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Titan, Bopeechee, Vulcan |
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South Australia, SA, Australia |
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Cu Au
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
Available as Full Text for direct download or on request. |
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The Titan iron oxide copper-gold-uranium occurrence is located ~35 km north of Olympic Dam, and 575 km NNW of Adelaide, in northern South Australia. The Vulcan prospect is located ~12 km to the east of Titan.
Titan along with Carrapateena, Olympic Dam, Prominent Hill, Moonta-Wallaroo and Hillside, and all of the 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.
See the Gawler Craton and Olympic IOCGU Province record for a summary of the regional, cratonic setting of the Olympic IOCG Province.
Titan lies on a broad WNW-ESE-trending, partially dislocated gravity ridge, and coincides with a local elongate anomaly that trends NNE-SSW at high angles to the axis of the ridge. It is located ~15 km to the NW of the clearly defined and rapid NE-SW-trending gradient between a magnetically active domain to the SE (which embraces the Olympic Dam deposit) and a bland, lower magnitude, relatively quiet domain to the NW that is punctuated by a small number of pronounced composite magnetic peaks, one of which coincides with Titan. The gradient between the two magnetic domains has been interpreted to represent a major fault zone. This same magnetic gradient corresponds to a similar, but less pronounced, gravity gradient from a more extreme domain to the SE, and a less active NW terrane.
The Titan mineralised system (previously the Bopeechee prospect of Western Mining Corporation - WMC e.g., Barratt, 1991; and the Ibbott prospect) corresponds to two parallel, closely coincident magnetic and gravity anomaly pairs. Each of these anomalies is elongated in a NNE-SSW direction.
The eastern magnetic-gravity anomaly pair has a 4.5 km gravity anomaly, with a 3 to 4 milligal peak, overlapping a 5000 nT magnetic peak. The magnetic anomaly extend over a 5 km, NNE-WSW oriented interval, with the central of three peaks of the magnetic anomaly being ~400 to 600 m west of the centre of the gravity peak. Vertical diamond drill hole BD1 (WMC, 1981) was sited close to the peak of both anomalies and passed through 652 m of Cambrian and Neoproterozoic shelf sediments before crossing the unconformity into basement at 607 m. The basement in this hole is predominantly composed of massive, to indistinctly bedded, medium- to coarse-grained arkose. These sedimentary rocks contain zones of magnetite, chlorite (after actinolite or tremolite) and quartz alteration with carbonate, apatite, pyrite and chalcopyrite as minor phases, cut by veins of the same mineralogy. Alteration and brecciation is more intense from 774 m, with up to 50% of the rock being replaced by magnetite, chlorite and quartz, doubling the magnetic susceptibility to 85 000 x 106 cgs units to the end of the hole at 941 m. This change corresponds to an increase in the total Fe from an average of ~19% above, to ~28% Fe below (Smith, Tasman Resources, 2004). Complete alteration results in a coarse-grained mosaic of magnetite, chlorite, quartz and feldspar completely obliterating original textures. These meta-sediments, which are interpreted to correlate with the <1850 to ~1740 Ma Wallaroo Group, are intruded by a series of un-metamorphosed, but altered porphyritic felsic dykes with chloritised feldspar phenocrysts in a fine-grained leucocratic groundmass. Dykes vary from 1 to 5 m in thickness, and may be equivalents of the Gawler Range Volcanics. This and subsequent holes have also encountered fine-grained mafic dykes up to 30 m, but typically <2 m thick. Pyrite is abundant throughout the basement in BD1 (which contains ~1% sulphides overall), occurring as disseminated grains and within veins, accompanied by minor chalcopyrite as irregular disseminated grains, within veins, and in some cases replacing pyrite. The entire basement sequence in this drill hole averaged 0.1% Cu, with peaks over widths of 1 to 15 m of 0.15 to 0.22% Cu. U3O8 varied from <4 to 38 ppm, ~20 ppb Au and 21.5% Fe (Barratt, 1991; Tasman Resources, 2002 to 2006).
The subsequent diamond core hole TI2 (Tasman Resources, 2003) intersected a similar sequence to BD1. It was located 300 m SSE of BD1, below the gravity anomaly peak, but offset from the centre of the magnetic anomaly, and intersected a similar sequence of rocks, after crossing the unconformity at 604 m. However, the interval below 710 m to ~745 m has a significant increase in the development of hematite replacing magnetite (almost complete, compared to only a few percent above 710 m), accompanied by a distinct development of yellow/green sericite mixed with iron-rich chlorite. Between 735 and 747 m, hematite is most strongy developed and is accompanied by heterolithic, matrix-supported breccias, consisting of highly altered angular clasts, up to about ten cm across, of previously magnetite-altered meta-arkose and largely unaltered mafic dyke rock in a matrix of comminuted wall rock of mafic silicate and/or mafic igneous rock, hematite-altered magnetite, carbonate and chlorite (Smith, Tasman Resources, 2004; Bastrakov et al., 2007). After 745 m, the hole passed through 16 m of fine grained altered, magnetite (with lesser hematite) bearing, mafic dyke material to the end of the hole.
Studies of the veining accompanying alteration (Skirrow, 2002) suggests a paragenesis of: i). early stage - red K feldspar (replacing albite), quartz, magnetite (observed within relicts of host arkose); ii). middle-stage - magnetite, chlorite (replacing actinolite/tremolite), quartz, red K feldspar (after albite), pyrite, chalcopyrite (distinct veins and vein networks with indistinct wispy vein margins); iii). late-stage - hematite after magnetite, local yellow/green sericite (+chlorite?), carbonate.
Based on the observations from the drill holes reported above, Bastrakov et al. (2007) and Smith (Tasman Resources, 2004) note that, in detail, magnetite-K feldspar-calc-silicate and hematitic alteration assemblages are well zoned in drill holes TI2 and others. Smith (Tasman Resources, 2004), has defined a number of zones based on alteration mineralogy and metal content.
Zone A is developed in the upper and lower parts of TI2, and much of BD1, dominated by magnetite-K feldspar-calc-silicate assemblages, comprising vein and replacement networks of magnetite, quartz, actinolite or tremolite, pyrite, hematite-dusted K feldspar and minor chalcopyrite. The rare examples of coarse bladed magnetite-hematite intergrowths suggest conditions close to hematite-magnetite equilibrium prior to or during magnetite-K feldspar-calc-silicate alteration, although rare pyrrhotite inclusions in pyrite imply locally reducing conditions during formation of magnetite-bearing assemblages. The magnetite dominated Zone A typically contains ~0.1% Cu, 1.4 to 1.7 wt.% S and and ~20 ppb Au.
Zone B is represented in the central section of drill hole TI2 (710 to 745 m), which is occupied by multistage breccias, mafic dykes and hematite-carbonate-chlorite alteration that cuts and replaces the magnetite-bearing assemblages. A narrower but similar Zone B is present in drill hole BD1. In contrast to Zone A, the characteristically hematitic altered Zone B contains only trace chalcopyrite and negligible pyrite, with 100 to 200 ppm Cu, 700 ppm S, 5 to 20 ppb Au suggesting an overprinting leaching phase (Bastrakov et al., 2007; Tasman Resources, 2002 to 2006). Despite the higher Cu:S ratio, nor bornite has been recognised. In both drill holes TI2 and TI4 (475 m SE of BD1), distinct concentrations of U (up to 230 ppm and mostly >10 ppm) occur within this central zone, at its contacts with Zone A, possibly reflecting an oxidation front during deposition. Micro-textural evidence from TI2 indicates that pyrite and chalcopyrite were replaced by hematite and carbonate in Zone B (Bastrakov et al., 2007). Martite replacement of magnetite decreases away from the central hematitic Zone B in TI2, although minor late-stage hematite, carbonate, muscovite, and chlorite (after protolith amphiboles) persists throughout the magnetite zones. Minor chalcopyrite is common in Zone B, suggesting a second stage of copper deposition during hematitic alteration.
Zone C - In later drill holes, e.g., TI3 (830 m SSE of BD1) and TI5 (1300 m NE of BD1), strongly altered, deformed and steeply dipping fine-grained feldspathic to carbonaceous and biotite-rich metasiltstones have been intersected. These rocks exhibit a strong shear foliation developed subparallel to compositional layering. Hydrothermal alteration overprints the shear foliation, locally penetrating along both the foliation and compositional layering. Where mineralised, they carry ~500 ppm Cu, ~9000 ppm S, ~6 ppb Au, and ~2 ppm Ag, and as such have undergone similar, but weaker alteration and mineralisation. These fine metasediments represent Zone C (Smith, Tasman Resources, 2004).
A further Zone D, only encountered in drill hole TI6 (450 m SSE of BD1), overprints Zone A via a transition zone, and contains an average of 0.255% Cu, 55 ppb Au, 1.2% S, 20% Fe (composed of fine hematite after magnetite) over an interval of 51 m.
The western magnetic-gravity anomaly pair at Titan is 2 km to the NW of the mineralised system described above, and has a gravity response over a 3.5 km, NE-SW elongated area, with a 2 to 3 milligal peak, offset 600 m to the south from a near circular, 2 km diameter magnetic anomaly with a 2500 nT peak. Vertical diamond drill hole BD2 was sited on the gravity peak and passed through 652 m of Cambrian and Neoproterozoic shelf sediments before crossing an unconformity marked by a basal sedimentary breccia with clasts of quartzo-feldspathic and foliated chlorite-rich lithologies in a dolomitic matrix, into basement at 657.4 m. The basement was represented by repeated intersections of amphibolites, chloritic phyllite, hematite-dusted black and pink cherty-shale, and fine grained mafic volcanic rocks. The hole was terminated at a depth of 830 m. The main amphibolite intersection was 100 m thick and was interpreted to represent a metamorphosed gabbro containing hematite after magnetite, pyrite and rare chalcopyrite. The cherty-shales and mafic volcanic units are variably sericite, chlorite and hematite altered, becoming more strongly veined and brecciated lower in the hole, occurring as an irregular mosaic of chert, quartz and chlorite with hematite dusting. The complete basement section averages 470 ppm Cu, with a few narrow 2 to 4 m thick intervals of 0.2 to 0.33% Cu (Barratt, 1991; Tasman Resources, 2002 to 2006).
The mineralised zone is cut on the eastern margin by a NNE-SSW trending normal fault that has dropped the unconformity by >300 m to form a graben filled with Mesoproterozoic (post 1424 Ma) Pandurra Formation arenaceous red beds (Smith, Tasman Resources, 2004).
The Vulcan prospect is a recently (2009) discovered hematite breccia-hosted Cu-Au system ~12 km east of the main Titan anomaly, and is defined by a gravity anomaly. Drilling has intersected hematite-rich alteration and Cu-Au±U mineralisation, with intersections that include 57 m @ 0.59% Cu, encompassing higher-grade zones such as 0.75 m @ 4.44% Cu, 1.34 g/t Au, 0.58 kg/t U3O8 and 0.65 m at 7.82% Cu, 2.41 g/t Au, and 163 m of Cu-Au mineralised hematite-rich breccias @ 0.23% Cu and 0.08 g/t Au. Another drill hole intersected 180 m of alteration and mineralisation with sulphide mineral zoning from bornite through chalcopyrite to pyrite + chalcopyrite at depth, a zonation pattern similar to that observed at Olympic Dam (Reeve et al., 1990). The gravity and magnetic data for the Vulcan prospect suggest possible continuity of hematite (+ minor magnetite)-altered rock over ~12 km2, which is comparable in size to the Olympic Dam deposit, although at a significantly greater depth (~850 m compared to ~350 m at Olympic Dam; Reid et al., 2013).
Mineralisation is associated with a variety of breccia types, varying from hematite dominant, made up entirely of hydrothermal minerals, to those predominantly of altered rock with preserved clasts of unaltered protolith rock. The richest mineralisation at Vulcan is within hematite-dominant breccias, which are composed of a fine-grained hematite-sericite-chlorite rich matrix enveloping angular to rounded aggregates of quartz, carbonate, sericite, chlorite, pyrite, chalcopyrite ± gold ± apatite± molybdenite. Iron oxide aggregates also found within these rocks are composite hematite-magnetite granules, with the former enclosing and altering the latter to pseudomorphs. Veinlets and larger aggregates up to 1 m across of coarse to very coarse chalcopyrite and pyrite, intergrown with bladed hematite in places, are also present. The overall mineralogy of the hematite breccia, is dominated by smaller, rounded aggregates of altered mylonitic granite, and single- and poly-crystalline carbonate and single crystal quartz grains. Hematite-pyrite-chalcopyrite aggregates are found within a matrix of microcrystalline sericite, chlorite and carbonate. Coarse-grained pyrite and chalcopyrite grains and bladed hematite are associated, and in places intergrown, with coarse-grained laths of molybdenite up to several mm in length. Late-stage carbonate veining is common, whilst carbonate and apatite occur with the hematite-rich sulphide aggregates. Locally, chlorite forms coarse clots or crosscutting veinlets within the brecciated matrix (paraphrased from Reid et al., 2013).
The most recent source geological information used to prepare this decription was dated: 2013.
Record last updated: 9/1/2015
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.
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Heinson, G., Didana, Y., Soeffky, P., Thiel, S. and Wise, T., 2018 - The crustal geophysical signature of a world-class magmatic mineral system: in Scientific Reports 2018:8, DOI:10.1038/s41598-018-29016-2.
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Reid A, Smith R N, Baker T, Jagodzinski E A, Selby D, Gregory C J and Skirrow R G, 2013 - Re-Os Dating of Molybdenite Within Hematite Breccias From the Vulcan Cu-Au Prospect, Olympic Cu-Au Province, South Australia : in Econ. Geol. v.108 pp. 883-894
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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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