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The geology and ore deposits of the Summit Camp, Boundary District, British Columbia Carswell, Henry Thomas

Abstract

The Summit Camp, now abandoned, is located seven miles north of the town of Greenwood in south-central British Columbia. Mineral deposits in skarn zones of the camp were mined for their copper, gold, and silver values. The oldest rocks in the Summit Camp are the contorted grey cherts of the Knob Hill Formation of Paleozoic (?) age. The Knob Hill Formation is overlain nonconformably by the Paleozoic Attwood Series, made up of the shales of the basal Rawhide Formation; the limestones, chert breccia, and limestone breccia of the Brooklyn Formation; and the pyroclastics, lavas, and greenstones of the Eholt Formation. The chert and limestone breccias of the Brooklyn Formation, interpreted by some earlier workers as the results of silicification and tectonic brecciation respectively, are considered to be of clastic sedimentary origin. There is a pronounced nonconformity between the Brooklyn and Eholt Formations. These sedimentary rocks were intruded in Mesozoic (?) time by the Emma Intrusive consisting of quartz diorite, diorite and minor gabbro. This event was followed by the emplacement of the Lion Creek Intrusive, which consists of quartz diorite and syenite. In Oligocene time the arkoses of the Kettle River Formation were deposited in fresh-water basins in the area. Earlier rocks were intruded by Miocene (?) phonolite and pulaskite, that also gave rise to flows of similar composition. Miocene (?) basic dikes are the latest rocks of the area. Mineral deposits of the camp contain magnetite, pyrite, pyrrhotite, chalcopyrite and tetrahedrite in a gangue of skarn minerals. Skarn has formed from Brooklyn limestone as a result of the addition of heat and large amounts of Si, Al, and Fe⁺⁺⁺ from the Lion Creek Intrusive. The intrusive assimilated large amounts of Ca and CO₂ in the process. Skarn zones are controlled by proximity to the Lion Creek stock, or by a contact of limestone with other rocks, or by the presence of channelways such as faults or permeable beds. Metallic minerals were introduced into the skarn zones along fractures and foliation planes with falling temperature. Epithermal precious metal veins that occur close to the Mesozoic (?) intrusives of the Boundary District are not found in limestone. It is believed that these veins were emplaced during a late stage in the cooling of the plutonic rocks. The earlier, higher temperature release of metals into the skarn deposits may be the result of the assimilation of CO₂ that locally prevented the solidification of the shell of the consolidated intrusive body. The mineralizing fluids responsible for the epithermal veins were trapped within the shell and released at a late stage by fracturing due to cooling.

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