The Rotowaro deposit trends north-south to the north of 618250mN and northwest-southeast to the south of 618250mN (Mt Eden Circuit 1949).

The dip is to the northwest at the northern end of the deposit and to the southwest along the western margin.

There are a series of northwest-southeast trending anticlines and synclines in the central and east of the deposit. Rotowaro is bounded to the southwest by the Mangakotukutuku Monocline, with a net throw of 90 m down to southwest, and to the northeast by the extension of the Waipuna Fault scarp.

There are only minor faults identified within the deposit, with throws less than 10 m in height. These faults are either recorded on historical underground mine plans or interpreted from structure contour plans derived from drill holes.

The area is underlain by indurated siltstones, with common sandstones, of the Mesozoic Newcastle Group, which is weathered to a depth of 5-30 m. This unit is referred to as “Basement” and has no economic significance.

The Waikato Coal Measures (WCM) lie unconformably on the basement and form the lower part of the Te Kuiti Group. The WCM consist mainly of mudstones and siltstones, often referred to collectively as “fireclay”, with common siderite concretions, referred to as “hardbars”.

There are three major coal seam groups within the WCM: Renown, Kupakupa and Taupiri.

The Taupiri seams are only represented in the Callaghan’s sector of the Rotowaro Coalfield, where they are confined to the structural trough between the Mangakotukutuku Monocline and the Waipuna Fault scarp.

Thickness patterns of seams lying close to basement are influenced by the paleo-relief developed on the basement contact, with thickening and thinning over basement valleys andridges respectively.

The upper part of the Te Kuiti Group consists of marine to marginal marine claystones, mudstones, sandstones and siltstones which are conformably overly the WCM. There is a regional unconformity at the top of the Te Kuiti Group, above which lie the Quaternary deposits of the Tauranga Group, consisting of interlayered alluvial clays, muds and highly weathered volcanic ashes of the Hamilton Formation.

The Rotowaro resource area covers approximately 11.5 km².

Within this area all seams are exposed in the operating mine. Prior to mining the Renown Seam roof wasas close as 6 m below the surface and the floor of the Taupiri Bottom seam is as deep as 290 m (-200m RL) below surface.

Coal thickness varies considerably throughout the Rotowaro area, from 28 m down to <0.5 m

The site operates using traditional truck and shovel open cut mining methods with parameters selected from long term experience of local conditions.

Mining recoveries - minimum recoverable coal seam thickness is 0.5 m. 1 % of the in situ is assumed to be lost and is not included in the Coal Resource Estimate.

Minimum mining thickness, seam compositing factors, losses associated with u/g mining and washery yield.

Truck and shovel has been determined to be most cost effective mining method given the multiple coal seams as well as the requirement for large quantity of ex-pit dumping initially required. This is the proven mining method in terms of past and present operations at site.

Geotechnical parameters for cut slope design were developed based on historical cut slope performance, slope back-analysis and laboratory testing of material strength parameters. Basic highwall design criteria include slopes in Waikato Coal Measures (fireclay and coal) and ‘softs’ (marine sediments, quaternary clays and old backfill). Slopes are designed to comply with a Factor of Safety that exceeds 1.2 and within BRL’s risk volume criteria which is a function of the probability of failure and potential failure dimensions. Consideration of underground workings intersecting highwalls also considered.

Mining dilution factors are minimum mining tk 0.5m, parting 0.1m, coal waste 10:1, roof/floor losses 0.15m (combined) per recoverable seam.

To account for minor unmodelled faults the quantity of in situ tonnes is downrated by 1%.

A ‘mining recovery’ variable is calculated in the reserve model to account for roof and floor losses of 150mm. The formula is (seam thickness – 0.15) / seam thickness and the result ranges from 0.700 (0.5m mining horizon) to ~0.985 (10m mining horizon).

Resource tonnes are calculated using estimated seam depletion quantities from historical records.
- KK seam first worked 30%, pillared 1.5m 55%, pillared 5.0m 65% and 8.0m 60%.
- TP seam: first worked 40% pillared 1.5m 55% pillared 5.0m 60%.
- TM seam first worked 20%, pillared 1.5m 55%, pillared 5.0m, 65%, pillared 8.0m, 60%, Pillared 10.0m, 55%.
- TL seam First worked 15%.

ROM tonnes are calculated by multiplying resource tonnes by mining recovery.

Coal sent to the washery is then ROM tonnes multiplied by the proportion of the seam coal requiring washing.

Proportion of coal sent to wash plant; unworked 11%, first worked 23%, pillared 59%.

The washery yield is currently modelled at 62%.

Clean coal sent direct to the Blending Plant (BP) from the pit is simply ROM tonnes less wash tonnes.

Total product coal is clean coal sent direct to BP plus washery product.

CQ values adjusted for product specs by adding 0.55% to ash, 5.3% to convert air-dried moisture to produce moisture.

Product coal specifications include ash, sulphur, fixed carbon, moisture and calorific value. Product specifications are adequate to meet contractual sales requirements.