Mine geology in fractured aquifer environments: Case study from Ernest Henry Mine

Session 11

Daniel Ashton

Ernest Henry Mining

When evaluating the complexity of an ore body, geotechnical and geological conditions are of paramount importance. However, hydrogeological factors can also play a large role in the complexity of mining a deposit. Ernest Henry Mine is influenced by regional and local water bearing formations, which have led to challenges throughout the lifespan of mining operations. In addition to conventional geology operational workflow, understanding hydrogeological water zone complexity has become critical to the success of mining activities.
As the mine advances deeper we are moving into areas with only large spaced (less than 100 metres) surface drilling with no water intersection information. Future mining at depth prompted a review of historic drill holes through which a new major structure (AB Fault) was identified. This broken zone was previously unidentified due to the high angle of the informing drilling. From this initial review, the characteristics of the structure were recognized to be similar to a previously encountered major fault that exhibited high pressure and high flow water. With anticipated potential pressures of 80 bar, steps were taken to de-risk a drilling campaign exploring in this area for resource definition and structure delineation. The initial diamond drill hole intersecting AB Fault encountered water flows of up to 40L/sec at 90 bar and 51 degrees Celsius, confirming interpretation. Subsequent targeted drilling intersected water allowing for definition of a new hydrogeological risk zone. Ongoing data analysis has developed the understanding of this aquifer, showing it to be a complex zone that may affect future sub-level cave performance.
In this paper we will discuss the hydrogeological complexities of mining in a hydrologically active environment. Using our experiences as a case study we will explore risk mitigation techniques and how this field is being incorporated into the mining workflow at Ernest Henry Mine.

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