Yarrie, Mt Goldsworthy, Nimingarra, Sunrise Hill, Shay Gap and Cundaline

Western Australia, WA, Australia

Main commodities: Fe
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The Mount Goldsworthy, Nimingarra, Sunrise Hill, Shay Gap, Cundaline and Yarrie deposits are distributed in that order over an interval of 85 km from WNW to ESE on the northern margin of the exposed Archaean Pilbara craton in northwestern Western Australia.   Goldsworthy and Yarrie are ~95 and ~180 km east and ESE of Port Hedland respectively.

The Yarrie and Nimingarra deposits continued operating following the closure of many of the Shay Gap-Sunrise iron deposits in 1993 which had commenced mining in 1972, and had in turn overlapped with and replaced the Mt Goldsworthy mine in the west that produced ore from 1966 to 1982. All are developed in the same or similar stratigraphy.

As distinct from the major iron ore deposits of the late Neoarchaean to early Palaeoproterozoic Hamersley Basin, also on the Pilbara Craton, these mines are developed within the underlying Palaeo- to Mesoarchaean 3.4 to 2.9 Ga granite-greenstone terrane. The greenstone belt stratigraphy has been subdivided into the lower dominantly volcanic 3.5 to 3.3 Ga Warrawoona Group of the Pilbara Supergroup and the upper mainly-sedimentary, 3.05 to 3.02 Ga Gorge Creek Group which belongs to the De Grey Supergroup. The Warrawoona Group has been subdivided into three main (ultra)mafic-felsic volcanic cycles and is 9 to 18 km thick. Regional mapping suggests the Warrawoona and Gorge Creek groups evolved as a near continuous succession with only minor internal unconformities (e.g., at the base of the 3.31 Ga Budjan Creek Formation, which overlies the Warawoona Group, and is in turn unconformaby overlain by the Gorge Creek Group following an interval of deformation at 3.15 Ga). Further to the south (50 to 100 km), granitoid plutonism (3.32 to 3.29 Ga and 3.27 to 3.23 Ga) and deposition of ultramafic to felsic volcanics and cherts of the Kelly and Sulphurs Springs are recorded during the gap between the Warrawoona and Gorge Creek groups. The lower Gorge Creek Group followed an ~100 m.y. period of relative quiescence during which concentrations of banded iron-formation and siliciclastics were deposited. These rocks are followed by a thick sequence of basaltic rocks, lesser felsic tuffs and volcaniclastic rocks, and finally by post 2.9 Ga clastic rocks that constitute the remainder of the De Grey Group, mainly to the west (Van Kranendonh et al., 2002; Podmore, 1990; Waters, 1998; Hickman and Van Kranendonh, 2012).

Both the Warrawoona and Gorge Creek groups suffered their most intense tectonic imprint together as a result of granitic diapirism resulting in the emplacement of the regional Carlindi, Muccan and Warrawagine batholiths between 3.0 and 2.8 Ga, which separate the sequence into isolated greenstone belts. The Mt Goldsworthy deposits lie within the Goldsworthy greenstone belt, separated by the Carlindi and Muccan granitoid batholiths from the Yarrie Greenstone Belt which hosts the bulk of the remaining deposits. Older >3.44 Ga tonalite-trondhjemite-granodiorite (TTG) rocks underlie or intrude the lower Warrawoona Group, but also constitute substantial volumes of the Carlindi, Muccan and Warrawagine batholiths (Van Kranendonh et al., 2002; Podmore, 1990; Waters, 1998; Hickman and Van Kranendonh, 2012).

The Fortescue Group, the lowest unit of the Mount Bruce Supergroup that hosts the main Hamersley Basin BIF units (in the Hamersley Group), overlies the Warrawoona and Gorge Creek groups approximately 25 km to the south of the Goldsworthy to Yarrie string of deposits (Van Kranendonh et al., 2002).

Just to the north of Yarrie, the Archaean rocks of the Gorge Creek Group are overlain by the gently dipping Mesoproterozoic Eel Creek Formation that comprises a ~30 m thick basal conglomerate which is locally hematitic, and grades upward into intercalated shales and sandstones and is intruded by dolerite sills. The Archaean and Proterozoic basement is overlain to the north by the near horizontal Permian Paterson Formation sediments and by extensive Cretaceous sandstones and younger sedimentary rocks of the Anketell Shelf of the Canning Basin (Waters, 1998).

Mineralisation is associated with the 1000 m thick, Cleaverville Formation in the lower sections of the Gorge Creek Group. In the Yarrie area, basement granitoids of the Warrawagine batholith are overlain by a 5 to 15 m thick basal quartzite, which is succeeded in turn by 400 m of banded iron formation (BIF), the Nimingarra Iron Formation, which is the basal member of the Cleaverville Formation and can be correlated with the footwall sequence at Mt Goldsworthy, 90 km to the west. Discontinuous, thin mudstone units in the lower sections of the BIF can be correlated with similar bands in the other deposits between Yarrie and Mt Goldsworthy. To the north, the BIF is overlain by red shale of the upper Cleaverville Formation. The host sequence is composed of steeply (50 to 75°) dipping banded iron formation, shale, mudstone and chert horizons, intruded to the south by a 2600 Ma granitoid batholith.   The Cleaverville Formation is overlain by a transition zone into a sequence of andesitic volcanics (Podmore, 1990; Waters, 1998).

The various ore deposits mined generally had reserves of the order of 1 to 10 Mt and occur as either Archaean Lodes or Mesozoic or Tertiary Crust types.

The Archaean Lodes occur as conformable, steeply dipping hematite lenses within the host BIF over vertical intervals of generally 50 to 150 m (but locally up to 320 m) and widths of 50 to 100 m. The ore is commonly massive structureless and microplaty hematite with some relict banding from the original BIF and is the result of metasomatic replacement of the original cherty BIF. This mineralisation appears to predate and/or is contemporaneous with the Proterozic dolerite dykes which intrude it.

Proterozoic conglomerate ore occurs within the basal Eel Creek conglomerates at Yarrie 10, where moderately hard, rounded to ellipsoidal hematitic pebbles and cobbles with an average 63% Fe content are cemented by a fine grained hematite-sand matrix, with shale interbed up to 0.25 m thick. The deposit, which laps onto Archaean shale to the south and Cleaverville BIF to the north, varies from 1.5 to 12 m in thickness, averaging 6 m.

The Mesozoic or Tertiary Crust types consist of irregularly shaped masses of platy, fissile hematite and form tabular deposits underlying the weathered laterite zone.   They vary in thickness from a few up to 25 m with irregular floors.

Some 34 Mt of ore had been mined from Mt Goldsworthy between 1966 and 1973, with a reserve remaining of 21 Mt @ 64.2% Fe, 4.8% Silica, 1.45% Alumina and 0.047% P in 1973 (Neale, 1975). These resources were exhausted by 1982.   Up to 1990, some 79 Mt of ore grading 62.7% Fe had been shipped from the Nimingarra, Sunrise Hill and Shay Gap deposits (Podmore, 1990; probably including ore previously attribued to the Mt Goldsworthy resource).   Ore reserves at that stage were quoted as 138 Mt @ 59.8% Fe, 9.4% Silica, 1.53% Alumina, 0.051% P (Podmore, 1990).   Between 1993 and 1996 14.5 Mt of ore was shipped from from the Yarrie Y2-3 deposit and 1.3 Mt from Y10 (Waters, 1998).

The reserves in the Yarrie mine area only in 2001 (BHP Billiton, 2002) were stated at:
    Y2-3 deposit - 6 Mt @ 66.0% Fe, 4.1% Silica, 1.1% Alumina, 0.031% P, 0.6% LOI.
    Y10 deposit - 11.9 Mt @ 61.4% Fe, 6.3% Silica, 2.9% Alumina, 0.099% P, 1.8% LOI.
    Y3-Y8 deposits - 15.3 Mt @ 57.4% Fe, 10.6% Silica, 3.2% Alumina, 0.039% P, 3.2% LOI.
    SHW7 deposit - 6 Mt @ 63.8% Fe, 6.3% Silica, 0.8% Alumina, 0.049% P, 1.3% LOI.

Total resources and reserves in 2011 (BHP Billiton, 2011) were:
    Measured + Indicated + Inferred resources - 169 Mt @ 61.5% Fe, 8.2% Silica, 1.3% Alumina, 0.05% P, 1.7% LOI.
    Proved + Probable reserves - 25 Mt @ 60.8% Fe, 8.2% Silica, 1.3% Alumina, 0.06% P, 2.6% LOI.

The most recent source geological information used to prepare this summary was dated: 2011.    
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
 References to this deposit in the PGC Literature Collection:
Kerr, T.L., O’Sullivan, A.P., Podmore, D.C., Turner, R. and Waters, P.,  1994 - IRON: Geophysics and iron ore exploration: examples from the Jimblebar and Shay Gap-Yarrie regions, Western Australia: in Dentith, M.C., Frankcombe, K.F., Ho, S.E., Shepherd, D.I. and Trench, A., (Eds.),  Geophysical Signatures of Western Australian Mineral Deposits, Australian Society of Exploration Geophysicists, Special Publications,   v.7 pp. 355-368
Neale J  1975 - Mount Goldsworthy Iron Ore Deposits, WA: in Knight CL (Ed.), 1975 Economic Geology of Australia & Papua New Guinea, Monograph 5 The AusIMM, Melbourne   v1 - Metals pp 932-936
Podmore D C  1990 - Shay Gap-Sunrise Hill and Nimingarra Iron Ore Deposits: in Hughes FE (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne   v1 pp 137-140
Waters P J  1998 - The Y2-3 and Y10 iron ore deposits , Yarrie: in Berkman D A, Mackenzie D H (Ed.s), 1998 Geology of Australian & Papua New Guinean Mineral Deposits The AusIMM, Melbourne   Mono 22 pp 371-374

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