The coal seams of interest in the Illawarra Coal Measures are the Bulli, Balgownie and Wongawilli Seams. At Russell Vale, the Illawarra Coal Measures are overlain by the Narrabeen Group, the thick sequences of Triassic Hawkesbury Sandstone and in parts, the Wianamatta Group.

The Wongawilli Seam is on average around 27m below the Bulli seam at Russel Vale. The Wongawilli Seam has a typical total thickness of 8 – 11 metres over the project area and is characterised by a series of kaolinitic mudstone partings in the seam. The basal part of the seam contains the highest proportion of coal and is typically targeted in underground mines in the area including Wongawilli and Dendrobium (South32 Limited).

Depth of cover to the Wongawilli ranges from 200-320m in the Wonga East area, increasing to 400- 450m in the west. Most of the variation in depth of cover arises from the surface topography.

The Wongawilli Seam dips towards the north-west at less than two degrees in the Wonga East area as shown. The dip direction swings to the west in the Wonga West area towards a broad syncline structure known as the South Bulli Syncline. In the eastern portion of the tenement boundary the coal seams outcrop on the escarpment.

There are several dykes that traverse the south-eastern project area mostly orientated in a WSW-ESE direction while occasional dykes (mostly trending NE to NW) are located to the west. Numerous dykes have been encountered in previous workings and they are typically less than 3m in thickness. Many have been altered to clay and do not cause major issues for underground operations.

A large area of silling in the Wongawilli Seam has been delineated through drilling and affects the northern part of the Wonga East area, limiting the mining area in a northerly direction. Sills are often present and associated with dykes and have preferentially intruded the coal seams. As the Wongawilli Seam is thick sills have intruded the seam at different levels and to varying degrees of replacement and heat affectation.

Large displacement faults in the Southern Coalfields consist primarily of normal faults with dips of between 70 and 85 degrees, trending NW or NNW. Another set of faults is in the coastal zone and trending NE although most faulting in the Wonga East area is oriented broadly WNW. Definition of faulting at Russell Vale is generally quite good based on the experiences of mining the overlying Bulli and Balgownie seams as fault locations are similar (slight offset) in the Wongawilli Seam.

The Wongawilli Seam has several well-known and easily identified claystone partings which generally increase towards the top of the seam. The Wongawilli Seam shows deterioration in quality in the north when compared to the southern part of the coalfields.

The basal working sections (from the base of the seam upwards) of the Wongawilli Seam in the Wonga East area deliver a moderate ash (>30%) coal. Raw ash content of the Wongawilli standard section generally increases from west to east across the Wonga East area coupled with decrease in working section height and decrease in yield. Raw ash content for the Wongawilli Standard section (excluding mining losses and dilution) ranges from 26 - 38% (ad) in the Wonga East area. Typically ranges between 29 and 34% (adb) in the proposed mining area (Clark, 2017).

The Wongawilli Seam is a mid-volatile bituminous coal which can be washed to produce a hard-coking coal product. Mean maximum vitrinite reflectance (RoMax) for the Wongawilli Seam typically rangesbetween 1.29 and 1.35% in the Wonga East area. The rank increases slightly in a westerly direction towards the axis of the South Bulli Syncline.

Clean coal testing shows that the washed product has high vitrinite content (80%), high CSN (8 – 9) and high fluidity (up to 2000 ddm), with low to moderate total sulphur (0.50%) and low phosphorus (0.003%). Product ash is slightly in excess of 10% due to the high inherent ash content.

The proposed method is bord and pillar with the pillar size being dictated by surface constraints and previously mined upper seams. There is to be no subsidence as the mine operation will be below a major water catchment area. Mining recovery will range from 30 to 40 percent.

Mains headings and panel insert headings will be developed by conventional cut and bolt mining equipment.

The plan does not utilise longwall mining or pillar extraction. The main development works, and Place Change panels are all designed as first workings with the coal pillars to be long-term stable with the appropriate factor of safety to ensure negligible subsidence of the overlying surface. Pillar dimensions are assumed to be one tenth (1/10) the depth of cover, with 5.5-metre-wide roadways mining a standard seam section of 2.45 metres to provide a favourable width to height ratio for the pillars.

Place Change panels feature five headings with a central coal clearance system, belt conveyors and flanking returns. All pillars in the Place Change panels are a minimum of 25m x 25m. Mains headings consist of four heading layouts driven to a height of 3.0 metres and a width of 5.5 metres with large pillars to ensure area stability and meet ventilation requirements.

Given the nature of the equipment selected dilution is expected to be minimal as the miner will cut from a welldefined floor to the floor of the First Machine Band which is also well defined. Any dilution or contamination resulting from mining will be removed in the processing plant.

Mining widths have been determined by the continuous mining equipment that will be used. For access, ventilation requirement and optimised mining recovery a cutting width of 5.5 metres will be used. The surface and underground infrastructure for mining is established.

The plant will be a single stage dense medium cyclone (DMC) processing plant. The rated capacity of the processing plant will be 750 tph ROM. The principal purpose of the DMC is to reduce the ash in the product coal.

It is expected that the overall yield through the processing plant will be 84% producing a 12% ash coking coal and a 26% ash thermal coal. Coking yield is expected to be 57% and thermal yield 27%. Rejects of 16% will account for the remainder. The coal will be exported as a lower ash, single product coal. A new 14 ktonne product stockpile and 1.5 ktonne reject stockpile will be established.

Product coal will then be transferred to a new truck loading bin from where it will be either loaded onto road trucks for transportation to PKCT or transferred to the product stockpile area for temporary stockpiling.