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 of each has been deduced from both textural and compositional evidence. While independent, these events made use of the same pre-existing fracture system along which the western subcomplex is situated. In order, these events were: intrusion of granitic fluids, alkaline metasomatism, and thermal metamorphism due to the emplacement of the Coldwell alkaline complex. Following the alteration events, and presumably a result of denudation, oxidization and leaching of the main mineralized zone has produced a supergene paragenesis of: calcite, tyuyamunite, hollandite and barite. The main mineralization 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-gervisite, aegirine-natalyite, barite, barylite, hollandite, coffinite, hematite, ilmenorutile, 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, aegirine-natalyite, zircon-thorite-coffinite solid solutions, Dy-xenotime-(Y), thortveitite, baotite, barylite and V-crichtonite). In addition, unique parageneses are reported, giving further insight into the geochemistry of Be, Ba, Sc, V, Nb, Ti and Cr and conditions of formation of phenakite, barylite, thortveitite, crichtonite, ilmenorutile, barian feldspars and zircon-thorite-coffinite solid solutions.
The Rare and Exotic Mineralogy of the Western Subcomplex of the Deadhorse Creek Diatreme, Northwestern Ontario