Western Australia, WA, Australia

Main commodities: Zn Pb
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Cadjebut - Western Australia - 3.9 mt @ 13.5% Zn, 3.9% Pb (Initial Res.).

The Cadjebut orebody occurs within the middle to upper Devonian Pillara Limestone on the Lennard Shelf in north-western WA. The exposed sections on the Lennard Shelf comprise mainly shallow marine carbonate and associated basinal siltstone and shale, and extend over 350 km interval in a WNW-ESE direction along the southern margin of the Kimberley block. Locally these unconformably overlie Ordovician carbonates. Cadjebut, like the other Zn-Pb mineralisation of the shelf, is hosted by platform, reef, fore-reef and shelf facies carbonates, ranging in composition from calcareous siltstone and shale, through silty dolomite to clean fossiliferous reef and platform limestone. The host unit is locally 450 m thick and has a basal arkosic siltstone, a lower dolomite, vuggy dolomite, and an upper dolomite.

The Cadjebut orebody comprises two strongly elongate and weakly sinuous stratabound 'ribbon-like' lenses, stacked one immediately above the other. These lenses plunge to the ESE at around 6° to 8°, generally parallel to the dip of bedding, and dip shallowly to flat to the NNE. They are each 80 to 100 m wide on average, but locally up to 150 m, are 3000 m long and from 4.2 to 4.6 m thick using a 7% Zn+Pb cut-off. The two lenses are separated by 6 m of interburden.

The high grade mineralisation is predominantly situated within carbonate-siltstone units, with the sulphides replacing the host rock, either through open space filling of pre-existing cavities or more direct replacement along more permeable lithological units. There are four types of ore, namely:
1) open space filling sphalerite and galena within solution collapse breccia above the type 2 ore;
2) banded replacement ore composed of thin bands of multi-coloured ribbon sphalerite ore, with banding not parallel to bedding. These are found near the base of each of the two ore lenses, being around 30 cm thick, but of very high grade;
3) late stage galena veins and veinlets; and
4) massive marcasite found on the lateral margins of the ore.

The general paragenesis appears to proceed from country rock (with corroded margins) to several pulses of fine grained cream to brown coloured sphalerite with coarse galena to purple-brown coarse grained colloform sphalerite to coarse grained marcasite to coarse grained galena and lastly calcite.

The most recent source geological information used to prepare this summary was dated: 1997.    
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
   Selected References:
Christensen J N, Halliday A N, Vearncombe J R, Kesler S E  1995 - Testing models of large-scale crustal fluid flow using direct dating of Sulfides: Rb-Sr evidence for early dewatering and formation of Mississippi Valley-type deposits, Canning Basin, Australia: in    Econ. Geol.   v90 pp 877-884
Murphy G C  1990 - Lennard Shelf Lead-Zinc deposits: in Hughes F E (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne   Mono 14, v2 pp 1103-1109
Tompkins L A, Eisenlohr B, Groves D I, Raetz M  1997 - Temporal changes in mineralization style at the Cadjebut Mississippi Valley-type deposit, Lennard Shelf, W.A.: in    Econ. Geol.   v92 pp 843-862
Tompkins L A, Pedone V A, Roche M T, Groves D I  1994 - The Cadjebut deposit as an example of Mississippi Valley-type mineralization on the Lennard Shelf, Western Australia - single episode or multiple events?: in    Econ. Geol.   v 89 pp 450-466
Tompkins L A, Rayner M J, Groves D I  1994 - Evaporites: in situ Sulfur source for rhythmically banded ore in the Cadjebut Mississippi Valley-type Zn-Pb deposit, Western Australia: in    Econ. Geol.   v 89 pp 467-492

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 takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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