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Warrawoona - Klondyke, Copenhagen, Coronation, Fieldings Gully

Western Australia, WA, Australia

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The Warrawoona Greenstone Belt is situated ~150 and ~25 km southeast of Port Hedland and Marble Bar respectively in the East Pilbara district of Western Australia, and falls within the Marble Bar Goldfield. The principal deposit within the belt is Klondyke, with satellite resources at Copenhagen, Coronation and Fielding's Gully (#Location: - Klondyke 21° 20' 19"S, 119° 53' 41"E).

The Greenstone Belt lies within the East Pilbara Terrane of the Pilbara Craton. The Pilbara Craton is composed of unexposed Eoarchaean to early Palaeoarchaean crust (3.80 to 3.53 Ga) of unknown extent; Palaeoarchaean granite-greenstone terranes (3.53 to 3.07 Ga); Mesoarchaean volcano-sedimentary basins (3.05 to 2.93 Ga); and post-orogenic Mesoarchaean granites (2.89 to 2.83 Ga).

Mineralisation within the Warawoona deposits occurs as quartz lodes within three main regional WNW-ESE to NW-SE shears, which are, from north to south, the Klondyke, Copenhagen and Fieldings Find shear zones. These shears converge eastward to form a single broad, composite shear zone in the East Klondyke section. The largest of these is the Klondyke Shear Zone where resources had been defined (to June 2019) over a strike length of 5 km, within a >12.5 km trend defined by extensive old workings. At Klondyke, as of March 2021, the Measured + Indicated Mineral Resources listed below extend from surface to a depth of 150 to 200 m and strike length of 3 km. Inferred resources are defined by sparser drilling for ~1 km on either end and beneath to depths of 200 to 500 m, without apparently closing the resource (Calidus Resources website, viewed April, 2021). Copenhagen and Coronation are on the Copenhagen Shear and Fieldings Gully on the Fielding's Find Shear to the west of Klondyke. Other prospects within the greenstone belt remain to be further tested, including Liberator, 5 km SW of Coronation; Ada North and Ada South, 2 km NE and 5 km NNW of Klondyke respectively; Salgash on the Klondyke Shear, 4 km north of Coronation; and Pryces West also on the Klondyke Shear, 13 km SE of Klondyke.

These three shear zones represent networks of quartz-calcite-sulphide-ankerite veins that are locally lined with heavily brecciated fuchsite-sericite-pyrite bearing mafic rocks. Visible gold often occurs in quartz veins throughout the mineralised package.

These shears zones are developed within the Palaeoarchaean 3525 to 3426 Ma Warrawoona Group which is dominantly composed of volcanic and sedimentary rocks. These include high-Mg basaltic lavas with lesser tholeiite, andesite, sodic dacite, potassic rhyolite, chert and banded iron formation (BIF), all of which have been metamorphosed to a greenschist facies assemblage. From north to south, the sequence comprises ultramafic and mafic volcanic rocks, the dominant lithologies, that have undergone moderate shearing and alteration; then to weakly to strongly carbonate altered and sheared ultramafic rocks with massive to foliated mafics; then a narrow band of fuchsite bearing schists with associated chert units that has been interpreted to be a mylonite; and finally a felsic volcanic sequence that lies largely to the south.

The Warrawoona Group rocks are sandwiched between the domal, 50 km diameter, Mesoarchaean (3.3 to 2.8 Ga) Mount Edgar Granitoid Complex to the north and the similar sized, oval shaped, domal, Palaeoarchaean (3.4 to 3.3 Ga) Corunna Downs Granitoid Complex to the south. The former is composed of weakly foliated medium- to coarse-grained monzogranite, granodiorite, tonalite and trondjhemite, whilst the latter is dominated by monzogranites, with rare tonalite, trondhjemite, granodiorite and syenite.

Four deformation events have been recognised in the Warrawoona Greenstone Belt: i). the earliest, which is represented by schistosity developed parallel to the margin of the Corunna Downs Batholith; ii). a tight isoclinal folding; iii). intense shear zones that are associated with gold mineralisation, with steep to near vertical dips, and are considered to have a reverse displacement; and iv). a local deformation observed in the eastern part of the greenstone belt.

Klondyke
  The Klondyke Deposit is hosted by the Apex Basalt of the Salgash Subgroup and the disconformably underlying, stratigraphically older, Duffer Formation of the Coongan Subgroup to its north. Both subgroups are members of the Warrawoona Group. The contact between the two units is apparently marked by a thin mylonite zone along the southern edge of the stratigraphically highest metasedimentary schist that defines the top of the Duffer Formation. All of the Klondyke host rocks are intensely deformed and altered, which with weathering, makes recognition of primary rock types difficult. As a consequence, Cr:Ti and Zr contents have been utilised to define mappable units. This work reveals a series of low-Cr and high-Cr mafic schists (the latter representing komatiitic basalt protoliths), and ultramafic schists, all juxtaposed by a series of ESE-trending sub-parallel shear zones, including the main Klondyke shear and the mineralised St George shear, ~200 m to the north. Several prominent chert units also occur within the succession.
  Klondyke is characterised by a strong, steeply dipping, WNW-trending foliation with a down-dip mineral lineation. The intensity of this foliation increases towards high strain zones. Locally, the foliation contains strong rodding of quartz, indicative of L-tectonites (indicating constrictional strain), although most areas have undergone intense flattening and vertical stretching (L-S tectonites; Collins et al., 1998). Pressure shadows on pyrite are common, indicating vertical elongation of between 1:5 and 1:8 (Miller et al., 2018). Boudinage related to this vertical stretching of quartz veins parallel to the foliation is common, whilst scattered tight to isoclinal folds through the Klondyke area have steep to vertical fold axes that are commonly parallel to the stretching lineation. The foliation transects older fabrics to produce a strong intersection lineation in many areas. This intersection lineation varies from vertical to steeply plunging and is parallel to the plunge of the fold axes. In many areas the stretching lineation is difficult to differentiate from the intersection lineation as they are sub-parallel.
  Mineralisation is concentrated around the Klondyke Shear, and is associated with quartz-carbonate-pyrite veins within sericite/fuchsite-carbonate-altered and intensely deformed mafic schists. Where mineralisation is strong, these quartz veinlets occur at a high frequency as parallel bands often showing bounding structures, both down dip and along strike. Both the shears and veining are sub-vertical to very steeply dipping to the SSW with a strike of ~110°. At least four sub-parallel shear zones are recognised and two of these are associated with historic gold workings. The individual shoots within these shear zones appear to have short strike lengths, but considerable vertical extent. Metallurgical samples to 150 m depth show free milling ore with gold recoveries of 93 to 96%.
  A 10 to 50 cm thick black chert band, known as Kopcke’s Leader, is exposed within the altered mafic schists. This chert band is persistent, both laterally and vertically, and provides a good indication of the location of mineralisation. Rock units and quartz-carbonate veins have strong egg-carton boudinage texture and are marked by a strong sub-vertical mineral/intersection lineation. One of the most prominent characteristics of sections through the ore zone is the strong asymmetry of the alteration, with fuchsite dominating in the footwall (northern side) and sericite alteration in the hanging wall to the south. This asymmetry is interpreted to indicate that Kopcke’s Leader is located at the contact between two different mafic units, namely: i). a high-Cr and high-Mg mafic unit below the chert in which fuchsite is developed and ii). a low-Cr mafic unit above the chert in which sericite is formed. This is further interpreted to indicate the contact marks an erosion surface where clastic deposition occurred during a hiatus in volcanism represented by the disconformity between the Apex Basalt and the underlying Duffer Formation. Kopcke's leader chert has a consistent strike and depth continuity over the resource area, providing a strong marker unit.
  Mineralisation generally comprises two parallel tabular zones separated by the Kopcke’s leader, each comprising high grade shear hosted zones within a broader, lower grade alteration halo. The better intersections within the high grade zones include 6 m @ 63.3 g/t Au and 27 m @ 5.9 g/t Au. When combined with the ~20 m wide composite alteration halo, the overall head grade, depending on cut-off, is ~1 to 2 g/t Au. (Calidus Resources).

Copenhagen
  Gold mineralisation in this deposit is hosted by a sheared high-Ti metabasalt unit sandwiched between two chert layers. This host unit occurs within a thick sequence of metabasalt and amphibole-chlorite-quartz mafic schists with a strong mineral lineation plunging at 30 to 60°SE, commonly parallel to the mineralised fold structure. The lode is 10 to 80 m thick, tapering to the east, and is strongly sheared and carbonate/silica altered. It is folded and appears to plunge shallowly to the east. It lies between an ~100 m thick chlorite-quartz schist, interpreted to represent a sheared mafic/basalt protolith to the north, and a 10 m thick unit of talc carbonate schist to the south.
  The mineralised unit and quartz veins are folded, defining a hook-shaped structure which plunges at between 30 and 60° ESE. Mapping in the old Copenhagen pit also observed a very strong easterly plunging L-tectonite fabric (33°/104°) associated with a strong mineral elongation, parallel to long axes of boudins in the host mafic rock. Strong jointing and quartz extension veins (015°/57°) developed perpendicular to the pervasive stretching lineation were interpreted to be a result of pure shear extension. The metabasalt and amphibole-chlorite-quartz mafic schists enclosing the mineralised unit have a strong mineral lineation plunging at 30 to 60°SE, commonly parallel to the mineralised fold structure (Sofoulis, 1993).
  All rock types in the mineralised zone contain up to 5 m thick horizons in which the rocks have undergone pale sericite and sulphidic alteration. Quartz veinlets and pods up to 10 cm thick, which are orientated parallel to the dominant cleavage, cut the rock. These veinlets may comprise up to 60 vol.% of the total rock volume and contain up to 10% disseminated fine-grained pyrite, as well as fine acicular arsenopyrite in the enclosing country rock. Acicular arsenopyrite appears to be strongly concentrated in narrow bands parallel to the main shear, whereas pyrite has a much broader distribution.
  A more planar fabric occurs along the centre of the pit, associated with the main shear juxtaposing the different lithologies, although the sense of movement is equivocal. A second vein set (152°/56°) is associated with the planar fabric and a flatter secondary foliation (180°/33°) is widely developed. A cross-cutting shear (220°/52°), with a reverse sense of movement is exposed on the northwest corner of the pit, is oblique to the main shear. This cross-cutting shear is apparently developed at the contact between felsic and mafic lithologies and appears to be unmineralised (Sofoulis, 1993).

Fielding's Gully
  This deposit is located on the east-trending Fielding's Find Shear. It lies within a sequence of sheared and hydrothermally altered volcanic and sedimentary rocks. The dominant topographical feature in the deposit area is a 30 m high ironstone ridge composed of sulphide-rich chert and iron carbonate that developed along the contact of felsic sedimentary rocks to the north and highly altered ultramafic rocks to the south (Martin, 1985). Gold mineralisation is interpreted to be hosted within a sedimentary horizon containing quartz lenses concordant with the overall strike of the unit. The sedimentary rocks comprise highly altered pyritic-fuchsitic-quartzite; mica-rich chloritic schist; quartz-carbonate; and quartz-feldspar-mica schists. Gold is hosted in folded quartz veins (Martin, 1985). The mineralised zone strikes at 100° and dips steeply south. The estimated strike extent is ~325 m but remained open in all directions in June 2020.

Mine construction commenced in 2021 based on the resources and reserves listed below.

JORC Compliant Mineral Resources, inclusive of Ore Reserves, are (Calidus Resources Limited ASX Announcement, June 2020):
  Klondyke Open Pit at 0.3 g/t Au cut-off
    Measured Resource - 2.3 Mt @ 0.98 g/t Au;
    Indicated Resource - 29.0 Mt @ 0.90 g/t Au;
    Inferred Resource - 8.3 Mt @ 0.81 g/t Au;
   TOTAL Open Pit Mineral Resource - 39.6 Mt @ 0.89 g/t Au; for 35.25 t of contained gold.
  Klondyke Underground at 1.5 g/t Au cut-off
    Indicated Resource - 1.0 Mt @ 2.87 g/t Au;
    Inferred Resource - 1.8 Mt @ 3.31 g/t Au;
   TOTAL Underground Mineral Resource - 2.7 Mt @ 2.83 g/t Au; for 7.8 t of contained gold.
  Copenhagen at 0.5 g/t Au cut-off
    Indicated + Inferred Resource - 0.3 Mt @ 4.54 g/t Au;
  Coronation at 0.5 g/t Au cut-off
    Inferred Resource - 0.5 Mt @ 2.19 g/t Au;
  Fieldings Gully at 0.5 g/t Au cut-off
    Indicated + Inferred Resource - 0.6 Mt @ 1.84 g/t Au;
  GLOBAL Mineral Resource - 43.7 Mt @ 1.06 g/t Au; for 46.4 t of contained gold.

Total Proved + Probable Ore Reserves for the Klondyke Open Pit, Klondyke Underground, St Georges Open Pit and Copenhagen Open Pit each at different cutoffs between 0.33 and 2.0 g/t Au, as of June 2020, were:
    13.609 Mt @ 1.2 g/t Au; for 16.2 t of contained gold.

Information for this summary has been sourced from various Calidus Resources Limited ASX Announcements (particularly that of 29 June 2020) and website (viewed April, 2021) and a 2017 Hartleys Limited investors report.

The most recent source geological information used to prepare this summary was dated: 2020.    
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.


  References & Additional Information

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, its employees and servants:   i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and   ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.

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