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Gingin Shorelines - Cooljarloo, Jurien, Donga, Gingin

Western Australia, WA, Australia

Main commodities: Ti Zr
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The Cooljarloo, Jurien and Donga heavy mineral deposits lie within the Perth Basin in Western Australia, in the northern segment of the Gingin shorelines north of Cataby, approximately 180 km north of Perth. Jurien is approximately 35 km NNW of Cooljarloo. The Gingin deposits are towards the south of the Gingin shorelines, 5 km NNW of Gingin and 80 km north of Perth.

The Perth Basin is an approximately 1000 x 15 km, north-south trending trough bounded to the east by the Darling Fault and to the west by the continental shelf which has undergone two major stages of evolution, namely:

i). An early Silurian to the early Cretaceous phase composed of a thick sequences of continental siliciclastic sediments with minor shallow marine sediments, during which time the basin was probably bounded by continental crust both to the east and west.
ii). A second phase that persisted from the early Cretaceous to the present, during which time the sediments represent a marginal sag basin, occurring as generally thin sequences of shallow marine sediments. Eustatic sea level changes over this period, and possibly some tectonic movement, have caused near-shore sediments to be deposited over much of the east-west extent of the basin, especially along the coastal plains.

The detrital heavy minerals of the Perth Basin include ilmenite, rutile and zircon which were derived from igneous and metamorphic rocks in the adjacent Archaean shield to the east in the interior of Western Australia, concentrated through multiple phases of weathering, erosion and deposition. Economic accumulations of heavy minerals are mostly found in high energy Cainozoic shoreline deposits, although significant accumulations also occur in older Cretaceous fluvial sediments.

Most of the high grade heavy mineral deposits of the Perth Basin occur as shoreline accumulations lying unconformably on Mesozoic sediments or weathered Precambrian basement. The extensive deposits against the Darling Scarp and the Whicher Scarp in the South Perth Basin (Yoganup, Boyanup, Waroona), and the Gingin Scarp in the North Perth Basin (Gingin, Cooljarloo, Eneabba) are of this type and are correlated together as the Yoganup Formation, of possible Pliocene age.

A younger series of shorelines, within Quaternary sediments, occur to the west of these deposits and are economically significant in the South Perth Basin near Capel, but have not been as significant to the north. These younger strandlines are known to exist in the North Perth Basin (near Dongara, Jurien and possibly Eneabba West), but are covered by a limestone ridge in most of the prospective areas. The younger strandlines typically contain higher garnet concentrations and less altered ilmenite than the older strands.

The various deposits are situated in what were northward facing embayments, with heavy minerals probably having been accumulated from a combination of longshore drift and wave action. Mineralisation is also partly controlled by the location of palaeo-drainages and sediment sources.

The mineralisation at Cooljarloo comprises detrital ilmenite, rutile, leucoxene and zircon with subordinate monazite and a gangue of alumino-silicates kyanite, staurolite, andalusite and tourmaline. These minerals were concentrated in near-shore sediments deposited during transgressive, interglacial peaks, probably in the Late Pliocene or Early Pleistocene. The deposits form a swathe of around 15 north-westerly trending, sub-parallel strands over a three-kilometre width. These have been described in the past as the 'Munbinea' shorelines (Baxer, 1977) and can be followed from Cataby to Badgingarra over a 40 km length of the Gingin Scarp.

The mineralisation is hosted by shallow marine and near-shore sediments that are between 20 and 50 m in thickness which unconformably overlie the fluvial sands and silts of the Upper Jurassic Yarragadee Formation. Some of the high grade mineralisation at Cooljarloo abuts the Gingin Scarp, which marks the eastern limit of the Cainozoic marine transgressions, with a significant amount of the mineralisation lying within a fan of strandline deposits to the west of the scarp. The mineralised sands near Cooljarloo were deposited in at least three sequences of marine transgression and regression, as follows:

i). First Transgression and Regression - this sheet unconformably overlies the Yarragadee Formation in much of the north-eastern part of Cooljarloo and is comprises a variable layer of silty, weakly carbonaceous, poorly sorted sand that is often grey-green in colour, or yellow-brown. It is typically 5 to 7 m thick with moderate levels of heavy minerals which are considerably finer than the overlying strandline mineralisation (0.12 mm compared with 0.18 for the overlying HM). It has a significantly higher level of monazite (1.3% compared to 0.4% in the overlying strandlines) and the ilmenite is less altered (TiO2 of 56% compared to 62% in the overlying strandlines).
ii). Second Transgression and Regression - comprising the mid-level deposits which were emplaced in three episodes between R.L. 44 and 64 m above sea level, and are characterised by thin lamellar of mineral sands, with small cross-set beds and massive disseminated mineral sands. These sands represent low energy conditions and deposition in a shallow marine environment, periodically disrupted by storm events that reworked up to 5 m of sand and destroyed any previous structure. The sands are medium-grained, well-rounded, well-sorted mature sediments that are grey to white in colour. They differ from units in other transgressions by the absence or low content of feldspar and are generally very clean with less than 5% clays. They are the sequence being mined at Cooljarloo (2006), together with the overlying third transgression minerals.
iii). Third Transgression and Regression - this third and final transgression appears to have been quite rapid, as much of the previous regressive sands were undisturbed. The sands in the regressive stage are coarser and more angular than the second transgression and contain more feldspar, and are taken to be less mature than the older lithologies. The heavy minerals are generally coarser and contain less rutile and zircon than the older, more mature mineral suits, with more alumino-silicates in the heavy mineral assemblage. The near-surface strands were deposited in seven or eight events over a three-kilometre wide coastal strip.

The deposits of the Gingin mine are in a similar setting, distributed over a NNW-SSE aligned interval of over 3 km.

Reserve and resource figures for Cooljarloo, Jurien and Donga include (Ticor, 2006):
    Total proved + probable reserves - 441.8 Mt @ 3.0% HM, containing 59% ilmenite, 5.1% rutile, 10% zircon, 2.9% leucoxene,
    Total measured + indicated + inferred resources (includes reserves) - 585.9 Mt @ 3.2% HM, containing 57% ilmenite, 5.6% rutile,
            10% zircon, 2.7% leucoxene

Reserves and resources for the Iluka Resources Mid-west Western Australia operations at December 2007, the bulk of which relate to their Gingin Mine (the balance at Eneabba - see the Eneabba record) are quoted as (Iluka Resources, 2008):
    Total proved + probable reserves - 106.0 Mt of ore, 7.71 Mt HM, 7.3% HM, 53% Ilmenite, 14% Zircon, 6% Rutile
    Total measured + indicated - inferred resources - 897.0 Mt of ore, 45.72 Mt HM, 5.1% HM, 50% Ilmenite, 11% Zircon, 6% Rutile

This summary was based on geological descriptions available via the Exxaro web site

The most recent source geological information used to prepare this summary was dated: 2007.    
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

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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