Chert with relict hopper moulds from Rocklea Dome, Pilbara Craton, Western Australia: An Archean halite-bearing evaporite

Abstract

Archean chert at Rocklea Dome, Pilbara Craton, Western Australia, has evaporitic structures that include moulds resembling halite hoppers, and apparent moulds and relicts of sulfate and carbonate minerals. The interpreted evaporite paragenesis has, therefore, an essentially modern aspect. Minute enigmatic peloids resembling primary bodies such as ooids or organic remains are present locally but are probably diagenetic. Correlation, based on lithology and structural position, with the middle Archean (3.3–3.5 Ga) Warrawoona Group is strongly indicated, suggesting that the chert provides the earliest evidence of halite hoppers so far reported, and a gross similarity in chemical composition between middle Archean seawater and present seas would be indicated.