Geochemistry of the mafic sequences in the Cloncurry District, Queensland: implications for crustal accretion and prospectivity

Abstract

The Cloncurry District, Queensland, is a classic Iron Oxide Copper Gold (IOCG) terrain. However, the geochemical characteristics of the numerous mafic intrusives (dominantly dolerite dykes), which are often spatially and temporally associated with mineralisation, have never been studied in detail. Specifically, the newly described dolerite-associated Great Australia-Taipan-Mongoose-Magpie (GATPMM) deposits are thought to represent a distinct Cu-Co-carbonate-rich, Au-poor style of IOCG mineralisation that has not been documented elsewhere in the district. Trace element geochemistry provides evidence that these dykes formed from lower crust fractionation and magmatic ascent throughout intracontinental extension. There are significant REE links to previously studied granites of the Naraku and Williams Batholith within the district, indicating a similar melt source for both igneous lithologies. Geochronological studies of hydrothermal titanite (1515± Ma) and apatite (1177±37 Ma and 1179±41 Ma) from the Mongoose prospect provide constraints on the age of initial intrusion and alteration and provide evidence for thermal-tectonic activity within the Eastern Succession ca. 1100-1200 Ma, possibly related to the Albany-Fraser and/or Musgravian Orogenies. Geochemical relationships between mineralised dolerite samples from the CuDECO Rocklands deposit and local barren dolerite samples are also analysed and display geochemical similarity. This is consistent with the interpretation that dolerite geochemistry alone is not an indicator of prospectivity and is not linked to the distribution of mineralisation.