Age, formation and tectonism of the Neoproterozoic Ruddock Creek zinc-lead deposit and host Windermere Supergroup, northern Monashee Mountains, southern Canadian Cordillera

The Ruddock Creek property is located in the northern Monashee Mountains, southern British Columbia. The deposit is hosted by Neoproterozoic metasedimentary rocks of the Mica Creek succession within the Windermere Supergroup. Structurally the Ruddock Creek property is interpreted to reside within the base of the Selkirk allochthon, in the immediate hanging wall of the Monashee décollement, a crustal-scale, northeast-directed thrust-sense shear zone. The Neoproterozoic strata have been complexly folded and transposed by Mesozoic deformation. U-Pb dates for deformational events range from ca. 116 to 63 Ma (63 Ma being the end of ductile deformation). The geometry of the main sulphide body indicates that the mineralized horizon was subject to all phases of deformation and was metamorphosed to amphibolite facies. Detrital zircon geochronology provides U-Pb ages that constrain the provenance for the host Windermere Supergroup, and define a maximum depositional age of ca. 663 Ma. The 663 Ma age is not common to the North American Cordillera, and is found almost exclusively in igneous rocks in central Idaho, suggesting south to north transportation of sediment along the Neoproterozoic rifted paleo-margin of western Laurentia. The 206Pb/204Pb isotope ages of galena, pyrite and pyrrhotite from several mineralized horizons that make up the Ruddock Creek deposit indicate an Early Cambrian, 535 ± 30 Ma model age of mineralization. Different colour sphalerites and calcite were analyzed to generate a Rb/Sr errorchron with an age of ore formation of 556 ± 420 Ma. Together the maximum age of deposition, the Pb isotope ages and the Rb/Sr errorchron reveal a spatial and temporal syngenetic relationship of the deposition of the Mica Creek succession within the Selkirk allochthon and the mineralized horizon at the Ruddock Creek property. Local basement topography, such as horst and graben structures resultant from rifting related to the final phase of breakup of Rodinia, may have focused fluid flow into carbonaceous host lithology at Ruddock Creek. Local structural and stratigraphic traps, hydrothermal fluids, as well as the redox state of the basinal brines, would ultimately have localized and controlled the precipitation of the sulphides.