Summary:
The Motheo asset includes the T3, A4 and A1 deposits.
T3 deposit
All major vein sets at T3 are mineralised and are interpreted to have formed as a progressive continuum through regional deformation. Veins formed during early flexural slip have in turn been deformed and commonly subject to folding, boudinage and reactivation. This has resulted in visually complex, composite vein geometries and paragenesis.
Mineralisation typically pinches out at depths of 5m to 10m below the surface. Above the mineralised zone, soil, sand, and calcrete extend to depths of 3m to 8m. Mineralisation has been mapped protruding into the calcrete horizon but does not outcrop at the deposit. Saprolite, with over 25% oxidation, occurs from 25m to 60m below surface, while saprock, with 1% to 25% oxidation, is found at depths of 55m to 85m. In oxidised zones, primary Cu sulphides are altered to malachite, chrysocolla, or covellite.
Mineralisation
The structurally controlled Cu-Ag-Mo mineralisation at T3 is characterised by coarse to semi-massive chalcopyrite, bornite, chalcocite and molybdenite within quartz-carbonate veins, with additional sulphides disseminated along bedding planes and foliation. These structures typically align sub-parallel to bedding, developing preferentially within the hangingwall limb of the main fault propagation fold (hangingwall zone). High-grade mineralisation often forms thick intercepts within fold hinges, with breccia and saddle-reef veins filled with copper and molybdenum sulphides. Lesser widths of mineralisation also occur continuously as envelopes along favourable stratigraphic horizons within the project area.
The T3 Mineral Resource extends over approximately 1.9km in strike length and 720m down-dip, with mineralisation open at depth and along strike. The deposit aligns with a 20° to 30° north-west dipping thrust zone, forming an epigenetic, structurally hosted 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 copper sulphides, mainly chalcopyrite, bornite, and chalcocite, are altered in weathered zones to malachite, chrysocolla, covellite, azurite, tenorite, and digenite.
Molybdenum presents at T3 as molybdenite with minor blebs of powellite in the hypogene domain, with rare wulfenite occurring in the saprolite 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 copper mineralisation and chlorite-sericite alteration.
Mineralisation begins shallowly (~10m below surface) and extends to the depths explored by drilling. Host rocks are interbedded sediments within a 300m thick sequence of limestone, marl, shale, black shale, siltstone, and sandstone of the lower D'Kar Formation. The D'Kar and Ngwako Pan Formation contact lies 150m to 200m below known mineralisation, suggesting that carbon-bearing black shales in the D'Kar Formation acted as a reductant, aiding metal precipitation from hydrothermal fluids along structural pathways.
A4 Deposit
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.
A1 deposit
A1 occupies a similar structural and stratigraphic position to that of the T3 and A4 deposits in that it occurs within a NE-SW trending periclinal anticline ("dome") with a core of Ngwako Pan Formation sandstone, overlain by a succession of shallow marine D'Kar Formation sediments.
Mineralisation is hosted within a moderately inclined, overturned fold in the lower D'Kar Formation, with a NE-SW trending axial plane. The northern limb has a shallow dip of 11 ^ 8 | the NW, while the southern limb dips steeply to the NW at 55 deg The folded host sequence is comprised of sandstone, siltstone, shale and carbonate units.
The structurally controlled Cu-Ag mineralisation at A1 occurs as coarse to semi-massive chalcopyrite, bornite and chalcocite within quartz-carbonate veins, with additional copper sulphides disseminated along bedding planes and foliation. These structures are typically sub-parallel to bedding and are preferentially developed in the hanging wall limb of the overturned fold. High-grade mineralisation is often focused within the fold hinge, where breccia and saddle-reef vein geometries are developed and infilled with Cu-sulphides.
Dimensions
The A1 deposit mineralised domain extents are approximately: along strike 1,800m (west to east); width varies from 225m to 75m; the top of the mineralised domains are 45m below the surface and extend for another 150m below that.