Hillgrove Copper Pty Ltd, a fully owned subsidiary of Hillgrove Resources Limited, owns and operates the Kanmantoo Copper Mines.
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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 300 km 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.
The geologic interpretation of the geometry of the mineralisation is conditional to the sulphide vein density and hence the spatial continuity is dependent on the applied copper cut-off grade. As a result, the highergrade copper zones do not have hard, planar boundaries. In reality, the boundaries between higher-grade copper zones and low-grade copper zones are subjective and spatially variable. To assist with the geological understanding, a 0.2% Cu wireframe has been interpreted to visualise the overall continuity of the copper mineralisation. If the economic cut-off grade is increased to 1.0% Cu, the mineral zones become truncated into a series of lenses and pods, with much higher variability in grade and spatial continuity.
Dimensions
• The Kanmantoo MRE has 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.
Within the Kanmantoo mineralised system, five mine areas have Mineral Resource Estimates - Kavanagh (including Spitfire), North Kavanagh, Nugent (including Saddle Zone), Valentines and Emily Star.
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.
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 dip of the Kavanagh mineralisation is generally steeply dipping (70° to 80°) towards the East.
Nugent
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.
Emily Star
The Emily Star Cu-Au mineralisation was mined as an open pit by Hillgrove from 2012-2015 and is the second largest Cu endowment on the Kanmantoo Mine Lease. The Emily Star mineralisation shows multiple Cu-Au zones with high Cu breccias that warrant further drilling to identify their continuity and tenor.