Gold mobility and biology during tectonic evolution of southern New Zealand

Abstract

Gold has been mobilised and redeposited by hydrothermal fluids in conjunction with mobilisation and redeposition of biological and inorganic carbon within the Southern Alps of New Zealand since the Miocene. Uplift and erosion has contributed detrital gold to rivers draining the mountains. Freshwater fish genetics show that early-formed rivers on the eastern side of the mountains transported gold parallel to the mountains for hundreds of kilometres before subsequent tectonic events dismembered those rivers to form the modern drainage system. The first major glaciation at a tectonic neck in the Southern Alps contributed to Early Pleistocene disruption of the gold-carrying drainage system, and also resulted in transverse separation of alpine terrestrial fauna. Deep crustal structural differences in the South Island that were inherited from Mesozoic tectonics have controlled the topographic evolution of Otago in relation to Canterbury and Southland structural blocks, which have in turn controlled evolution of freshwater fish species and redistribution of gold derived from the Mesozoic basement. Formation of a rain shadow in the Pliocene has permitted development of halophyte ecosystems where detrital gold has been recycled on the margins of Otago fold mountain ranges. Chemical mobilisation of gold has been facilitated by bacteria in a wide range of near-surface geological environments. (Figure presented.) Dave Craw. Photographer: Luke Easterbrook-Clarke.