Distinguishing pedogenic carbonates from weathered marine carbonates on the Yorke Peninsula, South Australia: Implications for mineral exploration

We present whole rock and strontium isotope geochemistry from geological profiles from the Yorke Peninsula in South Australia and provide a geochemical means of discriminating between Cenozoic marine carbonate-bearing rocks and Quaternary pedogenic carbonate-bearing rocks. Pedogenic carbonate-bearing rocks (commonly referred to as calcrete) are potentially useful mineral exploration sampling media whereas weathered marine carbonate-bearing rocks (limestone), are less useful. Distinguishing between the two in drill cuttings where textural information has been destroyed is difficult. Strontium isotope ratios are variable, strongly dependent on clastic sedimentary component and thus do not differentiate effectively between pedogenic and marine carbonate-bearing rocks. There is a systematic difference between Ca/Sr and Ca/Mg ratios in the pedogenic carbonate-bearing rocks compared to the weathered Cenozoic marine carbonate-bearing rocks. Pedogenic carbonate-bearing rocks have systematically lower Ca/Mg (< 28) and Ca/Sr (< 650) ratios than their marine counterparts Ca/Mg (> 35) and Ca/Sr (> 1260). This simple discriminant can be used to identify samples appropriate for carbonate sampling in mineral exploration, particularly in drill cuttings, as well as retrospective filtering of multi-element geochemical exploration data sets.