Potassium Metasomatism at the Polymetallic NICO Deposit, Northwest Territories, Canada

• Main Author: Robinson, Gregory B
• Format: Text
• Language: English
• Published: Scholarship@Western 2013
• Subjects: K-metasomatism; metasomatite; hydrothermal alteration; feldspar-phyric porphyry; detachment fault; Lou Lake; Geology; Canada; Northwest Territories; Treasure Lake
• Online Access: https://ir.lib.uwo.ca/etd/1688; https://ir.lib.uwo.ca/context/etd/article/3118/viewcontent/GBR_Msc_Thesis_2013_2nd_Revision.pdf; https://ir.lib.uwo.ca/context/etd/article/3118/filename/0/type/additional/viewcontent/Figure_3.2___Cross_Section_14_50W_Final.pdf; https://ir.lib.uwo.ca/context/etd/article/3118/filename/1/type/additional/viewcontent/Figure_3.3___Geology_of_the_NICO_Ramp_Revised.pdf

High temperature K-metasomatism pervasively replaced Paleoproterozoic volcanic and metasedimentary rocks at Lou Lake NWT. This replacement developed primarily at the structural interface juxtaposing non-metamorphosed Lou Lake volcanic rocks over Treasure Lake Group metasedimentary rocks. This crustal-scale fault developed coeval with the emplacement of anorogenic magmatism within a post-collision extensional setting. Emplacement of porphyry dykes into the fault breccia coincided with K-metasomatism at peak upper-greenschist to amphibolite-facies thermal conditions. The K-metasomatism resulted from co-mingling of descending crustal fluids and ascending potassic magmatic fluids along the decollement surface. Pervasive K-metasomatism resulted in complete replacement of precursor rocks by potassium feldspar. The pronounced element liberation and SiO2-Al2O3-K2O enrichment resulted in the homogenization of diverse rock types into brick-red potassium feldspar metasomatite characterized by high K2O/Na2O ratios and up to 13.4 wt%, K2O. The secondary microcline approaches end member orthoclase composition. Petrographic and isotopic evidence indicate associated iron oxide is an inherited component from precursor rocks. Oxidizing conditions were superimposed by continued flux of crustal fluids during a prolonged retrograde cooling history.