Large-scale geotechnical program, MCC Sanjin Mining, Western Australia

MCC Sanjin Mining is an open-pit magnetite mine located at Cape Lambert, near Karratha in Western Australia. Although concept designs had been prepared, there had been few relevant groundbreaking investigations. A pre-feasibility geological model had been prepared by others based on resource drilling with little targeting of waste units; however, there was no geotechnical model or geotechnical design.

PSM was engaged to complete a definitive feasibility level design to secure project go-ahead. PSM was also responsible for technical supervision of an extensive field investigation program and provision of designs for the open-pit and waste dumps.

The Cleaverville formation, the principal geological unit in the investigation area, consists of 1,500 m of BIF, chert and fine clastic meta-sediments and is a relatively underinvestigated formation.

The nine-month field investigation required 28 oriented diamond drill holes and eight RC holes totalling 8,000 m of diamond core and 2,500 m of RC drilling. There were up to three rigs and four geologists working continuously on rotating rosters.

Following rigorous assessment and modelling, PSM’s tailored approach included:

• Extensive use of ATV/OTV surveys to supplement geotechnical drilling and surface geotechnical mapping
• Field packer testing and installation of vibrating wire piezometers coupled with laboratory geotechnical testing to assess hydraulic conductivity
• Petrological testing to assess formation mineralogy
• Staged laboratory test program in parallel to the field investigation to shorten project duration and progressively develop geotechnical understanding of rock mass properties
• Preparation of designs for open pit approximately 8km long, 0.5 to 2 km wide with wall heights of up to 410 m.

PSM successfully undertook and managed a large-scale geotechnical field program. Hanging wall design inter-ramp slope angles exceeded the conceptual design parameters by between 6 to 12° resulting in considerable cost benefits to the client.

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