GEOLOGICAL ASPECTS FOR THE WET MUCK MATERIAL FORMING AT THE DEEP ORE ZONE (DOZ) BLOCK CAVE MINE, PAPUA, INDONESIA

The Deep Ore Zone (DOZ) Block Cave Mine is located at the southern area of the Jayawijaya Mountain Range (Papua), a part of the East Ertsberg Skarn System (EESS) that produces mineralization from Gunung Bijih Timur (GBT) Surface, Intermediate Ore Zone (IOZ), DOZ, and Deep Mill Level Zone (DMLZ) Block Cave Mines. This mine is an underground mine that utilizes the gravity flow system at three main levels (from 3079 until 3146 meters) and has produced about 140 million tons of ore with 1.06% Cu and 0.81 ppm Au, operated since 2000 with production was about 58k tons/day and production is being ramped up to 80k tons/day by the end of 2009 until now. The increase of production arouses many challenges and the most dangerous one is the wet muck flow because the impacts are relative to fatality and economic loss. The wet muck material is formed by fine (grain size < 5cm), saturated, and loose grains merge with the water appearance. Fine and loose grains come from skarn minerals group in the EESS and Tertiary Waripi Formation rock with low the Rock Quality Designation (RQD) characteristic such as Forsterite Skarn, DOZ Breccia / HALO (High Altered Ore), and Marble. In addition, old mines rocks at the upper of the DOZ Block Cave Mine reserve (Height of Draw / HOD is about 500 meters), like the IOZ Block Cave and GBT Surface Mines, migrate into the mine and increase the wet muck material. There are Endoskarn (yellow-green Garnet), Black Amorph Silica (BAS), and Sill Diorite. Long distance of rocks migration results the change of grains shape and size to be fine and loose grains. All rocks with fine and loose grains characteristic are bound by carbonate cement from Marble and merge with water appearance, create the wet muck material with saturated and/or near saturated characteristic. High rate of the subsidence surface rainfall at the top of the EESS (about 3900 meters) is the main source of the water appearance in the DOZ Block Cave Mine. Analysis of rock types distribution and water movement based on drawpoints mapping data (added with tracer test and water balance data from the Underground Hydrology) in DOZ Block Cave Mine determine the interpretation of the wet muck material distribution.