Roy Hill

Western Australia, WA, Australia

Main commodities: Fe
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The Roy Hill iron deposit is located on the northern side of the Fortescue Valley, in the Chichester Ranges of the northern Hamersley Basin on the Pilbara craton in Western Australia, ~25 km ESE of the Christmas Creek mine, 285 km SSE of Port Hedland and 100 km north of Newman.

The Roy Hill deposit is situated in the northern part of the Hamersley Basin, which has and areal extent of ~400 x 500 km, with an up to 10 km thickness of metasedimentary and metavolcanic rocks that includes the banded iron formations (BIF) of the Hamersley Group hosting the bulk of the developed iron mineralisation. The Hamersley Group falls within the Mount Bruce Supergroup, a late Archaean to Palaeoproterozoic platformal cover sequence of low-grade metamorphosed sedimentary and volcanic rocks, unconformably overlying the mid Archaean granite - greenstone terrain of the Pilbara Craton (Trendall and Blockley, 1970; Trendall, 1983). The Mount Bruce Supergoup comprises the regionally conformable Fortescue (~2770 to 2630 Ma), Hamersley and Turee Creek Groups.

See the Hamersley Basin Iron Province record for the regional setting and stratigraphy.

The Roy Hill deposit occurs at the base of the Hamersley Group in the Marra Mamba Iron Formation (MMIF), which conformably overlies the Jeerinah Formation at the top of the Fortescue Group (Harmsworth et al., 1990; Thorne and Trendall, 2001).

In the Roy Hill mine, the ore reserves are contained within the basal 300 m section of the Nammuldi Member, the lowermost unit of the MMIF and the Hamersley Group, immediately overlying the Fortescue Group. The Nammuldi Member comprises pale chert and cherty BIF interbedded with thin shales. The section of the Nammuldi Member in which ore has been developed at Roy Hill overlaps with and underlies that mined at the Christmas Creek and Cloudbreak mines to the WNW. The overall structure of the Roy Hill area is relatively simple, with the stratigraphy dipping very gently at 2 to 5° SSW (Clout, 2011).

The Hamersley Group is unconformably overlain by the Oakover Formation, a sequence of younger Tertiary lacustrine carbonate, silcrete and mudstone rocks that have been deposited in the palaeodrainage of the Fortescue Valley. The Fortescue Valley is mantled by a thick (up to 50 m) blanket of Quaternary flood plain alluvial sediments, derived from the erosion of the Hamersley and Chichester Ranges (Clout, 2011).

Banded iron mineralisation is restricted to the basal sections of the Nammuldi Iron Formation and varies from 2 to 44 m thickness, averaging 12 m, over a width of 1 to 7 km, and 23 km strike length. The mineralisation is flay lying and dips at between 2 to 10° to the south and south west. The central NW portion of the deposit comprises a well developed, thick low-phosphorous microplaty hematite mineralised core that has been overprinted by later supergene martite-brown goethite mineralisation. The NW and SE sections of the deposit comprise a sub-horizontal sheet of dominantly supergene martite-brown goethite replacement of BIF, accompanied by minor ochreous goethite (Clout, 2011). Vertical and lateral ore zonation patterns are similar to those described by Clout (2005) and Clout and Simonson (2005) for other Chichester, Marra Mamba and Brockman iron ore deposits.

The Roy Hill deposit is believed to represent the best developed microplaty-hematite mineralisation hosted by the MMIF outside of the large microplaty-hematite deposits hosted by the Brockman Iron Formation (Clout, 2011).

Published JORC compliant reserve and resource figures at a 55% Fe cut-off, as at July 2010 (Clout, 2011) were:
  Bedded ore
    Measured resource - 143 Mt @ 61.2% Fe, 0.067% P, 0.64% Mn, 4.15% SiO2 and 2.21% Al2O3
    Indicated resource - 505 Mt @ 59.0% Fe, 0.054% P, 0.88% Mn, 6.01% SiO
2 and 2.92% Al2O3
    Inferred resource - 440 Mt @ 58.8% Fe, 0.057% P, 0.79% Mn, 5.67% SiO
2 and 2.86% Al2O3
  Bedded ore
    Inferred resource - 15 Mt @ 55.8% Fe, 0.041% P, 0.46% Mn, 9.92% SiO
2 and 4.82% Al2O3
  Detrital ore
    Indicated resource - 5 Mt @ 56.0% Fe, 0.042% P, 0.60% Mn, 5.61% SiO
2 and 4.76% Al2O3
    Inferred resource - 120 Mt @ 56.2% Fe, 0.053% P, 0.73% Mn, 4.01% SiO
2 and 4.07% Al2O3
    SUB TOTAL 1228 Mt @ 58.8% Fe, 0.056% P, 0.80% Mn, 5.51% SiO
2 and 2.96% Al2O3
Lower grade material averaging 50 to 55% Fe
  Bedded ore
    total resource - 160 Mt @ 52.9% Fe, 0.047% P, 1.08% Mn, 11.71% SiO
2 and 4.48% Al2O3
  Detrital ore
    total resource - 935 Mt @ 52.5% Fe, 0.053% P, 0.89% Mn, 7.54% SiO
2 and 5.74% Al2O3
TOTAL RESOURCE - 2.323 Gt @ 55.9% Fe, 0.054% P, 0.85% Mn, 6.74% SiO
2 and 4.18% Al2O3
Proved + probable ore reserves as of December 2010 (Clout, 2011), prepared according to JORC (2004):
    561.6 Mt @ 59.3% Fe, 0.055% P, 5.68% SiO2 and 2.86% Al2O3

The mineable resource at December, 2011, was >991 Mt of bedded ore at a 55% Fe cut-off, and strip ratio of 4.56:1 (Clout, 2011).

This summary largely paraphrases Clout, 2011 from the AusIMM Bulletin, Issue 3, June, 2011.

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:
Clout J M F,  2011 - The Roy Hill Project: in   The AuslMM Bulletin The AusIMM, Melbourne   Issue 3, June, 2011 pp. 58, 60-62, 64-65

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