The Rotowaro deposit trends N-S north of 618250mN and NW-SE south of 618250mN. The dip is to the NW at the northern end of the deposit and to the SW along the western margin. There are a series of NW-SE trending anticlines and synclines in the central and east of the deposit. Rotowaro is bounded to the SW by the Mangakotukutuku Monocline, with a net throw of 90m down to SW, and to the NE by the extension of the Waipuna Fault scarp. There are only minor faults identified within the deposit, with throws less than 10m. These faults are either recorded on old underground mine plans or interpreted from structure contour plans derived from drillholes.

The area is underlain by indurated siltstones, with common sandstones, of the Mesozoic Newcastle Group, weathered to a depth of 5-30m. 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 Mangokotuku 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, thickening and thinning over basement valleys and ridges 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 11.5km².

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

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

The Rotowaro mine commenced opencast mining operations in 1958.

Geotechnical parameters for cut slope design were developed based on historical cut slope performance, slope back analysis and laboratory testing of material strength parameters. Slopes are designed to comply with a Factor of Safety that exceeds 1.2 and within BRL risk volume criteria which is a function of the probability of failure and potential failure dimensions.

Mining recoveries. Minimum recoverable coal thickness 0.5m. Unworked coal seam recovery 97%, first worked coal recovery 94% and pillared coal recovery 34%; - all include wash recovery.

Pit optimisation runs were completed to determine economic pit limits.

Thin seam cut-off limit determined from long term site experience and quality info related to sales product requirements.

Mining recoveries based on historic recoveries.

KK seam fw 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%.

Proportion of coal to wash plant Unworked 10%, First Worked 20%, Pillared 50%.