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Beltana, Aroona |
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South Australia, SA, Australia |
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Zn Pb
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Super Porphyry Cu and Au
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The Beltana and nearby Aroona willemite deposits are high grade hypogene non-sulphide zinc deposit in the northern Flinders Ranges of South Australia.
The Beltana and Aroona deposits are hosted by Lower Cambrian carbonates within the Arrowie basin, part of the Neoproterozoic to mid Cambrian Adelaide geosyncline, a large deformed sedimentary basin flanked to the west and east by crystalline basement of the Gawler Craton and Curnamona Nucleus respectively. The Adelaide geosyncline is a continental rift with up to 15 km of siliciclastics and lesser carbonates, capped by deep water platform and reef carbonates and siliciclastics during the Cambrian. From the mid Cambrian these carbonates were exposed and an unconformity developed with associated deep casting and little sedimentation until the Mesozoic.
The willemite mineralisation at Beltana is developed adjacent to a reactivated major growth fault (the Beltana fault) on the margin of the Arrowie basin and is hosted by ooid grainstone units of the Woodendinna Dolomite and the overlying Wilkawillina Limestone. These carbonate units overlie a basal Cambrian siltstone, mudstone claystone unit which unconformably overlies Neoproterozoic quartzites, conglomerates and carbonatic mudstones. These in turn unconformably overlie the Callana Beds, a Neoproterozoic unit of micaceous siltstones and sandstones with interbedded dolomite and evaporites.
The Beltana fault is a thrust with numerous associated splays which result in at least four repetitions of steep north-west plunging synclines of Cambrian rocks. The Beltana "diapir" a tight anticlinal core of Callana Beds, is exposed to the west of the Beltana fault, with stratigraphic relationships in the overlying conformable sequence indicating it was a basement high during Cambrian deposition. Within the Beltana pit the stratigraphic succession is a near complete west facing overturned sequence from the Woodendinna Dolomite, through the Wilkawillina Limestone to the siltstones and mudstones of the unconformably overlying Cambrian Billy Creek Formation.
Mineralisation is structurally controlled, associated with solution collapse brecciation in the footwall to the main ore. This breccia extends at least 100 m vertically and is accompanied by hematite rich hydrothermal zincian dolomitisation. The breccia is lead rich, and comprises polymictic rounded to angular clasts up to boulder size cemented by coronadite and include earlier brecciated and altered clasts. It has been faulted and forms the footwall to the ore deposit. The undulose lower margin to the breccia is draped with hematite rich clay and ironstone with up to 40% Fe which may be 5 m thick.
The Beltana deposits are embraced by a 20 km long zone of alteration associated with major structures and comprises hematite and zincian dolomite averaging 1 to 3% Zn near ore to barren dolomite on the periphery of the system. This alteration destroys primary textures by recrystallisation to produce coarse dolomite and hematite that may be up to 1 cm across. The level and extent of alteration depends on the host lithology and its permeability.
The bulk of the ore is hosted by the Wilkawillina Limestone, although a significant proportion of the central ore zone is hosted by the oolitic Woodendinna Dolomite. An envelope of 1 to 3% Zn and 0.5% Pb extends over a length of 450 m and plunges shallowly south enclosing the four distinct Beltana lodes, namely Northern Extension, Central Lead Zone, Central Willemite Lode and Southern Extension.
The Central Willemite Zone contains 85% of the resource and comprises two shoots. The upper is crescent shaped and extends to a depth of 125 m below surface at a dip of 45° NE, in the NE of the pit, is vertical in the south and is 40° N in the western part of the pit. The lower shoot has a south plunge and includes flat lodes to the east. The ore assemblage includes willemite, coronadite and lesser mimetite, hedyphane and smithsonite, with late stage gangue minerals of manganocalcite, dolomite and minor quartz.
The Central Lead Zone is within the solution collapse structure.
The Northern Extension is saucer shaped to a depth of 18 m, composed of white colloform willemite with prominent bands of hematite, but having more abundant Pb (hedyphane and coronadite) in several pockets near the surface.
The Southern Extension is a blind occurrence which was discovered in 1970 by rotary-percussion drilling south of the Main orebody. It differs from the other bodies in that it is parallel sided and dips at 70°E to a vertical depth of 100 m, but has a mineralogy of willemite, hedyphane and coronadite. The host is in part also a 6 m band of shale siltstone and conglomerate interbedded with the red dolomite of the Wilkawillina Limestone.
The pre-mining resource at Beltana totalled:
Main Orebody - 775 000 t @ 38.2% Zn, 2.3% Pb and
Northern Extension - 88 000 t @ 35.3% Zn, 2.0% Pb
Only these two are mineable.
The first mining was commenced in February 1974. Extraction is on a campaign basis over periods of three to twelve months. A limited quantity of Beltana ore is used as supplementary feed to Pasminco's Australian smelters, although the majority of sales are to overseas markets. The ore is direct shipping, with no upgrading or separation necessary, apart from crushing to -19 mm. The ore is trucked 20 km to Copley and railed 325 km to Port Pirie where Pasminco maintains a large smelter and port facility (Rangott, 1980; Carmichael, 1993).
Aroona 1 & 2
These deposits contain around 150 000 t @ 34.4% Zn, 1.6% Pb of mineable reserve, mainly in Aroona 1 (1987). The Aroona 1 orebody extends for a distance of over 240 m along the Norwest fault zone and is continuous to a depth of 37 m. The host is a 60°NE dipping block of red dolomite (probably altered Wilkawillina Limestone) which is bounded by faults on its upper and lower margins. While the orebody is generally concordant with the dolomite block, its position relative to the bounding faults is variable. The hangingwall may be either Neoproterozoic quartzite or red Cambrian dolomite, while the footwall may be red dolomite or overturned middle Cambrian siltstone and sandstone. It has similar chemistry and mineralogy to the Main orebody at Beltana, but less lead. There are no concentrations of Pb-Mn-As wad similar to those at Beltana.
For detail consult the reference(s) listed below.
The most recent source geological information used to prepare this decription was dated: 2003.
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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Selected References:
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Groves I M, Carman C E, Dunlap W J 2003 - Geology of the Beltana Willemite deposit, Flinders Ranges, South Australia: in Econ. Geol. v98 pp 797-818
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Harkins S A, Appold M S, Nelson B K, Brewer A M and Groves I M, 2008 - Lead Isotope Constraints on the Origin of Nonsulfide Zinc and Sulfide Zinc-Lead Deposits in the Flinders Ranges, South Australia : in Econ. Geol. v.103 pp. 353-364
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Hitzman M W, Reynolds N A, Sangster D F, Allen C R, Carman C E 2003 - Classification, genesis, and exploration guides for nonsulfide zinc deposits: in Econ. Geol. v98 pp 685-714
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Horn R A 1975 - Beltana and Aroona Willemite orebodies: in Knight C L, (Ed.), 1975 Economic Geology of Australia & Papua New Guinea The AusIMM, Melbourne Mono 5 pp 548-553
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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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