NOT SO COMPLEMENTARY THERMOMETRY - CONVENTIONAL ION-EXCHANGE AND TRACE ELEMENT (ZR-IN-RT AND TI-IN-QTZ) THERMOMETRY IN LOW P-T / FLUID-RICH METAMORPHIC ENVIRONMENTS, SENTINEL CU DEPOSIT, NORTHWESTERN ZAMBIA

Trace element thermometry has the potential to provide a robust method of constraining the temperatures of mineral growth or recrystallization associated with thermal and fluid events, especially in cases where mineral assemblages are less amendable to traditional thermometry. This method was applied to kyanite-bearing quartz-chalcopyrite veins within biotite-muscovite phyllite at the Sentinel Cu deposit, northwestern Zambia. The temperature conditions of vein emplacement and aluminum metasomatism, as well as the degree of deformation that affected the rocks after formation of the deposit are poorly constrained. Garnet-biotite assemblages in the phyllite and bounding quartz-biotite schists suggest equilibration at ~600 ⁰C (at ~6 kbars) prior to development of high strain domains that deform and recrystallize vein assemblages at ~450 ⁰C (at 4-5 kbars). However, such assemblages are rare and do not provide estimates of the temperatures accompanying vein emplacement and kyanite growth. To complement conventional thermometry and to assess their utility in metamorphosed ore environments, both Zr-in-rutile and Ti-in-quartz thermometry were employed with the aim of providing more robust temperature estimates across the phyllite package and quartz-biotite schist. Thermometry was conducted on quartz and rutile in vein and matrix domains; pressures were assumed to be between 4-6kbar. Zr-in-rutile thermometry suggested conditions of ~550-600 ⁰C within the less deformed domains and ~500-550⁰C in the highest strain zones. No temperature differences were detected between vein and matrix rutile. Ti-in-quartz suggested conditions of ~375-425 ⁰C. No temperature differences were detected between bright and dark cathodoluminescence quartz within veins and matrix, and no systematic differences occurred across the phyllite package and quartz-feldspar-biotite schist. This contradicts textural relationships, which suggest that veining occurred either prior to, or early in deformation. Further, the results indicate the possibility that disequilibrium effects associated with metasomatism in low P-T, fluid-rich environments and/or deformation-induced recrystallization of either rutile or quartz, limit the use of these techniques in some environments.