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Kanmantoo

South Australia, SA, Australia

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The Kanmantoo copper-gold deposit lies within the Kanmantoo Trough of the Adelaide Fold Belt, approximately 55 kms southeast of Adelaide in the Mount Lofty Ranges of South Australia.
(#Location: 35° 5' 43"S, 139° 0' 0"E).

Copper mineralisation was first recognised at Kanmantoo by two Cornishmen commissioned by the South Australian Company to prospect the district in 1846. The South Australian Company worked several pipe-like ore bodies down to depths of 60 m with dressed ore grades of 25 to 30% Cu shipped to Swansea (Wales) for smelting. Local smelting began in 1848, enabling treatment of ore with 12% Cu, too poor for the Swansea market. In 1851 the South Australian Company, disappointed with the lack of profitability of the mine, decided to withdraw from mining. Sporadic mining of small high grade copper and copper-gold underground mines took place, mainly before 1872, with the total production prior to World War I of over 60 000 tonnes of ore mined from the district, of which the Kanmantoo group of mines contributed ~24 000 t @ 8.5% Cu. In 1938, the deposit was drilled by Austral Development Company, who intersected 75 m @ 0.63% Cu, which at the time was uneconomic. Regional exploration by Broken Hill South Ltd., through its subsidiary Mines Exploration Pty. Ltd., in the 1960s, resulted in a drill program at Kanmantoo, the first of which intersected 130 m @ 0.95% Cu in October 1962, having drilled down the core of the pipe-like deposit. After a program of diamond drilling and underground testing, a 750 000 tpa of ore open pit was established in 1970 and the first concentrates shipped in 1971 (Verwoerd and Cleghorn, 1975). The operation was profitable until late 1974, when falling Cu prices rendered it unprofitable. The mine and facilities were owned by Kanmantoo Mines Ltd., a joint venture between Broken Hill South 51%, North Broken Hill 19.5%, Electolytic Zinc Company 19.5% and P.G. Hallof of Canada 10%. In 1972, following the liquidation of Broken Hill South, their share, and the management of the JV was assumed by CRA Limited, through its subsidiary Australian Mining and Smelting. Plans to develop an underground mine below the open pit were abandoned and the mine closed in June 1976 due to continuing low copper prices. Approximately 4.1 Mt @ 0.87% Cu and 0.07 g/t Au was mined from the open pit between 1971 and 1976. Exploration at Kanmantoo resumed in 2004 when Hillgrove Resources defined a cluster of eight Cu-Au-Ag deposits around the abandoned Kanmantoo Mines pit, enabling the development in 2010 of several open pit mines that were still in production in 2016. Open-pit mining ceased in May 2019, although processing of stockpiled ore continued into 2020. Rehabilitation and revegetation of the site is expected to take up to seven years. The total endowment at Kanmantoo in 2016 was estimated at ~0.35 Mt of Cu, 3 t Au and >90 t Ag (Rolley and Wright, 2017).

The Kanmantoo Trough is a fault controlled basin that developed during the Early Cambrian, adjacent to the late Neoproterozoic to Early Cambrian Adelaide Rift Complex. The trough was formed in the oceanic rift that opened along the generally north-south oriented Tasman Line during the late Neoproterozoic break-up of the Rodinia Supercontinent. The Tasman Line now separates the western domain of the current Australian continent, with only Precambrian basement, and Cambro-Ordovician attenuated continental and oceanic crust basement to the east. Extension leading up to this breakup began in the Adelaide Rift Complex at ~827 Ma (Priess, 2000). By 586 Ma, extensive alkaline, rift volcanic rocks had been deposited along a large area of the eastern margin of the preserved Neoproterozoic sequence from the Broken Hill area (Koonenberry Belt), through the eastern Mount Loft Ranges (Truro) to Tasmania (King Island). Approximately 200 km to the east, in western NSW and Victoria, the 350 x 50 km Dimboola Igneous Complex contains ~600 Ma ultramafic and mafic tholeiites, bonninites, volcaniclastic rocks and cumulate gabbros. To the immediate west of these, there is a similar sized belt of ~524 Ma basalts and gabbros with 'within-plate' and MORB chemistry (Rankin et al., 1991; VandenBerg et al., 2000). The Kanmantoo Trough was partially formed on oceanic crust to the east, lapping onto continental basement in the west, and was developed between the main cratonic block to the west, represented by the Adelaide Fold Belt, and the retreating continental block to the east, which is now believed to be part of North America (and/or South China). To the west of the Kanmantoo trough turbidites there is an extensive (up to 250 km wide) shallow water shelf sequence of Early Cambrian limestone that unconformably overlies Neoproterozoic rocks of the Adelaide Rift Complex that had undergone basin inversion (Glen, 2005). The Kanmantoo trough was dominantly filled between 526 and 514 Ma with a 7 to 8 km thick (Jago et al., 2003) high density clastic turbidite/flyschoid sequence (Haines et al., 2001) of rapidly deposited psammitic (now quartz-feldspar-mica schists) and lesser pelitic (now garnet-andalusite-biotite schists) sedimentary rocks, the Kanmantoo Group. Deposition was terminated by the onset of deformation at ~514 Ma (Foden et al., 2001). The Kanmantoo trough was the result of transtensional deformation in response to NE-SW extension (Haines and Flömann, 1998). The turbiditic sedimentary rocks of the Kanmatoo trough can be shown to have been derived from Antarctica (Flömannet al., 1998) and share the same 600 to 500 Ma zircons with Ordovician turbidites of the Lachlan Orogen further to the east. In contrast the source of the Adelaide Rift Complex sedimentary rocks was from Australian cratons to the west (Veevers, 2000). The rocks of the Kanmantoo trough subsequently underwent deformation, metamorphism and granite intrusion during the Middle to Late Cambrian (514 to 485 Ma) Delamerian Orogeny. This orogenic episode represents the global compressional event, related to the formation of the brief Panotia Supercontinent, which then broke up again during the Ordovician. Large masses of syn- and post-orogenic Delamerian granites are mainly found in the east of the trough and under cover over a NNW-SSE elongated belt of ~600 x 50 to 100 km. This convergent phase of the Delamerian cycle is interpreted to represent the forearc of an intraoceanic island arc setting, which may be represented by the Dimboola Igneous Complex (Glen, 2003). The Kanmantoo Group is overlain to the east by the thick Palaeozoic sedimentary succession of the Tasman Fold Belt, developed in the broad back arc basin to the Ordovician to Silurian intraoceanic Macquarie magmatic arc to the east in central New South Wales. The rocks of the Kanmantoo Group were overthrust onto and accreted to the main Australian section of Gondwana, and are now exposed over a 300 km long arcuate zone along the eastern margin of the eastern and southern Mount Lofty Ranges. They are also overlain to the east by poorly consolidated Tertiary Murray Basin sedimentary rocks.

Numerous copper, gold, lead, zinc, silver and pyrite deposits are hosted by the pelitic meta-sedimentary rocks of the Cambrian Kanmantoo Group over a 300 km strike length within the Kanmantoo trough. The Kanmantoo deposit is the largest of these. The Kanmantoo Group is composed of three transgressive-regressive events. The Tapanappa Formation, which represents the middle event, is uniquely characterised by sulphide rich siltstone lenses and Fe-Mn rich horizons within basinal greywackes-mudstone sequence. The Kanmantoo copper deposit is the largest of a group hosted by Cambrian schists after a sequence of sandstone and mudstone units, the Paringa Andalusite Member, a high-Fe quartz rich (graphite poor) meta-pelite in the upper part of the Tapanappa Formation.

Three regional deformation events are recognised within the Kanmantoo trough sequence (Belperio et al., 1998). D1 involved NW directed thrusting and produced a bedding parallel schistosity. D2 structures are dominant within the Kanmantoo Group, occurring as upright to inclined major folds that are generally north-south striking, and plunge shallowly southwards. The principle folds and the pervasive fabric at the Kanmantoo deposits is due to the D2 event. D3 resulted in tight to isoclinal, west to NW trending folds in zones of high strain, and in late shear zones, and is not eviden at Kanmantoo.

The mineralisation at Kanmantoo extends over a strike of at least 6 km, predominantly within the iron-rich Paringa Andalusite Member, now represented by a distinctive, Fe-Mg-rich suite of metamorphic minerals, including chlorite, biotite, almandine-rich garnet, staurolite and magnetite, a member of a regionally extensive garnet-biotite schist unit. The host generally occurs as a quartz-chlorite-garnet±andalusite unit, referred to as garnet-andalusite-biotite schist (GABS; Rolley and Wright, in press) which is characterised by large andalusite porphyroblasts in a schistose matrix of quartz, biotite, garnet and staurolite. Andalusite occurs in the lode schists in approximate inverse proportion to chlorite. This GABS unit is ~600 m wide at Kanmantoo and hosts all of the mineralisation. It is flanked to the east and west by quartz-mica schists predominantly composed of quartz and biotite, with lesser muscovite and plagioclase (SchiIler 2000; Both, 1990) and has a north to NNE strike and steep east dip.

The immediate hosts to ore at the main Kavanagh zone, mined in the 1970s, and the most studied, are chlorite rich, comprising an assemblage of quartz-chlorite-garnet±pyrrhotite±chalcopyrite, forming a mineralised core within the garnet-andalusite schist host. Like the mineralisation, the chlorite rich host envelope is pipe like in shape, but is complex in detail, with a steep northerly plunge, in contrast to the shallow south plunges of folds in bedding in the surrounding schists. Both the lode schists and the sulphide mineralisation that comprises the Kavanagh zone (or Main Lode), occur in a series of lenses within the gross pipe-like structure, which has maximum horizontal dimensions of 120 x 180 m and has been intersected to depths of at least 450 m below the surface. It strikes at 10° and dips at 75°E, plunging 80°N. Mineralisation is largely controlled by a set of north-south and NE striking structures and is best developed where these two structural trends intersect (SchiIler 2000; Both, 1990).

The main structure defined in the mine area by the generally well preserved relict bedding, is the Mine Synform, which plunges ~15°S. The mineralised pipe lies on the eastern limb of this structure. The dominant structural fabric is the S2 schistosity, accompanied by an erratically developed mineral lineation, which are both very regularly oriented. The schistosity, which has a north-south strike and dips at 73°E, is axial planar to the Mine Synform and all other mesoscopic and macroscopic folds. This schistosity is assigned to the regional D2 deformation. The mineral lineation has a steep SE plunge, whilst most fold axes plunge shallowly to the south. As a consequence, the pipe-like Main Lode is discordant to both the fold axes in bedding and the mineral lineation. Post-D2 structures are limited to brittle-style rare crenulations, kinks and joints (SchiIler 2000).

The main mineralised pipe in the Kavanagh zone is composed of multiple sulphide lenses each paralleling the NNE trending and steeply east dipping schistosity of the hosts rocks. Additional such lenses surround the main pipe and account for much of the known resource (Both, 1990). Veins in the mine are quartz, quartz-sulphide, sulphide or coarse-grained silicates and are either parallel to S2, or are slightly oblique, folded and boudinaged. Veins, which are oblique to S2 in the immediate mine surrounds, are mostly quartz, and are folded and boudinaged. These are older veins and are generally barren. Many minor shear zones occur in the mine, principally on the western limb of the Mine Synform where they are parallel or subparallel to S2. Some shear zones are important controls on the copper distribution (SchiIler 2000).

The host GABS unit is unaltered with well-developed S2 schistosity and porphyroblastic andalusites where distal to the mineralisation. As the mineralisation is approached, there is a transitions to a staurolite rich assemblage with the andalusites having corroded margins, accompanied by the initial appearance of chlorite and quartz-sulphide veining. Within the mineralised zone, the alteration is an intense biotite-garnet-chlorite schist in which the S2 fabric and andalusite has been obliterated, with sulphide, chlorite and quartz veining dominant. Quartz veining is associated with all mineralisation, but is generally more prevalent in the western mineralised areas.

In addition to the main Kavanagh zone, a network of surrounding mineralised zones or shoots have been outlined at Kanmantoo, controlled by a series of north-south striking shears that are parallel to S2 and dip at ~80°E, linked by a number of NNE to NE striking cross-shears (e.g., Mathew, Valentine and Kavanagh West which generally strike north-south, and the Nugent, Spitfire and Kavanagh deposits that strike NNE). These deposits occurs in the form of discordant stockworks within highly altered GABS. At a local scale, the higher grade copper shoots occur at the intersection of the north and NNE shears, and generally plunge at 65 to 75° with and azimuth of 40°. Most fall within a single halo of pyrite and pyrrhotite that extends over an area of 1.5 x 0.8 km, although the separate Emily Star zone is within a 250 m diameter area, ~250 m to the SW of the main zone. Chlorite also forms a significant alteration halo to the copper mineralisation, over an area of ~1 x 0.5 km, typically as replacement of biotite and andalusite, and as 2 to 20 mm selvages of intense chlorite (Rolley and Wright, in press).

The Spitfire zone, 250 m SSE of Kavanagh has bee affected by chlorite-garnet-biotite-magnetite alteration, and comprises a number of mineralised orientations including north-south (S2), 15° and 25° strikes. The latter orientation is distinctly characterised by strong magnetite alteration associated with intense chlorite development. This zone also has the highest gold endowment which may be a result of the stronger development of the NNE and NE fabrics.

The Nugent zone, 200 m SE of Spitfire, typically comprises staurolite-quartz-biotite alteration surrounding a strong quartz-chlorite ore zone. The mineralisation occurs as a planar, 45° strike and 80°E dipping body, with the north-south Biotite Schist unit contact faulted to the east where it is intersected by the Nugent mineralised zone.

The Emily Star mineralisation is located close to the hinge zone of a regional syncline. Mineralisation cross-cuts bedding and is not limited to the hinge zone, localised within S2 oriented and NW to NNW trending chlorite-quartz zones. Alteration is characterised by garnet-quartz-biotite with a smaller sulphur and chlorite halo surrounding the mineralisation.

The majority of the sulphide minerals in the mine area occur as disseminated, microscopic grains and as mesoscopic veins, both of which parallel the north-south S2 schistosity, or are found as irregular veins and patches. In vertical section, the copper mineralisation is very regularly distributed, forming steep shoots, some parallel to the schistosity and others slightly oblique with a NNE trend. Two styles of mineralisation, on the respective limbs of the Mine Synform, are defined: i). East Limb, characterised by a NNE trend, and an association with host rocks that have fabrics inferred to represent metamorphic crystallisation during high fluid pressures. and ii). West Limb, which are north-south trending in general, and are not associated with the fabrics of the East limb style (SchiIler 2000).

SchiIler (2000) indicates that microstructural studies indicate sulphide minerals were involved in all stages of the metamorphic and structural history. He also records S1 fabrics preserved in andalusite, garnet, staurolite and biotite porphyroblasts, with little evidence of crenulation of SI, suggesting S2 developed from SI, generally by rotation and recrystallisation of SI during flattening. Not all porphyroblasts were developed are coeval, with a series of porphyroblast forming reactions indicated in most rock types. The peak metamorphic pressure (3-4 kb) and temperature (480 to 565°C which are variable, depending on the geothermometers used) are similar for both lode schists and surrounding metasediments (SchiIler 2000).

The dominant minerals in the ore are chalcopyrite, pyrrhotite and magnetite in approximately equal proportions, with lesser pyrite, and minor or traces of ilmenite, cubanite, pentlandite, marcasite, mackinawite, sphalerite, bismuthinite, bismuth, cobaltite, galena, molybdenite, wolframite, gold and silver (Both, 1990).

Overall, chalcopyrite dominant mineralisation is weakly anomalous in gold, averaging around 0.1 g/t Au, with a Cu%:Au g/t ratio of ~100:1. However, to the east, e.g., in the Nugent, Spitfire and Schultze zones, there is a lower Cu%:Au g/t ratio of around 25:1, generally associated with quartz-pyrite and chlorite-pyrite veins, and shears striking NE on linking structures between north-south shear zones. Clusters of fine grained free gold over 10 mm areas have been observed in drill core with individual gold grains to 1 mm (Rolley and Wright, in press).

In October 2006 Hillgrove announced an Indicated and Inferred Resource of 28 Mt at 0.94% Cu and 0.2g/t Au.
In addition approximately 4 Mt @ 1% Cu were mined from 1970 to 1976.

Published ore reserves and mineral resources at the end of February, 2013 were (Hillgrove Resources, 2014):
  In situ resources
    Measured resources - 2.63 Mt @ 0.88% Cu, 0.10 g/t Au, 1.95 g/t Ag;
    Indicated resources - 21.77 Mt @ 0.82% Cu, 0.23 g/t Au, 2.21 g/t Ag;
    Inferred resources - 5.0 Mt @ 0.67% Cu, 0.13 g/t Au, 1.79 g/t Ag;
  Long term stockpiles
    Measured resources - 1.39 Mt @ 0.46% Cu;
    Indicated resources - 0.50 Mt @ 0.18% Cu;
  TOTAL resources - 31.30 Mt @ 0.78% Cu, 0.20 g/t Au, 2.11 g/t Ag.
  In situ reserves
    Proven reserves - 2.5 Mt @ 0.77% Cu, 0.08 g/t Au, 1.7 g/t Ag;
    Probable reserves - 18.2 Mt @ 0.72% Cu, 0.20 g/t Au, 2.0 g/t Ag;
    Inferred resources - 5.0 Mt @ 0.67% Cu, 0.13 g/t Au, 1.79 g/t Ag;
  Long term stockpiles
    Proven reserves - 1.4 Mt @ 0.46% Cu;
  TOTAL reserves - 22.1 Mt @ 0.71% Cu, 0.18 g/t Au, 1.9 g/t Ag.

The most recent source geological information used to prepare this summary was dated: 2006.    
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.


Kanmantoo

  References & Additional Information
   Selected References:
Both R A,  1990 - Kanmantoo Trough - Geology and mineral deposits: in Hughes F E (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne   Mono 14, v2 pp 1195-1203
Pollock, M.V., Spry, P.G., Tott, K.A., Koenig, A., Both, R.A. and Ogierman, J.,  2018 - The origin of the sediment-hosted Kanmantoo Cu-Au deposit, South Australia: Mineralogical considerations: in    Ore Geology Reviews   v.95, pp. 94-117.
Rolley, P. and Wright, M.,  2017 - Kanmantoo copper deposit: in Phillips, G.N., 2017 Australian Ore Deposits, The Australasian Institute of Mining and Metallurgy,   Mono 32, pp. 667-670.
Seccombe P K, Spry P G, Both R A, Jones M T and Schiller J C,  1985 - Base metal mineralization in the Kanmantoo Group, South Australia; a regional sulfur isotope study : in    Econ. Geol.   v80 pp 1824-1841
Tott, K.A., Spry, P.G., Pollock, M.V., Koenig, A., Both, R.A. and Ogierman, J.,  2019 - Ferromagnesian silicates and oxides as vectors to metamorphosed sedimenthosted Pb-Zn-Ag-(Cu-Au) deposits in the Cambrian Kanmantoo Group, South Australia: in    J. of Geochemical Exploration   v.200, pp. 112-138.
Verwoerd P J and Cleghorn J H,  1975 - Kanmantoo copper orebody: in Knight C L, (Ed.), 1975 Economic Geology of Australia & Papua New Guinea The AusIMM, Melbourne   Mono 5 pp 560-565


Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge.   It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published.   While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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