The local geological structure at Narrabri has been influenced by the presence of the Boggabri Ridge. The strata strike north-south and dip westwards at less than 5°. The stratigraphic sequence developed at the mine site includes the following units, described in descending order:

- Pilliga Sandstone – coarse grained quartz sandstone up to 60 m thick, which crops out in the western parts of ML1609 and EL6243;
- Purlawaugh Formation – up to 140 m thickness of thinly bedded sandstone and siltstone, with subordinate claystone and coal;
- Garrawilla Volcanics – up to 40 m thickness of alkali basalt flows with thin intervening mudstone and clastic rocks, unconformably overlying Triassic rocks where it is present;
- Deriah Formation – sporadically developed, lithic sandstone up to 15 m thick;
- Napperby Formation – siltstone, sandstone/siltstone laminate and fine- to mediumgrained quartz-lithic sandstone to 140 m thick;
- An intrusive basalt sill is present 30-35 m above the base of the Napperby Formation and is 15 to 20 m thick;
- Digby Formation – lithic, pebble conglomerate, typically 12-24 m thick, overlying the Black Jack Group; the boundary between the two being a low angle unconformity;
- Black Jack Group – consists of lithic sandstone, siltstone, claystone, coal and minor tuff; thickness is up to 70 m in the western part of ML1609 and less than 40 m thick in the east where the sequence is partially overlapped by the Digby Formation;
- The Hoskissons Coal, which forms the mineable resource at the property, has formation status and is part of the Black Jack Group;
- The Black Jack Group is underlain by a sequence of rock of marine sedimentary origin, namely the Watermark and Porcupine Formations;
- The marine sequence is underlain by the Maules Creek Formation, which is mined to southeast of Narrabri and is, in turn, underlain by the Leard Formation;
- The basement to the Gunnedah Basin sequence in the area comprises the dacite- to rhyolite- asalt and pyroclastic rocks of the Boggabri Volcanics.

The Hoskissons Coal consists of mainly of dull coal, comprising a lower ash basal section and a higher ash upper section. The full seam thickness within ML1609 and EL6243 is in the range 0 to 11.8 m thick; the seam is overlapped in the eastern part of the tenements by the conglomerate at the base of the Digby Formation. Over the area where the seam is being mined, and is planned to be mined, the full seam thickness is generally of the range 5-9 m thick. The basal 4.2 m section of the coal seam is defined as the working section for underground development within ML1609.

The Hoskissons seam is developed over an approximate area of 7,200 ha and occurs at depths ranging from 140 m in the east to 360 m in the west. The contained strike length of the coal seam is approximately 16 km whereas the down-dip width of the coal seam within the tenements is 4.5 km.

The Narrabri mine exploits coal from the Hoskissons seam. The seam is divided into two sections, namely an upper section (HC1) and a lower section (HC2). The lower section (HC2) contains low ash coal, suitable for underground mining and production of thermal coals (raw ash 8-13%). HC2 is 2.0 to 4.2 m in height and is the working section for the mine. The seam is thinnest in the east, where it is overlapped by the Digby Formation, but is consistently 4.2 m thick, allowing for thick seam longwall extraction. The upper section (HC1) contains high ash stony coal and tuffaceous claystone and as such, is higher in ash content.

The upper part of the seam (HC1) forms a mainly coal roof against the conglomerates of the Digby Formation, which is dominated by conglomerate (12-24 m thick) and consisting of hard lithic pebble- to cobble-size clasts (>100 mm) within a variable strength matrix.

Longwall mining is the predominant underground coal mining technique in use in Australia. It has significant safety, productivity and cost advantages over other coal mining methods. Both Narrabri North and Narrabri South Reserves assume the use of retreat longwall mining. In retreat longwall mining, two parallel sets of roadways (gateroads) are driven from main headings to block out an initial longwall panels. Panel widths can range from 100 to 440 m, and lengths can reach 4 to 5 km. Once the gateroads reach the extent of the longwall panel, a connecting roadway is driven, then the longwall face equipment is installed in this. As the longwall face retreats back to the main headings, the roof of the mined area behind the longwall collapses (goaf). Subsequent longwall blocks are formed up by driving more gateroads.

The mine design includes the following design parameters:
- The longwall panels mined during the MOP term (LW107-109) will range in length from approximately 2.9 km to 3.7 km. Longwalls 107 to 109 will be 400 m wide, with a total void width of approximately 408.9 m;
- The longwall panels are located at depths increasing from approximately 230m below the surface at LW106 to 325 m below surface at LW109 as the Hoskissons Coal Seam dips to the west;
- The longwall panels will have an average face extraction height of 4.3m taken from the floor of the seam (which is between 5m to 9.8m thick). The face height will be graded back to the gate roads at a height of 3.7m at the maingate and tailgate ends.
- The chain pillars formed between each longwall panel will be 3.7m high, with the pillar widths increasing as depth of cover increases;
- The longwall panel width to cover depth (W/H) ratio for LW107 to LW109 will range from 1.2 to 1.7. The chain pillar W/H ratio will increase from 8.0 at LW107 to 9.7 at LW109; and
- The chain pillars formed for the cut and flit panels will be 3.7m high, with the pillar widths increasing as depth of cover increase.

The longwall design is based on proven technology with an emphasis on reliability of equipment. The principal components of the system include:
- Double-ended ranging drum shearer rated at 4,500tph with full horizon control;
- An armoured face conveyor rated at 4,500tph with provision for single tailgate drive and dual maingate drives;
- Beam Stage Loader rated at 5,000tph; and
- High capacity two leg and four leg chocks shields with shearer initiation, base lift and high set functions.

Mining in LW107 panel, the first 400-metre wide panel at Narrabri began late in FY2017 and continued through FY2018. Mining was delayed by several mechanical problems, each of which have been rectified by the manufacturer over the course of the year. Production lost with these disruptions was not able to be recovered. A number of localised weighting events also slowed the retreat of the longwall and impacted
production.

To reduce the impact of weighting events, Whitehaven has employed a number of strategies which are having a positive impact. The more intensive primary and secondary support regime is a key component of this and has become the standard for new development in the working area of the mine that exceeds 250 metres depth of cover.

Narrabri production decreased by 5% to 6.1Mt (FY19: 6.4Mt). The decrease in production was a result of an additional two weeks taken to upgrade the longwall’s 398 leg cylinders that took place during the longwall relocation in the second quarter and a weighting event in March that caused a deferral of 500–600kt of longwall coal production. Following these two events, the Narrabri operation has delivered strong production performance. In April Narrabri recorded 1.0Mt ROM production – the second time in its history that it has recorded one million tonnes in a month.

Saleable coal production increased by 16% to 6.5Mt (FY19: 5.6Mt), reflecting improved mine yields, with annual yield increasing from 94% in FY19 to 99% in FY20. The improved yield partly reflects operational improvements at the CHPP.

The next longwall move from panel 109 to 110 is scheduled for the end of Q3 FY21.

Narrabri Stage 3 extension
The project seeks to convert Narrabri’s existing exploration licence into a mining lease and use the existing portals, CHPP, rail loop and associated infrastructure to extract, process and ship 80–100Mt of ROM coal using the longwall mining method. The project involves extending the longwall panels planned for the mining lease south of the current main roads into the contiguous Narrabri South Exploration Licence area, to extend the approved life of the mine from ~2031 to ~2044.

Coal Processing and Transport
Transportation of the mined coal to the ROM coal stockpile occurs via the conveyor drift from the Pit Bottom Area to the Pit Top Area. The ROM coal is then drawn from the ROM coal stockpiles via one of two reclaim valves and tunnels from where it is fed to a rotary breaker for size reduction and waste/stone removal. The broken coal is then transferred to a dry screen with the < 20mm coal fraction transferred directly to the thermal product coal stockpile area and the remainder transferred to the CHPP where the coal is washed. The fine and ultra-fine coal is mechanically dewatered via a belt press and added to the thermal product stockpile. The washed coal is transferred to the product coal stockpile area as either a thermal coal or Pulverised Coal Injection (PCI) grade product.

The bypass crusher is fed by dozer from the ROM stockpile. The coal is then conveyed over a screen to remove waste material. The coal is then crushed to =50 mm and fed by conveyor on the product stockpile as a thermal coal product.

The product coal is then drawn from the product stockpile via three reclaim valves and tunnels and conveyed to the train load-out bin. The loading of product coal via the drawdown valves and train loadout bin is fully automated with batches drawn from the stockpiles and loaded into train wagons on the Narrabri Mine Rail Siding.

Narrabri is producing a high energy export thermal coal and a low ash, low sulphur, low phosphorus, mid volatile PCI coal.

The Narrabri North process generates a PCI coal product from a low cut point that will produce a 7 - 8% ash product and a thermal product of around 12% ash is produced from the screening undersize and the Dense Media Cyclone (DMC) middlings.