Roseby Project - Little Eva, Blackard, Scanlan, Longamundi, Legend, Great Southern, Charlie Brown
Queensland, Qld, Australia
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The Roseby Project supergene oxide copper deposits, including Blackard, Scanlan, Longamundi, Legend, Great Southern, Caroline and Charlie Brown and the related Little Eva and associated primary IOCG deposits, are located within the Mt Roseby Corridor, approximately 65 km NNW of Cloncurry in north-west Queensland, Australia.
For geological background on the setting, see the Cloncurry IOCG Province record.
The Mt Roseby Corridor is occupied by weakly metamorphosed calc-silicates, siliciclastics and minor intermediate igneous rocks of the Mesoproterozoic Cover Sequence 2 Corella Formation in the Eastern Succession of the Mt Isa Inlier. In addition to the Little Eva and the Blackard deposits, the corridor also embraces the Dugald River discordant sediment-hosted (47.9 Mt at 12.1% Zn, 2.1% Pb, 44 g/t Ag) and Lady Clayre silica-dolomite hosted deposits (14 Mt at 0.56% Cu, 0.19 g/t Au).
Little Eva is the largest primary IOCG-style sulphide copper-gold deposit within the Roseby Project, and is located ~6 km north from the Blackard deposit. Fresh rock is overlain by a 5 to 25 m thick weathered zone of copper oxide mineralisation, in which copper occurs in both iron oxide and secondary 'oxide-zone' minerals (e.g., malachite). Mineralisation extends over a strike length of 1200 m, and is hosted within an intermediate feldspar porphyry unit of probable volcanic or shallow intrusive origin, which strikes north and dips 60° E. The porphyry ranges in width from 30 m in the north to over 300 m in the central zone. In the north, the porphyry is mineralised over its entire width, although in the central zone, while copper is ubiquitous, grades are lower. This mineralisiton occur as a series of linear, parallel sheets of higher grade separated by lower grade material. Within these zones, copper occurs on average as 0.1 to 2% coarse gained chalcopyrite as disseminations and veinlets, while only minor amounts of other sulphide minerals are present. The host rock is veined and altered to a hematite-albite-carbonate-quartz assemblage. Mineralisation is present to depths of >350 m. Metallurgical testing established an expected copper recovery of 95.8% to a concentrate grading 27.3% Cu and gold recovery of 94% for a concentrate grade of 5 g/t Au.
The Blackard-style mineralisation occurs as a group of supergene native copper deposits within the Mt Roseby Corridor. They are distributed along a north-south oriented, 5 to 60 m wide, folded and faulted copper-bearing unit within the Corella Formation, referred to as the Roseby Cupriferous Horizon. This horizon is exposed semi-continuously over a strike-length of around 30 km and is typified in outcrop by malachite-stained scapolite-biotite schist.
In the zone of oxidation and supergene enrichment, an approximately 30 m thick oxide cap which hosts some malachite resources, overlies a thick zone, locally extending to depths of 240 m, of supergene copper enrichment which comprises native copper with minor chalcocite. The supergene mineralisation is hosted by soft, clayey, scapolite schists derived from a dolomitic quartz siltstone and calc-silicate sequence. Native copper occurs as blebs, wafers and wire forms within the soft host.
The main Blackard deposit has a length of around 4 km and width of generally 100 m, but over sections up to as much as 400 m. The 0.5% cut-off mineralisation averages 40 to 80 m in vertical thickness, the top of which is at approximately 40 m below the surface.
The main Scanlan deposit is 10 km south of Blackard and has a length of around 1.5 km and width of generally 100 m, but over sections up to as much as 400 m. The 0.5% cut-off mineralisation averages 40 to 80 m in vertical thickness, the top of which is at a depth of approximately 40 m.
Below the base of weathering and the copper-only supergene deposits, the primary mineralisation comprises disseminated copper sulphides within carbonate-altered meta-siltstone and scapolitic calc-silicate. The sulphides are commonly zoned within the horizon, with chalcopyrite being found at the top, grading into bornite and finally to chalcocite at the base. Other sulphides are rarely seen, and the chalcocite and bornite have the characteristics of being primary in origin.
Generally, the cupriferous horizon within this interval does not have sufficient width or grade to be economic, although, in zones of increased deformation, particularly zones of tight to isoclinal folding, the width and grade is significantly enhanced.
At the Blackard deposit, lenses of hypogene copper mineralisation are found within the hinge zones of a syncline-anticline pair where the mineralisation occurs as fine-grained disseminated chalcopyrite, bornite and chalcocite within calcite alteration, breccia matrix and veining. Mineralisation is zoned, with low-grade, chalcopyrite-dominated assemblages surrounded by a broad halo of weak calcite alteration around these lenses, grading into bornite-chalcocite in the core of the lenses. This mineralisation occurs as disseminations, blebs and veinlets associated with hydrothermal alteration.
The global resource for deposits of the Mt Roseby Corridor in 2012 (Altona Mining Ltd ASX release, August, 2012) was:
Measured resource - 63.2 Mt @ 0.65% Cu, 0.05 g/t Au,
Indicated resource - 76.7 Mt @ 0.55% Cu, 0.06 g/t Au,
Inferred resource - 120.1 Mt @ 0.56% Cu, 0.04 g/t Au,
Total resource - 260.1 Mt @ 0.58% Cu, 0.05 g/t Au,
comprising 123.4 Mt @ 0.55% Cu, 0.10 g/t Au (Cu-Au deposits) + 136.7 Mt @ 0.61% Cu (Cu only deposits).
The largest copper-gold deposit is:
Little Eva - 100.3 Mt @ 0.54% Cu 0.09 g/t Au
The larger copper only deposits within this resource are:
Blackard - 76.4 Mt @ 0.62% Cu,
Scanlan - 22.2 Mt @ 0.65% Cu,
Longamundi - 10.4 Mt @ 0.66% Cu.
The most recent source geological information used to prepare this summary was dated: 2012.
Record last updated: 3/9/2012
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 to this deposit in the PGC Literature Collection:
Glacken I (principal author) 2009 - Independent mineral specialist report - merger of Vulcan Resources and Universal Resources - Extract, the Roseby Project: in Report by Optira Pty Ltd to KPMG Corporate Finance (Aust.) Pty Ltd pp. 13-34|
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