Western Australia, WA, Australia
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The Nifty sediment hosted copper deposit is hosted within the Neoproterozoic sub-greenschist facies of the Paterson Orogen, immediately to the east of the Archaean Pilbara Craton, some 450 km SE of Port Hedland, 200 km ESE of Marble Bar and 65 km west of Telfer, in Western Australia.
(#Location: 21° 39' 36"S, 121° 34' 12"E).
WMC Limited (WMC) discovered the Nifty deposit in 1981. Drilling of the oxide resource ultimately led to the discovery of the deep sulphide resource in 1983. WMC commenced an open pit operation on the relatively high grade part of the oxide mineralisation in 1993, extracting oxide, transitional and chalcocite mineral resources from which copper cathode was recovered via a heap leach and SX-EW method. Straits Resources Limited purchased the Nifty operation in 1998, and after operating it for 5 years, but proving an underground hypogene resource, on-sold it to Aditya Birla Minerals in March 2003, along with the surrounding exploration tenements. Underground development commenced in January 2004 to exploit the sulphide resource via a decline from the open pit, with the first concentrate being produced in March 2006. Open pit mining operations ceased in June 2006 and heap leaching ceased in January 2009. Metals X Limited took over ownership of the assets on 1 August 2016.
Nifty is situated within the NNW to NW trending, >1000 km long by 150 to 200 km wide Paterson Orogen which fringes the northeastern margin of the Archean to Paleoproterozoic West Australian Craton, and merges with the Musgrave Orogen to the SE. The Paterson Orogen is composed of two main elements, the Paleo- to early Mesoproterozoic metamorphosed igneous and sedimentary rocks of the Rudall Complex, and the unconformably overlying ~9 to 13 km thick, ~850 to 824 Ma Yeneena Supergroup of the >24 000 km2 Neoproterozoic Yeneena Basin.
The Rudall Complex comprises ~2015 to 1765 Ma Paleoproterozoic igneous and sedimentary rocks that were subjected to regional D1 and D2 deformation, metamorphism to granulite facies and granitic intrusion during the ~1800 Ma Yapungku Orogeny, followed by voluminous post-orogenic 1590 to 1310 Ma granitic intrusions only subjected to greenschist facies metamorphism. The complex also includes a domain of sheared peridotite, gabbro, pelitic schist and metaturbidites to the south and east (Bagas, 2004; Whitaker et al., 2010).
The Yeneena Supergroup represents the extensional, fault controlled, northwestern extremity of the ~2 million km2 Centralian Superbasin, developed where the latter encroached upon the Paterson orogen. The Yeneena Supergroup is the thickest measured section in the entire Super-basin, but only represents the first of four super-sequences contained therein. To the west and SW, it is in fault contact with both stratigraphically equivalent and younger rocks of the Officer Basin section of the Superbasin that laps onto the West Australian Craton. To the northeast, the Yeneena Basin and Rudall Complex are overlain by the extensive Phanerozoic Canning Basin (Huston et al., 2010).
The Yeneena Supergroup is subdivided into the Throssell Range and succeeding Lamil groups. The Throssell Range Group is composed of the Coolbro and overlying Broadhurst formations. The latter hosts both the Nifty and Maroochydore deposits.
The 2 to 4 km thick Coolbro Formation was deposited in an extensional rift setting. It commenced with a discontinuous basal conglomerate above the Rudall Complex unconformity, followed by coarse-grained planar to trough cross-bedded fluvio-deltaic sandstone which fines upwards. The upper half of the formation is more arkosic and is frequently cross-bedded, with sporadic pebbly and gritty lenses, and interbeds of shale and calcareous mudstone. The frequency of fine-grained intercalations increases upwards to transition into the overlying Broadhurst Formation. The provenance of detritus is the Rudall Complex.
The Broadhurst Formation is ~2 to 3 km thick and represents sag phase deposition. It is composed of two, dominantly carbonaceous, shale to pelitic schist units, separated by up to 500 m of argillaceous, turbiditic, greywacke and sandstone. Both shale-dominated sections include beds containing up to 10% pyrite and pyrrhotite, the latter identifiable in aeromagnetic data. The upper shale unit also closely coincides with conductive zones in ground and airborne electromagnetic data, interpreted to reflect carbonaceous and/or sulphide-bearing rocks. This implies the upper shale is, overall, more reduced and sulphidic than the lower. A few <100 m thick interbeds of limestone and dolostone are associated with the carbonaceous shale members. The upper and lower shale units are inferred to have been deposited in a sediment-starved euxinic basin. The Broadhurst Formation is structurally overlain by the laterally equivalent carbonate-rich Isdell Formation, which passes up into the Malu Formation quartz sandstones, the basal unit of the Lamil Group, marking renewed extension. Within the Nifty mine area, the Broadhurst Formation is intruded by an undated post-mineralisation dolerite dyke. A composite gabbroic to intermediate sill close to Maroochydore has been dated at 816±6 Ma. For detail of the Isdell and Lamil groups, see the separate Telfer record.
The Nifty deposit is hosted by the upper carbonaceous shale to pelitic schist unit of the Broadhurst Formation, which in the deposit area has been divided into four informal members:
• Footwall beds, which comprise grey to bluish-black, thinly laminated, carbonaceous, pyritic shale with micaceous and chloritic siltstone and minor pale grey dolomitic mudstone. Pyrite variably increases upwards, occurring as clots and blebs and bedding parallel trains of disseminated framboids.
• Nifty carbonate member, comprises two units separated by 1 to 4 m of black, very fine grained chloritic shale. The lower unit is 40 to 70 m of alternating 1 to 2 m thick beds of pale dolomitic mudstone and carbonaceous quartz-mica siltstone and shale that have been variably overprinted by quartz-dolomite alteration. The very similar upper unit is 25 to 60 m thick. Pyrite occurs as fine grained disseminated framboids, coarser clots and bedding parallel blebs and trains predominantly within the carbonaceous shales. The upper unit is followed by ~20 to 40 m of carbonaceous, pyritic, shale with minor interbedded siltstone that is generally unaltered and contains what are interpreted to be gypsum blades pseudomorphed by quartz, dolomite and rarely chalcopyrite. The Nifty carbonate member hosts the hypogene ore deposit, and is characterised by the abundance of interbedded carbonaceous shale and dolomitic mudstone compared to the enclosing units
• Pyrite marker bed, is ~1.5 to 22 m of finely laminated, blue-black carbonaceous shale with >5 m thick bands of >15% pyrite as isolated clots, concretions and framboids. The framboids increase upwards at the expense of the other forms.
• Hangingwall beds, which are located in the core of the Nifty Syncline and comprise >475 m of mainly thinly laminated dark grey to black carbonaceous siltstone and silty shales. They contain clots and framboids of pyrite, rare interbeds of light grey laminated dolomitic shale and micaceous silty shale.
Regionally, Nifty is located <15 km to the east of a major, NNW trending, growth fault, the Vines Fault, that influenced deposition of the Yeneena Group Supergroup. It also occurs close to the concealed intersection of the Vines Fault and the NW trending pre-Yeneena Supergroup Camel-Tabletop Fault that separates two domains of the Rudall Complex basement. Locally, five deformational events have been recognised in the Nifty open pit Anderson et al., 1997). DY1 produced isoclinal and angular upright folds, interpreted to accompany the onset of bedding-plane slip associated with NNE-directed contraction. This event is taken to be related to the Miles Orogeny and inversion of the Yeneena Basin, corresponding to the regional D3 deformation. The regional deformation events within the Paterson Province, are described in the Regional Setting section of the Telfer. DY2 is the main folding and cleavage forming event at Nifty, producing regional NW-SE fold axes that are doubly plunging, and SSW vergent thrusting. Of the remaining three events, the first is unnumbered, and localised in the Nifty pit, involving upright folds and a NNE-striking slaty cleavage. DY3 formed horizontal folds coaxial with FY2 structures, interpreted to be the consequence of extensional collapse at the end of the Miles Orogeny. DY4 is a late brittle event associated with the Paterson Orogeny. Peak metamorphic conditions occurred during DY2 and only reached sub-greenschist facies, with illite crystallinity indicating temperatures of 200 to 300°C (Anderson et al., 2001).
The Nifty deposit had a global resource of 99 Mt @ 1.7% Cu at a 0.5% Cu cut-off (Straits Resources 2000, quoted by Anderson et al, 2001). JORC compliant mineable resources at a higher cut-off are listed in the Reserve and Resource tables below. Ore occurs as both supergene oxide, sulphide and transition mineralisation to a depth of ~300 m and as stratabound hypogene sulphide hosted by carbonaceous and dolomitic shales, principally within the Nifty carbonate member, to a depth of ~600 m.
Hypogene mineralisation is localised in the northeastern limb and hinge of the 15°SE plunging, FY2 Nifty Syncline. It extends for >1200 m down plunge, with a width generally of ~450 m, and a thickness of 0 to 150 m. In addition to the plunge-parallel elongation, high-grade zones are also influenced by a NNW trend, particularly along the northeastern limb of the syncline (Huston et al., 2007). Mineralisation is simple, with the only major sulphide minerals being chalcopyrite and pyrite, and minor sphalerite and galena. It is mostly concentrated in highly silica-altered rocks of the Nifty carbonate member, and to a lesser degree, the pyrite marker bed.
Pyrite occurs in four main textural varieties. The oldest is framboidal, principally within carbonaceous shales, usually as <1 mm laminae of densely packed framboids.The second style is 20 to 200 µm, concentrically zoned, euhedral crystals. Euhedral pyrite also occurs as 50 µm to 10 mm crystals with 100 µm chalcopyrite inclusions.The interface between the two sulphides is commonly ragged, interpreted as evidence of pyrite dissolution. The fourth variant is in bedding parallel replacement zones, associated with quartz, sphalerite, galena and chalcopyrite in silicified shales and hydrothermal quartz-dolomite. The δ34S values for framboidal pyrite range, from -27 to +16‰ (mean -1.2±12.4‰), consistent with biogenic reduction of seawater sulphate (Anderson, et al., 2001). However, the δ34S values from euhedral pyrite are narrower, between -12.0 and +3.8‰ (mean -3.1±3.8‰), whilst chalcopyrite δ34S data range between -6.0 and +6.0‰ (mean -0.8±3.1‰). The close coincidence of mean δ34S vales for all three forms suggest the homogenization of sulphur from diagenetic framboidal pyrite is a possible source of the sulphur in chalcopyrite mineralisation, although Anderson, et al. (2001) question this on the basis of the lack of a similar wide range of sulphur isotope values from chalcopyrite. However, there is ample petrographic evidence of chalcopyrite and sphalerite replacing framboidal pyrite.
Chalcopyrite is dominantly cross-cutting, occurring as isolated spots and blebs, veins following both SY2 foliation and bedding, vein networks, as a matrix to breccias, and replacing carbonate minerals. Cross-cutting relationships suggest chalcopyrite precipitation occurred during DY2 deformation, and preceded bedding parallel mineralisation. Spots and blebs are preferentially found in the distal parts of the deposit, accompanied by pressure shadows of quartz and chlorite. Networks occur where veins following SY2 cleavage intersect bedding parallel mineralisation. Breccias are found in the core of the deposit, where earlier alteration and vein types form clasts with diffuse margins, set in a matrix of chalcopyrite, lesser euhedral pyrite, coarse dolomite and fine quartz. These may well be replacive pseudo-breccias. Replacive textures are the latest and most advanced stage of mineralisation.
Sphalerite is localised in the hanging wall succession, particularly the Pyrite Marker Bed, occurring as a continuous 2 to 20 m thick concordant layer as clots and small bedding parallel lenses. Galena is restricted to the Pyrite Marker Bed, with zones of the two metals not always coincident. Apatite occurs with quartz as 2 to 10 mm veins and stockworks along the fringes of the high grade ore zones, particularly to the SE. These veins also carry accessory to minor chalcopyrite, pyrite, disordered carbon and sphalerite, variable white mica, dolomite and trace galena and rutile. Anomalous uranium (to 1300 ppm), in the form of ningyiote [CaU(PO4)2·1-2H2O], is associated with framboidal pyrite and carbonaceous matter immediately adjacent to the apatite veining. Sm-Nd and U-Pb dating of apatite and galena from these veins gave ages of 791±42 and 811±39 Ma, respectively, which, assuming they are contemporaneous with the introduction of Cu, indicates the age of mineralisation. On the basis of fluid inclusion studies, the brines that formed the Nifty deposit were relatively saline (8 to 27 wt.% NaCl equiv.) and moderate temperature (>270°C; Huston et al., 2007).
Silicification is the dominant ore-related alteration, concentrated in the core of a concentrically zoned alteration pattern of four principal assemblages (Anderson et al., 2001):
i). Black quartz - predominantly microcrystalline silica with abundant enclosed carbonaceous material, euhedral pyrite and irregular chalcopyrite blebs, is restricted to the highest grade ore zones. Carbonaceous material is accompanied by abundant fluorapatite, with minor uraninite and pitchblende. Chemical and textural evidence suggests the black quartz assemblage formed by replacement of an original dolostone, now represented by rare coarsely crystalline dolomite inclusions
ii). Silicified dolomitic shale that forms an outer halo to the black quartz. It is restricted to pyrite-rich sedimentary rocks of the lowermost Hanging wall Beds, Pyrite Marker Bed and uppermost Footwall Beds. Shale and pyrite framboids are overprinted and replaced by quartz, coarse-grained, euhedral to subhedral pyrite±anhedral chalcopyrite ±galena±sphalerite;
iii). Hydrothermal quartz-dolomite, which grades inward from distal isolated 2 to 4 mm thick veins and spots of quartz-dolomite that coalesce to form recrystallised quartz-dolomite zones with wavy laminated quartz layers;
iv). Chloritic shale of limited extent, forms the outermost zone marginal to the quartz-dolomite zone.
Three main stages of veining are recognised. The pre-mineralisation stage includes bedding-parallel dolomite, folded bedding-parallel pyrite-quartz-dolomite and fracture controlled dolomite-quartz veins. Syn-mineralisation veins comprise chalcopyrite-dolomite, and cleavage parallel dolomite-quartz with trace chalcopyrite, in both the core of the alteration system and its margins. Post-mineralisation veining consists of coarse quartz and bladed carbonate (Anderson et al., 2001).
The supergene profile at Nifty resulted from weathering, oxidation and vertical redistribution of copper within the steeply dipping hypogene mineralisation along the northeastern limb of the Nifty Syncline. The resultant zoned supergene profile comprises an upper ~40 to 80 m of predominantly barren (hundreds to thousands of ppm Cu), limonitic and siliceous rock, the remnant of several hundred metres of eroded and leached hypogene mineralisation. This is progressively underlain by malachite±azurite, then malachite±cuprite±tenorite, followed by native copper and chalcocite zones, and finally via a transition to chalcopyrite of the hypogene mineralisation. A related flat lying, transgressive blanket of supergene oxide mineralisation is predominantly composed of malachite±azurite, hosted to the SW by the pyrite marker bed and the hanging wall beds, and to a lesser degree the footwall beds to the north. It is ~15 m thick and occurs at the same ~40 to 80 m depth as the similar malachite zone in the steep supergene zone. This blanket extends for up to 400 m laterally from the stratabound mineralisation, and is localised between the base of oxidation and the pre-mining water table.
Copper in both the concordant and transgressive supergene zones was derived from the same steeply dipping limb of the stratabound sulphide deposit. Weathering and resultant solution of Cu from hypogene sulphides formed an oxidised, low pH, cupriferous solution that was transported vertically and laterally down the hydrological gradient to flow along the paleo-water table. At the water table, the pregnant solution was neutralised by the un-oxidised carbonaceous pyritic enclosing sequence, drastically reducing the solubility of Cu. Dissolution and precipitation of Cu initially formed a supergene sulphide blanket at the water table, with initial chalcocite coating of hypogene chalcopyrite and pyrite culminating in complete replacement. A subsequent pulse of uplift and/or erosion lowered the water table and base of oxidation. This oxidised the existing chalcocite blanket to a malachite dominated assemblage, but also dissolved section of the chalcocite blanket to produce deeper supergene sulphide accumulations overprinting the main hypogene mineralisation.
Regional Mineral System
The hypogene mineralisation at nifty and Maroochydore is part of a basin-scale mineralised system related to fluid circulation within the sandstones of the Coolbro Formation, interacting with the Rudall Complex below, and Broadhurst Formation above (Huston et al., 2010). Deposition within the Yeneena Basin occurred between ~850 and 824 Ma in an extensional rift setting. Basinal brines were generated as the result of diagenesis when the pile exceeded ~10 km, and collected within aquifers of the permeable, siliceous, oxidised Coolbro Formation. From ~835 Ma, the generation and convection of these fluids was promoted by the continental scale mafic underplate of the Gairdner Large Igneous Province. These fluids scavenged metals and salts from the Yeneena Supergroup and from the upper Rudall Complex where structural permeability permitted (Huston et al., 2010). Where fluids encountered extensional faults prior to basin inversion, they could flow downward into the Rudall Complex basement. This was achieved by diagenetic brine reflux (or thermohaline convection) whereby dense brines displace lighter, hotter pore water at depth. Where suitable trap rocks were intersected in the basement or at the unconformity (e.g., graphitic or iron-rich rocks), uranium and related elements were precipitated to form deposits such as Kintyre at ~835±23 Ma (pitchblende age; Huston et al., 2010).
The onset of basin inversion from ~824 to 810 Ma (as proposed by Huston et al., 2010), reactivated prominent NW- to NNW-trending growth faults of the extensional phase to form dextral strike-slip and reverse faults, as well as recumbent folds within the Throssel Range Group. This corresponded to DY1 and DY2 deformation. The change of stress field to contraction and increase in lithostatic pressure was no longer compatible with downward fluid flow. Overpressured brines began to rise from the Coolbro Sandstone aquifer following thrust conduits that permitted cross-formational access to the reduced sulphide and carbonate rich shales of the upper Broadhurst Formation. Rare mafic intrusions to 816 Ma imply the Gairdner mafic igneous underplate was still influencing fluid circulation. Oxidised brines likely scavenged Cu from the arkosic sands of the Coolbro Formation, mafic rocks from the upper Rudall Complex and possibly Gairdner mafic intrusions. These sources are respectively inferred by evolved Sr isotopic data and relatively primitive hydrothermal Nd in fluid inclusions. The oxidised >270°C brines were reduced by the Nifty carbonate member. Copper was precipitated to react with sulphur released from the strongly pyritic beds and possibly anhydrite bearing carbonate rocks of that unit. This interaction formed the stratabound chalcopyrite rich carbonate replacement and silica-dolomite veining of the Nifty deposit between 811±39 and 791±42 Ma (Huston et al., 2007; 2010).
After a tectonic lull, punctuated by the emplacement of mafic dykes and sills between 750 and 700 Ma, a widespread granitic intrusive event between 645 and 605 Ma, is temporally coincident with the ~650 to 645 Ma sediment hosted Telfer Au-Cu deposit. Mineralisation at Telfer is hosted within the Malu Formation sandstone dominant succession of the Lamil Group, and as at Nifty, is associated with sulphidic quartz-carbonate veining with a strong stratigraphic and structural control. However, apart from the age and host sequence, Telfer. differs in the preponderance of extensive concordant veining concentrated in domal crests, the presence of significant gold, and the absence of extensive reduced sulphidic host rocks. See the separate Telfer record for detail.
Reserves, Resources and Production
WMC Resources originally published the following resources in 1991:
Oxide resource - 12.2 Mt @ 2.52% Cu
Primary sulphide resource - 26.3 Mt @ 4.6% Cu at a 2% Cu cutoff.
Prior to underground operations Straits Resources Limited outlined a reserve of 25.5 Mt @ 2.7% Cu and a resource of 39 Mt @ 2.5% Cu.
Straits Resources Ltd, estimated a global resource in 2000 of 99 Mt @ 1.63% Cu at a 0.5% Cu cut-off (Anderson et al., 2001).
Production, resources and leach pad (Huston et al., 2010
Production 1993 to 2009 - 16 Mt @ 2.4% Cu
Remaining resource, 2009 - 45.29 Mt @ 2.3% Cu
On leach heap, 2009 - 15.67 Mt @ 0.4% Cu
Remaining underground reserves at 31 March, 2012, were as follows (Aditya Birla, 2012):
Proved reserves - 22.04 Mt @ 2.3% Cu,
Probable reserves - 5.1 Mt @ 1.1% Cu,
Total reserves - 27.14 Mt @ 2.1% Cu,
Open pit resources recoverable by leaching (additional to underground reserves) at 31 March, 2012, were as follows (Aditya Birla, 2012):
Measured resources - 31.65 Mt @ 2.3% Cu,
Indicated resources - 8.70 Mt @ 1.1% Cu,
Inferred resources - 4.94 Mt @ 1.1% Cu,
Total resources - 45.29 Mt @ 2.1% Cu,
Remaining ore reserves and mineral resources at 31 March 2017, were as follows (Metals X Limited, 2016):
Ore Reserve - 9.75 Mt @ 1.58% Cu;
Mineral Resource - 54.84 Mt @ 1.41% Cu (includes reserves), composed of
Measured - 21.73 Mt @ 1.81% Cu,
Indicated - 19.42 Mt @ 1.25% Cu,
Inferred - 13.69 Mt @ 1.12% Cu,
made up of total resources for each ore type,
sulphide ore - 47.2 Mt @ 1.51% Cu,
oxide ore - 4.33 Mt @ 0.86% Cu,
heap leach - 3.31 Mt @ 0.74% Cu.
The most recent source geological information used to prepare this summary was dated: 2010.
Record last updated: 14/8/2017
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.
References to this deposit in the PGC Literature Collection:
Anderson B R, Gemmell J B, Berry R F 2001 - The geology of the Nifty Copper deposit, Throssell Group, Western Australia: implications for ore genesis: in Econ. Geol. v96 pp 1535-1565|
Huston D L, Maas R and Czarnota K, 2007 - The age and genesis of the Nifty copper deposit: back to the future: in Geoscience Australia Professional Opinion 2007/03 26p.|
Huston, D L, Czarnota, K, Jaireth, S, Williams, N, Maidment, D, Cassidy, K F, Duerden, P and Miggin, D, 2010 - Mineral systems of the Paterson region: in Roach, I C, (ed.), 2010 Geological and Energy implications of the Paterson airborne electromagnetic (AEM) survey, Western Australia, Geoscience Australia, Record 2010/12, pp. 155-218.|
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