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Maroochydore

Western Australia, WA, Australia

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Maroochydore is one of group of sediment hosted copper prospects and deposits localised within a >30 km2 area, ~100 km SE of Nifty , and 550 km SE of Port Hedland in Western Australia (#Location: 22° 11' 31"S, 122° 17' 45"E).

  Maroochydore was discovered in 1984 by Esso Exploration and has since been evaluated by a number of companies, but has not yet been developed. The mineral tenement is currently held by Metals X Limited.
  It is hosted within the Yeneena Basin, part of the NNW to NW trending, >1000 km long by 150 to 200 km wide Paterson Orogen. This orogen fringes the northeastern margin of the Archaean to Palaeoproterozoic West Australian Craton, and merges with the Musgrave orogen to the SE. It is overlain to the NE by the Phanerozoic Canning Basin.

  For detail of the regional setting and geology, see the separate Telfer and Nifty records

  Maroochydore, like Nifty, is hosted in the upper carbonaceous, sulphidic, shale unit of the Broadhurst Formation, ~1500 m above the top of the Coolbro Formation, structurally overlying the regional Camel-Tabletop Fault.
  The Maroochydore mineralised unit is up to 75 m thick and comprises two carbonaceous shale members, each of which is 25 to 40 m thick. These are separated by a dolomite marker, 15 to 20 m of pale grey, competent, massive dolostone to fine dolarenite. The upper carbonaceous shale becomes increasingly pyritic upwards, and more dolomitic towards the base. The lower unit comprises regularly interbedded dolomitic and carbonaceous shale. The footwall sequence is composed of interbedded carbonaceous shale and chloritic mudstone. The Broadhurst Formation is entirely masked by 10 to 110 m of glaciogene sediments of the Late Carboniferous to Early Permian Paterson Formation, mainly composed of clay, silt, sand and a basal pebble conglomerate. These are overlain by a variable thickness of Cenozoic superficial cover.
  The host rocks have been deformed into SW vergent, tight to open recumbent folds with relatively flat axes and 45 to 65°NE dipping axial planes, correlated with regional D
4 (or DY2 at Nifty) deformation. Axial plane parallel thrusts offset the overturned limbs of recumbent folds. Copper mineralisation occurs in two main forms. The first is fine-grained and concordant, closely associated with framboidal pyrite, which it rims and replaces, within the two carbonaceous shale units. The second is coarse-grained, within zoned dolomitic veins, occurring in saddle reefs along tight fold closures, particularly where dolostone beds are interlayered with carbonaceous shale. They also occur in the faulted steep limbs of recumbent folds and in fractured competent lithologies of the same folds. Hypogene mineralisation comprises pyrite, pyrrhotite and chalcopyrite, with traces of sphalerite and galena in a gangue of dolomite, quartz, phlogopite, chlorite, apatite and feldspar. These styles of mineralisation have been encountered over a thickness of 30 to 75 m and a strike length of >5 km, where they have been estimated to contain an average of ~0.5% Cu (Reed 1996 unpub., quoted by Anderson et al., 2001).
  In addition to the mostly sub-economic hypogene mineralisation, a zone of supergene enriched sulphides and oxides has a JORC compliant Mineral Resource of 48.63 Mt @ 1.0% Cu, 0.038% Co (Metals X Ore Reserve and Mineral Resource Statement, 2016).). Mineralisation occurs as a number of bodies immediately below the unconformity with the Paterson Formation, the largest of which forms a NW-SE elongated, >3 km by 200 to 600 m wide ribbon. It is superimposed upon a buried, synformal core of sulphidic carbonaceous shale of the Maroochydore mineralised unit.
Maroochydore setting
The supergene mineralisation also coincides with the trace of a 40 to 80 m deep depression in the unconformity, marking a relatively well-defined paleochannel. Supergene copper mineralisation is directly related to the depth of incision of the paleochannel and the base of oxidation relative to the unconformity. Copper was apparently derived from the oxidation and leaching of sulphides in low-grade hypogene mineralisation of the Maroochydore mineralised unit by meteoric water. This occurred where the base of oxidation was below the unconformity, distal to the Maroochydore deposit. The resultant low pH cupriferous solution was transported down the hydrological gradient of the paleochannel in the coarse aquifers at the base of the Permian sequence, to be deposited where the unconformity passed through the base of oxidation into the reduced Broadhurst Formation. Mineralisation was precipitated both within incised, reduced sulphidic shale of the Maroochydore mineralised unit, and to a minor degree in the basal glaciogene rocks. Mineralisation within sulphidic shale occurs in two separate zones. The upper, immediately below the unconformity is more continuous and thicker (5 to 50 m), situated 30 to 80 m below the surface, and appears to replace the upper carbonaceous shale. The lower is less well developed and is 80 to 120 m below the surface, most likely replacing the lower carbonaceous shale. Mineralisation comprises covellite, cuprite, malachite, azurite, native copper, minor chrysocolla, erythrite [Co
3(AsO4)2•8(H2O)] and ubiquitous sooty chalcocite. Later uplift and/or erosion, led to a lowering of the water table and base of oxidation, and partial oxidation of the exotic supergene sulphide sheet.

The hypogene mineralisation has been informally estimated to comprise ~140 Mt @ 0.5% Cu (Reed 1996 unpub., quoted by Anderson et al., 2001).

Supergene enriched sulphides and oxides have a Mineral Resource of 48.63 Mt @ 1.0% Cu, 0.038% Co (Metals X Limited resource statement, March 2017).

The most recent source geological information used to prepare this summary was dated: 2010.    
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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