The stratigraphy covered by the KCGM tenements consists of a basal ultramafic unit called the Hannan Lake Serpentinite. This ultramafic unit is overlain successively by the high magnesian Devon Consols Basalt, Kapai Slate, tholeiitic Paringa Basalt and the Black Flag sediments. Differentiated zones of dolerite and gabbro texture occur within the mafic sequence. The Golden Mile Dolerite, hosting the bulk of the Golden Mile and Mount Charlotte gold mineralisation, is a strongly differentiated layered gabbro, approximately 700m in thickness. The Golden Mile Dolerite is situated conformably between the Paringa Basalt and the Black Flag sediments. This entire stratigraphic sequence is intruded by numerous porphyry dykes of intermediate to felsic composition.

The Mt Charlotte style gold mineralisation is hosted within the Golden Mile Dolerite and is predominantly associated with pyrite in carbonate alteration haloes around quartz veins, with a minor proportion as relatively coarse free gold within the veins, commonly close to their margins. The veins vary in width from a few millimetres to a maximum of about two metres but are commonly between two centimetres and 50 cm wide. The vein spacing varies from 20 cm to tens of metres but is typically from 50 cm to two metres in areas mined as ore. Quartz is the dominant vein-fill mineral; accessory vein minerals include calcite, ankerite, scheelite, pyrite, pyrrhotite, and gold.

The Hidden Secret style gold minerali ........

Mt Charlotte Underground Mine
The Mt Charlotte underground mine is accessed via a portal within the Fimiston Pit (Super Pit) and the Cassidy Shaft. Production in Mt Charlotte is carried out utilising a combination of remnant Sublevel caving, modified Avoca and conventional longhole open stoping. In most cases, active and historic stopes are backfilled with development waste to save haulage costs.

The main Mt Charlotte orebodies are worked by sub-level caving; the dimensions and ground support for the mill-holes and access drives are determined using the rock mass Q value and structural information. Hidden Secret is mined using a combination of modified Avoca and Avoca mining methods; stope dimensions and backfilling requirements are determined using hydraulic radius and Q value, modified by location of major structures and rock mass changes.

Underground operations at Mt Charlotte are subject to mine seismicity. The mechanisms for seismic activity are well understood, and a combination of careful extraction sequencing and appropriate ground support in access drives is used to limit stress build-up (and thus event magnitude) and minimise damage from those seismic events which do occur.

Dilution factors are updated when there is sufficient data to do so and are based on the historical performance of each mining block and evaluation of the geotechnical block model. Average stope dilution specific to mining method and ranges from 10% to 20%.