• The alteration history of the Jbilet Winselwan CM carbonaceous chondrite: An analog for C-type asteroid sample return

      King, A; Russell, S; Schofield, P; Humphreys-Williams, E; Strekopytov, S (Wiley, 2018-12-13)
      Jbilet Winselwan is one of the largest CM carbonaceous chondrites available for study. Its light, major, and trace elemental compositions are within the range of other CM chondrites. Chondrules are surrounded by dusty rims and set within a matrix of phyllosilicates, oxides, and sulfides. Calcium‐ and aluminum‐rich inclusions (CAIs) are present at ≤1 vol% and at least one contains melilite. Jbilet Winselwan is a breccia containing diverse lithologies that experienced varying degrees of aqueous alteration. In most lithologies, the chondrules and CAIs are partially altered and the metal abundance is low (<1 vol%), consistent with petrologic subtypes 2.7–2.4 on the Rubin et al. (2007) scale. However, chondrules and CAIs in some lithologies are completely altered suggesting more extensive hydration to petrologic subtypes ≤2.3. Following hydration, some lithologies suffered thermal metamorphism at 400–500 °C. Bulk X‐ray diffraction shows that Jbilet Winselwan consists of a highly disordered and/or very fine‐grained phase (73 vol%), which we infer was originally phyllosilicates prior to dehydration during a thermal metamorphic event(s). Some aliquots of Jbilet Winselwan also show significant depletions in volatile elements such as He and Cd. The heating was probably short‐lived and caused by impacts. Jbilet Winselwan samples a mixture of hydrated and dehydrated materials from a primitive water‐rich asteroid. It may therefore be a good analog for the types of materials that will be encountered by the Hayabusa‐2 and OSIRIS‐REx asteroid sample‐return missions.
    • The Anatomy of an Alkalic Porphyry Cu-­‐Au System: Geology and Alteration at Northparkes Mines, NSW, Australia

      Pacey, A; Wilkinson, JJ; Owens, J; Priest, D; Cooke, DR; Millar, IL (Society of Economic Geologists, 2019-05-01)
      The Late Ordovician-Early Silurian (~455-435 Ma) Northparkes system is a group of silica-saturated, alkalic porphyry deposits and prospects which developed within the Macquarie Island Arc. The system is host to a spectacular and diverse range of rocks and alteration-mineralization textures that facilitate a detailed understanding of its evolution, in particular into the nature and controls of porphyry-related propylitic alteration. The first intrusive phase at Northparkes is a pre- to early-mineralization pluton that underlies all the deposits and varies in composition from a biotite quartz monzonite (BQM) to alkali feldspar granite (AFG). Prior to total crystallization, this pluton was intruded by a more primitive quartz monzonite (QMZ) that marks the onset of a fertile fractionation series. Towards its upper levels, the QMZ is porphyritic and locally rich in Cu sulfides. Subsequently, a complex series of syn-mineralization quartz monzonite porphyries (QMP) were emplaced. The QMP intrusions have a distinct pipe-like morphology and are ubiquitously K-feldspar altered with a crystal-crowded porphyritic texture. The textures of the QMPs and common occurrence of porphyry-cemented contact breccias indicate they were forcibly emplaced and of relatively low viscosity. The QMPs are therefore interpreted as crystal-bearing, silicate melt-aqueous fluid slurries that represent the conduits through which deep-seated magmatic-derived ore fluid was discharged into the shallow crust (1-2 km depth). Each deposit is centred on a multiphase cluster of QMP intrusions that drove discrete hydrothermal systems. Initial fluid evolution was similar in all the deposits, with three major alteration facies developed as largely concentric zones around the QMP complexes. The innermost zone is host to Cu sulfide ore and dominated by K-feldspar alteration. This transitions outwards through a shell of magnetite ± biotite alteration, with pyrite and minor chalcopyrite, to an outer halo of propylitic alteration. Generally, epidote, chlorite and pyrite are abundant in the most deposit-proximal propylitic zone, with a decrease in the abundance of pyrite, and then epidote, with increasing distance away from deposit centers. Propylitic alteration, particularly within relatively low permeability rocks, is fracture-controlled and a hierarchy of veins is observed. Veins of chlorite-quartz-pyrite ± calcite ± hematite ± epidote ± chalcopyrite (P1) appear to represent the principal fluid conduits. They are surrounded by pervasive and intense alteration halos with a distinct mineralogical zonation from vein-proximal chlorite-sericite (phengite) ± epidote ± pyrite, through hematite-sericite-chlorite ± epidote, ultimately to a vein-distal hematite-albite ± chlorite ± epidote assemblage. These P1 veins are surrounded by regions in which smaller epidote-chlorite ± calcite ± quartz ± pyrite veins (P2) are abundant, again with zoned alteration envelopes: vein-proximal chlorite-sericite (phengite) ± epidote ± pyrite grades out into an epidote-rich zone, which in turn transitions into vein-distal albite-hematite ± chlorite ± epidote. Areas of weakest propylitic alteration, distant from both P1 and P2 veins, are characterised by small epidote-only veinlets (P3) with albite-hematite halos. Mineralogical transitions across the propylitic zone are therefore repeated in the evolution from P1 to P3 veins, as well as in the halos around these veins. It is the overall vein abundance and overlap of associated alteration halos which controls the intensity and appearance of propylitic alteration in most rocks. Such scale-invariance and spatial relationships strongly suggests the transition from P1 to P3 veins reflects a broadly decreasing outward flux of (magmatic-derived?) fluid that passed through the fracture network and progressively reacted with country rocks. Further support for this hypothesis comes from cross cutting relationships and Rb-Sr dating of epidote (returning an age of 450 ± 11 Ma), which demonstrate the bulk of propylitic alteration was coeval with mineralization and potassic alteration. Late-stage fluid evolution at each deposit was unique. Much of the E48 orebody and locally the GRP314 deposit was overprinted by texturally-destructive, white sericite-albite-quartz-alunite ± chlorite alteration. In the E26 deposit, and in regions of the GRP314 deposit, a series of quartz-anhydrite ± pyrite ± Cu sulfide veins with distinctive, vein-proximal, sericite-dominant alteration halos cut the primary, deposit-concentric alteration facies. The vein-distal mineralogy of these alteration halos is controlled by their distance from deposit centers, changing from K-feldspar ± biotite in deposit-proximal veins to chlorite ± epidote-albite in deposit-distal veins. Late-mineralization QMPs at E26 and GRP314 also appear to be related to the generation of anhydrite-quartz ± sphalerite veins and a set of quartz-calcite-pyrite-sphalerite ± chalcopyrite ± galena veins. Post-mineralization magmatic activity produced relatively primitive and barren monzonite porphyries and younger alkali basalt dikes.
    • Ancient hydrothermal seafloor deposits in Eridania basin on Mars

      Michalski, JR; Dobrea, EZN; Niles, PB; Cuadros, J (2017-07-10)
    • The application of deep eutectic solvent ionic liquids for environmentally-friendly dissolution and recovery of precious metals

      Jenkin, GRT; Al-Bassam, AZM; Harris, RC; Abbott, AP; Smith, DJ; Holwell, DA; Chapman, RJ; Stanley, Christopher (2016-03)
    • Are coral reefs victims of their own past success?

      Renema, W; Pandolfi, JM; Kiessling, W; Bosellini, FR; Klaus, JS; Korpanty, C; Rosen, BR; Santodomingo, N; Wallace, CC; Webster, JM; Johnson, KG (2016-04-22)
    • Assessing Thallium Elemental Systematics and Isotope Ratio Variations in Porphyry Ore Systems: A Case Study of the Bingham Canyon District

      Fitzpayne, A; Prytulak, J; Wilkinson, JJ; Cooke, DR; Baker, MJ; Wilkinson, CC (MDPI AG, 2018-11-26)
      The Bingham Canyon porphyry deposit is one of the world’s largest Cu-Mo-Au resources. Elevated concentrations of thallium (Tl) compared to average continental crust have been found in some brecciated and igneous samples in this area, which likely result from mobilization of Tl by relatively low temperature hydrothermal fluids. The Tl-enrichment at Bingham Canyon therefore provides an opportunity to investigate if Tl isotope ratios reflect hydrothermal enrichment and whether there are systematic Tl isotope fractionations that could provide an exploration tool. We present a reconnaissance study of nineteen samples spanning a range of lithologies from the Bingham district which were analysed for their Tl content and Tl isotope ratios, reported as parts per ten thousand (ε205Tl) relative to the NIST SRM997 international standard. The range of ε205Tl reported in this study (−16.4 to +7.2) is the largest observed in a hydrothermal ore deposit to date. Unbrecciated samples collected relatively proximal to the Bingham Canyon porphyry system have ε205Tl of −4.2 to +0.9, similar to observations in a previous study of porphyry deposits. This relatively narrow range suggests that high-temperature (>300 °C) hydrothermal alteration does not result in significant Tl isotope fractionation. However, two samples ~3–4 km away from Bingham Canyon have higher ε205Tl values (+1.3 and +7.2), and samples from more distal (~7 km) disseminated gold deposits at Melco and Barneys Canyon display an even wider range in ε205Tl (−16.4 to +6.0). The observation of large positive and negative excursions in ε205Tl relative to the mantle value (ε205Tl = −2.0 ± 1.0) contrasts with previous investigations of hydrothermal systems. Samples displaying the most extreme positive and negative ε205Tl values also contain elevated concentrations of Tl-Sb-As. Furthermore, with the exception of one sample, all of the Tl isotopic anomalies occur in hydrothermal breccia samples. This suggests that ε205Tl excursions are most extreme during the migration of low-temperature hydrothermal fluids potentially related to sediment-hosted gold mineralization. Future investigation to determine the host phase(s) for Tl in breccias displaying both chalcophile element enrichment and ε205Tl excursions can potentially provide new information about hydrothermal fluid composition and could be used to locate sites for future porphyry exploration.
    • Biesiespoort revisited: a case study on the relationship between tetrapod assemblage zones and Beaufort lithostratigraphy south of Victoria West

      Day, M; Rubidge, BS (University of the Witwatersrand Johannesburg, 2018-12)
      The relationship between the tetrapod assemblage zones of the South African Karoo Basin and the lithostratigraphic divisions of the Beaufort Group is well-established, and provides an independent means of dating fossil occurrences. However, this relationship may not be consistent across the basin; a discrepancy exists between the historical tetrapod assemblages in the vicinity of Victoria West, Northern Cape Province, and the expected tetrapod assemblage zones based on mapped geology. In order to examine this disconnect, we collected fossils at two localities close to Biesiespoort railway station, a locality that was visited on a number of occasions by Robert Broom. Our fossil samples support the biostratigraphic determinations of Broom and thus confirm that the stratigraphic extent of the biozones at these localities differs from their type areas further south. The reasons for this are unclear but could be related to the northward younging of the lithological units, implying complex depositional processes, or result from difficulties in mapping. Nevertheless, caution should be exercised when using mapped geology near Victoria West as a guide to the age of fossils found there.
    • Calcitization of aragonitic bryozoans in Cenozoic tropical carbonates from East Kalimantan, Indonesia

      Di Martino, E; Taylor, PD; Kudryavtsev, AB; William Schopf, J (2016-04)
    • Cerromojonite, CuPbBiSe3, from El Dragon (Bolivia): A New Member of the Bournonite Group

      Foerster, H-J; Bindi, L; Grundmann, G; Stanley, Christopher (2018-09-21)
    • Cervelleite, Ag4TeS: solution and description of the crystal structure

      Bindi, L; Spry, PG; Stanley, Christopher (2015-08)