TALC PROTRUSIONS AT TALC LAKE, BRITISH COLUMBIA: A MAJOR COMPONENT OF THE GIANT, CAMBRIAN-AGE, HYDROTHERMAL, HYDROCARBON-DOLOMITE-BASE METAL-MUD VOLCANO SYSTEM ON THE KICKING HORSE RIM

Abstract

Field observations at the now-abandoned Red Mountain talc mine at Talc Lake, British Columbia revealed that the talc lithosome was emplaced in the solid state as a protrusion along the middle Cambrian Monarch Formation–lower Cambrian Gog Group contact. The talc protrusion occurs stratigraphically below and only a few hundred metres northeast of a Burgess Shale fossil locality near Mummy Lake. Layering in the talc lithosome is mylonitic in nature showing that the lithosome was emplaced in the sold state and self sheared itself, especially near its protrusive contacts with the Monarch Formation and the Gog Group. Coupled EDS-SEM analyses supplied qualitative analytical and photographic evidence of kerogen in the Red Mountain talc lithosome. Kerogen was confirmed in the talc protrusion and in other potentially related hydrothermal products including hydrothermal dolomite, hydrothermal magnesite, and hydrothermal muds at the classic Burgess fossil localities, by quantitative organic carbon (kerogen) analyses, which were supported by full major and trace element analyses. Follow-up work on kerogen-bearing samples, including most of the hydrothermal rock types, by GCMS analysis for hydrocarbon compounds revealed the presence of hydrocarbon markers (for example, butylated hydroxytoluene [BHT], n-C16, n-C17, pristane, n-C18, phytane, n-C21, n-C27, n-C30, and n-C31). The occurrence of these shared hydrocarbon markers suggest a common origin for the hydrothermalism that generated the greater Kicking Horse Rim magnesium anomaly. Exhalative reduced solutes associated with this hydrothermalism likely fueled microbial productivity that supported Burgess Shale faunal communities associated with the exhalative mud volcano/seep system at the top of the hydrothermal plume. The presence of the same hydrocarbon markers in world-wide kerogen-bearing serpentinites allows a linkage to serpentinite from which the talc was likely derived by dehydrational steatization of serpentinized peridotite in the mid-lower crust during middle Cambrian deep subduction or rifting.