Crocoite and associated minerals from Tasmania

The world's best and most plentiful crocoite specimens come from Tasmania, particularly the Adelaide and Red Lead silver-lead mines in the South Dundas mineral field, Dundas. The Dundas Extended, West Comet, Kosminsky and Platts Prospect, al lfrom this same mineral field, have also produced striking finds, as has the Kapi mine from the North Dundasfield. A third area between Savage River and Waratah, about 50 km north-north-east of the Dundas district, contains the Heazlewood (where crocoite was first found in Tasmania), Whyte River, Magnet and Washington Hay mines, all of which have produced some crocoite. There are also minor occurrences at Zeehan. These fields are associated with Cambrian serpentinites and/or amphibolites and serpentinite-derived greywackes; the silver-lead lodes lie mostly along the brecciated contacts of these bodies. Chromite, stichtite and chromian muscovite in the serpentinites and serpentine-derived sediments are the source of chromian in the crocoite. The mines originally worked Ag- and Pb-rich sulphide and carbonate-rich primary ores. Near the surface the lodes are mostly represented by deeply weathered, goethite rich vuggy gossans. Other secondary minerals include cerussite, anglesite, dundasite, petterdite, philipsbornite, coronadite, mimetite, pyromorphite, chlorargyrite and chalcophanite. The main factors in the genesis of the supergene minerals of the Dundas district are the super position of Cr-rich rocks with galena-rich veins, and deep weathering. Galena readily oxidises to form a number of supergene minerals, depending on pH, and the local availability of other anions in solution. Anglesite is usually first to form and is then overgrown or replaced by cerussite, crocoite or other lead minerals. Mimetite, pyromorphite, coronadite and other Pb minerals result from various local chemical processes in the gossans. Cerussite is less common in the Dundas district perhaps because of prevailing low pH groundwaters. These conditions led to an abundance of crocoite as it is more stable than most lead minerals at low pH

Reynoldsite, Pb_2Mn^(4+)_2O_5(CrO_4), a new phyllomanganate-chromate from the Blue Bell claims, California and the Red Lead mine, Tasmania

The new mineral reynoldsite, Pb_2Mn^(4+)_2O_5(CrO_4), occurs at the Blue Bell claims, near Baker, San Bernardino County, California, U.S.A., and at the Red Lead mine, Dundas, Tasmania, Australia. At the Blue Bell claims, reynoldsite occurs in subparallel growths and divergent sprays of thin prisms with a square cross section. At the Red Lead mine, it occurs as thin rectangular blades. At both occurrences, crystals are small (≤0.2 mm), and ubiquitously and multiply twinned. At both deposits, reynoldsite formed as a secondary mineral derived from the weathering of primary minerals including oxides and sulfides in the presence of acidic groundwater. Reynoldsite is dark orange-brown to black in color and has a dark orange-brown streak. Its luster is subadamantine and its Mohs hardness is about 4½. The mineral is brittle with irregular to splintery fracture and a poorly developed {001} cleavage. The calculated density is 6.574 g/cm^3 (Red Lead mine). The very high indices of refraction and dark color permitted only partial determination of the transmitted light optical properties. Electron microprobe analyses of Blue Bell and Red Lead reynoldsite provided the empirical formulas (based on nine O atoms): Pb_(1.97)Mn_(2.01)O_5(Cr_(1.01)O_4) and (Pb_(2.07)Sr_(0.04))_(∑2.11)Mn_(2.15)O_5(Cr_(0.87)O_4), respectively. The strongest powder X-ray diffraction lines for Red Lead reynoldsite are [d(hkl)I]: 3.427(021,110)52, 3.254(021,112,121)85, 3.052(112,111,022,103)100, 2.923(013,122)40, 2.5015(004,211,130)47, 1.9818(015,105,202,231)42, 1.7694(115,134,203,142,133)36, and 1.6368(223,043,221,124,224)36. Reynoldsite is triclinic with space group P1 and unit-cell parameters: α = 5.0278(7), b = 7.5865(11), c = 10.2808(15) Å, α = 91.968(12), β = 99.405(12), γ = 109.159(10)°, V = 363.81(9) Å_3, and Z = 2 (for a Red Lead mine crystal). The crystal structure of reynoldsite (R_1 = 10.2% for 902 reflections with F_o > 4σF for a Red Lead crystal) contains close-packed layers of edge-sharing Mn^(4+)O_6 octahedra parallel to {001}. These layers are composed of edge-sharing double chains of octahedra extending along [100], which in turn are linked to one another by sharing edges in the [010] direction. The thick interlayer region contains Pb^(2+) cations and CrO_4 tetrahedra. The 6s^2 lone-electron pair of the Pb^(2+) is stereochemically active, resulting in a one-sided Pb-O coordination arrangement. The structure bears strong similarities to those of the phyllomanganates, such as chalcophanite and birnessite

Complex REE systematics of carbonatites and weathering products from uniquely rich Mount Weld REE deposit, Western Australia

Carbonatite intrusive complexes are important hosts for Rare Earth Elements (REE) deposits and are commonly affected by surficial weathering processes. Mount Weld REE deposit of Western Australia is one of the world's richest REE deposits and here we present whole-rock and REE mineral geochemical data on compositions of primary and weathered carbonatites. The REE concentrations in magmatic carbonatites at Mount Weld vary by two orders of magnitude, suggesting a significant role of magmatic processes in REE enrichment in the carbonatite complex. The Th-Pb age 2056±67 (2σ) Ma of monazite-(Ce) from the carbonatite obtained by in situ LA-ICP-MS analyses confirm Paleoproterozoic age of the mineralization. The regolith samples preserve a detailed record of evolution from carbonatite to products of intensive weathering. The silica-cemented regolith (silcrete) contains monazite-(Ce) and apatite chemically identical to their carbonatite-hosted equivalents. The high-REE regolith containing 51.8 wt% ∑REE2O3 has some of the highest REE concentrations found to date, negative Ce anomaly and contains lithogenic monazite within matrix of florencite-(Ce) and rhabdophane-(Nd) and rhabdophane-(Nd) tubes resembling casts of plant material. The pronounced negative Ce anomalies in the ferruginous cap rock (ferricrete) and the high-REE regolith indicate intensive weathering, where Ce4+ was preferential removed relative to the REE3+. The presence of paleo-plants in the high-REE regolith implicates bio-assisted processes involved in the extreme REE fractionation. The diverse REE enrichment processes, which occurred in supergene environment of Mount Weld, have implications for the understanding of the genesis of REE deposits worldwide.</p

Biological role in the transformation of platinum-group mineral grains

Platinum-group elements are strategically important metals. Finding new deposits is becoming increasingly difficult owing to our limited understanding of the processes that affect their mobility in surface environments. Microorganisms have been shown to promote the mobility of metals around ore deposits. Here we show that microorganisms influence the mobility of platinum-group elements in mineral grains collected from Brazil, Australia and Colombia. Scanning electron microscopy showed biofilms covering the platinum-group mineral grains. The biofilms contained abundant platinum-group element nanoparticles and microcrystalline aggregates, and were dominated by Proteobacteria, many of which were closely related to known metal-resistant species. Some platinum-group mineral grains contained carbon, nitrogen, sulfur, selenium and iodine, suggesting the grains may be biogenic in origin. Molecular analyses show that Brazilian platinum–palladium grains hosted specific bacterial communities, which were different in composition from communities associated with gold grains, or communities in surrounding soils and sediments. Nano-phase metallic platinum accumulated when a metallophillic bacterium was incubated with a percolating platinum-containing medium, suggesting that biofilms can cause the precipitation of mobile platinum complexes. We conclude that biofilms are capable of forming or transforming platinum-group mineral grains, and may play an important role for platinum-group element dispersion and re-concentration in surface environments

Mortality after surgery in Europe: a 7 day cohort study

Background: Clinical outcomes after major surgery are poorly described at the national level. Evidence of heterogeneity between hospitals and health-care systems suggests potential to improve care for patients but this potential remains unconfirmed. The European Surgical Outcomes Study was an international study designed to assess outcomes after non-cardiac surgery in Europe.Methods: We did this 7 day cohort study between April 4 and April 11, 2011. We collected data describing consecutive patients aged 16 years and older undergoing inpatient non-cardiac surgery in 498 hospitals across 28 European nations. Patients were followed up for a maximum of 60 days. The primary endpoint was in-hospital mortality. Secondary outcome measures were duration of hospital stay and admission to critical care. We used χ² and Fisher’s exact tests to compare categorical variables and the t test or the Mann-Whitney U test to compare continuous variables. Significance was set at p&lt;0·05. We constructed multilevel logistic regression models to adjust for the differences in mortality rates between countries.Findings: We included 46 539 patients, of whom 1855 (4%) died before hospital discharge. 3599 (8%) patients were admitted to critical care after surgery with a median length of stay of 1·2 days (IQR 0·9–3·6). 1358 (73%) patients who died were not admitted to critical care at any stage after surgery. Crude mortality rates varied widely between countries (from 1·2% [95% CI 0·0–3·0] for Iceland to 21·5% [16·9–26·2] for Latvia). After adjustment for confounding variables, important differences remained between countries when compared with the UK, the country with the largest dataset (OR range from 0·44 [95% CI 0·19 1·05; p=0·06] for Finland to 6·92 [2·37–20·27; p=0·0004] for Poland).Interpretation: The mortality rate for patients undergoing inpatient non-cardiac surgery was higher than anticipated. Variations in mortality between countries suggest the need for national and international strategies to improve care for this group of patients.Funding: European Society of Intensive Care Medicine, European Society of Anaesthesiology