Rare and exotic mineralogy of the western subcomplex of the Deadhorse Creek "diatreme", Northwestern Ontario

Abstract

The Deadhorse Creek ‘Diatreme’ is a Proterozoic vent breccia that probably formed in response to early mid-continent rifting. Following emplacement of the breccia, the western subcomplex experienced three alteration events, producing the complex mineralogy observed in the main mineralized zone. Each event has produced a unique mineral paragenesis and the timing o f each has been deduced from both textural and compositional evidence. While independent, these events made use o f the same pre-existing fracture system along which the western subcomplex is situated. In order, these events were: intrusion o f granitic fluids, alkaline metasomatism, and thermal metamorphism due to the emplacement o f the Coldwell alkaline complex. Following the alteration events, and presumably a result o f denudation, oxidization and leaching o f the main mineralized zone has produced a supergene paragenesis of: calcite, tyuyamunite, hollandite and barite. The main mineralized zone was enriched in first- and second-row transition metals, rare-earth elements, beryllium, Th and U. The mineralization is represented by the presence of: aegirine-jervisite, aegirine-natalyite, barite, baryhte, hollandite, coffinite, hematite, Umenorutile, magnetite, monazite-(Ce), phenakite, pyrite, rutile, thorite, thorogummite, thortveitite, tyuyamunite, uraninite, V-crichtonite, xenotime-(Y), zircon, zircon-thorite-coffinite solid solutions and a few unnamed mineral species. The resulting mineralogy is both unique and complex, with several rare minerals and new compositional extremes reported (i.e., Nb-V-rutile, aegirine-jervisite, aegifine-natalyite, zircon-thorite-coffinite solid solutions, Dy-xenotdme-(Y), thortveitite, baotite, barylite and Vcrichtonite). In addition, unique parageneses are reported, giving further insight into the geochemistry o f Be, Ba, Sc, V, N b, Ti and Cr and conditions of formation of phenakite, baryhte, thortveitite, crichtonite, ilmenorutile, barian feldspars and zircon-thorite-coffinite solid solutions.