The Marandoo open-pit mine is located at the foot of Mount Bruce adjacent to the Karijini National Park, 50 km east of the town of Tom Price. The RTIO rail line skirts the northern margin of the ultimate pit.
PSM was engaged to undertake the geotechnical investigation and risk assessment for potential sinkhole and doline formation. The investigation included a precedent study drilling adjacent to an existing sinkhole.
The RTIO rail line is located on the northern margin of the proposed pit slope and marks the boundary of the Karijini National Park. The site geology comprises folded and faulted Archean bedrock sequences unconformably overlain by about 150 m of Cenozoic detritals including conglomerates, a thick lacustrine clay deposit and calcrete. The pre-mining water table is high, at approximately 30 m depth. The top of a thick calcrete sequence is co-incident with the pre-mining ground water level and soft to firm clay up to 100 m thick underlies the calcrete.
Engineering and technical opportunities included:
Following a rigorous assessment and modelling, PSM’s tailored approach included:
Two components of the field investigation were precedents for mining in the Pilbara. By using advances in drilling often employed in the civil industry, PSM successfully demonstrated a significantly improved understanding into the engineering properties of the geology than previously achieved. The sinkhole drilling study allowed an existing structure to be characterised and mechanisms of failure identified. By comparing the findings of the sinkhole study with site data, PSM identified low, moderate and high risk areas and made recommendations to monitor and mitigate that risk.
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