Implications of the 2740 Ma Cote Gold Au(-Cu) deposit for Archean gold metallogeny and porphyry Au deposit formation in the Archean Swayze greenstone belt, northern Ontario

International audienceOre-deposit models, which are fundamental to mineral exploration, result from integrating robust field observations with high-quality mineral-chemical-isotopic data. New discoveries departing from current models demand explanation, and in some cases new deposit models result (e.g., IOCG). The recent (2009/2010) discovery of the Cote Gold Au(-Cu) deposit in the Archean Swayze greenstone belt, northern Ontario, challenges the age-restricted view of porphyry Cu-Au models. The +8 Moz Au deposit is hosted by a subvolcanic tonalite-diorite intrusive complex where magmatic-hydrothermal breccia bodies occur. Gold mineralization, of disseminated-, fracture-and vein-types, is spatially associated with hydrothermal biotite and muscovite alteration that is similar to potassic and phyllic alteration, respectively, in porphyry-type settings. A robust program involving core logging and field mapping with structural analysis integrated with detailed petrographic studies, geochronology, lithogeochemistry, isotopes, and fluid inclusion studies (microthermometry and evaporate mound SEM-EDS analysis) was used to assess the deposit's origin. That the age of host rocks (U-Pb zircon, titanite) and timing of alteration (U-Pb titanite) and mineralization (Re-Os molybdenite) centre on 2740 Ma and pre-dates the age of regional deformation (ca. 2680 Ma), in addition to the co-spatial nature of mineralization and alteration, suggests a magmatic-hydrothermal connection. Structural analysis of auriferous quartz veins also indicates a relationship to the intrusive centre versus regional deformation, which is further supported by a 2740 Ma molybdenite age for one such gold-mineralized vein. Fluid-chemical data indicates fluid mixing with ?34S (py, cpy, moly = 0 ± 1‰) and fluid inclusions (mixed H2O-CO2 fluid (XCO2=0.10); Na-K-CaFe -Mn-Cl-F-S chemistry) suggesting a magmatic fluid reservoir whereas ?18O (qtz = 7-12‰) also indicates a possible seawater contribution. These observations are best reconciled with a deposit model involving Au(-Cu) mineralization originating from exsolution of magmatic fluids from a high-level, hydrous intermediate magma in the same manner as models for younger porphyry analogues

Observations and Recommendations for the Calibration of Landsat 8 OLI and Sentinel 2 MSI for Improved Data Interoperability

Combining data from multiple sensors into a single seamless time series, also known as data interoperability, has the potential for unlocking new understanding of how the Earth functions as a system. However, our ability to produce these advanced data sets is hampered by the differences in design and function of the various optical remote-sensing satellite systems. A key factor is the impact that calibration of these instruments has on data interoperability. To address this issue, a workshop with a panel of experts was convened in conjunction with the Pecora 20 conference to focus on data interoperability between Landsat and the Sentinel 2 sensors. Four major areas of recommendation were the outcome of the workshop. The first was to improve communications between satellite agencies and the remote-sensing community. The second was to adopt a collections-based approach to processing the data. As expected, a third recommendation was to improve calibration methodologies in several specific areas. Lastly, and the most ambitious of the four, was to develop a comprehensive process for validating surface reflectance products produced from the data sets. Collectively, these recommendations have significant potential for improving satellite sensor calibration in a focused manner that can directly catalyze efforts to develop data that are closer to being seamlessly interoperable

Influence of the Solar Spectra Models on PACO Atmospheric Correction

The solar irradiance is the source of energy used by passive optical remote sensing to measure the ground reflectance and, from there, derive the ground properties. Therefore, the precise knowledge of the incoming solar irradiance is fundamental for the atmospheric correction (AC) algorithms. These algorithms use the simulation results of a model of the interactions of the atmosphere with the incoming solar irradiance to determine the atmospheric contribution of the remote sensing observations. This study presents the differences in the atmospherically corrected ground reflectance of multi- and hyper-spectral sensors assuming three different solar models: Thuillier 2003, Fontenla 2011 and TSIS-1 HRS. The results show no difference when the solar irradiance model is preserved through the full processing chain. The differences appear when the solar irradiance model used in the atmospheric correction changes, and this difference is larger between some irrradiance models (e.g., TSIS and Thuillier 2003) than for others (e.g., Fontenla 2011 and TSIS)

Copernicus Sentinel-2 Collection-1: A Consistent Dataset of Multispectral Imagery with enhanced Quality

The Copernicus Sentinel-2 satellite mission, with its Sentinel-2A and Sentinel-2B units, offers since several years now a massive quantitative and qualitative resource for the Earth Observation community. Since the launch of Sentinel-2A in 2015, and Sentinel-2B in 2017, many lessons have been learnt leading to continuous improvements of the radiometric and the geometric performances. However, the current archive is composed of heterogenous processing baselines with inconsistent product formats and uneven data quality, which limits its use for multi-temporal monitoring applications. To overcome this limitation, the Copernicus program has undertaken a complete reprocessing with the latest processing baseline (05.00). It concerns the L1C (Top-OfAtmosphere reflectance) and L2A (Surface Reflectance) products. This paper recalls the features of Collection-1 products and gives an overview of the first validation results

Perspectives on the diagnosis and management of functional cognitive disorder: An international Delphi study

Background: Current proposed criteria for functional cognitive disorder (FCD) have not been externally validated. We sought to analyse the current perspectives of cognitive specialists in the diagnosis and management of FCD in comparison with neurodegenerative conditions. Methods: International experts in cognitive disorders were invited to assess seven illustrative clinical vignettes containing history and bedside characteristics alone. Participants assigned a probable diagnosis and selected the appropriate investigation and treatment. Qualitative, quantitative and inter-rater agreement analyses were undertaken. Results: Eighteen diagnostic terminologies were assigned by 45 cognitive experts from 12 countries with a median of 13 years of experience, across the seven scenarios. Accurate discrimination between FCD and neurodegeneration was observed, independently of background and years of experience: 100% of the neurodegenerative vignettes were correctly classified and 75%–88% of the FCD diagnoses were attributed to non-neurodegenerative causes. There was <50% agreement in the terminology used for FCD, in comparison with 87%–92% agreement for neurodegenerative syndromes. Blood tests and neuropsychological evaluation were the leading diagnostic modalities for FCD. Diagnostic communication, psychotherapy and psychiatry referral were the main suggested management strategies in FCD. Conclusions: Our study demonstrates the feasibility of distinguishing between FCD and neurodegeneration based on relevant patient characteristics and history details. These characteristics need further validation and operationalisation. Heterogeneous labelling and framing pose clinical and research challenges reflecting a lack of agreement in the field. Careful consideration of FCD diagnosis is advised, particularly in the presence of comorbidities. This study informs future research on diagnostic tools and evidence-based interventions

Geology of the orogenic Cheminis gold deposit along the Larder Lake-Cadillac deformation zone, Ontario

The Larder Lake - Cadillac deformation zone (LLCDZ) is one of two major, auriferous, deformation zones in the southern Abitibi subprovince of the Archean Superior Province. It hosts the Cheminis and the giant Kerr Addison – Chesterville deposits within a strongly deformed band of Fe-rich tholeiitic basalt and komatiite of the Larder Lake Group (ca. 2705 Ma). The latter is bounded on both sides by younger, less deformed, Timiskaming turbidites (2674 Ma - 2670 Ma). The earliest deformation features are F1 folds affecting the Timiskaming rocks, which formed either during D1 extensional faulting or during early D2 north-south shortening related to the opening and closure, respectively, of the Timiskaming basin. Continued shortening during D2 imbricated the older volcanic rocks and turbidites and produced regional F2 folds with an axial planar S2 cleavage. D2 deformation was partitioned into the weaker band of volcanic rocks, producing the strong S2 foliation, L2 stretching lineation, and south-side-up shear sense indicators, which characterize the LLCDZ. Gold is present in quartz-carbonate veins in deformed fuchsitic komatiites (carbonate ore) and turbiditic sandstone (sandstone-hosted ore), and in association with disseminated pyrite in altered Fe-rich tholeiitic basalts (flow ore). All host rocks underwent strong mass gains in CO2, S, K2O, Ba, As, and W, during sericitization, carbonatization, and sulphidation of the host rocks, suggesting that they interacted with the same hydrothermal fluids. Textural relationships between alteration minerals and S2 cleavage indicate that mineralization is syn-cleavage. Thus, gold was deposited as hydrothermal fluids migrated upward along the LLCDZ during contractional, D2 south-side-up shearing. The gold zones were subsequently modified during D3 reactivation of the LLCDZ as a dextral transcurrent fault zone.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Geochemical and microstructural evidence for in situ formation of pseudotachylitic Sudbury breccia by shock-induced compression and cataclasis

Pseudotachylitic breccias occur in the crater floor of large impact structures. Their origin is widely attributed either to shock melting and cataclasis during propagation of an impact shock wave, or to frictional melting and cataclasis during large slip displacements along crater collapse superfaults. By contrast, some models propose that the breccia matrices are allochthonous superheated melts from overlying impact melt sheets or from sites within the crater floor, which leaked into dilational fractures during collapse of the crater. In an effort to test these models, the compositions of pseudotachylite Sudbury breccias in the South Range of the Sudbury impact structure, Canada, were here compared to those of its associated impact melt sheet, the Sudbury Igneous Complex (SIC). The studied breccias occur along the contact between sandstone and a gabbro stock, and additional breccia bodies are located solely within these two lithologies. Major, trace element and lead isotope systematics suggest that the contact breccias are derived by mixing of comminuted gabbro and sandstone and that breccias hosted exclusively by sandstone or gabbro have compositions similar to their host rocks. The SIC has distinct chemical and isotopic compositions which argue strongly against the involvement of the impact melt sheet in the makeup of the breccias. Quartz and plagioclase in clasts and matrix of the breccias are transected by multiple microfractures and they have pervasive mosaic textures characterized by rolling and mottled undulatory extinction of micron-sized subgrain-like domains and new grains. These textures and strong local host control on chemical and clast composition of the breccias suggest that the breccias formed in situ by shock-induced compression and cataclasis of their host rocks during propagation of the shock wave. (C) 2010 Elsevier B.V. All rights reserved

Evidence for voluminous, bimodal pyroclastic volcanism, during rifting of a Paleoproterozoic Arc at Snow Lake, Manitoba

The thrust bounded McLeod Road - Birch Lake sequence (MB sequence) occurs within the Paleoproterozoic Snow Lake arc assemblage (SLA) of the Flin Flon Belt. Stratigraphic correlation of volcanic strata of the MB sequence with strata of the thrust bounded Chisel sequence, indicates that distinctive, submarine, eruption-fed, pyroclastic flow deposits are more extensive and voluminous than previously recognized (>10 km3). These voluminous felsic pyroclastic deposits define a distinct magmatic and explosive volcanic event during bimodal volcanism that accompanied rifting of the Snow Lake arc. The felsic pyroclastic deposits define the remnants of a basin, or of nested basins, that formed during arc rifting and subsidence, and their eruption immediately preceded formation of the Chisel sequence volcanogenic massive sulfide (VMS) deposits. Although the Chisel sequence ore interval is recognized in the MB sequence, the lack of VMS-related alteration indicates that VMS hydrothermal activity was restricted to the Chisel portion of the basin. However, the MB sequence is host to the younger Snow Lake gold mine, a 1.4M oz. (43,699kg) gold producer. The overlying MORB-like Birch Lake Basalts, if conformable with the MB sequence, may represent a progression from a rifted-arc to a back-arc setting, however if thrust fault bounded they may represent the initial phases of arc-rifting, prior to the voluminous felsic pyroclastic eruptions. Correlation and integrity of stratigraphy between the thrust bounded MB and the SLA sequences indicates that the bounding thrust faults, which developed during accretionary processes, have less regional significance than previously interpreted.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author