Quantifying fines migration in block caving through 3D experiments

Abstract

Fine material migration is one of the main challenges in the block/panel caving method because its presence can result in mud rush, inrush events, and early dilution. Sources of fines in block caving mines can include previous exploitation levels, presence of weaker rock, and secondary rock fragmentation during ore draw, among others. Then, one of the main tasks of mining design and planning is to identify, avoid and/or control when and in what magnitude this finer material could be extracted at drawpoints. Studies have been done regarding fine material migration in mining; however, recent studies have challenged current understanding about the main variables that control its mechanisms. This research aims to clarify some of the main variables controlling fine material migration through laboratory experiments of a block cave column during flow, scaled 1:50. Here, the variables studied are the ratio between the size of coarse and fine material, the particle-size-distribution of coarse material, the type of draw, and amount and location of fine material. Experimental results show that the ratio between coarse and fine material size is one of the more relevant variables: when this ratio increases, fine material migration also increases. Additionally, the coarse particle-size distribution has an important influence on fine material migration. A higher coefficient of uniformity (d 60 /d 10 ) will delay fine material migration. For example, when the coefficient of uniformity changed from 1.5 to 3.8, the amount of coarse material extracted before the fine material changed from 69% to 143%. Additionally, the presence of fine material does not appear related to changes in the extraction zone's final geometry as long as coarse material is drawn first. The flow experiments conducted quantify key variables that influence dilution entry into caving environments improving our understanding of the phenomenon of fine material migration for caving mines.