Summary:
The A4 deposit is a part of the Motheo asset.
The A4 project area lacks any outcrop of the Ghanzi Group, with the host meta-sediments covered by a shallow layer of calcrete, sand, and soil. Structurally similar to the T3 deposit, A4 sits within a NE-SW trending periclinal anticline or "dome," which features a core of Ngwako Pan Formation sandstone, overlain by shale, sandstone, siltstone, and carbonate layers of the D'Kar Formation. All mineralisation included in the resource estimate is contained within this D'Kar Formation sequence.
Mineralisation
The structurally controlled Cu-Ag-Mo mineralisation at A4 occurs as coarse to semi-massive chalcopyrite, bornite, chalcocite and molybdenite within quartz-carbonate veins, with additional sulphides disseminated along bedding planes and foliation.
The A4 Mineral Resource has been defined along an approximate 1.2km long strike length and 250m down-dip. Mineralisation remains open with depth, along stratigraphy, and along strike. The deposit aligns to a 20° to 30° north-west dipping thrust-sense shear zone, and is considered to be a structurally hosted, epigenetic deposit accommodating multiple phases of mineralisation formed as a progressive continuum through regional deformation. In the hangingwall zone, mineralisation is expressed as numerous stratiform and foliation-hosted, sub-parallel quartz-carbonate and stringer veins, with cumulative mineralisation true widths ranging from 10m to 80m. In the footwall limb of the main fault propagation fold (footwall zone) and away from the main hinge zone, mineralisation is more dominantly stratiform, often expressed as complex folded geometries.
Mineralisation is highly continuous, concentrically zoned, and follows a sequence common in similar copper systems. Mineral phases are relatively oxidised in the core of the deposit, becoming more reduced higher in the system. Primary Cu sulphides, mainly chalcopyrite, bornite, and chalcocite, are altered in weathered zones to malachite, chrysocolla, covellite, azurite, tenorite, and digenite. Molybdenum presents at A4 as molybdenite with minor blebs of powellite in the hypogene domain. Molybdenite is disseminated throughout the orebody but typically increases in grade toward the core of the mineralised system. High-grade molybdenite zones are typically associated with Cu mineralisation and chlorite-sericite alteration.
Mineralisation starts at shallow depth below surface (~10m depth) and extends to the limit of the drilling programs. Host rocks include limestone, marl, shale, black shale, siltstone and sandstone within a 300m wide sequence of interbedded sediments within the lower part of the D’Kar Formation. The contact between D’Kar Formation and the Ngwako Pan Formation is approximately 150m to 200m below the base of known mineralisation.