Cu-bearing fluid. Tetravalent, lattice-bound radiogenic Pb is proposed based on analogous evidence for U-bearing zircon. Calculating the crystal chemical formula to UO2 stoichiometry, the sum of cations (M*) is ~1 for most classes, but the presence of mono-, di-, and trivalent elements (ΣREY, Ca, etc.) drive stoichiometry toward hypostoichiometric M*O2–x. In the absence of measured O and constraints of hypostoichiometric fluorite-structure, charge-balance calculations showing O deficit in the range 0.15–0.36 apfu is compensated by assumption of mixed U oxidation states. Crystal structural formulas show up to 0.20 apfu Pb and 0.25 apfu ΣREY in Classes 1–3, while for Class 4, these are an order of magnitude less. Low-Pb and ΣREY subcategories of Classes 2 and 3 are similar to massive uraninite with ~0.2 apfu Ca. Other elements (Si, Na, Mn, As, Nb, etc.), show two distinct geochemical trends: (1) across Classes 1–3; and (2) Class 4, whereby low-Pb+ΣREY sub-populations of Classes 2 and 3 are part of trend 2 for certain elements. Plots of alteration factor (CaO+SiO2+Fe2O3) vs. Pb/U suggest two uraninite generations: early (high-Pb+ΣREY, Classes 1–3); and late (massive, Class 4). There is evidence of Pb loss from diffusion, leaching and/or recrystallization for Classes 2–3 (low-Pb+ΣREY domains). Micro-analytical data and petrographic observations reported here, including nanoscale characterization of individual uraninite grains, support the hypothesis for at least two main uraninite mineralizing events at Olympic Dam and multiple stages of U dissolution and reprecipitation. Early crystalline uraninite is only sparsely preserved, with the majority of uraninite represented by the massive-aphanitic products of post-1590 Ma dissolution, reprecipitation, and possibly addition of uranium into the system. Coupled dissolution-reprecipitation reactions are suggested for early uraninite evolution across Classes 1 to 3. The calculated oxidation state [U6+/(U4++U6+)] of the “early” and “late” populations point to different conditions at the time of formation (charge compensation for ΣREY-rich early fluids) rather than auto-oxidation of uraninite. Late uraninites may have formed hydrothermally at lower temperatures ( T < 250 °C). [1]: /embed/mml-math-1.gif

The Zijinshan orefield is a Cu–Au–Mo–Ag porphyry–epithermal mineralization system of Cretaceous age in southeastern China, comprising the Zijinshan high-sulfidation (HS) Au–Cu deposit, Luoboling porphyry Cu–Mo deposits, Yueyang low-sulfidation Au–Ag–Cu deposit, and Wuziqilong and Longjiangting intermediate-sulfidation (IS) Cu deposit. A number of Sn-(W)-sulfides occur in the Zijinshan orefield, including kiddcreekite, hemusite, colusite, vinciennite, stannoidite, mawsonite and kesterite. The occurrence represents the first report of hemusite, colusite and vinciennite in China. The relative abundance and diversity of Sn-(W)-sulfide-bearing assemblages make the Zijinshan orefield possibly unique in the world, and carries implications for the evolution of the mineralizing environment. Detailed electron probe studies of the Sn-minerals reveal that kiddcreekite, hemusite, mawsonite, stannoidite and kesterite have compositions close to ideal formulae. In contrast, colusite displays grain-scale zoning expressed by W, Sn and As. Vinciennite displays compositional variation depending on mineralization style: an average composition of Cu 10.74 Fe 3.88 Sn(As 0.85 ,Sb 0.08 )S 15.4 in the Zijinshan HS deposit, Cu 10.71 Fe 3.9 SnAs 0.85 S 15.34 in the Wuziqilong Cu deposit and Cu 10.76 Fe 3.7 Sn 1.02 (As 0.5 ,Sb 0.45 )S 15.54 with higher Sb contents (3.32%) in the adjacent Longjiangting Cu deposit. In the Zijinshan HS Au–Cu deposit, the main Cu-mineral assemblage varies from bornite-rich to digenite- to covellite-rich with increasing depth. Correspondingly, tin mineralogy varies from kesterite at upper levels to stannoidite-dominant at mid-to-upper levels of the copper orebody, to vinciennite- and mawsonite-dominant at depth, implying an increase in sulfidation and oxidation state downwards. Moreover, kiddcreekite is always partially replaced by wolframite and (hypogene) covellite at depth, also indicating overprinting by high- f O 2 and - f S 2 fluids in the covellite stage of mineralization. Kiddcreekite, along with a primary chalcopyrite–pyrite mineral association, occurs widely in the Zijinshan orefield (Zijinshan, Yueyang, Luoboling, Wuziqilong, Longjiangting and Dayanli), and is likely indicative of the early IS stage of epithermal system. Analogous with published data, kiddcreekite most commonly occurs in porphyry-style mineralization, implying the presence of the mineral has potential as an indicator of porphyry systems. Vinciennite-bearing Cu–Sn–As mineral associations occur in a specific position in the Zijinshan HS Au–Cu, Wuziqilong and Longjiangting Cu deposits, indicative of a transitional zone between porphyry and HS epithermal-style mineralization. The occurrence of the identified Sn-(W)-sulfide-bearing assemblages has considerable potential implications for understanding the architecture of a complex porphyry–epithermal environment and for exploration for underlying porphyry copper deposits. There is potential for discovery of a subjacent porphyry Cu deposit within the Zijinshan orefield.

The supergiant Olympic Dam Cu-U-Au-Ag deposit in South Australia is a type example of the iron-oxide copper–gold (IOCG) deposit family. Hosted entirely within heterogeneous breccia in 1.59 Ga granite, the deposit contains a volumetrically substantial and mineralogically diverse component of carbonate minerals. Carbonate minerals are always associated with ore minerals (sulfides, uraninite), implying a genetic relationship and providing an opportunity to use gangue carbonates to better understand ore formation. This study provides the first detailed and comprehensive petrographic and chemical/isotopic study of Olympic Dam carbonates, with a particular emphasis on petrography and texture, and an attempt is made to relate carbonate formation to local and regional events that have affected Olympic Dam. Based on a set of 196 carbonate-bearing samples, carbonate minerals are observed in all lithologies present at Olympic Dam. Carbonates occur as cement in breccia and conglomerates, as breccia clasts, in veins crosscutting ore-rich breccia and other rock types, in pores and ooids, and in the form of laminated carbonate. Siderite and siderite-rhodochrosite-magnesite solid solution are by far the most common carbonate types, whereas calcite, dolomite-ankerite solid solution and REE-fluorocarbonates are locally abundant. Single carbonate grains typically show compositional zones (simple or oscillatory) and replacement textures (including mutual replacement of carbonates with other carbonates and with hematite) are common. In the absence of consistent, deposit-wide paragenetic relationships, the carbonates were placed in seven associations based on host rock, mineralogy and texture: (1) coarse-grained calcite veins in weakly brecciated granite and rhyolite, (2) carbonates in strongly brecciated granite, (3) carbonate veins in bedded clastic facies, (4) carbonates in mafic and ultramafic igneous rocks, (5) massive barite-fluorite-dominated veins with minor carbonate, (6) laminated siderite, and (7) carbonate matrix in conglomerate-breccia-sandstone above the unconformity. Some of these associations can be related to regional tectonic events based on local context and relationships with dated assemblages. δ13C (−6.5‰ to −2‰) values for the carbonates show a relatively limited range whereas δ18O is more variable (+9.4‰ to + 20.9‰). C-O isotopic compositions for the various carbonate associations tend to overlap, suggestive of mixed fluid sources, recycling of older carbonate and perhaps other fractionation processes. The C-O isotope data overlap the compositional fields of several major carbon–oxygen reservoirs (magmatic, sedimentary) and carbon sources in local granite, felsic volcanics, older BIF and sedimentary rocks are all possible at different stages of carbonate deposition.

Spatial associations between banded iron formation and iron-oxide Cu-Au (IOCG) style mineralization are well documented in the Gawler Craton (South Australia), but the possible genetic relationships between these two distinct types of mineralization are hitherto unclear. A texturally conspicuous generation of coarse-grained silician magnetite, intergrown with carbonates and quartz, is observed in drillholes intersecting the ‘outer shell’ of the Olympic Dam IOCG-type deposit. This magnetite is characterised by high U-content (~50 ppm), siliceous chemistry, and unusual zonal textures with respect to Si-Fe-nanoprecipitates. Direct dating of this magnetite by laser ablation inductively coupled plasma mass spectrometry yields reproducible 207Pb/206Pb dates (1761 ± 16 Ma) that are significantly older than the granite hosting the deposit (1593 Ma), or the mineralized breccias constituting the Cu-U-Au-Ag resource (~1592–1589 Ma). The older, Fe-rich crustal material can be correlated with the ~1.76–1.74 Ga (meta)sedimentary Wallaroo Group, host to Fe-rich horizons across the Gawler Craton, including locations ~15 km NW of Olympic Dam. A generation of granitic rocks, which intruded bedrock at ~1.75 Ga are present ~30 km NE of Olympic Dam, and likely exsolved hydrothermal fluids that enriched pre-existing magnetite-bearing protoliths in both U and REE. Such material was physically, and likely chemically, incorporated into the ‘outer shell’ at Olympic Dam some ~150 Ma later, during granite uplift along faults. The coincidence between Fe-rich horizons/BIF and ~1750 Ma granitoids may have provided IOCG systems with an additional source of both Fe and U that predates the ~1.59 Ga craton-scale metallogenic event. The uranium concentrations in some South Australian IOCG systems represent major global anomalies in the element. A combination of the fortuitous geological circumstances outlined here, may help explain the highly anomalous accumulation of uranium found at Olympic Dam.

Trace element signatures in apatite are used to study hydrothermal processes due to the ability of this mineral to chemically record and preserve the impact of individual hydrothermal events. Interpretation of rare earth element (REE)-signatures in hydrothermal apatite can be complex due to not only evolving fO2, fS2 and fluid composition, but also to variety of different REE-complexes (Cl-, F-, P-, SO4, CO3, oxide, OH&minus, etc.) in hydrothermal fluid, and the significant differences in solubility and stability that these complexes exhibit. This contribution applies numerical modeling to evolving REE-signatures in apatite within the Olympic Dam iron-oxide-copper-gold deposit, South Australia with the aim of constraining fluid evolution. The REE-signatures of three unique types of apatite from hydrothermal assemblages that crystallized under partially constrained conditions have been numerically modeled, and the partitioning coefficients between apatite and fluid calculated in each case. Results of these calculations replicate the measured data well and show a transition from early light rare earth element (LREE)- to later middle rare earth element (MREE)-enriched apatite, which can be achieved by an evolution in the proportions of different REE-complexes. Modeling also efficiently explains the switch from REE-signatures with negative to positive Eu-anomalies. REE transport in hydrothermal fluids at Olympic Dam is attributed to REE&ndash, chloride complexes, thus explaining both the LREE-enriched character of the deposit and the relatively LREE-depleted nature of later generations of apatite. REE deposition may, however, have been induced by a weakening of REE&ndash, Cl activity and subsequent REE complexation with fluoride species. The conspicuous positive Eu-anomalies displayed by later apatite with are attributed to crystallization from high pH fluids characterized by the presence of Eu3+ species.

Symplectites comprising clausthalite (PbSe) and host Cu-(Fe)-sulphides (chalcocite, bornite, and chalcopyrite) are instructive for constraining the genesis of Cu-Au-(U) ores if adequately addressed at the nanoscale. The present study is carried out on samples representative of all three Cu-(Fe)-sulphides displaying clausthalite inclusions that vary in size, from a few µm down to the nm-scale ( 265 °C. A minimum temperature of 165 °C is considered for clausthalite-bearing symplectites from the relationships with antiphase boundaries in 6a digenite. The results show that alongside rods, blebs, and needle-like grains of clausthalite within the chalcocite that likely formed via exsolution, a second, overprinting set of replacement textures, extending down to the nanoscale, occurs and affects the primary symplectites. In addition, other reactions between pre-existing Se, present in solid solution within the Cu-(Fe)-sulphides, and Pb, transported within a fluid phase, account for the formation of composite, commonly pore-attached PbSe and Bi-bearing nanoparticles within the chalcopyrite. The inferred reorganisation of PbSe nanoparticles into larger tetragonal superlattices represents a link between the solid solution and the symplectite formation and represents the first such example in natural materials. Epitaxial growth between clausthalite and monazite is further evidence for the interaction between pre-existing Cu ores and fluids carrying REE, P, and most likely Pb. In U-bearing ores, such Pb can form via decay of uranium within the ore, implying hydrothermal activity after the initial ore deposition. The U-Pb ages obtained for such ores therefore need to be carefully assessed as to whether they represent primary ore deposition or, more likely, an overprinting event. A latest phase of fluid infiltration is the recognised formation of Cu-selenide bellidoite (Cu2Se), as well as Fe oxides.