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TitleFluids and ore forming processes in orogenic gold deposits of Newfoundland: Evidence from fluid inclusions and stable isotope studies
AuthorConliffe, J; Sandeman, H A I; Wilton, D; Laflamme, C; Honsberger, I WORCID logo
SourceAbstracts. GAC-MAC-IAH-CNC-CSPG 2022 Halifax; Geological Association of Canada-Mineralogical Association of Canada, Joint Annual Meeting, Abstracts Volume vol. 45, 2022 p. 90, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20220656
PublisherGeological Association of Canada
MeetingGAC-MAC-IAH-CNC-CSPG; Halifax; CA; May 15-18, 2022
Mediapaper; digital; on-line
File formatpdf
ProvinceNewfoundland and Labrador
NTS1; 2; 11P; 11O; 12A; 12B; 12G; 12H; 12I; 12P
Lat/Long WENS -60.0000 -52.0000 52.0000 46.0000
Subjectsmineralogy; orogenic regions; gold; fluid inclusions; stable isotope studies
ProgramTargeted Geoscience Initiative (TGI-6) Ore systems
Released2022 07 19
AbstractNewfoundland is a major emerging gold district containing numerous gold occurrences associated with Paleozoic crustal-scale fault systems. These include the Valentine Lake (3.14 Moz Au measured and indicated resource) and Cape Ray (0.84 Moz Au measured and indicated resource) gold deposits, as well as numerous recent discoveries along the northern margin of Ganderia in central Newfoundland Appalachians (e.g. Queensway and Moosehead prospects). These occurrences have characteristics typical of orogenic gold deposits, such as association with crustal-scale faults, syntectonic rock sequences, and lower greenschist to amphibolite facies metamorphism. However, there are significant variations in mineralization styles and settings between individual gold occurrences, including host lithologies, metal contents, and inferred mineralization depths. This study of some of these gold occurrences in central Newfoundland investigates variations in mineralizing fluids and ore forming processes. Herein, we present preliminary fluid inclusion results from a number of gold occurrences representing a diverse range of geological settings. Fluid inclusions have been studied in > 100 vein samples from > 10 deposits, with detailed petrographic analyses carried out using the Fluid Inclusion Assemblage (FIA) approach. The majority of samples proved unsuitable for fluid inclusion analysis, due to multiple generations of overprinting FIA or strong deformation of samples resulting in post entrapment modification of FIA. Where suitable FIA related to gold mineralization events have been identified, the mineralizing fluids appear to be variable in composition, with carbonic, aqueous-carbonic, and aqueous fluid types identified (XCO2 ranging from 0.03 to 1). The carbonic phase ranges from pure CO2 to rare CH4-dominated, and fluid salinities are generally low (< 10 eq. wt.% NaCl). These variations in fluid compositions are likely related to fluid unmixing and the geochemical influence of the host lithologies. Fluid inclusion homogenization temperatures range from 250 to 350°C, and isochore modelling indicate trapping at epizonal to mesozonal pressures (1 to 2.5 kbars). Future research will include more fluid inclusion studies (including a more complete geochemical characterization of mineralizing fluids) along with in situ sulphur isotope and trace-element analysis by LA-ICP-MS of sulphides associated with gold mineralization. These data will be used to better constrain the ore fluids and gold precipitation mechanisms in individual gold occurrences and identify factors responsible to the variations between orogenic gold occurrences in the central Newfoundland gold district.
Summary(Plain Language Summary, not published)
This contribution presents new results on fluid compositions from select gold-bearing zones in Newfoundland.

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