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Geology and mineralization of the stikine assemblage, Mess Creek area, northwestern British Columbia

University of British Columbia

The Stikine Assemblage in the Mess Creek area consists of Mississippian aged, variably altered, deformed, metamorphosed and mineralized schists, phyllites and greenstones. Original lithologies were mafic pyroclastics and epiclastics, felsic volcanic breccias to crystal-lithic ash tuffs, graphitic sediments, and gabbroic sills. Regional dynamothermal metamorphism to lower greenschist facies occurred between Late Permian and Middle Triassic time. Four phases of deformation are recognised including two early phases of northwesterly trending isoclinal, recumbent folding followed by easterly trending kink bank and chevron style folding, and northerly trending parallel-style folding. The first phase of folding was synchronous with metamorphism and produced a penetrative axial planar foliation. Second phase folds significantly outlasted thermal effects and produced a locally pronounced crenulation cleavage. Third and fourth phase folding also affected overlying Late Triassic sediments and could be related to terrane collision in Early Jurassic time. Three stages of plutonism occurred within the Mess Creek area. Potassium-argon and rubidium-strontium dates from plutons of the Hickman batholith indicate Early to Middle Triassic ages for quartz diorites and a Middle Jurassic age for quartz monzonites. Alkalic, generally syenitic plutons, commonly associated with porphyry Cu-Au deposits yield Early Jurassic ages. Gold and silver mineralization is hosted by structurally controlled quartz and quartz-carbonate veins and associated alteration. Two ages of alteration have been identified. Widespread and commonly conformable silicification and potassium metasomatism, characterized by a quartz-muscovite- carbonate assemblage, is pre-kinematic and attributed to volcanogenic hydrothermal systems. Foliation-parallel quartz veins associated with this alteration are ubiquitous but generally barren of precious metals. Later alteration, which consists of intense carbonatization, silicification and sericitization, is fracture controlled and commonly hosts gold and silver bearing veins that cut all deformation fabrics. Gangue and alteration mineralogy includes ankerite, siderite, quartz, albite, muscovite, fuchsite, chlorite, manganiferous dolomite, barite and lanthanide group phosphates. Ore mineralogy includes pyrite, sphalerite, tetrahedrite, arsenopyrite, chalcopyrite, galena, silver and bismuth tellurides, electrum and gold. Sulphide concentrations within veins range from massive to sparsely disseminated. Hydrogen metasomatism associated with mineralization produced compositional changes within host rocks that include the removal of Ca and Na and the addition of K and H. Precipitation of quartz, carbonates and sulphides was caused by a pH increase due to hydrolysis reactions with wall rocks. Potassium-argon and rubidium-strontium dating of alteration and mineralization yields Early Jurassic ages, which coincide with regional alkalic plutonism and possible time of tectonic accrection of allochthonous terranes.

Text

2010-08-30

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http://hdl.handle.net/2429/27955

Geological Sciences

University of British Columbia

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