Summary:
The Cloudbreak, Christmas Creek and Kutayi deposits lie within the Chichester Ranges, in northern Western Australia. Iron mineralisation is hosted by the Nammuldi Member which is the lowest member of the late Archaean aged Marra Mamba Iron Formation (MMIF). The Nammuldi Member is characterised by extensive, thick and podded iron rich bands, separated by equally extensive units of siliceous and carbonate rich chert and shale. The Nammuldi Member in the Chichester Range is interpreted to be up to 60 metres in true thickness. Underlying the Nammuldi Member rocks are black shales and volcanic rocks belonging to the Jeerinah Formation. Extended periods of tectonic activity have variably folded and faulted these rocks, together with weak metamorphism. Subsequent erosion and hardcapping or lateritic processes have altered these rocks, and present outcrop of Nammuldi Member represents a ridge of lowlying hills (relief up to 30 metres) throughout the prospect areas. These ridges are recognised as the Chichester Ranges.
Iron mineralisation characteristically comprises hematite, goethite and ocherous goethite, with variable degrees of alteration between these minerals. The main gangue minerals are kaolinite, quartz and gibbsite, with minor amounts of carbonates, either calcite or dolomite.
Iron is enriched in the parent BIF (iron layers banded with cherts and lesser carbonates) by processes of supergene and/or hypogene enrichment. In both processes, the original iron, which is present as magnetite bands within the BIF, is oxidised to hematite and goethite. Contemporaneous with the iron enrichment, the original gangue minerals are partially to fully leached out or may be replaced by iron minerals. These processes increase the iron content of the BIF depending upon the degree of enrichment. A volume loss of up to 35 per cent can occur with enrichment due to loss of gangue minerals. Microplaty hematite (MplH) is recognised in varying degrees throughout Fortescue’s Chichester Range deposits. This is interpreted to occur due to hypogene enrichment of the MMIF in proximity to tectonic structures (faults or tight folds), which have allowed upward fluid flow, and low-grade metamorphism of the parent rock, resulting in extensive hematite mineralisation.
The majority of the iron mineralisation is hosted by the Nammuldi Member which is the lowest member of the late Archaean aged Marra Mamba Iron Formation (MMIF). The NammuldiMember is characterised by extensive, thick and podded iron rich bands, separated by equally extensive units of siliceous and carbonate rich chert and shale. The Nammuldi Member in the Chichester Range is interpreted to be up to 60m in truethickness. Underlying the Nammuldi Member rocks are black shales and volcanic rocksbelonging to the Jeerinah Formation. Limited iron mineralisation also occurs in the overlying CID and Tertiary alluvial material.
Cloudbreak and Christmas Creek - Up to ~80km along strike and up to 5km plan width. Upper limit of mineralised domain is located between 0m to 125m below the surface. Lower limit of mineralised domain is located between 1m and 130m below the surface. The average thickness of the mineralised domain is 7.0m and the range of thickness is 1m to 28m.
Solomon Hub Deposits – Firetail, Kings and Queens. The Solomon Project area is situated approximately 60km to the north of the Tom Price township in the northern Hamersley ranges. Outcropping geology in the project area is dominated by the Dales Gorge, Whaleback Shale and Joffre Members of the Brockman Iron Formation which hosts large bedded iron deposits (BID) throughout the Hamersley Province. The Firetail deposit comprises the majority of BID tonnes at Solomon, where geologically favourable environments have allowed for the formation and preservation of large tonnages of bedded iron mineralisation.
Incised into the bedrock geology are regional palaeochannel systems, predominantly one to two kilometres in width, and stretching for tens of kilometres. During the Miocene period, deep chemical weathering and erosion of iron rich material into these fluvial channels has formed channel iron deposits (CID). The CID is subdivided into an upper ‘hard CID’ and a lower ‘ochreous CID’, there is also a semi-continuous middle CID layer which is difficult to detect with RC drilling. Clay lenses within the CID are observed as semi-discrete bands, often several meters thick. The clay lenses are somewhat discontinuous and of a poddy nature although often traceable between drill holes. CID of approximately 40km strike length is preserved in the Kings CID system, with an additional 25km of CID located in the Serenity deposit to the west. Other CID occurrences are also known throughout the Solomon project area. The material overlying the CID (and other areas) has been eroded from adjacent mineralised and un-mineralised bedrock. This clastic material is concentrated into horizons of elevated iron grade termed detrital iron deposits (DID), which forms part of the sequence of overlying late Tertiary aged alluvial and colluvial deposits.
Mineralisation within the Solomon area is hosted by buried Channel Iron Deposits (CID), Bedded mineralisation (BID and Detrital mineralisation (DID). Outcropping geology in the area is the Dales Gorge, Whaleback Shale and Joffre Members of the Brockman Iron Formation which contain the BID mineralisation. Incised into this bedrock geology are the large Channel systems which contain the DID and CID mineralisation.
Kings: The CID mineralisation has a strike length of 20km and a width of 1 - 2km. Though the CID mineralisation outcrops in the southeast corner of the deposit, the majority of the CID mineralisation is buried and occurs at depths of up to 40m below surface and the defined mineralised units have a thickness of between 1m and 65m.
Queens: The CID mineralisation has a strike length of 10km and a width of 0.5 - 1km. The CID mineralisation is buried and occurs at depths of up to 60m below surface and the defined mineralised units are between 1m and 65m thick.
Firetail: The bedded mineralisation has a strike length of 7km and outcrops on the north and south limbs of an anticline. Mineralisation is strata bound, has an average thickness of 20m and extends to a depth of 100m below surface in places.
The Eliwana deposit occurs on the southern limb of the Jeerinah anticline in the western Hamersley Province. The deposit covers a narrow zone that follows the outcrop of mineralised Brockman and Marra Mamba Iron Formations, with Tertiary sediments in the valleys separating these formations. Iron mineralisation predominantly occurs as bedded iron deposits (BID) with some detrital iron deposits (DID). The mineralisation, which occurs at surface and extends to depths of 350m below surface, is variably distributed across an area of approximately 40km along strike and 3.5km across strike.
The Marra Mamba Iron Formation outcrops in the north and dips towards the south around 15 to 20 degrees. Tertiary sediments occur in the valley. Minor occurrences of the Oakover Formation are mapped outcropping in the western portion of the project area. The main area of mineralisation occurs over an area 11km along strike and 400m across strike. Mount Newman Mineralisation occurs at surface in the north and at depths up to 200m to the south. The thickness of mineralisation averages 20m throughout the deposit and is found up to 50m in areas.
At Eliwana mineralisation is distributed variably within an area of approximately 40km in an east west direction and 3.5km in a north south direction. Mineralisation occurs at surface and extends to depths of up to 350 metres below the ground surface. The reported tonnes and grade in the Mineral Resource occur at depths of up to 350 metres.