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Cloncurry Iron Oxide Copper Gold Province

Queensland, Qld, Australia

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The Cloncurry IOCG Province broadly coincides with the Eastern Fold Belt, one of three sedimentological and structural domains that constitute the Mount Isa Inlier in northwest Queensland Australia. These domains are, from west to east:   i). the Western Fold Belt (WFB); ii). the central Kalkadoon-Leichhardt Belt (KLB); and iii). the Eastern Fold Belt (EFB) (Blake, 1987; Blake and Stewart, 1992; Page and Sun, 1998; Page et al., 2000; Foster and Austin, 2008).

The Cloncurry IOCG Province encompasses a number of significant IOCG deposits, including Ernest Henry, Mount Margaret - E1 and Monakoff, Mount Elliott-SWAN, Roseby - Little Eva, Starra-Selwyn (Mt Dore, Merlin), Mt Dore, Merlin, Eloise, Great Australia, Osborne/Trough Tank and others. Seperate or composite records describe each of these deposits on this database and may be accessed via the links above.

The Mount Isa Inlier is characterised by Palaeo- to Mesoproterozoic metasedimentary, rhyolitic and basaltic meta-volcanic rocks, gabbro, dolerite and widespread I- and A-type granitoids. An early history of basement formation and deformation was followed by several episodes of intracratonic rifting, accompanied by the development of a series of superbasins and the deposition of three cover sequences (e.g., Blake and Stewart, 1992; Page and Sun, 1998; Southgate et al., 2000). The dominant period of deformation took place during the Isan Orogeny from ~1600 to 1500 Ma (Page and Bell, 1986; Holcombe et al., 1991; Blake and Stewart, 1992). These sequences are intruded by five main periods of magmatism, ranging from 1860 to 1490 Ma.

The KLB separates the WFB and EFB, and comprises a core of predominantly older Cover Sequence 1 felsic volcanic and related intrusive rocks that correspond to the 1870 to 1850 Ma Barramundi Orogeny of northern Australia. Sparse basement rocks are exposed in the form of migmatites, gneisses, quartzites and micaschists within the southern WFB and the KLB, as well as the limited exposure of the Double Crossing Metamorphics to the west of Selwyn in the southern EFB. However, Foster and Austin (2008) have now suggested that the latter are correlates of the lower units of Cover Sequence 2. These basement metamorphics (with the exception of the Double Crossing Metamorphics) are overlain by Cover Sequence 1 rocks and related intrusions in the KLB. On the basis of zircon dating, they are believed to be late Archaean to Palaeoproterozoic in age, although the oldest inherited zircons from one block in the WFB are dated at 3.6 to 3.3 Ga, suggesting Archaean crust below at least the western Mount Isa Inlier, or alternatively Palaeoproterozoic sediments that included Archaean provenance clastics (Bierlein et al., 2008).

The WFB is largely composed of 1800 to 1595 Ma sediments and volcanics of Cover Sequences 2 and 3, deposited in three superbasins. It is principally divided into the Leichhardt River Fault Trough immediately to the west of the KLB, and the Lawn Hill Platform further to the west, each separated from its neighbour by a major north-south trending terrane boundary fault zone (Blenkinsop et al., 2008; Foster and Austin, 2008).

The EFB is divided into the western Mary Kathleen Fold Belt, and eastern Cloncurry District, separated by the Pilgrim Fault. Another major, northnorthwest trending, deep seated structure, the regional Cloncurry Fault bisects the Cloncurry District (Blenkinsop et al. 2008; Foster and Austin, 2008).

Most of the rocks of the Eastern Succession within the EFB were formed between 1790 and 1500 Ma and include sedimentary and volcanic rocks of Cover Sequences 2 and 3 (CS2 and CS3), deposited between 1790 and 1690 Ma and from 1680 to 1610 Ma respectively. CS2 includes the rift fill succession of mafic volcanic rocks of the lowermost Magna Lynn Metabasalt and the overlying predominantly clastic sediments and felsic volcanics that constitute the Tewinga Group (Argylla Formation); the Malbon Group (comprising the basaltic Marraba Volcanics with siltstones and sandstones, and the Ballara and Mitakoodi Quartzites), which are all overlain by the laterally more extensive platformal evaporitic carbonates (with minor volcanic and clastic rocks and the Overhang Jaspilite at the base) of the Corella and Doherty formations. The Corella and Doherty formations are now dominantly sodic-calcic altered calc-silicates. The lower rift phase members of the CS2 were deposited diachronously from west to east. The sequence was extensively intruded by the 1750 to 1730 Ma Wonga Granite, while the coeval Mount Fort Constantine volcanics separate the Corella and Doherty formations in the north. Minor tonalites, granitoids and diorite emplaced between CS2 and 3 have been dated at 1686 to 1660 Ma (including the Ernest Henry Diorite). The first significant deformation to affect CS2 (but not CS3) was the 1750 to 1735 Ma Wonga extensional event (Blake, 1987; Blenkinsop et al., 2008; Foster and Austin, 2008).

Cover Sequence 2 was deposited in two superbasins that extended across the Mount Isa Inlier. The first of these, the Leichhardt Superbasin accounted for almost all of the sequence in CS2, from the Magna Lynn Metabasalts to the Corella Formation, and was terminated by the Wonga Batholith magmatism. The initiation of the Calvert Superbasin during the period 1720 to 1700 Ma resulted in the sedimentation in a fluvial to shallow marine environment with the deposition of a series of quartzites (e.g., the Knapdale and Roxmere quartzite) and at least part of the Staveley Formation. Following a basin inversion event from 1700 to 1690 Ma in the Western Fold Belt, a period of NNE-SSW extension resulting in the deposition of the lower part of the Kuridala and Soldiers Cap Groups in the eastern part of the inlier. The Cloncurry Fault Zone probably developed during this period of NNE-SSW extension.

Cover Sequence 3, was largely deposited in the Isa Superbasin that can be recognised across the Mount Isa Inlier, in both the Western and Eastern fold belts. It extends further to the east than does CS2, is composed of quartzites, pelites, volcanic rocks and carbonates belonging to the broadly coeval, Soldiers Cap, Young Australia and Mount Albert groups, distributed respectively from east to west. The Soldiers Cap Group commences with arenites and pelites, minor carbonates, volcanic rocks and ironstones of the Kuridala Formation to the west of the Cloncurry Fault, and the equivalent Gandry Dam Gneiss further to the east. To the east, the succeeding section comprises the quartzites, conglomerates and iron formations of the Mount Norna Quartzite and the overlying basaltic Toole Creek volcanics which also includes calc-silicates and ironstones. The Young Australia Group, between the Soldiers Cap Group and the Pilgrim Fault, is a thinner sequence, commencing with the less well developed Kuridala Formation equivalent, the Roxmere Quartzite, overlain by the Answer Slate, and in turn by the Staveley Formation which comprises variably calcareous sandstone, siltstone and shale with minor basic volcanics and ironstones, and then the Agate Downs siltstone, followed by the uppermost unit, the Marimo Slate. To the west of the Pilgrim Fault, in the Mary Kathleen Fold Belt, the Mount Albert Group, a reduced succession, equivalent to the upper units of the Young Australia Group only, is composed of the Knapdale Quartzite and the overlying Lady Claire Dolomite. A hiatus in the upper CS3 was followed by emplacement of the minor 1625 Ma Tommy Creek microgranite and sediments mapped as the Tommy Creek Sequence and the upper Marimo Slate, with the Quamby Conglomerate to the west of the Pilgim Fault (Blake, 1987; Blenkinsop et al., 2008; Foster and Austin, 2008).

There appears to be some confusion with the division between CS2 and CS3 and the Calvert and Isa superbasins. This affects the Staveley and Kuridala Formations that are variously, wholly or partly, included in the Calvert superbasin (e.g., Betts et al., 2003), or the Isa Superbasin (e.g., Foster and Austin, 2008).

Deposition of CS3 in the EFB was terminated by the onset of the Isan Orogeny at ~1600 Ma, which was dominated by east-west compression and persisted until ~1500 Ma. The exact nature of Isan D1 deformation is uncertain, but seems to have involved overall north-south thrusting (Betts et al., 2006), and resulted in a regional, steep, east-west foliation (Rubenach et al., 2008). Greenschist to upper amphibolite peak metamorphism occurred between 1600 and 1580 Ma (D2) involving positive reactivation of basin-bounding structures and the development of anatectic pegmatites (e.g., the Osborne Pegmatite), followed by several retrograde deformations (D3, D4). The most significant crustal structures produced during the orogeny were kilometre scale upright folds and steep faults of D2a (Blenkinsop et al., 2008). D3 deformation was broadly synchronous with emplacement of the ~1550 to 1500 Ma Williams and Naraku batholiths, and included conjugate northeast- and northwest-trending open folds, predominantly north-south trending shear and fault zones, and widespread breccias which were best developed within Corella Formation strata (Marshall and Oliver, 2008). This resulted in: i). anastamosing shear zones that varied from a few to ~500 m wide and up to 50 km in strike length, ii). locally intense zones of veining, and iii). broad intervals of hydrothermal brecciation (Marshall and Oliver, 2008; Rusk et al., 2010). While discordant, polymict, transported breccias are locally common in the EFB, the most widespread breccias are confined to the Corella Formation, with negligible clast transport or mixing (Marshall and Oliver, 2008).

The Williams and Naraku batholiths resulted from a number of pulses of voluminous mafic and felsic potassic magmatism and were emplaced as tabular bodies at mid-crustal levels. Despite having A-type geochemical signatures, these granites are syn-tectonic and derived from high temperature crustal melting at pressures not exceeding 1000 MPa (Mark et al., 2005). Rubenach et al. (2008) propose that mafic rocks emplaced into the lower crust of the EFB (and elsewhere across the Mount Isa Inlier) caused the 1600 to 1580 Ma high temperature (580 to 670°C), low pressure (400 to 600 MPA) metamorphism and partial melting at the peak of metamorphism, and later contributed to the formation of the Maramungee Granites (1547 to 1545 Ma) and the 1550 to 1500 Ma Williams and Naraku batholiths. They support this proposition with the observation that most mafic rocks in the Inlier are predominantly high-Fe tholeiites, and therefore are unlikely to be direct mantle melts, but rather magmas that resided and fractionated in the lower crust, and produced a significant lower crustal thermal anomaly over an extended period.

Location

The tectonic framework and location of the main iron oxide-alkali altered mineralisation in the Eastern Fold Belt of the Palaeo- to Mesoproterozoic Mount Isa Inlier in northwest Queensland, Australia. The Subdivisions inset illustrates the Western and Eastern fold belts, separated by the 1870 to 1850 Ma Leichhardt Volcanics and Kalkadoon Granite of the central Kalkadoon-Leichhardt Sub-province. Both fold belts contain similarly aged 1790 to 1690 and 1680 to 1610 Ma cover sequences 2 and 3 sedimentary and volcanic rocks respectively, although the Western Fold Belt partially overlies a basement of either Archaean, or Palaeoproterozoic rocks of Archaean provenance. Cover Sequence 2 was deposited within both the Leichhardt and Calvert superbasins, while Cover Sequence 3 was within the Isa Superbasin. The Eastern Fold Belt is composed of volcanic and sedimentary rocks deposited in these three extensional rift basins that young and thicken to the east, intruded by the voluminous Wonga (1750 to 1730 Ma) and Williams-Naraku (1550 to 1500 Ma) batholiths which are pre- and post-Cover Sequence 3 respectively. Note the general broad oval shaped distribution of the envelope encompassing exposures of these batholiths. The Mafic/Ultramafic Magmatism inset (after Claoué-Long and Hoatson, 2009) shows that the widespread and numerous small dykes, sills and stocks intruding these rocks also young to the east, although the ~1680 Ma population is overlapped by some 1530 Ma intrusions within granites to the immediate northeast of the Mount Angelay Granite. The extent of regional-scale, mainly sodic-calcic, alteration is illustrated on the main plan, largely controlled by trans-crustal fractures (particularly the Pilgrim, Mount Dore and Cloncurry faults) which influenced both facies distribution during extension, and were reversed as thrusts during basin inversion. The alteration also has a strong overlap with the carbonate (evaporitic) rocks of the Cover Sequence 2 Corella Formation and possible similar rocks of the Cover Sequence 3 Staveley Formation. Note the distribution of iron oxide-alkali altered and IOCG sensu stricto mineralisation. The geological interpretation is after Foster and Austin, 2008 and previous sources quoted therein, while the alteration is after Kendrick et al., 2008; Mark et al., 2005; Oliver, 1995.

Regional Alteration

The Eastern Fold Belt (EFB) of the Mount Isa Inlier hosts regional-scale hydrothermal systems that include: i). barren regional sodic-calcic and lesser overprinting potassic alteration, and ii). granite-hosted hydrothermal alteration complexes with magmatic-hydrothermal transition features, e.g., Lightning Creek (Baker et al., 2008; Oliver et al., 2008; Oliver et al., 2009; Perring et al., 2000; Pollard, 2001).

Both, i). laterally co-extensive fault related zones, and ii). linear networks of anastomising, structurally controlled corridors of alteration that are developed over intervals of tens to hundreds of kilometres are evident within the EFB (Kendrick et al., 2008; Mark et al., 2005; Oliver, 1995). Alteration within these zones is dominantly sodic-calcic and occurred periodically over a 250 m.y. interval. The earliest extensive alteration of this type is characterised by large-scale sodic-calcic-potassic metasomatism, NaCl-rich scapolite and skarn development associated with the ~1.7 Ga Wonga phase granites in the MKFB (Oliver, 1995). However, the bulk of the sodic-calcic assemblages were associated with fluids that were initially dominantly sedimentary formation waters with lesser magmatic components prior to and during peak metamorphism at 1595 to 1580 Ma (Kendrick et al., 2008; Oliver et al., 2008; Baker et al., 2008). Fluid circulation was driven by the various pulses of magmatism and metamorphism caused by the inferred hot mafic underplate (and intraplate) underlying the region (Kendrick et al., 2008). These fluids leached evaporite rich units (e.g., the Corella Formation) in the cover sequences to become hypersaline (Kendrick et al., 2008), and are interpreted to have progressively scavenged metals from the volcanosedimentary pile to possibly be locally concentrated and sequestered into structurally focused fluid sites where they were available for further remobilisation (Oliver et al., 2008). The regional sodic-calcic alteration is represented by assemblages of albitic plagioclase +actinolite +titanite ±quartz ±magnetite ±diopsidic clinopyroxene replacing metabasaltic, calc-silicate, metapelitic and felsic igneous rocks. Alteration is associated with complex, hypersaline H
2O-NaCl-CaCl2-KCl-(?FeCl2) fluids with high Ca:Na ratios, overpressured in zones of retrograde brittle-ductile shear, brittle fracture and regional calc-silicate megabreccias. They occurred as multiple fluid buffered systems at 400 to 500°C and initial pressures of >200 MPa (de Jong and Williams, 1995). The major structures that have controlled the circulation of these fluids include the Cloncurry, Pilgrims and Mount Dore fault systems, some of which have been shown to continue steeply to depths in excess of 30 km (Austin and Blenkinsop, 2008).

This alteration is divided by peak metamorphism at 1595 to 1580 Ma, with dominantly regional albite earlier, and subsequent more structurally controlled albite-actinolite-magnetite-titanite±clinopyroxene, taking place synchronously with major granite (e.g., Williams-Naraku batholiths) emplacement (Baker et al., 2008). Large parts of the latter regional sodic-calcic alteration is associated with the formation of breccia complexes that are particularly well exposed along the Cloncurry fault, predominantly in the roof and along the margins of the Williams and Naraku batholiths, developed during multiple episodes of granitoid intrusion (de Jong and Williams, 1995; Mark, 1998; Mark and de Jong, 1996). Breccia zones up to hundreds of metres across comprise large (metres across) subangular to angular and small rounded clasts of albitised host rock in a matrix of sodic-calcic minerals. These textures suggest formation by upward escape of magmatic vapour phases, with alteration by later, high salinity magmatic fluids (Pollard, 2001). A direct connection between 1530 Ma intrusions, brecciation and alteration has been clarified by observations of sodic-calcic altered (albite, magnetite, hematite and actinolite with minor apatite) breccia pipes containing hydrothermal magnetite and local sulphides, emanating from contact aureoles to the Williams-Naraku batholith (e.g., in the Snake Creek area), possibly spatially connected to significant mineralisation (Oliver et al., 2006a; Cleverley and Oliver, 2005). This assemblage is similar to the mineralogy of veins and breccias found in the carapace of the Mount Angelay Granite, also part of the Williams-Naraku batholith (Mark and Foster, 2000).

In the area around Ernest Henry, the regional sodic-calcic alteration is irregularly overprinted by a range of potassic-, iron- and manganese-bearing minerals, including biotite, magnetite, almandine-spessartine garnet and K feldspar which have an overall spatial association with the ore deposit, but are found up to several kilometres from the orebody (Williams et al., 2005; Rusk et al., 2010). These may represent regional alteration, or an early pre-ore assemblage.

These regional scale alteration patterns were overprinted by district to deposit scale alteration patterns associated with the emplacment of the individual or groups of IOCG deposits within the province as listed at the start of this record.

The most recent source geological information used to prepare this summary was dated: 2010.     Record last updated: 7/9/2012
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
 References to this deposit in the PGC Literature Collection:
Baker T, Bertelli M, Fisher L, Fu B, Hodgson W, Kendrick M, Mark G, Mustard R, Ryan C and Williams P J,  2006 - Salt and copper in iron oxide-copper-gold systems, Cloncurry district, Australia - Abstract: in    Geochimica et Cosmochimica Acta   v70 A30
Baker T, Mustard R, Fu B, Williams P J, Dong G, Fisher L, Mark G and Ryan C G,  2008 - Mixed messages in iron oxide–copper–gold systems of the Cloncurry district, Australia: insights from PIXE analysis of halogens and copper in fluid inclusions: in    Mineralium Deposita   v.43 pp. 599-608
Foster D R W and Austin J R,  2008 - The 1800-1610 Ma stratigraphic and magmatic history of the Eastern Succession, Mount Isa Inlier, and correlations with adjacent Paleoproterozoic terranes: in    Precambrian Research   v.163 pp. 7–30
Hatton O J, Davidson G J  2004 - Soldiers Cap Group iron-formations, Mt Isa Inlier, Australia, as windows into the hydrothermal evolution of a base-metal-bearing Proterozoic rift basin: in    Australian J. of Earth Sciences   v51 pp 85-106
Mark G, Oliver N H S and Carew M J  2006 - Insights into the genesis and diversity of epigenetic Cu-Au mineralisation in the Cloncurry district, Mt Isa Inlier, northwest Queensland: in    Australian J. of Earth Sciences   v53 pp 109-124
Marshall L J, Oliver N H S and Davidson G J,  2006 - Carbon and oxygen isotope constraints on fluid sources and fluid–wallrock interaction in regional alteration and iron-oxide–copper–gold mineralisation, eastern Mt Isa Block, Australia : in    Mineralium Deposita   v41 pp 429-452
McLellan J G, Mustard R, Blenkinsop T, Oliver N H S and McKeagney C  2010 - Critical Ingredients of IOCG Mineralisation in the Eastern Fold Belt of the Mount Isa Inlier: Insights from Combining Spatial Analysis with Mechanical Numerical Modelling: in Porter T M, (Ed), 2010 Hydrothermal Iron Oxide Copper-Gold and Related Deposits: A Global Perspective PGC Publishing, Adelaide   v.3 pp. 233-256
Oliver N H S, Butera K M, Rubenach M J, Marshall L J, JCleverley J S, Mark G, Tullemans F and Esser D,  2008 - The protracted hydrothermal evolution of the Mount Isa Eastern Succession: A review and tectonic implications: in    Precambrian Research   v.163 pp. 108-130
Oliver N H S, Rubenach M J, Fu B, Baker T, Blenkinsop T G, Cleverley J S, Marshall L J and Ridd P J,  2006 - Granite-related overpressure and volatile release in the mid crust: fluidized breccias from the Cloncurry District, Australia: in    Geofluids   v.6 pp. 346-358
Oliver NHS, Cleverley JS, Mark G, Pollard PJ, Bin Fu, Marshall LJ, Rubenach MJ, Williams PJ and Baker T,  2004 - Modeling the Role of Sodic Alteration in the Genesis of Iron Oxide-Copper-Gold Deposits, Eastern Mount Isa Block, Australia: in    Econ. Geol.   v99 pp 1145-1176
Williams, P.J. and Pollard, P.J.,  2003 - Australian Proterozoic Iron Oxide-Cu-Au Deposits: An Overview with New Metallogenic and Exploration Data from the Cloncurry District, Northwest Queensland: in    Exploration & Mining Geology, CIM   v.10, No. 3, pp. 191-213.

 References to this deposit in PGC Publications: Want any of our books ? Pricelist
Williams P J, Skirrow R G, 2000 - Overview of Iron Oxide-Copper-Gold Deposits in the Curnamona Province and Cloncurry District (Eastern Mount Isa Block), Australia,   in  Porter T M, (Ed.),  Hydrothermal Iron Oxide Copper-Gold & Related Deposits: A Global Perspective,  v1  pp 105-122
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