SRK recently completed a Pre-feasibility level geotechnical assessment for a hillside iron ore operation in Eastern India, where pit slope design was fundamentally controlled by the complex geological and structural setting of the deposit.
The orebody occurs within a folded iron formation sequence that has undergone multiple phases of deformation, resulting in a characteristic dome-and-basin structural architecture. Subsequent weathering and supergene enrichment preferentially developed thick zones of weak friable ore within the structural basins, while competent Banded Ferruginous Quartzite (BFQ) remained dominant along the dome flanks and at depth. As mining advances through these structures, pit slopes transition from friable ore in the upper benches to competent hard rock in the lower slopes.
This geological setting created a unique geotechnical challenge. The transition zone between friable ore and hard rock does not occur as a simple contact, but as a heterogeneous mixture of weak and strong materials exposed within the same slope. Conventional approaches based on a single geotechnical domain or uniform bench geometry were considered impractical and risked either sterilising ore or introducing unnecessary geotechnical risk.
To address this challenge, SRK developed a three-dimensional structural model of the dome-and-basin geometry in Leapfrog© and assed the relative proportion of friable ore and hard rock expected to be exposed within successive pushbacks and final pit walls. The analysis showed that upper benches in the transition zone were frequently dominated by friable ore, often exceeding 70% exposure, while deeper benches became progressively dominated by competent BFQ.
This understanding enabled the development of a practical slope design framework. Bench configurations were tailored to the predicted material exposure, with weak-material design principles applied where friable ore dominated and hard-rock geometries adopted where competent BFQ became prevalent. Recognising that friable ore would naturally ravel to gentler angles during mining, bench widths were designed to accommodate degradation and routine clean-up activities while maintaining overall slope performance.
The structural model also formed the basis of a risk-based slope management strategy. Monitoring requirements, inspection frequencies, and Trigger Action Response Plans (TARPs) were linked to the anticipated distribution of friable ore and hard rock throughout the pit. Areas dominated by competent BFQ were assigned lower monitoring intensity, while transition-zone slopes were identified as higher-risk sectors requiring enhanced surveillance and ongoing performance review.
By predicting how the proportion of weak and strong rock changes with depth, the study transformed a deposit-scale geological model into a practical slope design and slope management tool. The approach enabled optimisation of ore recovery while maintaining acceptable geotechnical risk, demonstrating how detailed structural geology can directly influence both mine design and operational decision-making.
