Walker River Geophysics and Drilling Collaborative Exploration Initiative Round 18 Report

Abstract

DPG Resources Australia Pty Ltd was awarded co-funding under Round 18 of the Northern Territory Government's Geophysics and Drilling Collaborations Program to test airborne gravity gradiometer (AGG) targets within EL 24305 at the Walker River Project of Eastern Arnhem Land. The project targeted sediment-hosted Zn-Pb-Ag mineralisation within the Balma Group of the northern McArthur Basin, based on geological similarities between the Walker River Fault Zone and the Batten Fault Zone that hosts the world-class McArthur River (HYC) and Teena deposits. Between September and October 2025, five diamond drill holes totalling 2510.5m were completed, testing two of the three priority gravity targets. Drilling intersected the lower portion of the Baiguridji Formation siliciclastic rocks overlying more than 500m of Yarrawirrie Formation dolostones and siltstone and, in the deepest hole, the upper part of the Zamia Creek Siltstone. Integration of geological logging, portable XRF geochemistry, density measurements and structural observations enabled subdivision of the succession into ten litho-geochemical units, identification of several regionally correlatable marker horizons, and recognition of the Yarrawirrie Fault as the eastern margin of a fault-controlled depocentre within the Walker River Rift. Only minor base-metal mineralisation was intersected, comprising sparse pyrite, rare galena-bearing fractures and isolated elevated pXRF Zn-Pb-Cu- Ag- As-Bi chemistries. However, drilling also identified evidence for widespread hydrothermal fluid activity, including regionally persistent manganese-rich horizons, red-brown alteration interpreted as ferroan dolomite and pyrite-bearing fractures and sulphide laminations. These features indicate circulation of metalliferous basinal brines through favourable structural and stratigraphic pathways and display similarities to the broader hydrothermal alteration halos associated with major sediment-hosted Zn-Pb systems elsewhere in the McArthur Basin. Petrophysical studies demonstrated that the AGG targets are primarily caused by density contrasts between the siliciclastic Baiguridji Formation and the underlying dolostone-dominated Yarrawirrie Formation, locally enhanced by carbonate brecciation and structural thickening. Although the targeted gravity anomalies were not related to economic sulphide mineralisation, the results suggest that the Walker River Rift may represent the distal expression of a larger hydrothermal system. The program has significantly improved understanding of the stratigraphy, basin architecture, structural evolution and fluid history of the Walker River Fault Zone and provides a refined geological framework for future exploration targeting of sediment-hosted Zn-Pb-Ag mineralisation in the northern McArthur Basin.