Summary:
The pelitic meta-sedimentary rocks of the Cambrian Kanmantoo Group in the Adelaide Geosyncline are host to numerous copper, gold, lead, zinc, silver, pyrite deposits over a 300km N-S strike length of which Kanmantoo is the largest. The copper-gold deposits at Kanmantoo are hosted within meta-pelites that are regionally thermally altered to andalusite – sillimanite grade schists. The mine sequence is characterised by an abundance of andalusite dominant schists interbedded with quartz biotite schists. The Cu-Au mineralisation is emplaced post peak-metamorphism and syn to post peak deformation of the Delamerian Orogen from magmatic fluids in a structurally controlled shear system.
Within the Kanmantoo mineralised system four mine areas now have Mineral Resource Estimates – Kavanagh, North Kavanagh, Nugent and Emily Star.
Structural studies conducted by Hillgrove denote that the main controls on mineralisation are the north-south striking anastomosing shear zones and the north-east to north-north-east striking cross-shears and tension veins. This strong structural control is evident throughout the entire Kavanagh deposit.
The dip of the Kavanagh mineralisation is generally steeply dipping (70° to 80°) towards the East.
Geologic domains of the alteration envelope were predominately modelled on chlorite, sulphur and copper content with a moderate influence from structural knowledge gained during mining.
Dimensions
The Kanmantoo MREhas a north-south strike length of 500 metres, over a zone approx. 200m wide and over a depth of 500 metres below the Giant and Nugent Open Pits. Emily Star has a north-east strike length of about 350 metres, over a zone approx. 30m wide and a depth of 180 metres below the open pit. The NE and HW mineralisation domains each have a NW strike of about 200 m, 30 m width and between 160-200 m below the open pit.
All zones are open to depth and along strike.
Kavanagh Mineralisation The various Kavanagh Cu-Au mineralised zones are hosted within Biotite Chlorite Garnet Schist (BCGS) and/or Garnet Andalusite Biotite Schist (GABS) with sulphide distribution controlled by the structural fabric, both as finely disseminated sulphides along the S2 fabric and as massive sulphide veins. The sulphide mineralisation is dominated by coarse grained pyrrhotite and chalcopyrite with minor bismuthinite, pyrite and rarely free gold.
The Kavanagh Cu-Au mineral zones of intense sulphide veining and sulphides vary between 3 to plus 20 metres in width with haloes of lower density sulphide veining up to 10 to 20 metres in width.
The various Kavanagh lodes are characterised by their local alteration styles and mineral assemblage. For example, the East Kavanagh mineralisation is often associated with strong gold and bismuth endowment, whilst West Kavanagh has minimal gold and bismuth and has a higher ratio of pyrrhotite to chalcopyrite compared to Central Kavanagh.
The Nugent Cu-Au mineral zone strikes NE-SW (~040° direction) dips sub-vertically toward the south-east, with the mineralisation following the shear corridor and hosted within a silicified BCGS zone. The Nugent alteration system shows a significant increase in silica in comparison to the Kavanagh systems, both as a pervasive overprint and as defined quartz veins, with sulphide and gold mineralisation generally confined to zones of structurally complex quartz veining in a silica rich variety of the BCGS.
The Kavanagh mineralised lodes are generally within a broad sulphide alteration zone, within which there is localised variation in the concentration of copper sulphides. In contrast, the Nugent zone is generally a single zone of sulphide alteration of varying width and intensity of copper-gold. While both mineral systems have, on average, a consistent overall geometry, within the mineral zone, the higher grade portions can vary in length along strike and plunge.