Sr-Nd isotopic characteristics of the Kanmantoo Cu-Au deposit

Abstract

The Kanmantoo Cu-Au mine located 50km south-east of Adelaide hosts Delamerian mineralization debated to be epigenetic metamorphogenic with a degree of magmatic input or to have a syn-sedimentary origin. Studying existing mines within the Delamerian in combination with the sources of fluids and metals from which the deposit is derived is fundamental in characterising the exploration potential in South Australia. This study documents 8 Kanmantoo Mine samples and allocates the samples into groups based on hydrothermal, granitic and host rock origin. Hand samples, thin sections, geochemistry, and Sr-Nd isotopes have been analysed to constrain the characteristics of the mine that might determine its geological formation. Sr-Nd isotope analysis was conducted at the University of Adelaide clean laboratories and involved acid digestion, column chemistry and thermal ionization mass spectrometry. The study distinguishes ɛNd values age-corrected for 500Ma that indicate the most juvenile samples studied to be the Fule aluminous vein (ɛNd -11.4) and BK25 sulphide vein (ɛNd -12.3). Proximal host rocks (ɛNd -14.9) and distal host rocks (ɛNd -14.3) recorded less juvenile signatures compared to Kanmantoo Mine samples. The samples studied here indicate isotopic correlation most closely associated with Delamerian S-type granites, providing evidence that mineralization was not derived from an I-type source and formed from the partial melting of supracrustal rocks. The absence of any isotopic signature recognizing a nearby mantle-derived source suggests that the ore-bearing fluid was deposited from a syn-metamorphic hydrothermal system.