Combining in situ isotopic, trace element and textural analyses of quartz from four magmatic-hydrothermal ore deposits

This study couples in situ ¹⁶O, ¹⁷O and ¹⁸O isotope and in situ trace element analyses to investigate and characterize the geochemical and textural complexity of magmatic-hydrothermal quartz crystals. Euhedral quartz crystals contemporaneous with mineralization were obtained from four magmatic-hydrothermal ore deposits: El Indio Au–Ag–Cu deposit; Summitville Au–Ag–Cu deposit; North Parkes Cu–Au deposit and Kingsgate quartz-Mo–Bi–W deposit. The internal features of the crystals were imaged using cathodoluminescence and qualitative electron microprobe maps. Quantitative isotopic data were collected in situ using 157 nm laser ablation inductively coupled plasma mass spectrometry (for 40 trace elements in quartz) and sensitive high-resolution ion microprobe (for 3 isotopes in quartz). Imaging revealed fine oscillatory zoning, sector zoning, complex “macromosaic” textures and hidden xenocrystic cores. In situ oxygen isotope analyses revealed a δ¹⁸O range of up to 12.4 ± 0.3 ‰ in a single crystal—the largest isotopic range ever ascribed to oscillatory zonation in quartz. Some of these crystals contain a heavier δ¹⁸O signature than expected by existing models. While sector-zoned crystals exhibited strong trace element variations between faces, no evidence for anisotropic isotope fractionation was found. We found: (1) isotopic heterogeneity in hydrothermal quartz crystals is common and precludes provenance analysis (e.g., δD–δ¹⁸O) using bulk analytical techniques, (2) the trace element signature of quartz is not an effective pathfinder toward noble metal mineralization and (3) in three of the four samples, both textural and isotopic data indicate non-equilibrium deposition of quartz.     

The Projects for Onboard Autonomy (PROBA2) Science Centre: Sun Watcher Using APS Detectors and Image Processing (SWAP) and Large-Yield Radiometer (LYRA) Science Operations and Data Products

The PROBA2 Science Centre (P2SC) is a small-scale science operations centre supporting the Sun observation instruments onboard PROBA2: the EUV imager Sun Watcher using APS detectors and image Processing (SWAP) and Large-Yield Radiometer (LYRA). PROBA2 is one of ESA’s small, low-cost Projects for Onboard Autonomy (PROBA) and part of ESA’s In-Orbit Technology Demonstration Programme. The P2SC is hosted at the Royal Observatory of Belgium, co-located with both Principal Investigator teams. The P2SC tasks cover science planning, instrument commanding, instrument monitoring, data processing, support of outreach activities, and distribution of science data products. PROBA missions aim for a high degree of autonomy at mission and system level, including the science operations centre. The autonomy and flexibility of the P2SC is reached by a set of web-based interfaces allowing the operators as well as the instrument teams to monitor quasi-continuously the status of the operations, allowing a quick reaction to solar events. In addition, several new concepts are implemented at instrument, spacecraft, and ground-segment levels allowing a high degree of flexibility in the operations of the instruments. This article explains the key concepts of the P2SC, emphasising the automation and the flexibility achieved in the commanding as well as the data-processing chain.     

Ck-Reconstruction of Surfaces from Partial Data

In this paper, we study the problem of constructing a smooth approximant of a surface defined by the equation z = f(x ₁, x ₂), the data being a finite set of patches on this surface. This problem occurs, for example, after geophysical processing such as migration of time-maps or depth-maps. The usual algorithms to solve this problem are picking points on the patches to get Lagrange's data or trying to get local junctions on patches. But the first method does not use the continuous aspect of the data and the second one does not perform well to get a global regular approximant (C ¹ or more). As an approximant of f, a discrete smoothing spline belonging to a suitable piecewise polynomial space is proposed. The originality of the method consists in the fidelity criterion used to fit the data, which takes into account their particular aspect (surface's patches): the idea is to define a function that minimizes the volume located between the data patches and the function, and which is globally C ^k. We first demonstrate the new method on a theoretical aspect and numerical results on real data are given.     

Evolution and Morphodynamics of a Prograded Beach‐Ridge Foreland,Northern Baffin Island,Canadian Arctic Archipelago

Landward retreat (marine transgression) is a common response of coastal systems to rising relative sea level. However, given sufficient sediment supply, the coast may advance seaward. The latter response of gravel barriers has been recorded in parts of southeastern and northwestern Canada, where seaward‐rising sets of beach ridges are observed in areas of Holocene RSL rise. Cape Charles Yorke, northern Baffin Island, is a 5 km long gravel foreland characterized by seaward‐rising beach‐ridge crest elevations. The prograded morphology of the Cape Charles Yorke foreland is a prime example of coastal response to a combination of rising RSL and abundant sediment supply, an unusual and little‐documented pattern in the Canadian Arctic. The main gravel supply to Cape Charles Yorke is likely from eroding bedrock and raised marine deposits southwest of the foreland. Although not the dominant sediment source, the Cape Charles Yorke delta contributed to the formation of the foreland by sheltering it from easterly storm waves and providing an anchor point for the prograding ridges. The truncation of relict ridges by the modern shoreline suggests a recent regime shift from continuous deposition to predominant erosion. The cause and timing of this shift are unknown but could result from a recent dwindling in sediment supply, increased accommodation space, increased wave energy, and/or an accelerated rise of relative sea level.     

Syntectonic Mobility of Supergene Nickel Ores of New Caledonia (Southwest Pacific). Evidence from Garnierite Veins and Faulted Regolith

Supergene nickel deposits of New Caledonia that have been formed in the Neogene by weathering of obducted ultramafic rocks are controlled by fracture development. The relationship of tropical weathering and tectonic structures, faults and tension gashes, have been investigated in order to determine whether fractures play a passive role only, as previously thought; or alternatively, if brittle tectonics was acting together with alteration. Observation of time‐relationship, textures, and mineralogy of various fracture fills and fault gouges shows that active faulting has played a prominent role not only in facilitating drainage and providing room for synkinematic crystallization of supergene nickel silicate, but also in mobilizing already formed sparse nickel ore, producing the very high grade ore nicknamed “green gold”.     

The glacial inception as recorded in the NorthGRIP Greenland ice core: timing, structure and associated abrupt temperature changes

The mechanisms involved in the glacial inception are still poorly constrained due to a lack of high resolution and cross-dated climate records at various locations. Using air isotopic measurements in the recently drilled NorthGRIP ice core, we show that no evidence exists for stratigraphic disturbance of the climate record of the last glacial inception (∼123–100 kyears BP) encompassing Dansgaard–Oeschger events (DO) 25, 24 and 23, even if we lack sufficient resolution to completely rule out disturbance over DO 25. We quantify the rapid surface temperature variability over DO 23 and 24 with associated warmings of 10±2.5 and 16±2.5°C, amplitudes which mimic those observed in full glacial conditions. We use records of δ¹⁸O of O₂ to propose a common timescale for the NorthGRIP and the Antarctic Vostok ice cores, with a maximum uncertainty of 2,500 years, and to examine the interhemispheric sequence of events over this period. After a synchronous North–South temperature decrease, the onset of rapid events is triggered in the North through DO 25. As for later events, DO 24 and 23 have a clear Antarctic counterpart which does not seem to be the case for the very first abrupt warming (DO 25). This information, when added to intermediate levels of CO₂ and to the absence of clear ice rafting associated with DO 25, highlights the uniqueness of this first event, while DO 24 and 23 appear similar to typical full glacial DO events.     

Sites occupancy of Fe3+ in Garfield Nontronite: A spectroscopic study

New data on the structure of Garfield nontronite have been produced by the use of different spectroscopic techniques: Mössbauer spectroscopy, optical spectroscopy, X-ray absorption edges and EXAFS and NMR. The tetrahedral iron content is found to be no higher than 1 percent. All iron atoms belong to the octahedral sheet excluding the possibility of the presence of non crystallized phases. Some ambiguities remain about the coherence of the octahedral sheet because of the presence of two doublets in the Mössbauer spectrum and at least two lineshapes in NMR spectra of OH which correspond to different environments.