The roles of magmatic and hydrothermal processes in PGE mineralization,Ferguson Lake deposit,Nunavut, Canada

The Ferguson Lake Ni–Cu–Co–platinum-group element (PGE) deposit in Nunavut, Canada, occurs near the structural hanging wall of a metamorphosed gabbroic sill that is concordant with the enclosing country rock gneisses and amphibolites. Massive to semi-massive sulfide occurs toward the structural hanging wall of the metagabbro, and a low-sulfide, high-PGE style of mineralization (sulfide veins and disseminations) locally occurs ~30–50 m below the main massive sulfide. Water–rock interaction in the Ferguson Lake Ni–Cu–Co–PGE deposit is manifested mostly as widespread, post-metamorphic, epidote–chlorite–calcite veins, and replacement assemblages that contain variable amounts of sulfides and platinum-group minerals (PGM). PGM occur as inclusions in magmatic pyrrhotite and chalcopyrite in both the massive sulfide and high-PGE zones, at the contact between sulfides and hornblende or magnetite inclusions in the massive sulfide, in undeformed sulfide veins and adjacent chlorite and/or epidote halos, in hornblende adjacent to hydrothermal veins, and in plagioclase–chlorite aggregates replacing garnet cemented by sulfide. The PGM are mostly represented by the kotulskite (PdTe)–sobolevskite (PdBi) solid solution but also include michenerite (PdBiTe), froodite (PdBi₂), merenskyite (PdTe₂), mertieite II (Pd₈[Sb,As]₃), and sperrylite (PtAs₂) and occur in variety of textural settings. Those that occur in massive and interstitial sulfides, interpreted to be of magmatic origin and formed through exsolution from base metal sulfides at temperatures <600°C, are dominantly Bi rich (i.e., Te-bearing sobolevskite), whereas those that occur in late-stage hydrothermal sulfide/silicate veins and their epidote–chlorite alteration halos tend to be more Te rich (i.e., Bi-bearing kotulskite). The chemistry and textural setting of the various PGM supports a genetic model that links the magmatic and hydrothermal end-members of the sulfide–PGM mineralization. The association of PGM with magmatic sulfides in the massive sulfide and high-PGE zones has been interpreted to indicate that PGE mineralization was initially formed through exsolution from base metal sulfides which formed by magmatic sulfide liquid segregation and crystallization. However, the occurrence of PGM in undeformed sulfide-bearing veins and in their chlorite–epidote halos and differences in PGM chemistry indicate that hydrothermal fluids were responsible for post-metamorphic redistribution and dispersion of PGE.     

Post‐impact event bed (tsunamite) at the Cretaceous–Palaeogene boundary deposited on a distal carbonate platform interior

We show crucial evidence for the Cretaceous–Palaeogene (K–Pg) boundary event recorded within a rare succession deposited in an inner‐platform lagoon on top of a Mesozoic, tropical, intra‐oceanic (western Tethys) Adriatic carbonate platform, which is exposed at Likva cove on the island of Bra? (Croatia). The last terminal Maastrichtian fossils appear within a distinct 10–12 cm thick event bed that is characterised by soft‐sediment bioturbation and rare shocked‐quartz grains, and is interpreted as a distal tsunamite. Directly overlying this is a 2 cm thick reddish‐brown clayey mudstone containing planktonic foraminifera typical of the basal Danian, and with elevated platinum‐group elements in chondritic proportions indicating a clear link to the Chicxulub asteroid impact. These results strongly support the first discovery of a “potential” K–Pg boundary tsunamite on the neighbouring island of Hvar, and these two complementary sections represent probably the most complete record of the event among known distal shallow‐marine successions.     

Petrography and geochemistry of ejecta from the Sudbury impact event

Ejecta from the Connors Creek site in Michigan (500 km from the Sudbury Igneous Complex [SIC]), the Pine River site in western Ontario (650 km from the SIC), and the Coleraine site in Minnesota (980 km from the SIC) were petrographically and geochemically analyzed. Connors Creek was found to have approximately 2 m of ejecta, including shocked quartz, melt droplets, and accretionary lapilli; Pine River has similar deposits about 1 m in thickness, although with smaller lapilli; Coleraine contains only impact spherules in a 20 cm‐thick layer (impact spherules being similar to microkrystites or microtektites). The ejecta transition from chaotic deposits of massively bedded impactoclastic material with locally derived detritus at Connors Creek to a deposit with apparently very little detrital material that is primarily composed of melt droplets at Pine River to a deposit that is almost entirely composed of melt spherules at Coleraine. The major and trace element compositions of the ejecta confirm the previously observed similarity of the ejecta deposits to the Onaping Formation in the SIC. Platinum‐group element (PGE) concentrations from each of the sites were also measured, revealing significantly elevated PGE contents in the spherule samples compared with background values. PGE abundances in samples from the Pine River site can be reproduced by addition of approximately 0.2 wt% CI chondrite to the background composition of the underlying sediments in the core. PGE interelement ratios indicate that the Sudbury impact event was probably caused by a chondritic impactor.     

Mesoscale distribution of larval Euphausia similis in various water masses of the East Australian Current

Larval Euphausia similis were collected off temperate eastern Australia in spring 2004 and 2006 to evaluate the relationships between larval populations, mesoscale oceanographic variability, and the wider planktonic community. Larval E. similis were present in greater numbers in the East Australian Current (EAC) relative to productive coastal waters. Larval E. similis density was homogenous across the EAC—Tasman Sea frontal region, but larvae were smaller in the Tasman Sea. Larval E. similis density was not enhanced within a cold core eddy relative to the surrounding EAC. We observed a negative correlation between larval E. similis density and larval fish density, and a weak positive correlation with fluorescence. Evaluation of a significant fish density×fluorescence interaction term showed that the effect of fish density was reduced at high fluorescence values. Analysis of normalized biomass size spectrum (NBSS) provided evidence for potential competitive exclusion of copepods by krill. Data presented in this study suggest a predatory influence on surface E. similis populations by mesopelagic larval fish. The degree of predation appears to be dependent on food availability, potentially mediated by changes in the physiological condition of krill.     

Timing and thermochemical constraints on multi-element mineralisation at the Nori/RA Cu–Mo–U prospect, Great Bear magmatic zone, Northwest Territories, Canada

The timing of Cu–Mo–U mineralisation at the Nori/RA prospect in the Paleoproterozoic Great Bear magmatic zone has been investigated using Re–Os molybdenite and ⁴⁰Ar–³⁹Ar biotite geochronology. The Re–Os molybdenite ages presented are the first robust sulphide mineralisation ages derived from the Great Bear magmatic zone. Cu–Mo–U mineralisation is hosted in early to syn-deformational hydrothermal veins consisting of quartz and K-feldspar or more commonly tourmaline-biotite-quartz-K-feldspar, with associated wall-rock alteration assemblages being predominantly biotite. Sulphide and oxide minerals consist of chalcopyrite, molybdenite and uraninite with lesser pyrite and magnetite. Elevated light rare earth elements and tungsten concentrations associated with the Cu–Mo–U mineralisation have also been reported at the prospect by previous workers. Molybdenite and uraninite occur intimately in dravitic tourmaline growth zones and at grain margins, attesting to their syngenetic nature (with respect to hydrothermal veining). Two molybdenite separates yield Re–Os model ages of 1,874.4 ± 8.7 (2σ) and 1,872.4 ± 8.8 Ma (2σ) with a weighted average model age of 1,873.4 ± 6.1 Ma (2σ). Laser step heating of biotite from the marginal alteration of the wall-rock adjacent to the veins yields a ⁴⁰Ar–³⁹Ar maximum cooling age of 1,875 ± 8 Ma (MSWD = 3.8; 2σ), indistinguishable from the Re–Os molybdenite model age and a previously dated ‘syn-tectonic’ aplitic dyke in the region. Dravitic tourmaline hosts abundant primary liquid–vapour–solid-bearing fluid inclusions. Analytical results indicate liquid–vapour homogenisation at >260°C constraining the minimum temperature of mineralisation. The solids, which are possibly trapped, did not homogenise with the liquid–vapour by 400°C. Salinities in the inclusions are variable. Raman spectra identify that at least some of the solids are calcite and anhydrite. Raman spectra also confirm the vapour phases contain some CO₂; whereas clathrates or CH₄ was not observed or detected. Quartz grains only host secondary fluid inclusions, which fluoresce under ultraviolet light, indicating trapped hydrocarbons. We speculate that these resulted from Phanerozoic fluid circulation through the Proterozoic basement. The collective interpretation of the age, hydrothermal character and associated metals, high temperature and variable salinity suggests that the Nori/RA Cu–Mo–U mineralisation can be linked with the earliest stages of plutonism in the Great Bear magmatic zone. From a regional perspective, the mineralisation may pre-date the extensive multi-element mineralisation now recognised as part of the iron oxide copper–gold (IOCG) spectrum of deposits. As IOCG provinces generally contain a variety of mineralisation styles, we interpret this as the earliest phase of the extensive mineralising system.     

Microstructural and chemical transformations accompanying deformation of granite in a shear zone at Miéville,Switzerland; with implications for stress corrosion cracking and superplastic flow

At Miéville, in the Aiguilles-Rouges Massif, granitic rocks of the basement are deformed into mylonites within a major subvertical shear zone. The ambient temperature during translation is estimated at 250° C±30° C from fluid inclusion filling temperatures in syntectonic microveins, from ¹⁸O quartzilmenite of+15%, and from mineralogical criteria. Porphyroclasts of both oligoclase and orthoclase feldspar decrease from initial diameters of 20 mm and assume elliptical shapes during progressive deformation, due to recrystallisation of the margins to ultra-fine polygonal grains which extend out from the porphyroclasts in thin trails: the final stable grain size is <5 . The recrystallised feldspar has a composition of the parent porphyroclast,+albite, requiring relative gains of Na and losses of K+Ca compared to the precursor, and implying short range redistribution of the components during deformation. Decrease of free energy associated with the deformation catalysed change in feldspar composition, coupled with stored strain energy in the porphyroclasts may account for recrystallisation to a stable aggregate of ultrafine grain size. The long trails imply exceptionally high ductility, which, coupled with microstructural criteria, and admixture of quartz from neighbouring pure quartz aggregates by grain boundary sliding, is interpreted in terms of superplastic flow. Estimated temperatures of T/T _m0.2 for the inferred superplastic deformation is lower by a factor of 2 than previously recorded for this flow michanism in silicates. The feldspar and quartz probably accomodated grain boundary sliding by intercrystalline diffusion.Biotite responds to deformation by bendgliding, kinking, and recrystallisation in mantles. The reaction of high-Ti parent grains to low-Ti biotite+Fe-muscovite+ ilmenite+chlorite is catalysed at all of these microstructural sites. Progressive deformation of the fine-grained products in the mantles is coupled with steady reaction to low-Fe muscovite+epidote+ sphene+rutile resulting in exceptionally ductile trails, as for the case of feldspar.Biotite grains have pervasive networks of nondisplacive intragranular fractures. At the fracture tips increase of the stress intensity has catalysed the reaction of high-Ti parent grains to low-Ti biotite+muscovite+ ilmenite which occupy the fractures. The fractures propagate and coalesce resulting in mechanical breakdown of the parent grains: these microstructures are believed to be examples of natural stress corrosion cracking. These features are also abundant in feldspar porphyroclasts where at fracture tips orthoclasesecondary orthoclase+albite, and oligoclasesecondary oligoclase+albite. Stress corrosion cracking may be significant in the steady state deformation of crustal rocks at low temperatures when intracrystalline plasticity is not generally dominant.Two way mass balance calculations utilising major and selected trace element data, reveal that deformation of the granite was essentially isochemical, involving average additions of <1 % H₂O+CO₂, at approximately constant specific gravity. The parameters Fe²⁺/Fe and ¹⁸O_{whole rock} maintain relatively constant values across the shear zone, and this also implies limited participation of fluids in the deformation. Alkali elements and titanium display the largest percentage variation during progressive deformation, whereas SiO₂, Al₂O₃, and P₂O₅, together with V, Ni, Cr,Y,Zr, and Nb remain relatively constant. All variations decrease at increasing states of deformation and this is interpreted in terms of mechanical mixing of chemical inhomogeneities of the granite precursor within the shear zone. Constraints imposed by variations in abundance of the relatively immobile elements imply that volume changes accompanying deformation in the shear zone were less than ±10%.     

Exposure to sewage plumes and the incidence of deformities in larval fishes

Point-source impacts such as sewage plumes can cause significant degradation of larval habitat. Data on larval abundance, current speed and the shape of surface and subsurface sewage plumes off the coast of Sydney, Australia, indicated that long-shore currents can transport large numbers of larvae through plumes that can potentially affect the health of larvae. Deformities to the notochord, eyes and head were found in samples of preserved wild larvae. Some deformities (e.g. Lateral curl of the notochord) were probably caused by preservation and ‘packing effects’ (shaped by organisms and objects in the sample), while others (e.g. half-pigmented eyes and corrugated notochord) were unlikely to have been caused by sampling artefacts. Deformed larvae were found in waters around Sydney that are influenced by multiple sewage outfalls, and at locations up to 250 km from Sydney. It was concluded that deformities were caused by natural and potentially anthropogenic factors. Cyto- and histopathological studies of larvae are required. Moreover, relationships between oceanography and concentrations of pollutants in plumes are needed to further assess impacts of pollutants on assemblages of vulnerable planktonic animals.     

对人文科学所遭受抨击的回应

长期以来,不少人站在功利角度,对人文科学进行了颇多抨击。本文意欲对此做出有理有据的反击。首先,文章概述了人文科学在政界、民间和实践领域所遭受的非议,并寻找出主要的批评者及其拥护者。其次,作为申辩内容的一部分,本文详细阐述了人文学科的核心优势。这些优势涵盖了哲学和实用科学领域,包括为知识创造提供批判性视角,使生活丰富多彩,培养应对未来不确定性和复杂性的技能,以及增强理性和维持大学机构的收入和信誉度。最后,本文提出人文学者不仅要开展相关学科里非常重要的理论和实证研究,还必须将捍卫和保护人文科学纳入到专业活动中来。