Sequences, Synsedimentary Structures, and Sub-Basins: the Where and When of SEDEX Zinc Systems in the Southern McArthur Basin, Australia

Abstract

The late Paleoproterozoic upper McArthur Group (River Supersequence) is a dominantly shallow marine carbonate platform sequence. Deeper water shaley rocks of the Barney Creek Formation of this Supersequence host the supergiant HYC Zn-Pb-Ag deposit. Three higher order sequences, the Emmerugga Depositional Sequence, the Barney Creek Depositional Sequence, and the Lynott Depositional Sequence, make up the River Supersequence in the southern McArthur basin. Within the Barney Creek Depositional Sequence, there are 26 lithofacies that can be grouped into seven facies associations, each representing specific and coeval sedimentary environments. This complex facies mosaic formed in response to a sinistral transpression event during regional north-south extension. Basin architecture was controlled by major meridional strike-slip structures, such as the Emu, Tawallah, and Hot-Springs faults. Although these structures have a later, postsedimentation history, they also controlled the distribution of the different facies of the Barney Creek Depositional Sequence. North- to northwest- trending segments of these structures were transtensional, whereas structures oriented east of north were transpressional. Transtension resulted in the development of significant local accommodation and sub-basin development and allowed substantial thicknesses of deeper water, fine-grained sediments, which are potential hosts to Zn-Pb-Ag SEDEX deposits, to accumulate. Locally, in platform and slope facies of the Barney Creek Depositional Sequence, the orientation and vergence of kinematic indicators, such as neptunian dikes and intrafolial folds, may indicate the direction to deeper shaley facies.