Geology of the Eureka Peak and Spanish Lake Map Area (NTS 093A)
Paper 1990 - 3
View Paper (PDF, 9.6MB)
Fig 5 - Geology of the Eureka Peak (PDF, 949kB)
Fig 6 - Geology of Spanish Lake Area (PDF, 459kB)
Paper 1990-3 covers the geology and mineral deposit types of the Eureka Peak and Spanish Lake areas. The area is within the Quesnel Terrane of the Intermontane Belt, adjacent to the Omineca Belt - Intermontane Belt tectonic boundary. It represents a convergent zone between the arc related Quesnel Terrane and parautochthonous Barkerville Terrane. The boundary is defined by the Eureka thrust.
Underlying the area are Middle Triassic to Early Jurassic sedimentary and volcanic rocks represented by the Quesnel River Group and the Nicola Group, respectively. Petrologic and geochemical studies suggest protoliths of island arc and marginal basin affinities (Bloodgood, 1987a). The Quesnel Terrane structurally overlies the Barkerville Terrane, represented by Hadrynian to early Paleozoic metasediments of the Snowshoe Group and the Late Devonian to Middle Mississippian Quesnel Lake gneiss. The base of the Quesnel Terrane is marked by mylonitized mafic and ultramafic rocks of the Crooked amphibolite.
Correlation of features across the boundary has established the structural continuity in the region and recognition of structural features common to both terranes that developed in response to plate convergence. The deformational history involves two phases of coaxial folding, accompanied by extensive pressure solution, and later overprinting by northeast trending fractures. Synchronous with first phase deformation, thrust faults and detachment surfaces developed, primarily along stratigraphic contacts due to contrasting rheologies of the adjacent lithologies. Second phase deformation established the regional map pattern, folding both the fault surfaces and the tectonic boundary.
Synchronous to the deformation, regional metamorphism is evidenced by the growth of minerals characteristic of amphibolite facies in the Barkerville Terrane and greenschist facies in the Quesnel Terrane. Cleavage surfaces have acted as a locus along which pressure solution occurred, providing a pathway for the migration of fluids generated during regional metamorphism.
Mineral exploration within the Triassic black phyllites has been ongoing since the Barkerville gold rush. Three mineral deposit types have been recognized within the area, all of which have important structural and stratigraphic controls. Remobilization of gold and sulphide minerals during regional metamorphism is characteristic of syngenetic lode gold mineralization. Porphyry copper mineralization occurs in association with alkalic stocks within the metavolcanic Nicola succession. And, vein mineralization associated with zones of intense listwanite and carbonate-silica alteration has also been recognized. In each case, fracture formation and cleavage development accompanying regional metamorphism and deformation have provided the pathway for the migration of hydrothermal and mineralizing fluids.
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