Contents lists available at ScienceDirect Journal of Geochemical Exploration journal homepage: www.elsevier.com/locate/gexplo Distinguishing pedogenic carbonates from weathered marine carbonates on the Yorke Peninsula, South Australia: Implications for mineral exploration Keryn Wolff a,⁎ , Caroline Tiddy a,1 , David Giles a,1 , Steven M. Hill b , Georgina Gordon b a Deep Exploration Technologies Cooperative Research Centre (DET CRC), Department of Earth Sciences, University of Adelaide, Australia b Geological Survey of South Australia, Department of Premier and Cabinet, South Australia ARTICLE INFO Keywords: Regolith Calcrete Carbonate Limestone Strontium isotopes Ca/Sr ratios Mineral exploration ABSTRACT 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 re- ferred 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 carbo- nate-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. 1. Introduction Carbonate-dominated regolith has a widespread global distribution concentrated in the mid latitudes (Batjes, 2012; Chen et al., 2002) (Fig. 1). This material includes a range of weathered carbonate-bearing rocks, including limestone, as well as in situ, transported and reworked pedogenic carbonate-bearing rocks (sometimes referred to as calcrete but can also include dolomite), derived from atmospheric (e.g. dust and rain) accessions. The vast global extent of these lithologies has gener- ated much interest in their origin, chemistry and paleo-environmental significance (Chen et al., 2002; Dart et al., 2012; Milnes, 1992; Milnes and Hutton, 1983; Poustie and Abbot, 2006; Quade et al., 1995). Carbonate-bearing rocks have been widely studied for their stron- tium ( 87 Sr/ 86 Sr) isotopic composition to trace calcium source and mo- bility, soil carbonate origins and sedimentary environments (Dart et al., 2012; Liu et al., 2013; Quade et al., 1995; Zhao et al., 2009). This method has also been applied to trace sources of other elements such as using strontium (Sr) as a proxy for calcium (Ca) (Dart et al., 2007; Dart et al., 2012; Liu et al., 2013; Quade et al., 1995; Van der Hoven and Quade, 2002). Strontium isotopic studies using marine carbonate- bearing rocks typically relate to the chemistry of the water in which they are formed and are commonly used for the purpose of dating (e.g. Burke et al., 1982; Howarth and McArthur, 1997; McArthur et al., 2001; McArthur et al., 2012). Pedogenic carbonate-bearing rocks (such as calcrete) are widely used as a mineral exploration sampling medium (Chen et al., 2002; McQueen et al., 1999; Poustie and Abbot, 2006), and have been suc- cessfully utilised to discover and delineate various economic resource deposits around the world (Ghavami-Riabi et al., 2008; Lintern et al., 2005). The Challenger Gold Deposit within the Gawler Craton, South Australia (Fig. 2) was discovered following a regional carbonate rock sampling program (Poustie and Abbot, 2006). A dramatic increase in interest in carbonate geochemistry followed (Chen et al., 2002; Lintern et al., 2012; Reith et al., 2011; van der Hoek et al., 2012). It is essential, although often very difficult, to distinguish marine carbonate-bearing rocks from pedogenic carbonate-bearing rocks when undertaking a carbonate sampling program. This difficulty in distinction arises due to weathering of marine carbonate rocks typically resulting in re- crystallization and pedogenic overprinting rendering the resulting sample morphology indistinguishable. This can be problematic in http://dx.doi.org/10.1016/j.gexplo.2017.06.019 Received 13 February 2017; Received in revised form 7 June 2017; Accepted 28 June 2017 ⁎ Corresponding author at: Department of Earth Sciences, Mawson Building, University of Adelaide, North Terrace Campus, Adelaide, SA 5005, Australia. 1 Now at Future Industries Institute, University of South Australia E-mail address: keryn.wolff@alumni.adelaide.edu.au (K. Wolff). Journal of Geochemical Exploration 181 (2017) 81–98 Available online 08 July 2017 0375-6742/ © 2017 Elsevier B.V. All rights reserved. MARK