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Carosue Dam - Karari, Whirling Dervish, Luvironza, Montys Dam, Twin Peaks
Western Australia, WA, Australia
Main commodities: Au


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The Carosue Dam cluster of gold deposits is located ~105 km northeast of Kalgoorlie, in the Pinnacles greenstone belt, of the central Kurnalpi Terrane, of the Yilgarn Craton in Western Australia (#Location: 30° 8' 58"S, 122° 21' 35"E).

These deposits with Ore Reserves and/or Mineral Resources outlined include the Karari and Whirling Dervish deposits and the Luvironza, Monty's Dam, Twin Peaks and several smaller resources, all of which are distributed over a NNW-SSE aligned interval of ~14 km, parallel to and immediately to the east of the NE dipping major regional Keith-Kilkenny Fault. For the regional setting see the Yilgarn Craton Overview record.

During the early 1890s, CRA Exploration Ply Ltd employed Rotary Air Blast (RAB) drilling to define an ~400 m long coherent anomalous gold zone in the Carosue Dam area, with supporting Cu, Pb, Zn and Ba. This was followed up with a diamond hole in the centre of the target area that intersected two zones of anomalous gold; 26 m @ 130 ppb associated with a syenite, and 54 m @ 210 ppb, including two narrow zones of >1 g/t within a strongly foliated hematitic zone. In the late 1980s, Aberfoyle Pty Ltd undertook a calcrete sampling program that confirmed the gold anomalous zone in which Karari would later be found, and then tested it with a reverse circulation (RC) drill hole that intersected 12 m @ 2.05 g/t and 12 m @ 3.03 g/t Au. Further RAB drilling led to the discovery of Whirling Dervish and Luvironza. In 1988, Pacmin Mining Corporation acquired the project and undertook an extensive RC and diamond drilling program to define Indicated + Inferred resources of 40.1 Mt @ 1.7 g/t Au, for ~68 tonnes of contained gold. PacMin commenced mining at Karari and Luvironza in June 2000, and in 2001 purchased tenements to the north that included the Twin Peaks and Monty's Dam resources. In June 2001, PacMin was taken over by Sons of Gwalia Limited, who continued the existing mining operations and developed Monty's Dam and Twin Peaks. Saracen Mineral Holdings acquired the property in October 2005, which became a Northern Star operation after that company merged with Saracen. Mining has continued through that period to the present (2022).

The regolith in the Karari-Whirling Dervish section of the cluster varies from 50 to 75 m in thickness, including 5 to 20 m of transported cover. Of the latter, the top 1 to 6 m is predominantly calcrete. At Karari, the calcareous surface soils carry anomalous >200 ppb Au that covers an area of ~400 x 1000 m. This anomaly has been transported ~100 m to the south from the high-grade basement-hosted mineralisation. In comparison, at Whirling Dervish, calcareous material in the upper 3 m of overburden carries 15 to 50 ppb Au, with the centre of the anomaly having been displaced by ~50 m to the north and NE of the basement mineralisation. The contact between the transported cover and underlying saprolite is transitional, marked by a zone of red colouration, magnetic ferruginous nodules and polymictic gravel fragments. The underlying saprolite below the calcrete anomaly is depleted in gold.

The bulk of the Carosue Dam deposits are located in the hanging wall of the regional NW to NNW-striking and moderately ENE dipping Keith-Kilkenny Fault. The gross stratigraphy of the district surrounding Carosue Dam, from WSW to ESE, commences with a sequence of 2.72 to 2.68 Ga greenstones which are intruded by the NNW-SSE elongated, 20 x 7 km, composite Relief Monzogranite batholith, composed of 2.68 to 2.61 Ga granite gneiss and assorted granitoids. The greenstone sequence is predominantly composed of a continuous basalt unit to the west, followed to the east by discontinuous thick lenses of andesite and rhyolite with minor dolerite, which pass eastward into, and interfinger along strike with, a thick sequence of shales. The latter locally contains thin units of 'magnetic sediment'. The shales of this greenstone sequence are bounded to the east by the Keith-Kilkenny Fault which forms the eastern boundary of the Gindalbie Domain, the western-most segment of the Kurnalpi Terrane. This east dipping fault is overlain by a monotonous sequence of metamorphosed quartz-lithic sandstone with minor siltstone and grit of the Carosue Basin exposed over a width of between 1.5 and 7.5 km, parallel to the fault. Lithic clasts within these sedimentary rocks are dominated by aphanitic and porphyritic, felsic to intermediate, quartz-poor, volcanic to subvolcanic igneous rocks, with minor granite and lesser but variable fragments of feldspar and quartz. The sequence is regarded as being a volcaniclastic unit. The lithic clasts are commonly pink to red, due to a dusting of hematite. Bedding is generally poorly developed or poorly preserved but locally, graded bedding and low-angle trough crossbedding indicate younging to the east. Geochronological data indicate a depositional age of ~2660 Ma for the metasediments (Kositcin et al., 2008). All of the Carosue Dam deposits, other than possibly Twin Peaks, are hosted within this unit. These volcano-sedimentary rocks have been intruded by numerous quartz-poor alkalic dykes, sills and elongate plugs of monzonite, monzodiorite, syenite and lamprophyre that are largely elongated parallel to the strike of the sedimentary package. These intrusives range from a few metres to >1 km in width. They are most voluminous over the strike interval occupied by the Carosue Dam deposits, where the basin and underlying greenstones are cut by a swarm of north-south trending of post-intrusion faults. These intrusives appear to thin and become less well developed by ~5 to 10 km to the NNW and SSE. The Carosue Basin package is unconformably underlain to the east by a thick, more deformed, 2.72 to 2.68 Ga greenstone package, predominantly composed of basalt with thinner intercalations of ultramafic rocks, high-Mg basalt, peridotite and dolerite to gabbro. These are in turn intruded in the east by the elongate 2.61 to 2.68 Ga Galvalley Monzogranite batholith (Witt and Mills, 2017; Witt, Mason and Hammond, 2009; Witt and Hammond, 2008).

In the Carosue Dam area, the Carosue Basin is attenuated between the large Relief and Galvalley monzogranitic intrusions to the west and east respectively, and is cut by a swarm of north-south faults (Czarnota et al., 2010). It is interpreted to represent the southern extension of the ~2655 Ma Pig Well-Yilgangi Basin (Wilt and Hanunond, 2008), one of a series of a late-stage depositories unconformably overlying Neoarchaean 2720 to 2660 Ma greenstone belts of the Kalgoorlie and Kumalpi Terranes.

The five main deposits at Carosue Dam are, from north to south: Twin Peaks, Monty's Dam, Luvironza, Whirling Dervish and Karari, each separated by between 2 and 4 km. The cluster lies within a >30 x 3 km alteration halo corridor that comprises:
i). a core of potassic (biotite) and sodic (albite) alteration, found in close spatial association with alkalic intrusions. Most of the gold deposits lie within this zone, where enrichment of Cu, Mo and Ag is found proximal to, and As and Zn distal to, mineralisation. The associated alkalic intrusions are magnetite-bearing, allowing their extent to be delineated in magnetic data in poorly exposed terrain. The potassic alteration of these intrusions and adjacent metasedimentary rocks is characterised by an assemblage of biotite ±K feldspar, magnetite, chalcopyrite and pyrite. The presence of magnetite is taken to imply it was the product of a moderately oxidised hydrothermal fluid. The potassic alteration is locally overprinted by a sodic albite-ankerite-pyrite-rutile assemblage in which all of the main component minerals contain Fe in a reduced state. This sodic assemblage is commonly, but not consistently, accompanied by minor hematite dusting, which is interpreted to reflect a later overprint by an oxidised fluid (Witt, Mason and Hammond, 2009).
ii). a medial zone of muscovite alteration, which hosts the Twin Peaks deposit. Apart from Twin Peaks, however, the muscovite alteration zone is essentially barren. Twin Peaks differs from the other Carosue Dam deposits, which are spatially associated with oxidised alkalic intrusions and magnetite bearing potassic alteration. In contrast, it contains pyrrhotite and arsenopyrite, implicating a reduced ore fluid, and is associated with minor lamprophyric intrusions; and
iii). a distal chlorite alteration zone (Witt and Hammond, 2008). Similar chloritic alteration is also associated with some of the north-south faults cutting the Carosue Basin sedimentary sequence. Chlorite alteration may possibly be related to regional greenschist facies metamorphism.

Karari

The geology of the Karari open pit has been divided by Witt, Mason and Hammond (2009) into the:
i). footwall metasedimentary sequence, composed of metamorphosed fine- to coarse-grained sandstone and siltstone, with intercalated chloritic shale. These rocks are dominated by detrital quartz with lesser feldspar and phyllosilicate minerals, and up to 1% pyrite. A foliation is defined by muscovite and chlorite which wraps around individual clastic grains. These phyllosilicates are considered to represent an unaltered metamorphic assemblage, with the exception of intense chlorite-carbonate alteration that occurs within several metres of the Footwall Fault. Cross- and graded bedding are relatively common, in contrast to the feldspar-rich volcaniclastic sedimentary rocks of the central mineralised zone, although no consistent direction of younging could be established due to the degree of folding. This sequence is to the west of the Keith-Kilkenny Fault, and is considered part of the western greenstone sequence rather than the Carosue Basin;
ii). central mineralised zone, which is is dominated by metamorphosed volcaniclastic sedimentary rocks, which belong to the Carosue Basin, and are intruded by monzonite porphyry, lamprophyre and diorite dykes. It is interpreted to represent a downfaulted, higher-level exposure of the magmatic system represented by the eastern intrusive complex. The volcaniclastic sedimentary rocks of this zone are predominantly composed of angular to rounded, quartz-poor, intermediate to felsic lithic fragments with lesser quartz and feldspar mineral clasts, and generally <10% phyllosilicates, mainly biotite, muscovite or chlorite, depending on the alteration facies, as described above. Graded- and low-angle crossbedding locally indicate younging to the west, and as such the beds are overturned. Lithic clasts within the sedimentary rocks are generally <5 mm long, and the rocks are generally moderately well sorted, with rare isolated clasts up to several centimetres across in volcaniclastic sandstone. A well developed foliation, defined by phyllosilicate minerals wraps around lithic and mineral clasts, although the clasts are not generally strongly flattened. The occurrence of igneous dykes within this sedimentary succession, and the porphyritic textures of the dykes, is interpreted to suggest a relatively shallow crustal level for this zone, in contrast to the eastern intrusive complex. Lamprophyre and monzonite porphyry dykes are similar to those of the eastern intrusive complex, although the monzonite porphyry dykes are more strongly altered in this zone. The central mineralised zone is bounded to the west and east by the Hanging Wall and Footwall Faults respectively. These, and other associated faults are brittle-ductile structures that are several metres to as much as 51 m wide. They are characterised by intense fracturing and cataclasis with locally superimposed ductile strain, which produces an anastomosing fabric that wraps angular rock fragments.
iii). eastern intrusive complex. This intrusive complex is dominated by coarse-grained monzonite and porphyritic monzonite intruded by numerous dykes of monzonite porphyry, syenite porphyry and lamprophyre, and locally contains low-grade copper mineralisation. Tectonic strain in the eastern intrusive complex is weak and igneous textures are well preserved throughout (Witt, Mason and Hammond, 2009).
Economic gold mineralisation is confined to the central mineralised zone, where it is hosted by zones of sodic alteration. Five lodes have been defined. These gold lodes are steep tabular zones of sodic alteration within a more extensive area of potassic alteration. They are spatially associated with monzonite porphyry dykes, and are characterised by albite-ankerite-pyrite-rutile (sodic) alteration of the dykes and enclosing metasedimentary rocks. Hematite dusting occurs in fine-grained albite and carbonate in the sodic alteration zones but is interpreted as a later (post-gold) event. Gold grades are directly correlated with the abundance of disseminated and stringer pyrite, with lodes being relatively enriched in As and W. Other pathfinder elements such as Mo, Cu, Zn, Pb, Bi, Te and Ag are most enriched in the eastern intrusive complex. Late quartz ±carbonate veins are low-grade to barren. Sodic alteration zones contain numerous veins and veinlets, which contain a variety of assemblages, several of which are mutually overprinting. The following vein types have been recognised, as follows (after Witt, Mason and Hammond, 2009):
i). Late carbonate with quartz, chlorite, biotite and dolomite, which are common, generally <5 mm thick occurring as massive calcite-rich veinlets, stringers and fracture-veinlets;
ii). Quartz - which are common, especially in zones of sodic alteration, but locally extend a short distance into the adjacent potassic alteration zone. They are composed of massive to zoned buck white quartz veins and minor carbonate, which is generally <10% to absent;
iii). Quartz–carbonate, which contain minor biotite, chlorite, pyrite and, less commonly, minor albite or microcline. They include >10% carbonate as calcite or dolomite, generally concentrated at the margins and have variable thicknesses.
iv). Pyrite-rich veinlets and stringers with accompanying carbonate, biotite and microcline, which are locally common in zones of strong sodic alteration, and normally include up to 45% disseminated pyrite. Pyrite-microcline veinlets are particularly common in the Hanging Wall Lode, where they cut sodic-altered, brecciated monzonite porphyry. They are moderate to common and generally <5 mm thick.
v). Quartz–pyrite, which are massive to laminated with grey quartz, occurring as <5 mm veinlets that are uncommon, although there is a good correlation between their presence and gold grades of >4 g/t. Pyrite comprises up to several percent of the veins and may occur as very fine-grained disseminations or as lamellae. Quartz has a fine-grained, grey, cherty appearance.
vi). Biotite-rich veinlets and stringers are locally abundant in sodic alteration zones of the volcaniclastic sedimentary rocks, but are absent to minor in the monzonite porphyry dykes. They are dominantly composed of biotite, but are locally overprinted by chloritic alteration. Minor calcite and/or pyrite may also be present in thicker veinlets, some of which are zoned from a calcite core to biotite-rich margins. Magnetite and chalcopyrite have been observed in some biotite-rich veinlets.
vii). Magnetite veinlets and stringers, with minor quartz, carbonate and pyrite, that are rare, but where present are generally <5 mm thick.

Whirling Dervish

Whirling Dervish is a NW-striking orebody located 1.2 km north of the Karari deposit, on the opposite side of the north-south Osman fault, but still hosted within the Carosue Basin meta-volcaniclastic sedimentary sequence. The mineralised ore zones are silicified and cut and offset by a major NW-SE fault. The larger gold-bearing lodes, south of the latter fault, are associated with monzonite porphyry intrusions and surrounding alteration halos of weakly to moderately hematitic, silicified, banded sandstone. North of the same fault, smaller lodes are strongly altered quartz-albite-pyrite zones that are texturally destructive, rich in quartz veining and locally brecciated (Witt and Mills, 2017).

Twin Peaks

Twin Peaks is the northernmost of the Carosue Dam cluster, and has been deposited on the opposite side of the Keith-Kilkenny Fault, within siliciclastic sedimentary rocks of the western greenstone sequence. It is an ~150 x 50 m, meta-sedimentary hosted, moderately east plunging, pipe-like body that is approximately co-linear with the intersection between bedding and a swarm of subvertical WSW-striking fractures. Preserved meta-sedimentary textures indicate the host rocks were siltstone and sandstone with only minor mudstone. Mineralisation is interpreted to have formed where a bedding-parallel strike-slip faulting intersected a minor asymmetric fold, creating a compressional jog. The mineralised pipe contains abundant faults and fractures of various orientations, and can be subdivided into a proximal muscovite-ankerite-sulphide, a medial ankerite and a distal calcite zone. Gold is concentrated in the central and the inner medial zones, whilst the distal calcite zone only contains <10 ppb Au. All visible gold occurs within laminated quartz-ankerite veins, which pass out into low-grade or barren quartz-calcite veins in the calcite zone. Gold is associated with elevated sulphide levels, where it is hosted by pyrrhotite and arsenopyrite. The intensity of carbonate alteration is a key control on gold distribution, grades of >2 g/t Au having a carbonate saturation index of >0.45. Tungsten, arsenic and antimony have the closest spatial association with gold (Witt and Mills, 2017.

Reserves and Resources

The total gold endowment (production plus resources) as of 31 July 2017 at Carosue Dam was 124 tonnes (Witt and Mills, 2017).

Remaining underground Ore Reserves as at 31 July, 2017 at Karari and Whirling Dervish (Saracen Resource and Reserve Report, July 2017) were;
  Probable Reserve - 6.412 Mt @ 3 g/t Au for 19.25 tonnes of gold;
 TOTAL Ore Reserve - 6.412 Mt @ 3 g/t Au for 19.25 tonnes of gold;
  Measured Resource - 1.570 Mt @ 3.2 g/t Au;
  Indicated Resource - 19.371 Mt @ 2.4 g/t Au;
  Inferred Resource - 6.058 Mt @ 1.7 g/t Au;
 TOTAL Mineral Resource - 26.897 Mt @ 2.3 g/t Au for 61.8 tonnes of gold
NOTE: Mineral Resources are exclusive of Ore Reserves.

Remaining underground Ore Reserves and Mineral Resources, as at 31 March, 2022 (Northern Star Resources Limited, Annual Mineral Resource and Ore Reserve Statement, 3 May 2022) were;
  Proved Reserve, Open Pit - 0.588 Mt @ 1.2 g/t Au; Underground - 4.019 Mt @ 3.0 g/t Au; Stockpiles - 2.526 Mt @ 1.8 g/t Au;
  Probable Reserve, Open Pit - 15.996 Mt @ 1.5 g/t Au; Underground - 6.124 Mt @ 2.7 g/t Au;
 TOTAL Ore Reserve - 29.252 Mt @ 1.9 g/t Au for 55 t of contained gold.
  Measured Resource, Stockpiles - 2.526 Mt @ 1.8 g/t Au;
  Measured Resource, Open pit - 3.794 Mt @ 1.6 g/t Au;
  Measured Resource, Underground - 7.583 Mt @ 3.0 g/t Au;
  Indicated Resource, Open pit 22.687 Mt @ 1.7 g/t Au;
  Indicated Resource, Underground 12.685 Mt @ 2.5 g/t Au;
  Inferred Resource, Open pit 10.467 Mt @ 1.6 g/t Au;
  Inferred Resource, Underground 5.977 Mt @ 2.9 g/t Au;
 TOTAL Mineral Resource - 65.718 Mt @ 2.1 g/t Au for 132 tonnes of gold.
NOTE: Mineral Resources are inclusive of Ore Reserves.

The most recent source geological information used to prepare this decription was dated: 2017.    
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.


Carosue Dam

  References & Additional Information
   Selected References:
Witt, W.K. and Hammond, D.P.,  2008 - Archean gold mineralization in an intrusion-related, geochemically zoned district-scale alteration system in the Carosue basin, Western Australia: in    Econ. Geol.   v.103, pp. 445-454.
Witt, W.K. and Mills, D.,  2017 - Carosue Dam gold deposit: in Phillips, G.N., (Ed.), 2017 Australian Ore Deposits, The Australasian Institute of Mining and Metallurgy   Mono 32 pp. 245-248.
Witt, W.K., Mason, D.R. and Hammond, D.P.,  2009 - Archean Karari gold deposit, Eastern Goldfields Province, Western Australia: a monzonite-associated disseminated gold deposit: in    Australian J. of Earth Sciences   v.56, pp. 1061-1086,


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