The CSA Mine is located on Consolidated Mining Lease No 5 (1992) (CML5), which is owned and operated by Cobar Management Pty Limited (CMPL). CMPL is wholly owned by MAC Copper Limited (formerly Metals Acquisition Limited).
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Summary:
The CSA deposit is located within the Cobar mineral field in the Cobar Basin, a north-south mineralised belt containing copper, gold, and lead-zinc mineralisation. Mineralisation at the CSA mine is hosted within the Silurian-age CSA Siltstone, a steeply dipping sequence of interbedded siltstones and sandstones.
The CSA mineralisation occurs in five known systems: Eastern, Western, QTS North (QTSN), QTS Central (QTSC) and QTS South (QTSS). The mineralisation is structurally controlled, associated with fault/shear zones and arranged in an en-echelon pattern. The Cobar Fault and the Chesney Fault are the major controlling faults at the CSA mine. The mineralised systems occur at the intersections of two sets of steeply dipping (~85°) structures, a dominant north-northeast (“NNE”) trending set (S1) and a NNW trending set (S2). These two structural trends formed due to east-west compression leading to a complex fault/shear system with dilation zones (S3) at intersections. The NNE shears can be up to 100m wide and contain parallel quartz veining of variable intensity.
Within the five mineralised systems, multiple lenses of mineralisation occur; lenses typically are 5-30m wide, have short (<300m) strike lengths but long vertical continuity down plunge (>1,000m). The lenses are interpreted by CMPL as discrete parallel to sub-parallel stacked lenses.
The host rock for the mineralisation, the CSA Siltstone, contains thinly bedded siltstones and mudstones with fine to medium grained sandstones. Bedding strikes north-northwest and dips steeply west. Cleavage trends north and dips steeply east.
QTSN is developed from 600m below surface and is the main mineralised system at CSA, currently containing around 65% of the total copper metal in the estimated Mineral Resource and accounting for approximately 80% of current production tonnes. QTSN consists of around 30 separate lenses which trend north-south and extend down plunge from 600m to >2,000m. To date, the deepest mineralised intercept at QTSN is at around 8,050m Relative Level (“RL”), 2,200m below surface with surface at 10,250mRL. The main lenses consist of semi- massive to massive chalcopyrite bounded to the north and south by zones of chalcopyrite and quartz veining.
QTSC was discovered in 2014; it is located 300m south of QTSN and is developed from a depth of around 1,200m below surface. The system consists of two principal lenses with strike lengths of 150m and widths of 10m.
QTSS is located approximately 200m south of QTSC at a depth of around 700m below surface. QTSS is essentially mined out except for the QR1 lens which was discovered in 2005. This lens lies below and to the south of the mined-out area and has a down plunge extent in excess of 400m, a strike length of 90m and a maximum width of 15m. The mineralisation consists of a zone of quartz-chalcopyrite-chlorite veining.
The Eastern system is located 100m west of QTSN, starting at 250m below surface and consisting of two principal lenses with strike lengths of 50-80m and widths of 10m. Copper mineralisation occurs as quartz-sulphide veining in chlorite-altered siltstone, with occasional pods of massive sulphide.
The Western system outcrops at surface and approximately the upper 100m of the sulphide mineralisation has been oxidised. The system is hosted in pervasively silicified and chloritised siltstone. Mineralisation occurs as zones of quartz-sulphide veining with a number of small high-grade pods of copper or lead-zinc. The lead-zinc mineralisation is concentrated in the upper portion of the system with copper dominant at depth. There are four narrow, copperrich lenses which have a strike length of around 45m, an average width of 7m and extend down plunge up to 200m.
Mineralization and Alteration
Chalcopyrite (CuFeS2) is the dominant copper sulphide phase in all five systems. Copper mineralisation occurs in three distinct forms: as massive sulphide with dominant chalcopyrite and minor pyrrhotite (iron sulphide) and cubanite (CuFe2S3), as semi-massive sulphide with either quartz or chlorite alteration and associated with quartz-sulphide veining of variable intensity. Massive sulphide contacts can be sharp, but the majority of mineralised lenses have gradational contacts with a mineralisation envelope occurring around the more massive mineralisation.
Cubanite is present as a minor copper species, mainly in QTSC. Sphalerite (zinc sulphide) and galena (lead sulphide) are also present but principally only in the upper part of the Western system which is the only system of the five that is exposed at surface. There are no lead-zinc lenses included in the CSA resources or the Cube re- stated Mineral Resource. Silver (Ag), grading 10-50 grams per tonne (“g/t”) is present as acanthite (Ag2S) and shows a weak to moderate correlation with copper. Good metallurgical recoveries are achieved and a high-quality copper concentrate produced grading around 26-27% Cu with silver credits.
Merrin Mine
The Company has recently defined a distinct upper zone of the CSA Copper Mine, above 900 metres below surface level, now referred to as “The Merrin Mine”. This area, previously described as a series of deposits (including QTSS Upper) and levels, has been designated as a separate operational domain.
Within the Merrin Mine, MAC has reported an Inferred Mineral Resource for zinc mineralisation, and has also identified substantial copper mineralisation. While this copper is not yet reported in a resource-compliant format, the Company has sufficient geological confidence to initiate mine planning for the extraction of both copper and zinc from this zone.