Summary:
The deposit contains both detrital and bedded-hosted iron mineralisation.
The detrital portion of the deposit is a Brockman Iron Formation-derived detrital iron deposit overlying the bedded Dales Gorge Member of the Archean Brockman Iron Formation.
The bedded-hosted portion of the deposit contains iron mineralisation which occurs as a highphosphorus Brockman Iron deposit with a weathering overprint.
Brockman 2-Nammuldi (B2N) geology
The BS2 Main, BS2 Extension and BS2 West deposits (collectively known as Brockman Central deposits) occur along an east-west orientated ridge formed by outcrops of Marra Mamba and Brockman Iron Formations on the northern flank of the Brockman Syncline, which rises over 350 m above the adjacent valley floor. Bedded mineralisation deposits typically extend from outcrop into the valley and are covered by the later Cenozoic detritals/valley fill. The HPB mineralisation is largely restricted to the Dales Gorge Member of the Brockman Iron Formation, with minor mineralisation in the Whaleback Shale and Joffre Members.
The Nammuldi deposits are located in the Marra Mamba Iron Formation (MMIF) on the northern flank of the Brockman Syncline, to the north of the Brockman 2 Central deposits. The deposits consist of six lenses from Lens A through to Lens F and extend over a strike distance of 18 km. The majority of the bedded mineralisation occurs within the Mount Newman Member, with minor mineralisation occurring within the upper MacLeod Member and lower West Angela Member of the Wittenoom Formation. Hydration occurs near surface over mineralisation and can be up to 30 m thick, and various amounts of semi-consolidated detrital lenses cover the range front. Detrital accumulations also occur over the MMIF in the west through to the Wittenoom Formation in the east. These accumulations can be up to 150 m deep and comprise layers of colluvial material, unmineralised detritals, calcrete, clay, Red Ochre Detritals (ROD), limonitic clay and manganiferous clay. The water table varies from 574 to 585 mRL, resulting in approximately 90% of mineralisation located below water table.
The Lens G deposit is the most easterly of the Nammuldi lenses, occurring at the nose of the Brockman Syncline. Mineralisation is constrained to a length of three km and maximum width of 0.8 km, in a northwest striking orientation. High grade hematite-goethite mineralisation occurs generally in the Mount Newman Member of the MMIF, with lower grade mineralisation within the upper MacLeod Member and lower West Angela Member of the WF. Approximately 69% of the mineral resource is below water table.
The Brockman Syncline 3 (BS3) Extension is located to the southwest of Lens G and consists of the Diesel, Sandleford, Monkey, Creekside, Orbe, Lauriston, Brokenwood and MM-J deposits. The south-eastern side of the Brockman Syncline consists of a northeast striking Marra Mamba ridge, separated to the larger Brockman ridge in the northwest by a colluvial valley of between 1.1 km to 2.1 km wide. There are numerous narrow north-west trending dolerite dykes cross the Brockman and MMIF. The Brokenwood, Lauriston and Monkey deposits are mineralised Brockman Formation, mainly confined to the Dales Gorge and Whaleback Shale Members, while the Diesel, Creekside and MM-J deposits are mineralised MMIF. A variable thickness hydrated capping overlies the high-grade mineralisation. The bedded iron formations have been extensively eroded to form the detrital iron deposits at Orbe and Sandleford. Approximately 38% of the BS3 Extension mineral resource is below water table.
BS4 geology
Mineralisation at BS4 occurs along east-west orientated ridges formed by outcropping Brockman Iron Formation and MMIF. These ridgelines form the boundary between the Boolgeeda Creek and Beasley River catchments. The operation at BS4 can be divided in two distinct regions:
• A northerly region of mild deformation with shallow north to north-east trending open folds (Boolgeeda Valley) hosting the Brockman Syncline 1 (BS1) deposits.
• A southerly region of intense deformation, where the more resistant iron formations form prominent ridges and the major iron deposits occur (Southern Strike Valley). This area hosts the BS4 Main, BS4MM, Endeavour, BS4MN and BS3 deposits.
Within the BS4 area, the following deposits are hosted within the Brockman Iron Formation:
• BS1 deposits lie 7.5 km north of BS4, approximately 17 km in length (east - west) and between 600 m to 1,800 m wide.
• BS4 Main deposits, east-west trending over a strike length of 14 km and up to 1.4 km wide.
• Endeavour deposits lie immediately east of BS4 which strike approximately 3.5 km in length (east - west) and between 300 m to 1,000 m wide.
• BS3 deposits lies km northwest of Endeavour, approximately 3.0 km in length (east - west) and between 600 m to 1,800 m wide.
Deposits at BS4 Main, Endeavour, BS3 and BS1 all consist of High Phosphorous Brockman (HPB) iron mineralisation hosted within BIF in the Dales Gorge, Whaleback Shale and Joffre Members of the Brockman Iron Formation. Northwest-southeast trending dolerite dykes that cross these deposits often intrude along these faults, as well as bedding parallel sills. Approximately 75% of mineral resource is above water table across these deposits.
Deposits at BS4 Main, Endeavour, BS3 and BS1 all consist of High Phosphorous Brockman (HPB) iron mineralisation hosted within BIF in the Dales Gorge, Whaleback Shale and Joffre Members of the Brockman Iron Formation. Northwest-southeast trending dolerite dykes that cross these deposits often intrude along these faults, as well as bedding parallel sills. Approximately 75% of mineral resource is above water table across these deposits.
Silvergrass East (SGE) geology
The SGE deposit is located on the northern limb of the east – west trending Jeerinah Anticline. The deposit occurs on either end of an embayment within the broader east - west trending ridge line of the MMIF and is over 7 km in strike length (east - west) and between 200 m to 3 km wide. Approximately 65% of the mineral resource is below water table. In the Silvergrass area, the MMIF forms low topographic ridges, which are separated from the high ranges of the Brockman Iron Formation by broad detrital-filled valleys.