Abstract
New geological, bulk chemical and mineralogical (QEMSCAN and FEG-EPMA) data are presented for albitite-type uranium deposits of the Mount Isa region of Queensland, Australia. Early albitisation of interbedded metabasalt and metasiltstone predated intense deformation along D2 high strain (mylonite) zones. The early sodic alteration paragenetic stage includes albite, riebeckite, aegirine, apatite, zircon and magnetite. This paragenetic stage was overprinted by potassic microveins, containing K-feldspar, biotite, coffinite, brannerite, rare uraninite, ilmenite and rutile. An unusual U-Zr phase has also been identified which exhibits continuous solid solution with a uranium silicate possibly coffinite or nenadkevite. Calcite, epidote and sulphide veinlets represent the latest stage of mineralisation. This transition from ductile deformation and sodic alteration to vein-controlled uranium is mirrored in other examples of the deposit type. The association of uranium with F-rich minerals and a suite of high field strength elements; phosphorous and zirconium is interpreted to be indicative of a magmatic rather than metamorphic or basinal fluid source. No large intrusions of appropriate age outcrop near the deposits; but we suggest a relationship with B- and Be-rich pegmatites and quartz-tourmaline veins.
Highlights
Uranium deposits of the Mount Isa Uranium District (Queensland, Australia) are examples of the epigenetic and structurally-controlled albitite-hosted uranium deposit type, known as metasomatite-type or Na-metasomatite-type
We suggest that the mineralogical and bulk chemical data are best interpreted in terms of a distal magmatic origin for the uranium and high field strength elements (HFSE) and that fluorine complexing of uranium was responsible for uranium transport
Albitite-type uranium deposits of the Mount Isa district are comparable in many respects to other albitite-type uranium deposits, differing mainly in the fact that their host rocks are metabasalt and metasiltstone
Summary
Uranium deposits of the Mount Isa Uranium District (Queensland, Australia) are examples of the epigenetic and structurally-controlled albitite-hosted uranium deposit type, known as metasomatite-type or Na-metasomatite-type. Albitite-type uranium deposits are widespread and economically significant but generally are poorly understood, with respect to the age of ore formation, relationship to regional deformation events, the nature of the mineralising fluids, their sources and physico-chemical conditions of ore deposition [1]. Mount Isa hosts sixteen significant albitite-type resources including the world-class deposit at Valhalla and satellite deposits at Skal and Bikini (Table 1). Most of these deposits were found during the 1950s by prospectors, but with the exception of Mary Kathleen have not been developed due to low grade (
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