Carrapateena, Khamsin, Fremantle Doctor
South Australia, SA, Australia
Cu Au U
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The Carrapateena iron oxide copper-gold deposit, which is located within the Olympic IOCG Province on the eastern rim of the preserved Gawler craton in northern South Australia. It is ~100 km SSE of Olympic Dam and ~130 km north of Port Augusta in South Australia, immediately to the SW of the Carrapateena embayment on the central-western shore of Lake Torrens.
Exploration and Discovery
Following the discovery of the Olympic Dam IOCG deposit in 1975, the Gawler craton was subjected to increased exploration activity. In the immediate Carrapateena area, this resulted in a number of holes being drilled at the Salt Creek prospect in the late 1970s and early 1980s by a joint venture partnership of Carpentaria Exploration and Seltrust, targeting gravity and/or aeromagnetic highs. Salt Creek is approximately 10 km northwest of where Carrapateena was later to be discovered. One of these holes, SASC04, was completed at 1250 m and intersected hematite-sericite altered granitoids of the Mesoproterozoic Donington Suite from a depth of 540 m to the bottom of the hole, but without significant associated copper mineralisation. The titles held were subsequently relinquished, although preservation of the core at the South Australia Drill Core Reference Library provided important encouragement and information for later explorers (Fairclough, 2005; Vella and Cawood, 2006). In the mid-1990s, RMG Services Pty Ltd (RMGS) applied for Exploration Licenses to the south of Carrapateena, in the southern part of Lake Torrens, with the aim of providing salt for a proposed petrochemical plant at Port Bonython. During subsequent research in the Geological Survey of South Australia, the principal of RMGS, Rodolfo Gomez, was attracted to the potential for IOCG mineralisation in the Gawler craton. As a consequence, the company applied for EL 2170 (subsequently EL 2879) in 1996, based on the premise that the presence of the Torrens Hinge Zone through the area made it prospective for this style of mineralisation (Vella and Cawood, 2006). The Torrens hinge zone marks the transition from the thick Neoproterozoic succession of the Adelaide Geosyncline intracratonic rift complex to the east, and the flat lying equivalent sedimentary sequences of the Stuart Shelf that overlie the Meso- and Palaeoproterozoic, and Archaean rocks of the eastern Gawler craton which host the major IOCG deposits.
Interpretation of regional aeromagnetic and gravity data, acquired by the Geological Survey of South Australia, indicated an Olympic Dam style potential field anomaly at Carrapateena. Additional gravity data was collected by a joint venture of RMGS and General Gold Resources Ltd., confirming the presence of a discrete gravity response. In 2003-04, a joint venture was formed between MIM Exploration Pty. Ltd. (formerly Carpentaria Exploration), Terramin Australia Ltd. and RMGS, and further gravity data collected. MIM also completed six 5 km long, 200 m spaced (north-south) lines of induced polarisation (IP) and magnetotelluric (MT) surveying, using its then proprietary MIMDAS system (Fairclough, 2005). Although interesting anomalies were detected on the northern end of two of the MIMDAS lines, MIM withdrew from the JV due to corporate issues related to their takeover by Xstrata. Terramin also withdrew soon after to concentrate their attention on other projects (Vella and Cawood, 2006, Fairclough, 2005). Many geophysical similarities to the Olympic Dam deposit were recognised by Chris Anderson and Associates, consultants to RMGS. These included broadly coincident gravity and aeromagnetic anomalies, although of a much lower magnitude with gravity peaks of ~2.5 mGal, compared to 17 mGal at Olympic Dam, 22 mGal at Acropolis and 6 mGal at Wirrda Well, and magnetic highs of ~200 nT, compared to the ~1600 nT at Olympic Dam, ~5500 nT at Acropolis and ~1800 nT at Wirrda Well (Vella and Cawood, 2006). It should be noted however, that the northern part of the Olympic Dam-Carrapateena district is dominated by strong, areally extensive magnetic responses, due largely to broad magnetite alteration, encompassing the Olympic Dam, Acropolis and Wirrda Well mineralised systems which are all characterised by strong, discrete magnetic anomalies. In contrast, to the southeast, Carrapateena is situated on the edge of a weak magnetic anomaly, within a more subdued magnetic regime.
A 3D geological inversion of geophysical data also proved encouraging, as was the recognition of a slight offset, but otherwise broad coincidence, between the gravity and magnetic peaks (Fairclough, 2005). The Carrapateena deposit is situated on the southwestern margin of a broad, diffuse and weak to moderate amplitude magnetic anomaly with a 200 nT peak, with more recent detailed data revealing it is associated with a superimposed weak but more discrete, north-south elongated ellipsoidal magnetic anomaly (Vella and Cawood, 2006). The gravity anomaly at Carrapateena, which is also ellipsoidal, has an amplitude of ~2.5 mGal and a diameter of ~3.5 km, forming a discrete bullseye over the deposit. This anomaly is part of a larger subdued NE-trending gravity anomaly, the geometry of which is influenced by NE striking faults superimposed upon the overall NW oriented structural grain of the surrounding area. The NE gravity trend extends for a further 2 km to the subsequently discovered Fremantle Doctor prospect and is interpreted to represent a continuation of iron oxide alteration along a NE structural zone. The Carrapateena magnetic anomaly also lies within a broader, moderate amplitude, NW-trend, interpreted to reflect a mafic intrusive body. The SW boundary of gravity and magnetic anomalies are defined by a prominent NW-trending structure. This structure is evident in the regional magnetic data and extends to the subsequently discovered Khamsin deposit (Sawyer et al., 2017).
Interpretation of the MIMDAS data suggested a deep conductive zone coincident with, or slightly north of the 'coincident' gravity and magnetic response. Modelling of chargeability data produced more ambiguous results, with anomalous responses interpreted to be at shallower depths within the Neoproterozoic cover rocks (Vella and Cawood, 2006, Fairclough, 2005).
In 2005, RMGS applied for funding from the South Australian Government’s PACE exploration incentive program to finance four drill holes to test the anomalies, later to be reduced to two, the first targeting the MIMDAS and the second, the discovery hole, to test the coincident gravity and magnetic anomalies. The first of these holes, CAR001 commenced with a 240 m reverse circulation (RC) pre-collar that was terminated in cover sequence Woomera Shales. The diamond core tail continued on through the cover sequence and then intersected a broad zone of basaltic rocks to a total depth of 571 m, with reported steely hematite and crackle breccia, but no significant mineralisation.
It is now apparent that CAR001 was sited within 100 m outside of the Carrapateena Breccia Complex (CBC), and less than 200 m from the main copper-sulphide zone of the Carrapateena ore deposit. The second hole CAR002, which was vertical and collared 500 m due south of CAR001, had a 299 m RC pre-collar, again ending in cover shales, before the diamond core tail which was completed at a total depth of 654.2 m in June 2005. The hole passed into basement at 476 m, from where it intersected 178.2 m of variable intensity hematite alteration, sulphide development and brecciation of the CBC to the end of the hole. This mineralised interval averaged 1.83% Cu, 0.64 g/t Au, 0.21% Ce, 0.13% La and 59 ppm U (Vella and Cawood, 2006, Fairclough, 2005).
Teck Resources Limited acquired an interest in the project later the same year, becoming the manager. Over the following years the deposit was delineated and a maiden resource estimated. However, by 2011 Teck determined that Carrapateena did not fit the company's long range development plans, and reached an agreement with OZ Minerals for the latter to acquire the asset. OZ Minerals continued delineation of the deposit and then undertook a feasibility study which recommended an underground sub-level cave operation. Following a three-year construction period, the first concentrate was produced in December 2019.
Carrapateena, Olympic Dam, Prominent Hill, Moonta-Wallaroo and Hillside and all of the other significant known IOCG mineralised systems of the Gawler craton are hosted within Palaeo- to Mesoproterozoic rocks and are distributed along the eastern edge of the currently preserved craton to define the Olympic IOCG Province.
The oldest rocks of the Gawler craton comprise Mesoarchaean to early Palaeoproterozoic metamorphics and igneous suites that form a core to the craton, immediately to the west of the Olympic IOCG Province. On its eastern margin, and within the Olympic IOCG Province, this older nucleus was overlain after ~2000 Ma by the Hutchison Group, a sequence of subaerial to shallow marine clastic and chemical metasedimentary rocks, with minor felsic and mafic volcanic rocks, that were deposited on a continental passive margin (Parker, 1993; Daly et al., 1998). Along the eastern margin of the craton, including the Carrapateena district, the cratonic core and the Hutchison Group were both intruded by ~1850 Ma granitoids of the Donington Suite during the Cornian orogeny (Hand et al., 2007; Reid et al., 2008). This suite is dominated by granodiorite gneiss, with subordinate metamorphosed alkali-feldspar granite, gabbronorite, tonalite and quartz monzonite intrusions with mafic dykes (Ferris et al., 2002). Between ~1770 and 1740 Ma, subsequent to the emplacement of the Donington Suite, extension along the eastern, northern and western margins of the craton, resulted in the development of a series of extensive basins, some of which contain bimodal volcanic rocks, including the Wallaroo Group, which is extensively developed within the Olympic IOCG Province and is an important host to IOCG alteration and mineralisation. During the Palaeoproterozoic, the Curnamona Province is believed to have collided with and been accreted to the Gawler craton in the east. A major linear discontinuity in magnetic and gravity data beneath the Neoproterozoic cover of the Adelaide Geosyncline intracratonic rift complex is interpreted to mark the suture zone (Hayward and Skirrow, 2010, and sources quoted therein). The interval between ~1730 and ~1630 Ma encompasses both the Kimban Orogeny (1730 to 1690 Ma), Ooldean Event (1660 to 1630 Ma), and the widespread emplacement of various felsic igneous rocks, and formation of several small intracontinental sedimentary basins (Hand et al., 2007).
Towards the close of the Palaeoproterozoic, from ~1630 to 1615 Ma, the Nuyts Volcanics and St Peter Suite bimodal magmas were emplaced in the southwestern part of the Gawler craton, which although poorly exposed, cover an extensive area (Fanning et al., 2007). Between ~1600 and ~1575 Ma the centre of magmatism shifted eastward with the development of the high-volume intrusive Hiltaba Suite and extensive co-magmatic bimodal Gawler Range Volcanics (GRV) to form a large felsic igneous province (covering a preserved area of >25 000 km2) over the central and eastern parts of the Gawler craton, including the Olympic IOCG Province. Between 1580 to 1550 Ma, magmatism progressed eastward to form the Benagerie volcanics and Bimbowrie Suite I- and S-types in the Curnamona Province, the easternmost development of the diachronous eastnortheast-trending corridor of continental I- and A-type magmatism that extends across the Gawler and Curnamona cratons from the St Peter Suite in the southwestern part of the craton (Hayward and Skirrow, 2010).
Known significant IOCG districts/deposits within the Olympic IOCG Province, including Carrapateena, are found where oxidised (magnetite-series), A-type granitoid plutons of the 1595 to 1575 Ma Hiltaba Suite which were emplaced into an accreted Palaeoproterozoic terrane, and where mafic volcanic rocks of the lower GRV are most abundant. These rocks were emplaced during a short-lived episode of NNW-SSE extension that approximately coincided with eruption of the GRV (~1595 to 1590 Ma), preceded and followed by more protracted NW-SE to NNW-SSE contraction (Hayward and Skirrow, 2010).
Tectonism subsequently appears to have migrated northwards and westward, with the ~1570 to 1540 Ma Kararan and 1470 to 1440 Ma Coorabie orogenies respectively. The Archaean to Mesoproterozoic crystalline basement rocks of the Gawler craton were not subjected to any substantial deformation after ~1450 Ma until the early Palaeozoic Delamerian orogeny (Parker, 1993). Much of the Olympic IOCG Province is overlain by flat lying Neoproterozoic to Lower Palaeozoic sedimentary rocks of the Stuart Shelf, equivalents of the sedimentary succession of the Adelaide Geosyncline intracratonic rift complex which separates the Gawler craton and Curnamona Province and was the result of extension preceding and during the rifting and break-up of the Rodinia supercontinent from immediately to the east of the Curnamona Province.
The Carrapateena deposit is hosted by the variably deformed quartz granite and quartz diorite of the Donington Suite, regionally variously dated from 1843 ±4.1 Ma on Yorke Peninsula to 1860.4 ±4.1 Ma elsewhere in the Olympic Domain, but with an age of 1857 ±6 Ma at Carrapateena (dates all U-Pb zircon; Jagodzinski, et al., 2007). This intrusion is interpreted to occur as an extensive, up to 30 x 15 km block, bounded to the east by the Torrens Hinge Zone and to the west by the Gawler Range Volcanics and metasedimentary rocks of the Hutchison and Wallaroo Groups. In the vicinity of Carrapateena, it is characteristically coarse- to medium-grained, with a weak to moderate foliation, and shows increasing brecciation towards the margins of the deposit.
The Palaeo- to Mesoproterozic rocks are unconformably overlain by clastic sedimentary units of the 1424 ±51 Ma Pandura Formation (Fanning, Flint and Preiss, 1983) and intruded by NW-trending, regional 827 Ma Gairdner Dyke Swarm representing a large igneous province (Wingate et aI., 1998). The Pandurra Formation is unconformably overlain by Neoproterozoic sedimentary rocks of the Stuart Shelf. In the immediate Carrapateena deposit area, the Pandura Formation is absent. The cover sequence unconformably overlying the host Donington Suite basement is ~470 m thick, and belong to the ~650 to 635 Ma Marinoan age Umberatana and Wilpena groups, as follows:
• an up to 10 m thick, variably developed basal conglomerate composed of well rounded clasts of granite, volcanic rocks, quartz and hematite, some of which are mineralised, within a fine grained matrix;
• Whyalla Sandstone, which is ~65 m thick and has been assigned to the Umberatana Group. The basal suite is composed of variably gritty siltstones to sandstones with minor, locally stromatolitic, dolostone interbeds (Vella and Cawood, 2006). These have been stratigraphically subdivided into ~40 m of shales and siltstones of the Angepena Formation at the base, overlain by ~30 m of the Reynella Siltstone, with ~10 m of dolostones of the Nucceleena Formation at the top;
• Tregolana Shale Member, previously the Woomera Shale Member, which is ~270 to 300 m thick, and belongs to the Wilpena Group. It is composed of dark red-brown shale with blue-grey silty interbeds;
• Cooraberra Sandstone, comprising ~25 to 40 m of purple-brown, medium‐ to fine-grained arenite;
• Simmens (or Arcoona) Quartzite Member, which is made up of ~90 m of coarse‐grained quartzite that is exposed throughout the region (Vella and Cawood, 2006).
See also the Gawler Craton and Olympic IOCGU Province record for a more detailed outline of the regional setting.
Image below - Simplified schematic sketch block-model of the Carrapateena copper-gold deposit showing the stratigraphic setting; the extent of the bornite and chalcopyrite ±pyrite and hematite breccia zones at the unconformity between the Mesoproterozoic host Donington Suite granitoids and the Neoproterozoic cover rocks (after Brodovcky, 2010; Tiddy, 2021; see the following image for more detail); and the generalised shape, dimensions and distribution of the copper-gold ore zones below this surface (interpreted from a ‘wire-frame’ model in Brodovcky, 2010; OZ Minerals Mineral Resource sections reproduced in Credit Suisse Research Report, 2014; OZ Minerals Pre-Feasibility Study, 2016; Sawyer, 2013; Sawyer et al., 2017; OZ Minerals ASX release block model 2019; Tiddy et al., 2021). The deposit has a bornite dominant core that is partially enwrapped to the northwest by a steeply plunging, lensoid to sheet-like zone of barren, massive, commonly grey, vuggy breccia (shown in mauve) that has been completely altered to hematite. This barren breccia is in contact with, and defines the northwestern limit of the bornite core. The bornite core is mantled on the other three sides by a chalcopyrite ±pyrite rich zone, that, in turn, passes into a pyrite-chalcopyrite periphery, corresponding to a generally outward and downward decreasing chalcopyrite:pyrite ratio (Sawyer et al., 2017). The deposit is hosted within, and is surrounded by a fringe of hematite breccia.
The Carrapateena deposit is hosted by strongly brecciated granitoids (variably foliated and/or sheared gneissic quartz-granite and quartz-diorite) which have been dated at 1857 ±6 Ma (U-Pb zircon; Jagodzinski, et al., 2007) and are assigned to the Palaeoproterozoic Donington Suite. It occurs within the core of a north-south oriented, 30 x 100 km mass of that suite, that is overlain 10 to 15 km to the west by ~1590 Ma mafic and felsic volcanic rocks of the Gawler Range Volcanics, that are comagmatic with the Hiltaba Suite granitoids that host the Olympic Dam deposit.
The ore deposit lies beneath a ~470 m thickness of flat-lying Meso- and Neoproterozoic sedimentary cover rocks as described above. It has a north-south elongated area of ~800 x 600 m where truncated by the unconformity surface above the Palaeoproterozoic host rocks. The deposit was exposed to surficial oxidising conditions prior to deposition of the cover sequence, with a well-developed upper leached iron-oxide zone at the unconformity. This zone of oxidation is ~20 m thick and is in part moderately vuggy. It does not contain significant copper or gold mineralisation, but is underlain by an interval averaging 4 m thick with gold grades that exceed those of the underlying sulphide mineralisation. In addition, in the upper few metres of sulphide mineralisation the copper minerals typically have a lower sulphur content but similar Cu grades to the underlying mineralisation. For example, chalcocite can occur above bornite, or bornite above chalcopyrite. No oxide copper minerals have been observed (Sawyer et al., 2017).
Mineralisation is confined to a near vertically plunging, pipe-like body composed of hematite-sericite-chlorite-carbonte breccias, the Carrapateena Breccia Complex (CBC). This pipe is interpreted to be developed adjacent to a NE to NNE-trending complex zone of faulting and occurs at the junction with an intersecting, prominent, NW- trending structure evident in aeromagnetic data. The latter fault also appears to be associated with the Oak Dam and Wirrda Well IOCG deposits (Hayward and Skirrow, 2010).
The lateral extent of the pipe tapers at depth, but mineralisation is known to extend to ~1900 m below the unconformity. The composition and intensity of the breccia complex varies from weakly brecciated granite, through monolithic and heterolithic clast- to matrix-supported hematite-rich breccias. Granitoid clasts (or preserved clasts) become less frequent and more rounded towards the centre of the breccia complex, whilst the degree of alteration becomes more intense. The hematite content also varies from traces to complete replacement. Clasts and fragments within the breccia complex are derived from Donington Suite granitoids, metasedimentary gneiss and schist, and the Gawler Range Volcanics. They are predominantly medium grained, gneissic diorite, with granite gneiss and vein quartz, variably altered to chlorite, sericite and hematite. There are also hematite-dominated clasts of earlier breccia phases within a matrix with a variety of textures that have also been altered to an assemblage of hematite, quartz and sericite. Relict clasts and fragments are commonly completely altered to hematite. Where granitic clasts are present within the complex, sericite alteration (after feldspar) is prevalent. Clast shape is highly variable, ranging from angular to well-rounded. Many of the latter clasts are milled and rounded such that the 'breccia' may have the appearance of a 'conglomerate' when samples are viewed in isolation. Rounded, colloform-banded (ex-carbonate), pebble and cobble-sized hematite/sulphide clasts are common, particularly in more intensely altered grey hematite breccias. Granite-rich breccias are commonly clast-supported and exhibit crackle and 'jigsaw' textures near the margin of the breccia pipe, and have been subjected to red-brown hematite alteration. Mafic and felsic dykes are found near the margins of the breccia complex. However, there are locally zones where the dominant or only clast type is from these dykes (Sawyer et al., 2017).
Some rocks within the deposit, have well-developed graded bedding and are predominantly composed of sand and silt-sized rounded quartz and hematite grains, and are interpreted to be sedimentary origin. U-Pb dating of detrital zircons from these interspersed fine-grained 'sediments' indicates they were derived primarily from 1847 ±12 Ma Donington Suite intrusives (Sawyer et al., 2017). In addition, a weakly mineralised chloritic rock with the appearance of a conglomerate containing well-rounded Gawler Range Volcanic, clean quartz and other lithic clasts, set within a fine grained matrix, occurs within the deposit, containing detrital zircons which are predominantly dated as Mesoproterozoic, with a minor Paleoproterozoic population (Sawyer et al., 2017). These sedimentary and volcano-sedimentary rocks are chlorite and hematite altered, but barren of sulphides and REE mineralisation (Neumann, 2019). Well mineralised and altered rocks, interpreted to represent internally derived 'sediments', have been recognised in the central parts of Carrapateena and the upper sections of Khamsin (Neumann, 2019).
The principal zones of economic Cu and Au mineralisation at Carrapateena are hosted by hematite breccias as discussed below, with higher grade copper intersections are typically associated with a grey hematite matrix within strongly brecciated granite. However, as at Olympic Dam and Prominent Hill, there is also a 'barren' hematite breccia zone located towards the northern margin of the deposit. This barren zone is characterised by massive, frequently vuggy grey hematite breccias which have been leached of almost all silicates, with sulphides being visually absent.
Two dominant end member alteration assemblages are differentiated at Carrapateena (Sawyer et al., 2017). These are frequently found separately, but are not mutually exclusive, usually occurring as varying combinations or transitions between both. They are:
• Hematite-white mica ±quartz which predominates in the upper 500 m of the breccia complex. Hematite is the dominant alteration mineral within the breccia complex, ranging from selective replacement of specific minerals in the host granite, to infill between clasts in breccias of various textures, through to massive total hematite replacement of clasts and matrix in the barren hematite zone. Hematite also occurs as clasts in hematite-infill breccia, whilst some altered clasts have banded colloform textures suggestive of replacement of carbonate (Sawyer et al., 2017).
Locally, hematite has textures indicating replacement of magnetite. Magnetite is found, together with hematite as breccia infill, in some parts of the deposit, particularly in the south. Where magnetite is present, so is chlorite typically, along vvith pyrite and minor chalcopyrite, and in some instances siderite (Sawyer et al., 2017).
As the abundance of hematite increases, so does the alteration of protolith feldspars to white mica. Plagioclase and K feldspar may both be preserved within tens of metres laterally from the deposit in rocks that lack significant hematite alteration, other than a regional dusting of feldspars. In rocks that have been moderately hematite-altered, plagioclase is typically absent although potassic feldspar may still be abundant, but in zones of intense hematite alteration and brecciation, both feldspars are absent, having been altered to micas. As such, fine grained white-mica alteration typically occurs with hematite, and this hematite-white mica assemblage is commonly associated with high Cu-grade mineralisation. Bulk rock geochemistry of samples where white mica is the dominant aluminosilicate suggests that its composition is K-rich and approximately equivalent to muscovite. Electron microprobe analyses, however, indicate that the composition of white mica is more variable in detail (Sawyer et al., 2017). Electron microprobe and bulk rock geochemistry both indicate that mica in mineralised samples at Carrapateena is low in F, unlike the high-F micas that occur at Olympic Dam (McPhie el al., 2011).
In some parts of the barren hematite zone, white mica occurs in hematite-altered rocks where other silicate minerals (including quartz) are noticeably absent. This differs from Olympic Dam and Prominent Hill, where the most iron-rich rocks arc described as hematite-quartz breccias (Reeve el al., 1990) and iron oxide-silica alteration to steely hematite (Belperio, Flint and Freeman, 2007) respectively.
• Chlorite ±hematite, which predominates within the breccia complex deeper than 500 m below the unconformity. Chlorite alteration is commonly found as a replacement, particularly of feldspars, but may also be intergrown with minerals that have textures suggestive of hydrothermal infill. It is often spatially separated from white-mica alteration, although the two may occur together. Microprobe analysis of selected chlorite grains indicate they contain more Fe than Mg, and can be described as a chamosite. Whilst chlorite and hematite commonly occur together, zones of dominantly chlorite alteration generally have a low hematite content. Hematite replacement textures after chlorite have been recorded. Chlorite alteration may also be distributed regionally within the Donington Granite, as is fine-grained hematite and white mica, although district-scale alteration tends to be much less intense compared to that within or near to the breccia complex (Sawyer et al., 2017).
Carbonate minerals are typically found as infill and clasts. Some late carbonate veins are recognised, although only representing a small proportion of the carbonate content of the breccia complex. Carbonate is irregularly distributed, with siderite and ankerite being the more common form in the mid-upper drilled part of the deposit, whereas dolomite is more abundant at depth. Other accessory alteration minerals include barite, anhydrite (particularly in the barren hematite zone), fluorite (that is typically accompanied by chlorite rather than white-mica), florencite, bastnasite and monazite (Sawyer et al., 2017).
Sulphide mineralisation occurs as disseminated grains that range in size from 0.1 to 4 mm, and are intimately associated with hematite. The bulk of the economic mineralisation at Carrapateena is hosted within hetorolithic hematite-rich breccias. The principal hypogene sulphide minerals are pyrite, chalcopyrite, bornite and minor chalcocite. Hypogene copper mineralisation was formed by direct precipitation as open-space pore fill and by replacement of pre-existing pyrite. Copper sulphide veins are relatively minor. Pyrite exhibits evidence of replacement by chalcopyrite, which may then be subsequently replaced by bornite. Re-Os isotopic analysis and dating of pyrite reported by Sawyer et al. (2017) from two samples of pyrite-bearing hematite breccia gave a weighted average age of 1598 ±6 Ma, considered to indicate the timing of the initial phase of sulphide mineralisation. The deposit also contains rare earth element (REE) and U-bearing minerals with monazite and uraninite being the dominant ore minerals respectively. Both have a close spatial and temporal relationships with bornite (Sawyer et al., 2017).
As illustrated in the image above, copper sulphide mineralisation at Carrapateena has been divided into zones that are characterised by i). bornite and ii). other copper sulphides, principally chalcopyrite and pyrite with lesser accompanying bornite. Note however, that while the main resource has a high grade core of bornite, these zones are not necessarily reflective of grade, but rather the principal copper sulphide present.
The main resource is cored by a near vertical 'cylinder' of high grade bornite rich mineralisation hosted by hematite breccias generally containing >90% hematite. This bornite core is bounded on its northeastern margin by a barren, irregular sheet of extreme hematite altered breccia, while it is mantled on its other three sides by a chalcopyrite dominant zone which, grades outward and downward to chalcopyrite-pyrite and pyrite-chalcopyrite assemblages with the increase in pyrite and corresponding decrease in Cu content. Over the same interval, the tapering of Cu grades broadly corresponds to a decrease in the intensity of hematite alteration. The eastern side of the barren hematite breccia sheet is fringed by mainly pyrite-chalcopyrite mineralisation, known as the 'Eastern pyrite-chalcopyrite zone' (Sawyer et al., 2017). The eastern bornite zone, into which the discovery hole CAR002 was drilled, appears to be more limited in extent, hosted within hematite breccia containing >90% hematite, and adjacent, less intensely altered brecciated granite.
Compared to the surrounding Donington Granite, the breccia complex contains enhanced levels of Cu, Au, S, Mo, W, U, Fe, Co, light rare earth elements (LREE), Eu, Nb, Te, Bi, Ni, Se, Nd, Ag, P, heavy REE (HREE) and Sn; but is relatively depleted in K, Rb, Na, Cs, AI, Si, Hf, Zr and Ti. The bulk of the deposit has lower concentrations of Ba and F compared to the surrounding granite, although there is considerable variation at the local scale. Carbon, Ca, Mg and Mn vary localy, depending on the carbonate mineralogy and distribution (Sawyer et al., 2017).
Zn and Pb concentrations tend to increase on the periphery of the deposit compared to the core of significant Cu mineralisation, while some dykes contain elevated Zn. Where chalcopyrite is the dominant Cu sulphide, the relationship between Au, Ag and U becomes erratic, although where bornite predominates, average Ag and Bi grades are higher than in the chalcopyrite zones. The barren hematite zone has higher average grades of Fe, light REE and Au than zones containing visible copper sulphide mineralisation (Sawyer et al., 2017).
A study of the chemistry of hydrothermal monazite associated with IOCG mineralisation at Carrapateena by Tiddy et al. (2021), has recognised a correlation with elevated LREE with >22.5 wt.% La; >37 wt.% Ce and >63 wt.% La+Ce, accompanied by depletion of Y and/or Th to <1 wt.%, and Nd of <12.5 wt.% within such monazite grains. These contrast with background levels of <45 wt.% La+Ce and >1 wt.% Y and/or Th, which may indicate monazite that is of metamorphic origin or associated with shear zones. These geochemical observations are supported by a similar investigation at Prominent Hill (Forbes et al. (2015). However, in contrast to Prominent Hill, mineralisation at Carapateena also appears to overlap into fields where monazite grains have La+Ce intermediate values between these limits, i.e., 63 and 45 wt.%, but <1 wt.% Y and/or Th, and preserved Nd of >12.5 wt.%. The two studies have also demonstrated that these geochemical signatures can survive weathering, erosion, transport/dispersion and redeposition into younger cover sequence materials that overlie mineralised basement rocks and provide a footprint to mineralisation larger than the deposit alone. This was best shown in samples collected up to a metre, and sometimes more, above bedrock in Neoproterozoic diamictites at Carrapateena and Permian glacials at Prominent Hill. These anomalous monazites were found in cover diamictites that also contained clasts of hematite breccia, skarn altered and granite clasts (Tiddy et al., 2021). At Prominent Hill, the these analyses in isolated grains of monazite corresponded to whole-rock values of >75 ppm La and >155 ppm Ce taken to be anomalous, and (La+Ce):Y and (La+Ce):Th ratios of >30:1 and 32:1, respectively, considered 'compelling'. This assumes all light rare earth elements in the cover sequence are hosted within monazite (Forbes et al. (2015).
Reserves and Resources
An audited inferred (OZ Minerals, 2011) resource for the main deposit, in the southern half of the deposit area, at a cut-off of 0.7% Cu, totals:
203 Mt @ 1.31% Cu, 0.56 g/t Au, 0.27 kg/t U308, 6 g/t Ag;
The northern half, has a potential to contain a further:
25 to 45 Mt @ 1.0 to 1.1% Cu, 0.4 g/t Au, 0.14 kg U308.
The estimated Mineral Resource at 31 October 2012 (Oz Minerals ASX Release, 21 January, 2013) has been upgraded to:
Indicated Resource at
0.3% Cu cut-off - 392 Mt @ 0.97% Cu, 0.39 g/t Au, 165 ppm U, 4.2 g/t Ag;
0.5% Cu cut-off - 282 Mt @ 1.20% Cu, 0.48 g/t Au, 197 ppm U, 5.2 g/t Ag;
0.7% Cu cut-off - 202 Mt @ 1.43% Cu, 0.56 g/t Au, 227 ppm U, 6.2 g/t Ag;
Inferred Resource at
0.3% Cu cut-off - 368 Mt @ 0.58% Cu, 0.21 g/t Au, 120 ppm U, 2.3 g/t Ag;
0.5% Cu cut-off - 193 Mt @ 0.76% Cu, 0.26 g/t Au, 144 ppm U, 2.8 g/t Ag;
0.7% Cu cut-off - 90 Mt @ 0.96% Cu, 0.30 g/t Au, 162 ppm U, 3.6 g/t Ag;
Total Resource at
0.3% Cu cut-off - 760 Mt @ 0.78% Cu, 0.30 g/t Au, 143 ppm U, 3.3 g/t Ag;
0.5% Cu cut-off - 475 Mt @ 1.02% Cu, 0.39 g/t Au, 175 ppm U, 4.2 g/t Ag;
0.7% Cu cut-off - 292 Mt @ 1.29% Cu, 0.48 g/t Au, 207 ppm U, 5.4 g/t Ag;
Ore reserves at 18 August, 2014 and mineral resources at 31 November 2013 (OZ Minerals ASX releases), were:
Indicated + Inferred Resources at 0.3% Cu cutoff - 800 Mt @ 0.8% Cu, 0.3 g/t Au, 3.3 g/t Ag, 0.155 kg/t U;
probable reserves, lift 1 from 470 to 970 m below surface - 110 Mt @ 0.9% Cu, 0.5 g/t Au, 5.3 g/t Ag;
probable reserves, lift 2 from 970 to 1470 m below surface - 160 Mt @ 1.0% Cu, 0.4 g/t Au, 4.3 g/t Ag;
TOTAL probable reserves - 270 Mt @ 0.9% Cu, 0.4 g/t Au, 4.5 g/t Ag.
JORC compliant Mineral Resources as at 25 September 2015 (OZ Minerals press release to the ASX) were as follows, based on a AUD 120/t NSR (AUD=USD 0.78) cut-off:
Indicated resource - 55 Mt @ 2.4% Cu, 0.9 g/t Au, 11.7 g/t Ag, 335 ppm U;
Inferred resource 6 Mt @ 2.5% Cu, 0.7 g/t Au, 11.6 g/t Ag, 257 ppm U;
TOTAL resource 61 Mt @ 2.4% Cu, 0.9 g/t Au, 11.7 g/t Ag, 328 ppm U.
JORC compliant Mineral Resources as at 18 November 2016 (OZ Minerals press release to the ASX August, 2017) were as follows, based on a AUD 70/t NSR cut-off:
Measured Resource - 61 Mt @ 1.4% Cu, 0.6 g/t Au, 6.3 g/t Ag;
Indicated Resource - 65 Mt @ 1.6% Cu, 0.6 g/t Au, 7.0 g/t Ag;
Inferred Resource - 8 Mt @ 0.8% Cu, 0.4 g/t Au, 3.5 g/t Ag;
TOTAL Resource 134 Mt @ 1.5% Cu, 0.6 g/t Au, 6.5 g/t Ag.
JORC compliant Mineral resources as at 30 June 2020 (OZ Minerals 2020 Mineral Resources and Ore Reserves Statement ) were as follows:
Measured Resource - 130 Mt @ 0.96% Cu, 0.42 g/t Au, 3.6 g/t Ag;
Indicated Resource - 500 Mt @ 0.62% Cu, 0.26 g/t Au, 2.9 g/t Ag;
Inferred Resource - 330 Mt @ 0.32% Cu, 0.16 g/t Au, 2.0 g/t Ag;
TOTAL Resource - 950 Mt @ 0.57% Cu, 0.25 g/t Au, 2.7 g/t Ag.
JORC compliant Ore Reserves as at 30 June 2020 (OZ Minerals 2020 Mineral Resources and Ore Reserves Statement ) were as follows:
TOTAL Probable Reserve - 220 Mt @ 1.1% Cu, 0.45 g/t Au, 4.4 g/t Ag.
For more detail see: Porter, T.M., 2010 - The Carrapateena Iron Oxide Copper Gold Deposit, Gawler Craton, South Australia: a Review; in Porter, T.M., (ed.), Hydrothermal Iron Oxide Copper-Gold and Related Deposits: A Global Perspective, v. 3 - Advances in the Understanding of IOCG Deposits; PGC Publishing, Adelaide, pp. 191-200. This record comprises both additional information and an update of that paper.
The satellite Khamsin copper-gold deposit, ~10 km to the northwest of Carrapateena, is also an iron oxide copper-gold (IOCG) occurrence. Mineralisation is hosted within the Khamsin Breccia Complex, a polymictic granite-hematite-carbonate breccia which is surrounded by altered Donington Suite granite and some dykes, and is overlain by approximately 460 to 680 m of mostly Neoproterozoic sedimentary cover. Mineralisation occurs as fine- to medium-grained blebby disseminations of chalcopyrite, rare bornite and minor chalcocite, and mostly occur as either disseminations in the breccia matrix or within clasts (OZ Minerals ASX release, 2014).
The first drill hole into the deposit intersected 440.6 m @ 0.43% Cu, 0.08 g/t Au from 1005.4 m depth, including 26.7 m @ 1.48% Cu, 0.13 Au g/t from 1005.4 m, within a broader zone of 569.6 m @ 0.39% Cu, 0.08 g/t Au from 1003 m (Oz Minerals ASX Release, 21 January, 2013). The hole was drilled at a dip of -55° and azimuth of 173°. This mineralised intersection comprises a strong, grey hematite and chlorite altered, clast and matrix supported, heterolithic granite breccia.
The alteration and mineralisation style encountered is comparable to that intersected on the margins of the main Carrapateena deposit. This mineralisation coincides with a significant gravity feature that is both larger in size and has the same intense residual gravity response as that related to the Carrapateena deposit. It displays a prominent co-incident magnetic feature located within the central portion of the gravity anomaly. Depths to basement for Khamsin vary between 480 and 630 m below surface (Oz Minerals, 2013).
The Khamsin prospect was previously the Salt Creek anomaly that was tested by a number of vertical drill holes in the late 1970s and early 1980s following the discovery of Olympic Dam, targeting the gravity and/or aeromagnetic highs. One of these holes, SASC04, was completed at 1250 m and intersected hematite-sericite altered granitoids of the Mesoproterozoic Donington Suite from a depth of 540 m to the bottom of the hole, but without significant sulphide or associated copper mineralisation.
Mineral resources at 26 May 2014 (OZ Minerals ASX release), were:
Indicated + inferred resources at 0.3% Cu cutoff - 202 Mt @ 0.6% Cu, 0.1 g/t Au, 1.7 g/t Ag, 0.086 kg/t U.
An arm of the broadly coincident ~1.5 mGal gravity and 200 nT magnetic anomalies that reflect the Carrapateena deposit extend a further 2 km to the north-east overlie the Freemantle Doctor deposit and represent a continuation of iron oxide alteration. This deposit is hosted within Donington Suite granite and is unconformably overlain by ~480 m of unmineralised Neoproterozoic sediment rocks. Mineralisation and alteration is similar to that at Carrapateena.
Mineral Resources at 12 November 2018 (OZ Minerals ASX release), were:
Inferred resources at 0.4% Cu cutoff - 104 Mt @ 0.7% Cu, 0.5 g/t Au, 3 g/t Ag.
The most recent source geological information used to prepare this summary was dated: 2021.
Record last updated: 21/9/2021
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.
Fairclough, M., 2005 - Geological and metallogenic setting of the Carrapateena FeO-Cu-Au prospect - a PACE success story: in Mesa Journal v.38, pp. 4-7.|
Hayward N and Skirrow R, 2010 - Geodynamic Setting and Controls on Iron Oxide Cu-Au (±U) Ore in the Gawler Craton, South Australia: in Porter T M, (Ed), 2010 Hydrothermal Iron Oxide Copper-Gold and Related Deposits: A Global Perspective PGC Publishing, Adelaide v.3 pp. 119-146|
Katona, L., 2020 - Geophysical signatures of IOCG prospects in the Olympic Cu-Au Province: in Mesa Journal v.92, pp. 26-37.|
Porter T M, 2010 - The Carrapateena Iron Oxide Copper Gold Deposit, Gawler Craton, South Australia: a Review: in Porter T M, (Ed), 2010 Hydrothermal Iron Oxide Copper-Gold and Related Deposits: A Global Perspective PGC Publishing, Adelaide v.3 pp. 191-200|
Sawyer, M., Whittaker, B. and de Little, J., 2017 - Carrapateena iron oxide Cu-Au-Ag-U deposit: in Phillips, G.N., (Ed.), 2017 Australian Ore Deposits, The Australasian Institute of Mining and Metallurgy, Mono 32, pp. 615-620.|
Tiddy, C., Zivak, D., Hill, J., Giles, D., Hodgkison, J., Neumann, M. and Brotodewo, A., 2021 - Monazite as an Exploration Tool for Iron Oxide-Copper-Gold Mineralisation in the Gawler Craton, South Australia: in Minerals (MDPI) v.11, 30p. doi.org/10.3390/min11080809.|
Vella, L. and Cawood, M., 2006 - Carrapateena: discovery of an Olympic Dam-style deposit,: in Preview, Australian Society Exploration Geophysicists, Issue 122, pp. 26-29.|
Vella, L. and Cawood, M., 2012 - Geophysical Characteristics of the Carrapateena Iron-Oxide Copper-Gold Deposit,: in 22nd International Geophysical Conference and Exhibition, 26-29 February 2012 - Brisbane, Australia, ASEG Extended Abstracts, 2012:1 5p. doi.org/10.1071/ASEG2012ab160.|
Vella, L. and Emerson, D., 2009 - Carrapateena: physical properties of a new iron-oxide copper-gold deposit;: in Australian Society of Exploration Geophysics, Extended Abstracts, 2009 (1) 13p.|
Vella, L., 2013 - Carrapateena: Discovery and Early Exploration: in https://www.aseg.org.au/ 23rd ASEG Conference and Exhibition, Exploration Undercover Workshop, 15th August, 2013, https://www.aseg.org.au/ sites/default/files/2013_Uncover_Vella_L.pdf, 55p.|
Zhu, Z., 2016 - Gold in iron oxide copper-gold deposits: in Ore Geology Reviews v.72, pp. 37-42.|
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