CSA mine exploits a ‘Cobar-type’ Cu–Pb–Zn±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 Cu–Pb–Zn 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 (400 m) and narrow width (100 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 quartz–sulphide within ore, and from vughs in barren quartz veins. Lack of early primary inclusions precluded direct determination of fluids associated with D
2–D
3 ore and vein emplacement. Similarly, decrepitation (by near-isobaric heating) of the two oldest secondary populations precluded direct determination of fluid phases immediately following D
2–D
3 ore and vein emplacement. Post-decrepitation outflow (late D
3 to early post-D
3) is recorded by monophase CH
4 inclusions. Entrained outflow of deeply circulated meteoric fluid modified the CH
4 system; modification is recorded by H
2O+CH
4 and H
2O+(trace CH
4) secondary populations and by an H
2O+(trace CH
4) primary population. The contractional tectonics (D
2–D
3) of ore emplacement was superseded by relaxational tectonics (D
4P) that facilitated meteoric water penetration and return flow.Under D
2 prograde metamorphism, entrapment temperatures (Tt) and pressures (Pt) for pre-decrepitation secondary inclusions are estimated as Tt300–330 °C and Pt1.5–2 kbar≈Plith (the lithostatic pressure). Decrepitation accompanied peak metamorphism (
T350–380 °C) in mid- to late-D
3, while in late-D
3 to early post-D
3, essentially monophase CH
4 secondary inclusions were entrapped at Tt350 °C and Pt=1.5–2 kbar≈Plith. Subsequently, abundant CH
4 and entrained meteoric water were entrapped as H
2O+CH
4 secondaries under slowly decreasing temperature (Tt330–350 °C) and constant pressure (Pt1.5–2 kbar). Finally, with increasingly dominant meteoric outflow, H
2O+(trace CH
4) populations record decreasing temperatures (Tt>300 to <350 down to 275–300 °C) at pressures of Phydrostatic<Pt (1 kbar) <Plith (1.5 kbar).The populations of inclusions provide insight into fluid types, flow regimes and P–T conditions during parts of the deposit's evolution. They indirectly support the role of basin-derived CH
4 fluids in ore formation, but provide no insight into a basement-sourced ore-forming fluid. They fully support post-ore involvement of meteoric water. The poorly constrained entrapment history is believed to span 10 Ma from 395 to 385 Ma.
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