The lower Proterozoic turbidites from the Eldorado area were deposited into a tectonically active graben-like basin. The submarine fan responsible for their deposition prograded in a north west direction. The turbidites are middle absent sequences typical of deposition on a middle to lower submarine fan.
Changes in the sea level of this basin are reflected in the sediments. A relative rise in sea level, due to fault movements in the basin, produced quiescent periods and a mineralization phase. Fluids responsible for the formation of a metal rich brine were originally deep seated fluids which rose to the surface on fault planes.
A transgressive mineralization phase is present throughout the Tennant Creek field. The ironstones in the Eldorado area represent stratiform oxide facies lenses, which are laterally equivalent to the extensive banded iron-formation. Variations on the style of mineralization are evident in other areas.
The fluids responsible for the formation of the predominantly oxide facies decreased in temperature and fO2 on mixing with the basin waters. Conditions of ore formation were T = 200º ; fO2 = approximately 10-38 ; pH = approximately 5 and Σ= 10-4 . Oxidizing conditions are dominant throughout the basin during periods of quiescense in the turbidite sequence.
A major deformation episode postdates deposition of the early Proterozoic, Tomkinson Creek Beds. This deformation produced a regional, gentle to open fold style and axial plane cleavage. Tectonic dewatering plays only a minor and initial role in cleavage formation. The stratiform ironstone lenses deformed in a variable manner depending on their relative plasticity. Many underwent a diapiric uplift, as a consequence of deformation and they assumed a lensoidal shape subparallel to the axial plane cleavage.