Two unusual copper showings that are spatially associated with Zn-Pb districts (Borden Basin [Nanisivik; Mesoproterozoic host]; Cornwallis [Polaris; Paleozoic host]), were studied using in-situ micro-analytical techniques to determine their origin. The Surprise Creek showing (Mesoproterozoic Nanisivik Fm. host) contains three assemblages: (A1) dolomite (D) 1 (δ18O = 30‰), D2 (δ18O = 24‰), sphalerite, galena, and pyrite (Py) 1 (δ34S = 0‰); (A2) digenite (Dg), bornite (Bn), and Py2 (δ34S = 21‰); and (A3) calcite (Cc) (δ18O = 12‰), covellite (Cv), smithsonite, cerrusite, hematite (Hmt) and malachite (Mal). A decrease in Th, salinity, and δ18O values, but a constant REE pattern in A1, indicates mixing of two reduced fluids under low fluid:rock. The introduction of a Cu-bearing sulphide fluid precipitated A2. Light δ18O values together with -Ce and +Y anomalies suggest an oxidised meteoric fluid for A3. Metals and sulphur were incorporated into basinal fluids from the stratigraphic column and mixed on site. The Storm showing (Paleozoic Allen Bay Fm. host) contains four assemblages: (A1) D1 (δ18O = 28.9‰), chalcopyrite (Cpy) 1, Py1 (δ34SCpy,Py = 0‰), and Bn; (A2) Cc1 (δ18O = 13‰), Cpy2, Py2 (δ34SCpy,Py = 15‰), and Dg; (A3) D2 (δ18O = 26‰), Cpy3 (δ34S = 20‰), Py3 (δ34S = 17‰); and (A4) Cc2 (δ18O = 10‰), Cv, native copper, Hmt, gypsum, and Mal. The Th (~100°C), salinity (17 wt.% NaCl eq.), heavy δ18O values, flat REE pattern with a +Eu anomaly, and δ34S data indicate that A1 reflects possible mobilisation of hydrothermally sourced components under high F:R. An oxidised (-Ce anomaly), low Th and salinity (100°C and 0.4 wt.% NaCl eq.), meteoric-dominant fluid precipitated A2. Assemblage 3 reflects a change in amount or proportion of sulphate-derived S in the system based on increased δ34S values. An oxidised, isotopically light fluid produced A4. The acidic (dissolved pyrite) oxygenated fluid that precipitated secondary, oxidised Copper phases may indicate a degree of supergene enrichment.
