Quartz oxygen isotopes from Tick Hill area in Mount Isa Inlier: indication of a regional fluid overprint

Abstract

At the Tick Hill gold deposit, δ18Oquartz data for the mineralised lithologies and surrounding rocks are similar and fall within a narrow range of 10.5–13.7‰ V-SMOW. The highly mineralised quartzo-feldspathic mylonite has quartz δ18O (δ18Oquartz) values of 11.3–13.6‰, which are similar to values for the surrounding rocks both locally and regionally, i.e. δ18Oquartz by itself does not provide a useful exploration tool. The δ18Oquartz values from the Tick Hill area most likely reflect the late Isan hydrothermal overprint at 1525–1520 Ma. The origin of the altering fluids is unclear, as the δ18Oquartz values overlap with reported δ18O values calculated for both metamorphic and igneous fluids. When combining the δ18Oquartz results with δ18Ocalcite results available from the literature, a temperature of 350–550 °C was calculated, which is consistent with observed alteration assemblages associated with gold mineralisation. KEY POINTS The δ18Oquartz values (10.5–13.7‰ V-SMOW) of Au-rich quartz–feldspar mylonite are indistinguishable from the altered host rocks both local and regional. The narrow range of δ18Oquartz values for the rock units in the Tick Hill area and Mary Kathleen Domain most likely reflect a regional fluid overprint. The post-mineralised quartz–calcite veins yield higher δ18Oquartz values (14.1–17‰), possibly reflecting (partial) re-equilibration of minerals locally formed in late cataclastic fault rocks.