Petrography and stable isotope geochemistry of alteration and mineralization in the Rambler volcanogenic massive sulphide deposit, Baie Verte, Newfoundland

Weick, Reinhold James (1993) Petrography and stable isotope geochemistry of alteration and mineralization in the Rambler volcanogenic massive sulphide deposit, Baie Verte, Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

The Rambler is one of the five VMS deposits of the Consolidated Rambler Mines properties which occur in the Pacquet Harbour Group; a deformed and metamorphosed sequence of volcanic and sedimentary rocks located on the east half of the Baie Verte Peninsula in Central Newfoundland. The deposit contains alteration and base metal sulphide assemblages typically associated with VMS mineralization, but is highly deformed and occurs as a northeast trending, shallow dipping, ellipsoidal body, above a prominent imbricate shear zone. The syn-kinematic quartz + muscovite ± chlorite assemblages in the shear zone are of uncertain origin, but similar to the alteration in several epigenetic / mesothermal gold prospects which occur throughout the Baie Vert region. The alteration and sulphide assemblages associated with the deposit and its shear zone are cut by quartz-carbonate veins which contain their own characteristic alteration assemblages. All alteration assemblages are overprinted by disseminated biotite related to a late metamorphic event. -- Oxygen isotope thermometry and calculated δ¹⁸O and δD fluid values confirm a complex thermal and fluid history in the Rambler deposit. An early high temperature event is recorded by the isotopic composition of a dark green variety of chlorite in massive sulphide horizons, which equilibrated with a high ¹⁸O magmatic fluid; δ¹⁸O and δD values of +9.0 to +9.4‰ and -39‰ at 430 to 480°C. A decrease in temperature (-200 to 300°C) and shift in δ¹⁸O and δD fluid values to +4.4 and +4.6‰, and -26 to -37‰, respectively, are associated with the occurrence of a pervasive secondary light green chlorite which may have equilibrated with a mixture of seawater and metamorphic fluids during greenschist metamorphism and deformation of the Pacquet Harbour Group. The presence of an additional low ¹⁸O (< +5‰) low D (<-60‰) fluid during deformation is suggested by δ¹⁸O and δD mineral values of +6.4 to +8.2‰ and -55 to -70‰ for muscovite which are out of equilibrium with values of +2.9 to +7.5‰ and -57 to -73‰ for coexisting chlorite. Low δ¹⁸O chlorite fluid values of 0 to +4.1 ‰ at 180 to 200°C may be related to an influx of meteoric waters during the formation of quartz-carbonate veins. -- Metamorphic biotite in the stratigraphy of the deposit appears to have equilibrated with a high ¹⁸O fluid, with δ¹⁸O values as high as +7.5 ‰ and δD values of -41 to -49‰ at temperatures of 540 and 560°C. Similar biotite occurs in contact metamorphic assemblages along the margin of the Burlington Granodiorite to the west of the Consolidated Rambler Mines properties. -- Alteration mineralogy and isotopic composition of the low ¹⁸O-low D fluid which affected the Rambler is distinct from the isotopic composition of the CO₂-rich, low D fluids in equilibrium with chlorite and muscovite during the formation of two epigenetic / mesothermal gold deposits in the Baie Verte and Springdale regions. The replacement of seafloor assemblages in massive sulphide horizons by syn-kinematic assemblages in the footwall shear zone suggests the distinct low ¹⁸O-low D hydrothermal fluid may have evolved from the influx and mixing of formational and meteoric fluids during the obduction and imbrication of the Pacquet Harbour Group and its emplacement over the Laurentian continental margin.

Item Type: Thesis (Masters)
URI: http://research.library.mun.ca/id/eprint/6703
Item ID: 6703
Additional Information: Bibliography: leaves 130-151.
Department(s): Science, Faculty of > Earth Sciences
Date: 1993
Date Type: Submission
Geographic Location: Canada--Newfoundland and Labrador--Baie Verte
Library of Congress Subject Heading: Petrology--Newfoundland and Labrador--Baie Verte; Sulphides

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