Regional patterns in standardised and transformed pathfinder elements in soil related to orogenic-style mineralisation in southern New Zealand

Soil samples collected at 50-70 cm depth at 8 km-spaced sample sites over 40,000 km2 of southern New Zealand were analysed for their chemical composition. Nine pathfinder elements (Ag, As, Au, Bi, Mo, Sb, Sn, Te, W), which are useful in exploration for orogenic-style mineralisation, were z-score normalised using two different matrices to account for both lithology and metamorphic grade, which vary significantly across the survey area. Interrogation of interpolated plots of the normalised data, relative to known orogenic-style deposits (Au +/- Sb +/- W), highlights chemical associations that varied between deposit types, and between similar deposit types mineralised under varying pressure-temperature-time conditions. Active mining for orogenic-style Au along the Hyde-Macraes Shear Zone is coincident with a regionally-significant, multi-element soil anomaly (Ag, As, Au, Mo, Sn, Te, Sb, W). The chemical associations vary along strike of the mined-portion of the shear, such that the northwest has high Ag, Au, Mo, Sn, and Te relative to the southeast which has high Sb, W in soil anomalies, hinting at chemical complexity along the shear. The chemical footprint of this deposit is readily identified in the 8 km-spaced grid, considerably expanding the chemical footprint previously inferred from hard rock studies. Historic orogenic W mines are associated with high As, Au, Bi, W in soil anomalies, and historic Sb mining with high Bi in soil anomalies. Chemical soil anomalies are likely related to the progressive metamorphic breakdown of minerals, especially rutile and pyrite. Several multi-element soil anomalies that are coincident with known orogenic mineralisation, also occur in areas that have not been mined, and explored only at a reconnaissance level. This study demonstrates the importance of normalisation of chemical data in complex geological settings and highlights the value that can be extracted beyond only plotting raw-concentration, single element maps, and the significant opportunity in multielement studies of soil in mineral exploration for orogenic-style mineralisation.