The mineralogy and mineral associations of platinum-group elements and precious metals in the Aurora Cu-Ni-Au-PGE deposit, Northern Limb, Bushveld Complex

Aurora is a platinum-group element (PGE) prospect hosted in the Northern Limb of the Bushveld Complex, South Africa. It is one of only three deposits discovered in the Northern Limb so far to be hosted in the melanocratic-leucocratic gabbroic cumulates of the Main Zone of the Rustenberg Layered Suite (Aurora, Moorddrift and Waterberg T Zone deposits), rather than in predominantly ultramafic rocks (e.g. Platreef). The host cumulates at Aurora have been divided into three principal units and they intrude the dolomites of the lower Transvaal Supergroup. Base metal sulphide (BMS) mineralisation with PGE is present in the leucogabbronorites and gabbronorites of Unit 2, and in coarse grained gabbronorite veins which intrude the peridotites of Unit 1. These veins contain up to 50% interstitial pyrrhotite-pentlandite-chalcopyrite ± pyrite. Unit 2 contains 1–3% pentlandite-pyrrhotite-chalcopyrite assemblages, and 1–5% chalcopyrite ± pyrite/pyrrhotite associated with hydrothermal alteration. The PGE content of Aurora however is predominantly controlled by the presence of platinum-group minerals (PGM), not BMS. LA-ICP-MS analysis of sulphides shows the BMS in Aurora have lower PGE concentrations than other Bushveld magmatic sulphides, with pentlandite carrying much lower concentrations of Pd (average 23 ppm) than the Platreef or the Merensky Reef. SEM-EDS analysis of 26 sections characterised 995 platinum-group minerals (PGM) and precious metal-bearing minerals (PMM), with a total area of 27850 μm2 and an average size of 28.2 μm2. Of the PGM and PMM identified in Aurora 85% (by area) are Pd-Te-Bi minerals, with 6% Pd-Te minerals, 4% electrum and 3% Ag-Te minerals, along with minor Pd-Bi, Pd-As, Pt-Te-Bi, Pt-As and Pt-S minerals that collectively comprise 2% of total area. Only 25% of the PGM and PMM in Aurora are BMS hosted, with the rest hosted in silicates. Of the total PGM and PMM area 22% are hosted in alteration-silicates (quartz, chlorite or actinolite) in an alteration halo around sulphides. Unusually, 52% of the PGM and PMM are spatially removed from BMS, instead hosted in alteration silicates and within cracks in primary silicates away from any BMS. This indicates a multi-stage ore genesis model, with hydrothermal remobilisation of PGE important for ore formation. The style and host rocks for mineralisation in the Aurora deposit are fundamentally different from other deposits in the Northern Limb of the Bushveld hosted in ultramafic rocks, such as the Platreef, GNPA member deposits and the F zone of the Waterberg deposit, all of which contain a greater diversity of PGM and BMS with higher precious metal contents. The mineralisation most similar to Aurora is the T Zone of the Waterberg deposit, located to the north of Aurora, which been suggested to be an along-strike equivalent of the Aurora Main Zone mineralisation. However, despite strong similarities in PGM mineralogy and S isotope signatures there are significant differences in BMS mineralisation and host lithology meaning it is unlikely they are directly linked stratigraphically. At present it seems more likely that Aurora and the Waterberg T Zone reflect similar fluid-influenced processes operating in different parts of the Main Zone, perhaps at different times and in different structural basins, rather than a continuous mineralised zone along strike

Sulfur isotope and trace element systematics of zoned pyrite crystals from the El Indio Au-Cu-Ag deposit, Chile

We present a comparative study between early, massive pyrite preceding (Cu–Ag) sulfosalt mineralization in high-temperature feeder zones (‘early pyrite’) and late pyrite that formed during silicic alteration associated with Au deposition (‘late pyrite’) at the El Indio high-sulfidation Au–Ag–Cu deposit, Chile. We use coupled in situ sulfur isotope and trace element analyses to chronologically assess geochemical variations across growth zones in these pyrite crystals. Early pyrite that formed in high-temperature feeder zones shows intricate oscillatory zonation of Cu, with individual laminae containing up to 1.15 wt% Cu and trace Co, As, Bi, Ni, Zn, Se, Ag, Sb, Te, Au, Pb and Bi. Late pyrite formed after (Cu–Ag) sulfosalt mineralization. It contains up to 1.14 wt% As with trace Cu, Zn, Pb, V, Mn, Co, Ni, Ge, Se, Ag, Sb, Te, Pb and Bi, as well as colloform Cu-rich growth bands containing vugs toward the outer edges of some crystals. Plotting the trace element data in chronological order (i.e., from core to rim) revealed that Co and Ni were the only elements to consistently co-vary across growth zones. Other trace elements were coupled in specific growth zones, but did not consistently co-vary across any individual crystal. The δ34S of early pyrite crystals in high-temperature feeder zones range from −3.19 to 1.88 ‰ (±0.5 ‰), consistent with sublimation directly from a high-temperature magmatic vapor phase. Late pyrite crystals are distinctly more enriched in δ34S than early pyrite (δ34S = 0.05–4.77 ‰, ±0.5 ‰), as a consequence of deposition from a liquid phase at lower temperatures. It is unclear whether the late pyrite was deposited from a small volume of liquid condensate, or a larger volume of hydrothermal fluid. Both types of pyrite exhibit intracrystalline δ34S variation, with a range of up to 3.31 ‰ recorded in an early pyrite crystal and up to 4.48 ‰ in a late pyrite crystal. Variations in δ34Spyrite at El Indio did not correspond with changes in trace element geochemistry. The lack of correlation between trace elements and δ34S, as well as the abundance of microscale mineral inclusions and vugs in El Indio pyrite indicate that the trace element content of pyrite at El Indio is largely controlled by nanoscale, syn-depositional mineral inclusions. Co and Ni were the only elements partitioned within the crystal structure of pyrite. Cu-rich oscillatory zones in early pyrite likely formed by nanoscale inclusions of Cu-rich sulfosalts or chalcopyrite, evidence of deposition from a fluid cyclically saturated in ore metals. This process may be restricted to polymetallic high-sulfidation-like deposits

Numerical simulation of spreading drops

We consider a liquid drop that spreads on a wettable surface. Different time evolutions have been observed for the base radius r depending of the relative role played by inertia, viscosity, surface tension and the wetting condition. Numerical simulations were performed to discuss the relative effect of these parameters on the spreading described by the evolution of the base radius r(t) and the spreading time tS. Different power law evolutions r(t) ∝ tⁿ have been observed when varying the parameters. At the early stage of the spreading, the power law t½ (n = 1/2) is observed as long as capillarity is balanced by inertia at the contact line. When increasing the viscosity contribution, the exponent n is found to increase despite the increase of the spreading time. The effect of the surface wettability is observed for liquids more viscous than water. For a small contact angle, the power law t½ is then followed by the famous Tanner law t1/10 once the drop shape has reached a spherical cap

Investigating a potential geothermal play in the southern Sydney Basin

Geothermal energy is a renewable resource that will be part of the world’s transition to clean power production. Different technologies can be utilised to extract heat or produce geothermal-based electricity. The Geological Survey of NSW has identified several regions across the state where there are higher than average geothermal gradients. These regions in the southern Sydney Basin are investigated with the aim of determining if the high temperatures might be related to subsurface rocks with relatively high concentrations of radiogenic isotopes that might create a ‘hot dry rock’ play. Rock properties are tested that would be required to generate a geothermal resource. Existing and potential engineering technologies (i.e. geothermal-based electricity, heating and cooling applications accompanied by heat pumps, geothermal-hybrid systems, and mine-based geothermal technologies) are also further reviewed. Overall this study provides insights into future opportunities and challenges to harnessing geothermal energy in NSW

Changes in serum biomarker profiles after percutaneous mitral valve repair with the MitraClip system

Background: Mitral regurgitation (MR) is one of the most common valvular diseases. Percu­taneous mitral valve repair with the MitraClipTM system is a novel percutaneous mitral valve repair (PMVR) technique for high-surgical-risk patients. However, the effect of PMVR on cir­culating cardiac or inflammatory biomarkers and their association with individual functional, echocardiographic and clinical outcomes is poorly investigated. Methods: A group of 144 patients with functional or degenerative MR (age, 75 ± 11 years; 41% females) underwent PMVR with the MitraClip system at the University Heart Center Zu­rich. Serum biomarkers as N-terminal pro-B-type natriuretic peptide (NT-proBNP), C-reactive protein (CRP) and creatinine were obtained from venous sampling at baseline and follow-up of 3–6 months. Results: Median NT-proBNP decreased insignificantly from 2,942 (IQR 1,596–5,722) to 2,739 (IQR 1,440–4,296) ng/L, p = 0.21. NT-proBNP changes did not correlate with baseline left ventricular (LV) ejection fraction or LV dimensions, with New York Heart Association class on follow-up, or with clinical events on follow-up. CRP levels reached a peak on the third postoperative day at 34.0 mg/L with a subsequent slow decrease over the ensuing days. Conclusions: Despite successful PMVR, NT-proBNP remain fairly unchanged on follow-up and changes in NT-proBNP levels are poor predictors of functional improvement or clinical outcome after MitraClip treatment

Changes in serum biomarker profiles after percutaneous mitral valve repair with the MitraClip system

BACKGROUND Mitral regurgitation (MR) is one of the most common valvular diseases. Percu-taneous mitral valve repair with the MitraClipTM system is a novel percutaneous mitral valve repair (PMVR) technique for high-surgical-risk patients. However, the effect of PMVR on cir-culating cardiac or inflammatory biomarkers and their association with individual functional, echocardiographic and clinical outcomes is poorly investigated. METHODS A group of 144 patients with functional or degenerative MR (age, 75 ± 11 years; 41% females) underwent PMVR with the MitraClip system at the University Heart Center Zu-rich. Serum biomarkers as N-terminal pro-B-type natriuretic peptide (NT-proBNP), C-reactive protein (CRP) and creatinine were obtained from venous sampling at baseline and follow-up of 3-6 months. RESULTS Median NT-proBNP decreased insignificantly from 2,942 (IQR 1,596-5,722) to 2,739 (IQR 1,440-4,296) ng/L, p = 0.21. NT-proBNP changes did not correlate with baseline left ventricular (LV) ejection fraction or LV dimensions, with New York Heart Association class on follow-up, or with clinical events on follow-up. CRP levels reached a peak on the third postoperative day at 34.0 mg/L with a subsequent slow decrease over the ensuing days. CONCLUSIONS Despite successful PMVR, NT-proBNP remain fairly unchanged on follow-up and changes in NT-proBNP levels are poor predictors of functional improvement or clinical outcome after MitraClip treatment

Aktuelle Fragen zum schweizerischen und internationalen Kapitalmarktrecht - 17. Tagung zu Kapitalmarkt – Recht und Transaktionen – Tagungsband 2021

Der vorliegende Tagungsband „Kapitalmarkt – Recht und Transaktionen“ legt den Schwerpunkt wie jedes Jahr auf aktuelle Entwicklungen im Finanz- und Kapitalmarktrecht unter besonderer Berücksichtigung von Transaktionen in diesem Bereich. Das Jahr 2021 stand noch immer unter dem Eindruck der Corona-Pandemie, war aber auch geprägt durch dynamische technologische Weiterentwicklung sowie die noch immer fortschreitende Zunahme der Regulierung. Die Beiträge im vorliegenden Tagungsband befassen sich mit dem für die Schweiz neuen Phänomen der SPACS (special purpose acquisition companies), Lombardkrediten und Margin Calls, Streitigkeiten mit ESG-Bezug, der FIDLEG-Umsetzung im Bereich Corporate Finance, Neuerungen bei der Emittentenregulierung, der LIBOR Ablösung sowie dem neuen Institut des Kapitalbandes im revidierten Aktienrecht

Comparison of 3 T and 1.5 T for T2* magnetic resonance of tissue iron.

BACKGROUND: T2* magnetic resonance of tissue iron concentration has improved the outcome of transfusion dependant anaemia patients. Clinical evaluation is performed at 1.5 T but scanners operating at 3 T are increasing in numbers. There is a paucity of data on the relative merits of iron quantification at 3 T vs 1.5 T. METHODS: A total of 104 transfusion dependent anaemia patients and 20 normal volunteers were prospectively recruited to undergo cardiac and liver T2* assessment at both 1.5 T and 3 T. Intra-observer, inter-observer and inter-study reproducibility analysis were performed on 20 randomly selected patients for cardiac and liver T2*. RESULTS: Association between heart and liver T2* at 1.5 T and 3 T was non-linear with good fit (R (2) = 0.954, p < 0.001 for heart white-blood (WB) imaging; R (2) = 0.931, p < 0.001 for heart black-blood (BB) imaging; R (2) = 0.993, p < 0.001 for liver imaging). R2* approximately doubled between 1.5 T and 3 T with linear fits for both heart and liver (94, 94 and 105 % respectively). Coefficients of variation for intra- and inter-observer reproducibility, as well as inter-study reproducibility trended to be less good at 3 T (3.5 to 6.5 %) than at 1.5 T (1.4 to 5.7 %) for both heart and liver T2*. Artefact scores for the heart were significantly worse with the 3 T BB sequence (median 4, IQR 2-5) compared with the 1.5 T BB sequence (4 [3-5], p = 0.007). CONCLUSION: Heart and liver T2* and R2* at 3 T show close association with 1.5 T values, but there were more artefacts at 3 T and trends to lower reproducibility causing difficulty in quantifying low T2* values with high tissue iron. Therefore T2* imaging at 1.5 T remains the gold standard for clinical practice. However, in centres where only 3 T is available, equivalent values at 1.5 T may be approximated by halving the 3 T tissue R2* with subsequent conversion to T2*

T1 at 1.5T and 3T compared with conventional T2* at 1.5T for cardiac siderosis

Background: Myocardial black blood (BB) T2* relaxometry at 1.5T provides robust, reproducible and calibrated non-invasive assessment of cardiac iron burden. In vitro data has shown that like T2*, novel native Modified Look-Locker Inversion recovery (MOLLI) T1 shortens with increasing tissue iron. The relative merits of T1 and T2* are largely unexplored. We compared the established 1.5T BB T2* technique against native T1 values at 1.5T and 3T in iron overload patients and in normal volunteers. Methods: A total of 73 subjects (42 male) were recruited, comprising 20 healthy volunteers (controls) and 53 patients (thalassemia major 22, sickle cell disease 9, hereditary hemochromatosis 9, other iron overload conditions 13). Single mid-ventricular short axis slices were acquired for BB T2* at 1.5T and MOLLI T1 quantification at 1.5T and 3T. Results: In healthy volunteers, median T1 was 1014 ms (full range 939–1059 ms) at 1.5T and modestly increased to 1165ms (full range 1056–1224 ms) at 3T. All patients with significant cardiac iron overload (1.5T T2* values <20 ms) had T1 values <939 ms at 1.5T, and <1056 ms at 3T. Associations between T2* and T1 were found to be moderate with y =377 · x0.282 at 1.5T (R2 = 0.717), and y =406 · x0.294 at 3T (R2 = 0.715). Measures of reproducibility of T1 appeared superior to T2*. Conclusions: T1 mapping at 1.5T and at 3T can identify individuals with significant iron loading as defined by the current gold standard T2* at 1.5T. However, there is significant scatter between results which may reflect measurement error, but it is also possible that T1 interacts with T2*, or is differentially sensitive to aspects of iron chemistry or other biology. Hurdles to clinical implementation of T1 include the lack of calibration against human myocardial iron concentration, no demonstrated relation to cardiac outcomes, and variation in absolute T1 values between scanners, which makes inter-centre comparisons difficult. The relative merits of T1 at 3T versus T2* at 3T require further consideration