Mineralogy of the deadhorse creek volcaniclastic breccia complex,northwestern Ontario,Canada |
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| Authors: | Eric?G?Potter Email author" target="_blank">Roger?H?MitchellEmail author |
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| Institution: | (1) Department of Geology, Lakehed University, 955 Oliver Road, Thunder Bay, Ontario, CANADA P7B 5E1 |
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| Abstract: | The Proterozoic Deadhorse Creek volcaniclastic breccia complex was emplaced in Archean metasedimentary and metavolcanic rocks
of the Schreiber-White River greenstone belt adjacent to the Proterozoic Coldwell alkaline complex. The western sub-complex
of the Deadhorse Creek breccia consists of metasomatically-altered breccia, a U-Be-Zr-rich main mineralized zone and a Zr-Y-Th-rich
carbonate vein. The main mineralized zone is enriched in beryllium, thorium, uranium, first and second row transition elements,
and rare earth elements. The major minerals present include: albite; potassium feldspar; quartz; calcite; apatite; and phenakite.
Accessory minerals include: aegirine-jervisite; aegirine-natalyite; allanite; barite; barylite; coffinite; Ca-Mn-silicate;
magnetite; monazite-(Ce); niobian vanadian rutile; pyrite; thorite; thorogummite; thortveitite; uraninite; vanadian crichtonite;
xenotime-(Y); zircon and hydrated zircon; and zircon-thorite-coffinite solid solutions. The carbonate vein consists of dolomite-ankerite
and calcite with accessory zircon, xenotime, and monazite. Barite, baotite and Ba-rich feldspars, were formed during metasomatism
of the earlier-formed and genetically-unrelated volcaniclastic breccia adjacent to the main mineralized zone. The complex
mineral assemblage of the fault-controlled main mineralized zone is considered to have formed in three stages. An initial
emplacement of a “granitic” melt/fluid was followed by introduction of CO2-bearing Cr-Nb-V-Ti-enriched alkaline fluids. The latter reacted with minerals which had crystallized from the “granitic”
melt/fluid to produce the exotic V-, Sc- and Nb-bearing mineral assemblage. Subsequently, a supergene suite of minerals, consisting
principally of calcite, thorogummite, hollandite and tyuyamanite, formed during post-Pleistocene alteration was superimposed
onto the pre-existing Proterozoic age mineral assemblage. The major mineralogy of the main mineralized zone is essentially
‘granitic” and the melts/fluids are considered to be derived from an A-type granite source. However, the Deadhorse Creek mineralization
is older (1129±6 Ma) than the A-type quartz syenites of the adjacent Coldwell complex (1108±1 Ma) which are the nearest potential
sources of such melts. Thus, the source of the “granitic” melt together with that of the Cr-Nb-V-Ti-bearing alkaline fluids
remains enigmatic. |
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