Genetic significance of fluid inclusions in the CSA Cu-Pb-Zn deposit Cobar Australia

Elsevier Science Bv
Publication Type:
Journal Article
Ore Geology Reviews, 2004, 24 (3-4), pp. 241 - 266
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2004000204.pdf1.73 MB
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CSA mine exploits a `Cobar-type CuPbZn±Au±Ag deposit within a cleaved and metamorphosed portion of the Cobar Supergroup, central New South Wales. The deposit comprises systems of `lenses that encompass veins, disseminations and semi-massive to massive CuPbZn ores. The systems and contained lenses truncate bedding, are approximately coplanar with regional cleavage and similarly oriented shear zones and plunge parallel to the elongation lineation. Systems have extreme vertical continuity (>1000 m), short strike length (not, vert, similar400 m) and narrow width (not, vert, similar100 m), exhibit vertical and lateral ore-type variation and have alteration haloes. Models of ore formation include classical hydrothermalism, structurally controlled remobilisation and polymodal concepts; syntectonic emplacement now holds sway. Fluid inclusions were examined from quartz±sulphide veins adjacent to now-extracted ore, from coexisting quartzsulphide within ore, and from vughs in barren quartz veins. Lack of early primary inclusions precluded direct determination of fluids associated with D2D3 ore and vein emplacement. Similarly, decrepitation (by near-isobaric heating) of the two oldest secondary populations precluded direct determination of fluid phases immediately following D2D3 ore and vein emplacement. Post-decrepitation outflow (late D3 to early post-D3) is recorded by monophase CH4 inclusions. Entrained outflow of deeply circulated meteoric fluid modified the CH4 system; modification is recorded by H2O+CH4 and H2O+(trace CH4) secondary populations and by an H2O+(trace CH4) primary population. The contractional tectonics (D2D3) of ore emplacement was superseded by relaxational tectonics (D4P) that facilitated meteoric water penetration and return flow.
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