Geoscience Map 1993-7: Geology of the Bralorne (North half) and Northeastern Dickson Range Map Areas
(NTS 92J/14, 15)
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Geoscience Map 1993-7 presents the geology of the Bralorne (North half) and Northeastern Dickson Range Map Areas (92J/14, 15). The publication consists of a 1:50 000 scale geology map with legend and reference list.
The area is underlain by Ophiolitic assemblages, strata of the Cadwallader, Bridge River and Relay Mountain terranes, and overlap assemblages. The Ophiolitic assemblages include an assemblage of serpentinite, serpentinized ultramafite, and listwanite altered rocks; the Permian and younger Shulaps Ultramafic Complex with a harzburgite unit and a serpentinite melange unit; and the Bralorne-East Liza Complex of pillowed and massive greenstones, diabase, gabbro, diorite, soda granite, serpentinite and minor limestone and chert. Cadwallader Terrane strata include the Upper Triassic Cadwallader and Tyaughton Groups, the Lower to Middle Jurassic Last Creek Formation, and the Jurassic (?) Downton Lake unit. The Cadwallader Group is represented by the Hurley Formation, which consists of a volcanic greenstone-tuff unit, a unit with similar rocks intercalated with sandstone, tuffaceous sandstone, limestone and conglomerate, and a unit comprised mainly of sandstone, calcarenite and siltstone. Tyaughton Group strata are dominated by conglomerate and conglomeratic sandstone intercalated with sandstone. The Last Creek Formation contains sandstone, siltstone and conglomerate, and black shale layers. The Downton Lake unit comprises mainly siliceous argillite and siltstone. Bridge River Terrane components include the Bridge River Complex and the Cayoosh Assemblage. The Bridge River Complex consists of Mississippian to Middle Jurassic strata consisting of pelitic and calcareous schist, metachert and marble; serpentinite with knockers of other Bridge River rocks; and ribbons chert, argillite, phyllite, greenstone and lesser limestone, gabbro, diabase, sandstone, conglomerate and serpentinite; Triassic and perhaps older blueschists include non-schistose greenstones with minor amounts of blue amphiboles; Upper Triassic mainly pillowed to massive greenstones and Lower Norian limestone; and Jurassic and perhaps older argillite, sandstone and chert. The Cayoosh Assemblage is of Jurassic and/or Cretaceous age. It contains the Gun Lake clastic unit, of mainly sandstone, siltstone and shale; and the Traux Creek polymict conglomerate. The Relay Mountain-Bridge River overlap assemblage consists of the Lower and perhaps Upper Cretaceous Taylor Creek Group and the Upper Cretaceous Powell Creek Formation. The Taylor Creek Group has a lower volcanic sandstone, conglomerate and shale unit; the Dash Formation of mainly chert pebble conglomerate, chert-rich sandstone, shale and siltstone; and the Lizard Formation with micaceous sandstone and shale. The Silverquick Formation comprises mainly pebble to cobble conglomerate, and the Powell Creek Formation is mainly volcanic breccia and lapilli tuff. Tertiary rocks include Paleocene and perhaps Eocene basalt flows and flow breccia, and possibly Eocene dacite and volcanic breccia.
Intrusive rocks in the area include Cretaceous (?) gabbros; Late Cretaceous granodiorite; Late Cretaceous and/or Early Tertiary diorite and gabbro, hornblende-bearing porphyries, quartz diorite to granodiorite, and granite; Possibly Eocene hornblende-biotite-quartz-feldspar porphyry and Miocene or Pliocene mafic plugs.
The map area is cut by a northwest-trending system of dextral strike-slip faults that was active in Late Cretaceous time. Northerly trending splays of the Relay Creek-Marshall Creek fault system connect with the Yalakom fault system to define a large-scale extensional duplex structure. This fault system steps across and bounds the northwestern margin of the Shulaps ultramafic complex at its southeastern end. In contrast to the extensional zone to the northwest, the Shulaps complex may have been deformed and uplifted during Late Cretaceous movement on the bounding strike-slip fault systems.
The map area includes the Bridge River mining camp, which is British Columbia’s foremost historical gold producer from low sulphide mesothermal quartz veins. Other known and potential deposit types in the area are copper-molybdenum porphyries, pluton-associated high sulphide auriferous veins, skarns, scheelite-stibnite or stibnite-only veins, gold-silver polymetallic veins, epithermal gold-silver veins and cinnabar veins and disseminations.
Metallic mineral concentrations within or adjacent to strike-slip faults or associated structures have a close spatial relationship with plutons or dykes. The age of mineralization seems closely tied to igneous activity between Late Cretaceous and Early Tertiary time. The protracted history of mineralization and plutonism combined with differential uplift across faults has led to the juxtaposition of deposits of contrasting structural level. In addition, the ultramafic rocks have small chromite concentrations, and potential for jade, magnesite and chrysotile. Cinnabar veinlets and disseminations occur locally near the Bridge River fault.
At the south end of Taseko Lake, the Taylor Windfall property is a historic gold producer. A fracture-related silicified zone carries pyrite, tennantite, chalcopyrite and minor sphalerite in a chlorite-sericite gangue. Other gold-bearing silicified zones occur and several properties have been explored for their porphyry copper gold potential. Most mineralization is apparently related to Eocene intrusive rocks.
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