Carbon compounds in the West Kimberley lamproites (Australia) : Insights from melt and fluid inclusions

Petrological and geochemical studies of lamproites can provide useful insights into the nature of their lithospheric mantle sources, but their geochemical and mineralogical diversity has complicated our understanding of their primary/parental melt composition, volatile (CO2, H2O) inventory and magmatic evolution. To help address this issue, we present a detailed study of different generations (primary, pseudo-secondary, secondary) of crystal, and melt and fluid inclusions in olivine, Cr-spinel and perovskite from three olivine lamproites in the Ellendale Field of the West Kimberley Province (Australia) in order to understand the composition and evolution of their parental magmas. Melt inclusions in the different host minerals and from each of these localities are broadly similar to each other and consist of glass, alkali/alkali-earth (Mg-Ca-K-Na-Ba) carbonates, phosphates and chlorides, in addition to minerals typical of lamproite groundmass (fluorapatite, perovskite, phlogopite, diopside, wadeite, Mg-ilmenite, Fe-Mg-Ti-Cr spinel). The dominant volatile species in the melt and fluid inclusions is CO2 based on Raman data. Heating experiments of melt/fluid inclusions in olivine show significant phase transformations in which the carbonate may separate into an immiscible carbonate-rich sulphatebearing fraction or exsolve a CO2 fluid. Our results indicate that carbonates, along with alkali/alkali-earths, halogens and sulphur, became progressively concentrated in the West Kimberley lamproitic magmas during crystallisation, leading to the entrapment of a complex array of daughter minerals, some not previously reported from lamproites and, in some inclusions, immiscible carbonate melt. The widespread occurrence of daughter carbonates in melt/fluid inclusions in lamproite minerals is at odds with their apparent paucity in the lamproite groundmass. The presence of carbonate and the abundance of CO2-rich and H2O-poor melt and fluid inclusions are attributed to the preferential partitioning of CO2 into the vapour and retention of H2O in the magma during degassing, coupled with H2O loss by post-entrapment modification of the inclusions through H+ diffusion. (C) 2022 Published by Elsevier B.V. on behalf of International Association for Gondwana Research.Peer reviewe

Feldspar mineralogy and rare-earth element (re)mobilization in iron-oxide copper gold systems from South Australia: a nanoscale study

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, andREE-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

Tin-bearing magnetite with nanoscale Mg-Si defects: Evidence for the early stages of mineralization in a skarn system

Tin-bearing magnetite is reported from several types of magmatic-hydrothermal ore deposits. The question of whether tin is incorporated within solid solution, as Sn4+, or as nanoinclusions remains open, however. We report a micron- to nanoscale investigation of Sn (Mg, Si)-bearing magnetite from serpentinite in the Dulong Zn-Sn-In skarn, South China, with the dual aims of understanding the mechanisms involved in accommodating Sn and associated elements into the Fe-oxide, and the inferences that this carries for constraining the early stages of skarn formation. Magnetite preserves a range of textures that record the evolution of metasomatism during prograde growth of grain cores and retrograde rim replacement. Observations reveal the presence of chondrodite and sellaite (MgF2) as nanoscale inclusions preserved in magnetite. This implies initiation of the Dulong mineralizing system during a humite-bearing, magnesium skarn stage. Magnesium-Si defects, forming along (110) planes prior to Sn-enrichment, are recognized for the first time. Release of high volatile, F-rich fluids is interpreted to lead to precipitation of cassiterite inclusions along <111*> directions in magnetite

Recovery of Rare Earth Elements Minerals from Iron-Oxide-Silicate-Rich Tailings: Research Review

The rapid depletion of high-grade rare earth elements (REE) resources implies that future supplies may be augmented with low-grade ores, tailings, and other unconventional resources to meet cut-off grades and, subsequently, supply demands. This paper presents an amalgamation of studies conducted on selected complex low-grade iron-oxide-silicate-rich tailings, with the overall aim of developing efficacious methods and associated process mineralogy characterization for enhanced REE minerals recovery and upgrade. To this end, a summary of the overarching key results from froth flotation, magnetic separation, and gravity separation studies of the tailings and their implications are presented in this review. Reconciliation of all the findings reveals lucid links between feed ore properties, mainly mineralogy and particle size distribution, as the key influential factors that affect the beneficiation of real complex low-grade tailings, although distinct differences in physicochemical properties of the valuable and gangue minerals may exist. It is clearly established that the unliberated association between REE and gangue minerals within the ore can lead to either synergistic or antagonistic effects on the quality of concentrates produced. Furthermore, the limitations presented by the poorly liberated minerals are exacerbated by their “fine” nature. With appreciable recoveries obtained using such readily available conventional separation methods, the tailings provide additional REE value to the primary commodities; hence, such material could be considered a potential resource for REE beneficiation. The learnings from the respective beneficiation studies are significantly important as they provide the knowledge base and greater understanding of the mineralogical characteristics and beneficiation response of REE minerals in typical complex, low-grade tailings

Recovery of Rare Earth Elements Minerals from Iron-Oxide-Silicate-Rich Tailings: Research Review

The rapid depletion of high-grade rare earth elements (REE) resources implies that future supplies may be augmented with low-grade ores, tailings, and other unconventional resources to meet cut-off grades and, subsequently, supply demands. This paper presents an amalgamation of studies conducted on selected complex low-grade iron-oxide-silicate-rich tailings, with the overall aim of developing efficacious methods and associated process mineralogy characterization for enhanced REE minerals recovery and upgrade. To this end, a summary of the overarching key results from froth flotation, magnetic separation, and gravity separation studies of the tailings and their implications are presented in this review. Reconciliation of all the findings reveals lucid links between feed ore properties, mainly mineralogy and particle size distribution, as the key influential factors that affect the beneficiation of real complex low-grade tailings, although distinct differences in physicochemical properties of the valuable and gangue minerals may exist. It is clearly established that the unliberated association between REE and gangue minerals within the ore can lead to either synergistic or antagonistic effects on the quality of concentrates produced. Furthermore, the limitations presented by the poorly liberated minerals are exacerbated by their “fine” nature. With appreciable recoveries obtained using such readily available conventional separation methods, the tailings provide additional REE value to the primary commodities; hence, such material could be considered a potential resource for REE beneficiation. The learnings from the respective beneficiation studies are significantly important as they provide the knowledge base and greater understanding of the mineralogical characteristics and beneficiation response of REE minerals in typical complex, low-grade tailings

Focused Ion Beam and Advanced Electron Microscopy for Minerals: Insights and Outlook from Bismuth Sulphosalts

This paper comprises a review of the rapidly expanding application of nanoscale mineral characterization methodology to the study of ore deposits. Utilising bismuth sulphosalt minerals from a reaction front in a skarn assemblage as an example, we illustrate how a complex problem in ore petrology, can be approached at scales down to that of single atoms. We demonstrate the interpretive opportunities that can be realised by doing this for other minerals within their petrogenetic contexts. From an area defined as Au-rich within a sulphosalt-sulphide assemblage, and using samples prepared on a Focused Ion Beam–Scanning Electron Microscopy (SEM) platform, we identify mineral species and trace the evolution of their intergrowths down to the atomic scale. Our approach progresses from a petrographic and trace element study of a larger polished block, to high-resolution Transmission Electron Microscopy (TEM) and High Angle Annular Dark Field (HAADF) Scanning-TEM (STEM) studies. Lattice-scale heterogeneity imaged in HAADF STEM mode is expressed by changes in composition of unit cell slabs followed by nanoparticle formation and their growth into “veins”. We report a progressive transition from sulphosalt species which host lattice-bound Au (neyite, lillianite homologues; Pb-Bi-sulphosalts), to those that cannot accept Au (aikinite). This transition acts as a crystal structural barrier for Au. Fine particles of native gold track this progression over the scale of several hundred microns, leading to Au enrichment at the reaction front defined by an increase in the Cu gradient (several wt %), and abrupt changes in sulphosalt speciation from Pb-Bi-sulphosalts to aikinite. Atom-scale resolution imaging in HAADF STEM mode allows for the direct visualisation of the three component slabs in the neyite crystal structure, one of the largest and complex sulphosalts of boxwork-type. We show for the first time the presence of aikinite nanoparticles a few nanometres in size, occurring on distinct (111)PbS slabs in the neyite. This directly explains the non-stoichiometry of this phase, particularly with respect to Cu. Such non-stoichiometry is discussed elsewhere as defining distinct mineral species. The interplay between modular crystal structures and trace element behaviour, as discussed here for Au and Cu, has applications for other mineral systems. These include the incorporation and release of critical metals in sulphides, heavy elements (U, Pb, W) in iron oxides, the distribution of rare earth elements (REE), Y, and chalcophile elements (Mo, As) in calcic garnets, and the identification of nanometre-sized particles containing daughter products of radioactive decay in ores, concentrates, and tailings

Carbonates at the supergiant Olypmic Dam Cu-U-Au-Ag deposit, South Australia part 2: Sm-Nd, Lu-Hf and Sr-Pb isotope constraints on the chronology of carbonate deposition

Mineralization at the supergiant Cu-U-Au-Ag Olympic Dam deposit (South Australia), the 'uranium endmember' of the iron-oxide copper-gold (IOCG) spectrum of ore deposits, is hosted in a breccia complex developed entirely within granite of the 1.59 Ga Hiltaba Suite (Gawler Craton). Earlier studies suggested brecciation and mineralization occurred within a magmatically-driven hydrothermal system at 1.59 Ga, with a critical role for mafic-ultramafic intrusions. In contrast, recent radiometric dating of the breccia complex indicates a prolonged, multi-stage history of brecciation and mineralization from 1.59 to 0.5-0.4 Ga. Ca-Fe-Mg-Mn-carbonate gangue minerals are associated with ore minerals at virtually every stage of mineralization. In a companion study (Apukhtina et al., 2020), this mineralogically, texturally and compositionally diverse carbonate mineral suite was assigned to seven associations defined on the basis of host lithology and texture. Here we report Sm-Nd, Pb-Pb and Lu-Hf isotope ages for these carbonates, which are used to examine the chronology of carbonate deposition. Initial Sr-Nd isotopic compositions are used to place constraints on fluid sources. Sm-Nd and Pb-Pb isotope systematics of calcite veins in similar to 1.59 Ga IOCG ore indicate 1.59-1.55 Ga deposition ages. Likewise, locally abundant laminated siderites have Sm-Nd ages in this age interval. A world-first attempt to apply Lu-Hf dating to carbonate gangue in an ore deposit yields ages that are 70-100 Ma younger than corresponding Sm-Nd ages, presumably reflecting isotopic exchange of carbonate Lu-Hf isotope systems with host rocks. Sm-Nd ages for carbonates assigned to other carbonate associations (hosted in highly altered inferred 1.59 Ga basalt and picrite; diverse settings within granite-dominated breccia; locally abundant megaclasts of green and red bedded sandstone/mudstone sequences; similar to 0.82 Ga doleritic dykes) are more diverse and range from similar to 1.59 to 0.5 Ga. The structurally youngest carbonates (unbrecciated fluorite-barite veins; carbonate matrix in polymict conglomerate above the breccia complex) yield similar to 0.50 Ga Sm-Nd ages. Inferred carbonate ages are broadly consistent with radiometric dates for other hydrothermal minerals (e.g., hematite, uraninite, apatite, fluorite). They suggest that mineralization initiated at 1.59 Ga was reworked and possibly increased in size in response to large-scale tectonic, magmatic, sedimentary and hydrothermal events. Initial Sr-87/Sr-86 in the carbonates is higher and more variable (0.710-0.752, average similar to 0.721) than could be explained by ore and gangue mineral formation from magmatic-hydrothermal fluids during a single event at 1.59 Ga, a model favored in several earlier studies. By contrast, carbonate formation over a long period, as inferred from the Sm-Nd chronology presented here, would allow ingrowth of Sr-87 in the granitic host rocks to develop the heterogeneous initial Sr-87/Sr-86 recorded in the carbonates. Carbonate-bearing fluids appear to have sourced Nd (and most likely also Sr) locally, within the host granite and breccia, with contributions from mafic rocks. The emerging evidence for protracted, multi-stage mineralization implies that single-stage models for Olympic Dam need to be revisited and that all studies of sulfide and gangue minerals in this deposit require careful radiometric dating. We speculate that the polymetallic nature and unusually large metal reserves of the Olympic Dam mineralization are related to its multi-stage formation history

The Mixed-Layer Structures of Ikunolite, Laitakarite, Joséite-B and Joséite-A

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

Trace Element Analysis of Minerals in Magmatic-Hydrothermal Ores by Laser Ablation Inductively-Coupled Plasma Mass Spectrometry: Approaches and Opportunities

Laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) has rapidly established itself as the method of choice for generation of multi-element datasets for specific minerals, with broad applications in Earth science. Variation in absolute concentrations of different trace elements within common, widely distributed phases, such as pyrite, iron-oxides (magnetite and hematite), and key accessory minerals, such as apatite and titanite, can be particularly valuable for understanding processes of ore formation, and when trace element distributions vary systematically within a mineral system, for a vector approach in mineral exploration. LA-ICP-MS trace element data can assist in element deportment and geometallurgical studies, providing proof of which minerals host key elements of economic relevance, or elements that are deleterious to various metallurgical processes. This contribution reviews recent advances in LA-ICP-MS methodology, reference standards, the application of the method to new mineral matrices, outstanding analytical uncertainties that impact on the quality and usefulness of trace element data, and future applications of the technique. We illustrate how data interpretation is highly dependent on an adequate understanding of prevailing mineral textures, geological history, and in some cases, crystal structure

Detection of Trace Elements/Isotopes in Olympic Dam Copper Concentrates by nanoSIMS

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—or lack thereof, in cases of surface adherence or fracture fill—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—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