The Iron Baron mining area (IBMA) lies at the northern end of the Middleback Ranges (MBR). The local geology in the vicinity of the IMBA, as described in SIMEC Mining (2015a) is as follows:

Hematite in the MBR occurs as stratabound Palaeoproterozoic deposits of the Lower Middleback Iron Formation (LMIF), which is part of the Hutchison Group. The Hutchison Group forms part of the Cleve Subdomain of the Gawler Craton, and lies on its western edge. The Cleve Subdomain comprises tightly folded, high-grade metamorphic rocks that are mainly derived from marine shelf sediments and mafic and acidic volcanics (Parker 2012). The Hutchison Group in the MBR is composed of the Warrow Quartzite and the Middleback Subgroup, although the Warrow Quartzite is not identified at all locations. The Middleback Subgroup comprises the Katunga Dolomite, the LMIF, the Cook Gap Schist and the Upper Middleback Iron Formation (UMIF). The LMIF hosts the Middleback Ranges’ hematite deposits.

MBR iron ores formed through supergene enrichment; a process which selectively dissolved waste minerals and replaced them with iron ore mineralisation. Preferential enrichment occurred in carbonate facies iron formation, dolomitic marble and, to a lesser degree, silicate facies iron formation. The silicates were much less soluble than the carbonates, and resulted in patchy mineralisation in the silicate iron facies (Yeates 1990). Magnetite was recrystallised and remobilised during a period of metamorphism and deformation. Multiple periods of uplift, erosion and weathering resulted in the oxidation of magnetite to hematite and martite through supergene processes. The formation of iron ore requires fluids to move through the rock. Most deposits lie on the western side of the range, adjacent to a major fault or mylonite zone along the western edge of the range, which may have provided this pathway. The process was most intense where the dolomite and carbonate facies were thickened and then subsequently exposed during the supergene process (Yeates 1990).

Central Iron Baron mining area (IBMA) geology
The Central Iron Baron deposits include the Little Baron, Big Baron, East Baron, Iron Prince and Iron Prince North ore bodies.

The Iron Prince deposit is located at the northern end of the IBMA. Prior to mining the resource was approximately 1500 m long and 180 – 240 m wide. Most of the ore was located in a north/north-east striking syncline which plunges 8º south. The syncline is fault bounded to the east and west in a graben-like structure. The western fault is more prominent and dips 60 – 80º east. The footwalls to the bounding faults consist of granite gneisses that, from previous petrological studies, are described as granodiorite-adamellite granitoids which represent both late syntectonic granitoids possibly of the Lincoln Complex and pre-early syntectonic granitoids possibly equivalent to the Minbrie Gneiss. A number of later stage cross faults and folds further complicate the structure, creating an undulating base to the ore. These structures terminate the ore along strike. The main ore body is made up of hematite lenses intercalated with amphibolite dykes.

The deeper and more extensive southern end of the ore body is underlain predominantly by pink-red, ferroan, (and to a lesser extent by grey-white) dolomite. Minor argillaceous schists and banded iron formation also occur. The shallower northern end (Prince South Stage 2 deposit) is more variable and is intercalated with more amphibolite and schists and less dolomite. Red ore is more common in the northern part of Iron Prince. Red ore is generally more schistose and has a ‘greasier’ texture than the harder more massive blue ore common in the South Prince. Blue ore often retains relict banding and varies from fine grained hard to soft, friable hematite.

The Little Baron and Big Baron deposits occupy a similar structure to the Iron Prince and lie adjacent to the Western (NNE striking) Fault. These deposits are the southern strike extension of the Iron Prince deposits. The geology of the ore bodies is similar to Iron Prince although red ore is less common and the Baron deposits are predominantly underlain by schists and banded iron formations (BIF) with minor dolomite.

Several amphibolite dykes intrude the deposit, including a possible ultrabasic rock identified by petrological work. The eastern ore body occupies a second synclinal structure to the east of the Big Baron. The syncline is faulted off to the north and does not appear adjacent to the Little Baron or the Iron Prince deposits. The two synclines are separated by an anticline which has been extensively intruded by amphibolite. The eastern ore body is extremely irregular. Hematite pods are intercalated with clay schists and amphibolite. Remnants of BIF and dolomite are less common.

Substantial scree ore deposits have been identified around the flanks of the current mining operations, particularly on the north and western slopes of the Central IBMA. Two major resources have been identified; the Empress to the north and the Baroness to the west. A smaller resource has also been identified to the east of the East Baron deposits. The Baroness and Empress scree deposits are the detrital concentrations of iron ore scree from the Iron Baron and Iron Prince deposits respectively. The scree deposits are formed by the erosion of well exposed iron ore deposits such as the Iron Prince and Big Baron ore bodies and have accumulated over time in alluvial fans at the foothills of the in-situ iron deposits.

Both the Empress and Baroness deposits are wide in nature and have lateral extents greater than a kilometre. Typical iron grades have been shown to vary from ~30-60% Fe with sand, clays, calcrete and other gangue rock types as the main components considered to be deleterious to the iron grade. The smaller scree deposit on the eastern flanks of the East Baron pits is similar nature to the Empress, with a clay cemented product. A substantial paleochannel of scree ore in the vicinity also contains a good quantity of high grade material flowing east from the faces.

Iron Queen Geology
The Iron Queen deposit is on the far eastern flanks of the northern MBR.
The geology consists predominantly of the Lower Middleback Iron Formation (LMIF), the preferred host to mineralisation. The Katunga Dolomite outcrops in several places to the north and west and at depth beneath the deposit, and significant volumes of amphibolite occur to the north and east of the mined area. The Iron Queen deposit was mined during the 1980’s and consists of two main pods of hematite ore. The southern pod has been almost completely mined out, while the northern pod remains unexploited. Significant amounts of amphibolite intrude the deposit including high magnesium olivine/pyroxene porphyritic mafic to ultramafic intrusives. Hematite ore is associated with schists and BIF. The overall structure is broadly synclinal and plunges approximately 20º south. The two main ore pods appear to have been dislocated along a north trending strike slip fault. The western block appears to have moved approximately 100 m north. Granitic rocks appear to confine the ore to the north and east and a prominent north-south fault/breccia zone exists on the western side of the deposit.

There are scree ore deposits on the eastern flank of the Iron Queen deposit. The upper sections of the scree appear to be cemented calcrete agglomerations materials, whilst the lower flanks are more loosely consolidated hematite cobbles.

Operations within the Iron Baron Mining Area (IBMA) in 2020 included hematite mining in the Iron Queen, Warrior and Cavalier pits, crushing, screening, ore beneficiation, train loading and tailings deposition in the South Prince pit.

This section provides a general summary of mining activities within the IBMA that are similar across each of the different mining areas that make up the IBMA e.g. Central IBMA, Iron Cavalier, Iron Queen, Iron Sultan, BSA mining area, Iron Warrior and Scree deposits.

Mining Methods
Mining at the IBMA, with the exception of free-dig scree ore mining, is a traditional open pit hard rock mining operation using an interrupted drill, blast, load and haul cycle to remove overburden (waste rock) and expose and haul ore for crushing, screening and processing, into a primary lump and fines product for export.

Pit design is a conventional layout of angled batters (between 50º to 60º) and flat berms (between 8 to 12 m in width). The bench height varies from 6 m to 8 m and the height between berms varies from between 12 to 24 m. The batter angle, berm width and the height between berms give the overall slope angle (from pit crest to pit toe). This angle is critical to successful mining and is determined by rigorous geotechnical engineering considerations.

Ramps for pits and WRDs will generally have a gradient of no more than 1:10.

The general shape of a pit, and whether there are any stages (i.e. a starter pit followed by progressively larger pits), is determined by a process of analysis and optimisation using specialised software that takes into account the ore body, the pit design parameters, the projected mining costs and projected revenue.

Drilling for blasting programs is carried out by in-hole hammer drill rigs capable of drilling holes typically between 126 mm and 165 mm in diameter. Depth is in accordance with bench height. Pattern sizes vary to suit ground conditions such as hardness or the depth of the shot. Drill holes are loaded with ammonium nitrate fuel oil (ANFO) by a mobile manufacturing unit (MMU). Blasting takes place during set times on day shift only.

The broken dirt is loaded into dump trucks capable of hauling approximately 90 tonne per load by either a 120-tonne or 190-tonne operating weight hydraulic excavator. Topsoils removed during initial surface excavation are moved to a storage location for use during rehabilitation. Waste overburden is moved to WRDs that are reshaped when mining is completed to complement (as far as practical) the existing landform.

With the exception of Iron Sultan material, the ore from all other mining areas is hauled to a ROM pad where it is stockpiled and then fed into the main crushing and screening plant to generate either a feed stockpile for the IPF, which includes an ore wash plant and the existing Ore Beneficiation Plant (OBP), producing fines product ready for export, or to generate a lump/fines product from the main crusher plant for Direct Shipping Ore (DSO).

Ore from the Iron Sultan deposit will be hauled to a ROM located south from the new IPF, to be loaded into a hopper through a separate crusher plant circuit, specifically designed to handle the Sultan material.

The scree ore deposits will be mined using a combination of open pit and open push surface mining techniques. The open pit methodology is traditionally used for mining iron ore deposits and results in an excavation equal in volume to the total mined material. The ‘open push’ method involves mining a starter void, or box-cut, using the open pit method and then filling this void with waste from adjacent workings. This void creation and subsequent filling is undertaken in strips.

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The Iron Baron mining area (IBMA) operations include a main 7.2 Mtpa crushing and screening facility, providing a -32mm feed to a new ore wash plant facility and the existing Ore Beneficiation Plant (OBP), which together forms the Integrated Processing Facility (IPF). The IPF has a nominal 2.5 Mtpa output, for beneficiating Low Grade Ore (LGO) and scree ore resources at IBMA and providing high grade blending stocks for the Whyalla export blend.

Ex-pit ore will be transported to the Run of Mine (ROM) stockpile area at Iron Baron Central where it will be loaded into the Iron Baron crushing and screening (C&S) plant, producing two stockpiles: feed for the new IPF, and a lump / fines product for Direct Shipping Ore (DSO) or lump feed to the Blast Furnace at the Whyalla Steelworks. Lump and fines (DSO) products produced will be hauled to the rail head and loaded onto rolling stock for delivery to SIMEC Mining’s port facilities and the Whyalla Steelworks Blast Furnace. Low grade o ........