Coal resources on the Stockton Plateau are restricted to the Middle to Late Eocene aged Brunner Coal Measures (BCM). The BCM unconformably overlies the Ordovician aged Greenland Group greywackes and argillites, which has been extensively intruded by Cretaceous granites and porphyry (Berlins Quartz Porphyry). Due to the stratigraphic nature of coal measures, the coal seams generally lie in a horizontal or sub-horizontal plane. The resource has a dip to the northeast at the northern end of the deposit and to east along the western margin. Folding and faulting through the coal seams can create localised changes in dips up to 80°.

Stockton
The Mangatini coal seams are the main coal seams of the Stockton deposit. The seams have been given the abbreviation M. There are the three seams M1, M2, and the M3. The M2 seam is the predominant seam over the deposit and splits into four segregated seams in places. The M1 seam is thin and discontinuous stratigraphically below the M2 and not considered for resource estimation. The M3 is a rider seam to the M2 however the seam is discontinuous and often not recovered during mining. The M3 is not considered during resource estimation.

The Stockton resource area covers approximately 22.9km², a roughly rectangular shape up to 3.5km wide (E-W), and 8km long (N-S).

Within this area all seams are exposed in the operating mine, with in situ coal between 0m and 50m below the original ground surface.

Coal thickness varies considerably over the deposit, from 28m (areas with structural thickening) down to <0.5m (areas with coal seam poorly developed). On average the remaining coal resource has an average thickness of 8-10m.

The M3 rider seam to the main M2 seams is on average 0.5m thick but can have localthicknesses of 3m.

Upper Waimangaroa
The Mangatini coal seams are the main coal seams of the Upper Waimangaroa Deposit. The seams have been given the abbreviation M. There are the three seams M1, M2, and the M3. The M1 and M2 seams are the predominant seams over the deposit. Seam splitting is commonacross the deposit and can lead t correlation complications. No distinct marker horizons arepresent between the seam. Correlations are based on detailed cross sections completed across the deposit. The M1 and M2 seams are the dominant seams targeted for mining and can vary in thickness. The M2 seam overlies the M1 seam. The M3 is a rider seam to the M2. The M3 seam is considered for resource classification in the Cypress consented area where it exceeds the minimal mining cut-off of 0.5m. The M3 seam is characterised by having high sulphur (>4%) and is generally poorly developed.

The Upper Waimagaroa resource area covers approximately 4km², a roughly rectangular shape up to 2km wide (ESE-WNW), and 10km long (NNE-SSW).

Within this area all seams are exposed at outcrop along the western margin of the MP. With the bulk of the in situ coal between 0 and 150m below the original ground surface.

Coal thickness varies considerably over the deposit, from over 20m (areas with structural thickening) down to <3m (areas with coal seam poorly developed). On average the cumulative (M1 and M2) coal resource has an average thickness of 8m.

The M3 seam is on average 0.5m thick.

Stockton
The mining method is conventional drill and blast, load and haul open pit mining operation. This utilises truck and excavator for waste movement, while coal is loaded using a combination of loaders and excavators with haulage to the run-of-mine (ROM) hopper CHPP, or stockpiles using dump trucks. The operations are supported by additional equipment including dozers, grader and watercarts. The selected mining method is based on long term experience of local conditions.

Minimum recoverable in situ thickness is 0.5m.

Geotechnical parameters are based on geotechnical studies undertaken by the Stockton engineering geologists. Specific parameters are applied to each pit. Pit designs have been based on geotechnical constraints and parameters. The typical highwall configuration is a batter height of 15m with batter angles between 30°- 76° using 8.5m wide benches. A maximum 10% gradient and 23m wide running surface is being used for in pit ramps and roads.

Pit limits have been updated based on pit optimisation studies with restrictions for current land and mineral access determined by mining permits and granted consent limits.

Pit optimisations used current cost and revenue assumptions. The latest pit optimisation study was completed by Golder Associates (NZ) Limited in 2018.

Additional recovery factors for Millerton, Hope Lyons and Rockies mining block areas include losses for historical underground extraction, fire effected coal, and where the overburden material has collapsed into the coal seam.

Approximately 60% of total Coal Reserve tonnes require washing to make a marketable product.

Minimum mining widths are dependent on volumes to be excavated and the size of the fleet to be used. Typically for the bulk excavator and truck fleet this is approximately 30m. For the small excavators and trucks this is approximately 15m.

Current mining methods require the following infrastructure; haul roads, drainage, pumps, sumps and dam structures, lime dosing plants, coal stockpile areas, CHPP, coal load out and bins, aerialropeway, train load out and bins, workshop, offices, and contractor facilities. Much of this
infrastructure is in place with the main new infrastructure required being related to water anagement and access such as sumps, dams and water control as the mining progresses into new areas.

Upper Waimangaroa
The mining method is conventional drill and blast, load and haul open pit mining operation. This utilises truck and excavator for waste movement, while coal is loaded using a combination of loaders and excavators with haulage to the Run of Mine (ROM) stockpiles, directly to the CHPP, or to other intermediate stockpiles using dump trucks. The operations are supported by additional equipment including dozers, graders and watercarts.

Different parameters are applied to each pit. Pit designs have been based on geotechnical constraints and parameters. The typical highwall configuration is a batter height of 15 m with batter angles between 30°- 63° using minimum 8.5 m wide benches. Maximum of 10% gradient and a 23 m wide running surface is being used for in pit ramps and roads.

Minimum recoverable in situ thickness is 0.5 m. All coal qualities quoted are on an Air-Dried Basis (adb).

Minimum mining widths are dependent on volumes to be excavated and the size of the fleet to be used. Typically for the bulk excavator and truck fleet this is approximately 30m. For the small excavators and trucks this is approximately 15m.

Current mining methods require the following infrastructure: Haul Roads, Drainage, dewatering and transfer pumps, sumps and dam structures, Lime Dosing Plants, coal stockpile areas, CHPP, coal load out and bins, aerial ropeway, train load out and bins, workshop, offices, store, maintenance and contractor facilities. Most of this infrastructure is in place with the main new infrastructure required being sumps, dams and water control as the mine expands into undisturbed areas.

Stockton
Bypass Coal is defined as coal recovered that is not contaminated by rock or other materials and which when mined, is a saleable product (ash <8%).

Wash Coal is defined as coal that requires processing/washing prior to becoming a marketable product. The feed cut-off grade depends on the ash source, being either >8% and <35% if in situ ash, or >8% and <50% for coal contaminated with non-coal material.

Approximately 60% of total Reserve coal tonnes require washing to make a marketable product.

Stockton has a CHPP in operation to produce a marketable product.

The CHPP has an online analyser for identifying coal that is out of specification.

Additional samples are sent for petrographic analysis (Romax).

The processes used are standard for the coal industry and so are well tested technologies. This has also been backed up by bulk samples being taken and tested for washability, yield and recovery factors.