The Porphyry Gold Mine is located 150 km north east of Kalgoorlie, Western Australia. Some intermittent mining was undertaken at the site in the 1930's and 40's and in 1984 Pioneer Concrete Services Limited and Poseidon Limited in joint venture recommenced operations. A new treatment plant of capacity 240 000 tonnes/yr was commissioned and open pit mining commenced._x000D_
The mineralisation at Porphyry is associated with a gently dipping (25) shear zone which lies within a quartz monzonite intrusion. This style of mineralisation made the open pit atypical of other goldfields oxidised ore pits.During 1986 the feasibility of mining reserves by underground methods was further investigated. The in-situ geological reserve grade derived principally from exploration drilling was, using open pit mining results, significantly reduced. The lower grade necessitated consideration of minimum waste development and high mining efficiencies. It was decided to locate a decline in the orebody and room and pillar stope._x000D_
By December 1986 the open pit was nearly depleted having produced over 800 000 tonnes of ore and approximately eight million tonnes of waste. A contract to mine underground was awarded and mining commenced in a series of adits driven on exposed ore. Once open pit equipment was finally withdrawn a permanent decline was commenced and production increased to 240 000 tonnes/yr._x000D_
Nearly all development including the decline is kept in ore, the main exception being a hanging wall return ventilation drive located across the top of the orebody. The stoping method, room and pillar, has been modified from initial concepts as experience was gained. The stopes are mined using hydraulic jumbos and trackless equipment. The combination of a small workforce and virtually total mechanisation has permitted operations to successfully continue in mined grades of 3.3 - 4.3 g/tonne._x000D_
The operations at Porphyry are somewhat unusual in a number of aspects other than the above. The mine is fully self contained and operates without any regional or head office technical and administrative support. The remote minesite is the only office and all purchasing, recruiting, accounting etc is undertaken from there.