Classification of slope failures in magnetite–apatite pit walls by type and volume, and the planetary jointing impact evaluation in this context

Abstract

Effect of planetary jointing on initiation of slope failures in a test magnetite–apatite open pit mine is evaluated. First, all slope collapses documented in the last three decades in the pit are classified. It is found that 83 % of slope failures are flat and V-shaped. The pie diagram constructed using the data base on joints which participate in initiation of slope failures shows that the process of slope collapse is assisted by steeply dipping weakened surfaces adjoining the northeastern lineament stretched along the Murmansk–Oslo line. The less traceable cracks congenial (but with flatter dip angles) to the direction of the northwestern lineament elongated along the Kola Peninsula. The faults associated with the north–south Kola–Rhine–Libyan lineament are observed sporadically. The maximum density is a feature of inclined joints formed in the post-carbonatite period. For estimating effects of the lineaments on slope collapses which cause large damages to open pit mining, the collapses are grouped by their volume, m3: 1—0–200; 2—200–500; 3—500–1000; 4—1000–5000; 5—5000–10000; 6—more than 10000. In the test magnetite–apatite pit mine, the most often collapses have volumes to 200 m3 (52.5 %), and rarer collapses have volumes of 500–1000 m3 (17.3 %) and 1000–5000 m3 (15.8 %). The slope collapses with volumes of 10000 m3 are 3.6 %, and the rest 10.8 % are the collapses with volumes of 200–500 m3 (9.3 %) and 5000–10000 m3 (1.5 %). Open pit mining operations suffer greatly from slope collapses with volumes larger than 10000 m3, which embrace some benches and require considerable expenses connected with elimination of after-effects. Fractures which condition these collapses mostly lie at the graph poles confined to the lineaments. The largest slope failures with the volumes of 67 114 and 80 000 m3 took place on the east pit wall, and are initiated by the faults co-directed with the north–south lineament. This implies the direct influence exerted by lineaments on initiation of slope collapses which inflict the greatest damage to open pit mining. At the same time, smaller size flat and V-shaped failures are caused by the post-carbonatite tectonics, while the cracks associated with the lineaments have a miner part.