Overview

Deposit type

• Sedimentary

Summary:

Mount Thorley Warkworth (MTW) is located within the Sydney Basin of New South Wales (NSW), a world–class export thermal coal mining district.

The Sydney Basin is a north-south trending basin, containing generally flat lying Permian Triassic sequences, approximately 250 km long, averages 100 km in width, ranges from 2km to 4km in depth and covers an area of approximately 37,000 km2 onshore and 15,000 km2 offshore.

Sedimentation in the Sydney Basin can be divided into many distinct depositional episodes, related to marine transgression and regression an terrestrial sedimentation. In the Sydney Basin the total thickness of the sedimentary package ranges on average from 2 to 3 km over much of the basin, based primarily on drill-hole records and deep seismic profiles.

Coal bearing formations in Permian aged sediments are extensive in the Sydney Basin and range in depth from near the surface to over 1 km. The Sydney Basin is divided into five major coalfields; Southern, Central, Newcastle, Hunter and Western, and comprised of black anthracite coal bed of a few centimetres to several meters, interbedded with sandstones, shales, tuffs and claystone. During coal bore drilling in the late 19th Century a number of bores encountered flows of natural gas.

The Late Permian coal measures show sources of both oil and gas, with the offshore basin possibility more prone to oil Fine grained sediments deposited during the brief marine incursions that took place during the Late Permian may also have some potential as oil sources.

Mining Methods

• Truck & Shovel / Loader
• Dragline

Summary:

The proposed mining method within MTW is the same as that currently employed. Large electric face shovels, hydraulic excavators and front-end loaders are utilised to load haul trucks to remove pre-strip and parting material. Draglines are used to expose lowest coal seams. Ancillary equipment in the form of drills, graders, rubber-tyred dozers and water carts will provide the mining equipment with support as required. Coal is extracted by front-end loaders and/or excavators loading haul trucks.

The current mining equipment will continue to be used. In general, changes may occur due to replacement or as technology changes.

Overburden and Interburden Material
Overburden removal at MTW is centred on shovel pre-stripping methods and dragline “stripping”. Multiple bench pre-stripping is used to expose shallower coal seams with a combination of dragline and shovel operations to remove lower interburden. Overburden removal operations generally proceed as follows:

- Tree clearing and timber harvesting is carried out under contract. Topsoil removal is carried out under contract using small earthmoving equipment such as a D6 bulldozer with a loader and trucks.

- Overburden is drilled. Generally holes stop short of the coal seams to reduce blast damage to vthe coal. Hole diameters range from 200mm to 270mm. Drill patterns depend on hole depth and hole diameter but pattern sizes will generally range from 5m x 6m to 10m x 12m.

- The overburden material is blasted according to design parameters specific to the geology, the presence of water, and the type of machine intended to dig the material. Overburden and interburden greater than 2.0m in thickness require fragmentation by drill and blasting.

- Overburden/interburden removal is performed by one of three basic methods:

- Shovel / Truck Fleet: The majority of the uppermost seams in the sequence are exposed using an electric shovel loading 240 and 320 tonne trucks. Overburden waste is hauled to dumps located across the site.
- Dragline: Single or double pass removal of loose overburden into previous strip, leaving a thin layer of material overlying the coal seam.
- Dozers: Dozers will be used to remove thin layers of interburden by directly pushing blasted overburden material into the previous void.

Coal
If the coal seam was uncovered by dragline, the thin layer of rock will be cleaned by tracked and wheeled dozers and graders. The coal seams may be blasted, ripped by dozers or free-dug by loaders depending on the nature and thickness of the coal. FrontGend loaders will operate with 180 tonne capacity trucks which haul the raw coal to either the North or South CPPs.

Mine Design
There are currently three operational pits at MTW:
- Loders pit,
- West pit and
- North pit.

Comminution

Crushers and Mills

Processing

• Centrifugal concentrator
• Wet Screening
• Wash plant
• Spiral concentrator / separator
• Gravity separation
• CHPP
• Desliming
• Crush & Screen plant
• Flotation
• Dense media separation
• Dewatering

Summary:

Mineral Processing
Coal will be washed in both the North CPP and South CPP in accordance with market requirements.

North CCP
The North CPP has a nominal capacity of 6.6 million washed saleable tonnes per annum, additional capacity is available through the North CHPP’s bypass facility. This system has not been tested to its maximum capabilities, however historically around 6% of the Run-of-Mine (ROM) coal has been bypassed annually or as high as 1Mt per annum.

The North CPP is a two module plant, each capable of a raw feed rate of 800tph. Raw coal is screened into two sizes, with coarse coal of diameter > 1.4mm treated in a single or two-stage dense medium cyclone circuit and the fine fraction washed in a two-stage spiral process.

The coarse coal circuit relies on relatively simple gravity separation, with coal particles floating in a magnetite and water mixture known as dense medium. The heavier non-coal material sinks while the coal floats. The speed of separation is enhanced for coarse coal particles by pumping the combined dense medium and ROM coal slurry through 1.15 m diameter dense medium cyclones. Products are dewatered in vibrating basket centrifuges prior to stockpiling.

Fine coal is cleaned in a process circuit that does not use a dense medium. It is mixed with water and pumped through classifying cyclones to remove the very fine particles (de-sliming), which generally contain a very high proportion of non-coal materials including clays. The deslimed fines are then fed to spiral separators, which separate materials by gravity, taking advantage of the differing centrifugal effects produced by coal and non-coal particles as they wind their way down the spiral pathways.

Ultra-fine coal from the classifying cyclone overflow is sent to the Beneficiated Dewatered Tailings (BDT) plant, where the coal fraction is separated by a two stage flotation circuit, deGwatered and sent to clean coal stockpiles. Reject material is sent to the tailing thickener for dewatering and thickening before being pumped to a final disposal location within the tailings storage facility.

Coarse reject is disposed of in the active mine dumps and “mixed” with normal waste dumping of the mining operations.

The coal is washed in accordance with market requirements at the North CPP, which operates 7 days a week, stopping for maintenance one day every month.

South CCP
The South CPP has a nominal capacity of 5.3 million saleable tonnes per annum. ROM coal is delivered by rear dump trucks into two raw coal receival bins. The coal is then broken down to a maximum size of 125mm in two rotary breakers, then stacked by two automatic luffing and slewing rail mounted stackers on a single 70,000 tonne design capacity raw coal stockpile.

The raw coal is reclaimed using a bridge type scraper reclaimer to a 300 tonne surge hopper where the feed is split between two 600 tph CPP modules.

Raw coal is wet screened with the +31.5 mm oversize fraction transferred to a dense medium drum. The drum product is crushed through a double roll crusher before being transferred to the clean coal stockpiles. -31.5 mm fraction is screened at 0.5 w/w mm on de-sliming screens with the -31.5 + 0.5 w/w mm fraction being treated in two stages of dense medium cyclones.

The coarse coal circuit relies on gravity separation, with coal particles floating in a magnetite and water mixture known as dense medium. The heavier non-coal material sinks while the coal floats. The speed of separation is enhanced for coarse coal particles by pumping the combined dense medium and ROM coal slurry through dense medium cyclones. Rejects from the primary DMC stage are rewashed at a higher density in the secondary dense medium cyclone to ensure efficient recovery of combustible material. Products are dewatered in vibrating basket centrifuges prior to stockpiling.

The -0.5 w/w mm undersize materials from the de-sliming screens is pumped through two stages of classifying cyclones to remove the high ash clay slimes prior and to thickening and feeding this material to the flotation circuit for recovery. Reject material is sent to the tailing thickener for dewatering and thickening before being pumped to a final disposal location within the tailings storage facility.

Coarse reject is disposed of in the active mine dumps and “mixed” with normal waste dumping of the mining operations.

The coal is washed in accordance with market requirements at the South CPP, which operates 7 days a week, stopping for maintenance one day every month.

Coal Stockpiles
North
ROM coal is delivered from the mine into two raw coal receival hoppers. The coal is then sized through 3 stage Abon crushers to a top size of 50 mm, which is then stacked via two automatic luffing and slewing rail mounted stackers on twin 47,000 tonne design capacity raw coal stockpiles.

Clean coal products are reclaimed from one of two stockpiles at the CPP which have a total design capacity 158,000 tonnes. Two reclaimers are used to feed, via conveyor, the train loading bin at the Mt Thorley Coal Loader (MTCL) facility. Coal is dispatched through this facility by rail to PWCS at Newcastle.

Bypass coal is crushed and sized to 50mm and conveyed around the CPP directly to the product stockpiles.

The North CPP also uses an emergency stockpile (CC8) as required. The raw and product coal stockpiling facilities and operations have not changed since the previous reporting period.

South
ROM Coal is delivered from the mine into two raw coal receival hoppers. The coal is then broken down to a top-size of 125 mm in two rotary breakers, then stacked via two automatic luffing and slewing rail mounted stackers on a single 70,000 tonne design capacity raw coal stockpile.

Clean coal products are reclaimed from stockpiles using a bucket wheel reclaimer that feeds the train loading bin at the MTCL facility. Coal is dispatched through this facility by rail to PWCS at Newcastle. The raw and product coal stockpiling facilities and operations have not changed since the previous reporting period.

Water Supply

Summary:

Surface Water
2021 was a wetter than average year with a total of 979.6 mm rainfall recorded at MTW’s Charlton Ridge Meteorological station. The average annual rainfall at Charlton Ridge is 668mm, as calculated from 2007 to 2021 annual totals.

Construction of sediment water management structures for the western advancing pre-strip at Warkworth was completed in quarter one 2021. These structures were designed in accordance with the NSW Blue Book, Managing Urban Stormwater: Soils and Construction, Volume 2E Mines and Quarries. Remote boundary monitoring systems were installed on the additional new pre strip sediment dams (54N and 55N). Construction of the Warkworth North Pit North drainage upgrade works was completed during the reporting period to improve water management and mitigate the risk of unauthorised water releases from site.

Groundwater
Groundwater monitoring activities were undertaken in 2021 in accordance with the MTW Water Management Plan and groundwater monitoring programme. The monitoring results are used to establish and monitor trends in physical and geochemical parameters of surrounding groundwater potentially influenced by mining.

Water Management
An adaptive management approach is implemented at MTW to achieve the following objectives for water management:
• Fresh water usage is minimised;
• Impacts on the environment and MTW neighbours are minimised; and
• Interference to mining production is minimal.

This is achieved by:
• Preferentially using mine water for coal preparation and dust suppression where feasible;
• An emphasis on control of water quality and quantity at the source;
• Segregating waters of different quality where practical;
• Recycling on-site water;
• Ongoing maintenance and review of the water management system; and
• Releasing water to the environment in accordance with statutory requirements.

Production

Operational metrics

Personnel

Job Title	Name	Phone	Profile	Ref. Date
CHPP Maintenance Superintendent	Leah Miller			Sep 29, 2023
Environmental & Community Manager	Gary Mulhearn	02-6570-1734		Sep 29, 2023
Health, Safety & Training Manager	Adam Rice			Sep 29, 2023
Maintenance Manager	Warwick Gloster			Sep 29, 2023
Mining Superintendent	Robert McGrath			Sep 29, 2023