Test mining with raise caving mining method: one-time chance to prove the concept?

Abstract

Raise caving is a novel mining method, which is based on the raise mining method. Raises play a central role in the method and are utilised for different purposes. In the de-stressing variant, raise caving, the de-stressing slots are created first in a so-called de-stressing phase. The de-stressing slots have a tabular shape, and their objective is to provide stress shadows for mining activities in the subsequent production phase.To prove the concept and provide input parameters for a feasibility level evaluation, a limited scale trial is required.Located at the depth of LKAB's Kiruna mine in Sweden (a +25 Mtpa underground, sublevel caving (SLC) iron ore mine), the raise caving test site will be constructed in deeper parts of the mine, in an area partially prepared for SLC but mining not yet initiated. Geotechnical investigations and numerical modelling preceding development work are underway with first de-stressing raise scheduled for early 2023. Mining activities and consequent preliminary method evaluations are due during 2023-2024 with the final, a feasibility level, study to be completed by the end of 2025.The site selection process focused on locating a site that is, in key aspects, comparable with the future mining environment in the deeper parts of the mine. These are rock stress (direction and magnitude), geology and geotechnical properties. Additional aspects assessed were absence of major weakness zones, minimised negative impact for mine's performance and life-of-mine (LOMP), and relatively rapid execution of the test site construction. Both Malmberget and Kiruna mines were considered as potential sites.During the extraction of the pillar at the test site, the behaviour and condition of the pillar is continuously monitored. Other aspects to be evaluated are the feasibility to work in high stress environments during de-stressing slot development (tunnelling, raiseboring, longhole drilling), during mucking waste rock dilution entry, ore flow and ore recovery rate from a single-level mucking location.When proven successful, the raise caving can contribute to a safe and cost-effective alternative mining method in high stress environments. This paper describes steps taken in selection of a test site and integration with mine production activities.