SUB-BASINS, DEPOSITIONAL CYCLES AND THE TECTONO-SEDIMENTARY SETTING OF THE HYC ZN-PB-AG DEPOSIT

The giant HYC deposit is hosted by a fine grained pyritic and carbonaceous member of the McArthur Group known as the Barney Creek Formation. ‘Typical’ Barney Creek Formation is dominated by sub-wave base dolomitic siltstone and shale. Work presented here, based on a new detailed facies analysis, indicates that an agitated shoreline facies co-existed with these ‘deeper water’ deposits. Recognition that the Coxco Dolomite Member is a distinctive transgressive marker unit allows several time-equivalent facies associations to be distinguished. These include slope and platform margin sediments deposited contemporaneously with ‘deeper water’ lithofacies generally mapped as Barney Creek Formation. These facies associations can be considered as members within a genetically related, tectonically generated depositional package here termed the Barney Creek Depositional Cycle (BCDC).

The BCDC records a fundamental change from the generally stable shallow marine platformal conditions which persisted throughout much of the Palaeoproterozoic McArthur Group. Accelerated subsidence and transition to periods of sub-wave base, marine sedimentation were accompanied by generation of a complex fault-controlled palaeotopography and seismic activity as evidenced by rapid lateral and vertical facies variations, predominance of mass flow depositional processes and domains of liquefaction, talus and gravitationally/seismically-induced slide breccias. Subsidence histories were highly variable at the basin-scale, producing a compartmentalised sub-basin geometry and fragmentation of the underlying, carbonate-dominated platformal ‘basement’.

Facies architecture implies a sub-basin geometry involving interplay of major, multiply reactivated NW- to NNE-trending fault zones and roughly E-W trending ‘hinge zones’ or growth faults. Marked facies variation occurs across structures of both orientations. However, in terms of generating basin foundering maxima, E-W trending structures were subordinate to deep-seated, broadly meridionally-striking fault segments, adjacent to which are the thickest accumulations of BCDC strata.