The surface geology of the HVO, MTW and Ashton coal leases is dominated by outcrops of the Jerry’s Plains and Vane Subgroups which form the Whittingham Coal Measures. The main rock types of this subgroup include sandstone, siltstone and conglomerate, which occur with subordinate coal and tuffaceous claystone.

HVO is located on the asymmetric southerly plunging Bayswater Syncline. The Auckland area is located on the western flank of the Camberwell Anticline and dips more steeply than the western limb of the Bayswater Syncline. The West Pit is located on the eastern flank of the Muswellbrook Anticline. The Barrett seam outcrops in the east of the Auckland area on the Camberwell Anticline.

The sedimentary pile in the Sydney Basin has asymmetrical thickness distribution. The thickest accumulations are along the easterly-dipping Hunter-Mooki Thrust Fault System suggesting that subsidence was greatest along that fault. The sedimentary sequence thins to the west due to the sediments onlapping into the basement rocks in the west. The Hunter Coalfield is a district- scale north-eastern subdivision of the Sydney Basin. The Permian coal bearing stratigraphic section occurs within the Whittingham Coal Measures.

HVO uses dragline and truck and shovel methods, and is operational 24 hours a day, seven days a week.

Coal is loaded using a combination of loaders and excavators with haulage to the ROM hopper undertaken using rear dump trucks. The operations are supported by additional equipment including dozers, graders and water carts.

All pit end-walls have benched and battered designs based on the existing operation with allowances made for increasing depth of mining. The design provides for mining roadways and catch benches.

Coal loss and dilution factors are also applied and vary by the equipment type uncovering the various coal seams (i.e. excavator/truck versus dragline). Typical roof and floor coal loss thickness ranges from 5-25cms. Typical roof and floor waste dilution thickness ranges from 3- 7cms.

HVO comprises three separate previous mines namely Howick, Hunter Valley and Lemington Assets which included the following:
- The Lemington Mine, which began production in 1971, was acquired and merged into HVO in 2001.
- Coal production began at the Howick Coal Mine in 1968 in what is known as the West Pit at HVO. In 2000 the Howick Coal Mine became part of Rio Tinto's Hunter Valley Operations as a result of the merger with Hunter Valley Mine.
- The Hunter Valley No. 1 Mine began production in 1979.

The HVO site area is approximately 20 km long (North to south) and 10 km wide. HVO is divided into HVO North (HVON) and HVO South (HVOS) which are separated by the Hunter River which flows through the HVO leases. There are a number of current active pits and potential future developments at HVO, with the existing operation producing approximately 20Mtpa of run-of-mine coal which results in approximately 14 to 15Mtpa of coal products.

Mine Design
Coal is planned to be mined from up to 10 separate pits over the life of the mine.

At HVON the current active mining area is the West pit, however there has been recent mining in the Wilton and Carrington pits. West pit is a dragline pit whereas the Wilton and Carrington pits are planned to be mined via truck and shovel methods only. The West pit targets a Barrett seam floor. Coal seams from the Barrett seam at the bottom of the pit up to the Lemington seam are found in the West pit area with the upper seams more developed as the pit progresses down dip to the southeast.

A centre bridge system is used by the dragline at West pit to gain access into each successive cut. The coal beneath the centre bridge is not recovered with a low-wall ramp system used to gain access to the Liddell and Barrett coal seams at West pit. The pre-strip operations are undertaken by electric rope shovels and large hydraulic excavators loading rear dump trucks. Pre-strip waste is placed into the inpit dumps with coal mined by front end loaders and hydraulic excavators hauled to either of the CHPP’s.

Within HVOS, there are two currently operating pit areas; Cheshunt 1 and 2 and Riverview. Riverview pit is located to the west of the Cheshunt pits on the western limit of the HVO lease boundary and has planned to pit limits of approximately 1.2 km wide (west to east) and 1 km north to south. Riverview is a dragline operation with truck and shovel pre-strip with the pit advancing to the south. In the north, the basal seam of the pit was the Warkworth seam (area mined out), with the central area of the pit the Warkworth seam splits away from the Bowfield seam and the floor of the pit is stepped up to a Bowfield floor.

Cheshunt 1 and 2 pits are adjoining mining areas located at the northern end of the HVOS area. The pits are mined by truck and shovel methods with waste being hauled to out of pit / inpit dumps to the north east of the pits either via the eastern endwall or cross pit access between the Cheshunt 1 and Cheshunt 2 pits. A ramp system up the advancing waste dump has been developed which provides access to a number of active dump tip heads. The combined length of operating face at the two pits is approximately 3 km. The pits are developed to the south and southwest and are a subset of the Cheshunt Deep pit extension which is planned in later years of the mine life. Coal seams from the Warkworth seam down to the Barrett seam are identified in the area, however the Cheshunt 1 and 2 pits mine down to the Bayswater seam floor only.

The future pits at HVO are the Cheshunt Deep Pit, Southern, Auckland, Carrington East and Auckland South Pits. The Cheshunt Deep Pit is scheduled to be completed in 2041 at which time the Southern, Carrington East and Auckland South Pits will be developed to maintain the total site production rate of approximately 20Mtpa. As these pits are depleted, the Auckland pit will be developed in 2052 with the operation transitioning to a lower production rate of 10Mtpa before completion in 2060.

At HVO potential underground mining targets have been identified in the Arties Seam, Liddell Seam and Barrett Seam.

HVO Arties Seam
The depth below open cut final voids appears to be sufficient to protect the underground from connection to the surface.

The Arties Seam thickness ranges in thickness from 1.5m to 2.3 m.

HVO site infrastructure, consisting of two coal preparation plants and two coal loading points.

Coal is transported to one of two Coal Handling and Preparation Plants (CHPPs) (Coal Handling and Preparation Plant) where it is crushed to size and processed to remove impurities. Processing produces saleable coal, along with coarse and fine reject materials. Coarse rejects are disposed of in-pit and fine rejects are placed in a tailings dam. Each CHPP site has storage facilities for processed (saleable) and raw (unprocessed) coal.

HVO Coal Handling and Preparation Plants (CHPP)
HVO utilises two wash plants in the HVO north area. The plants are considered to be well maintained and are capable of typical industry benchmark utilisation of 7,200 hours per year, however ongoing maintenance is required. Debottlenecking of plant circuits where necessary and with a consistent feed of coals to not overload any part of the processing circuit, should enable a total throughp ........