Experimental Investigation of the Engineering Rock Character of Altered Granite: A Case Study of the Fengliushan Polymetallic Deposit in Gejiu Mineral District, China

A highly altered rock mass can have adverse impacts on the stability of stopes and drives in underground mines. This work presents a case study investigating the rock characterization and engineering behavior of altered granites of Fengliushan Sn-Cu polymetallic deposit in Gejiu mineral district of China. The altered granites are formed by hydrothermal metasomatism of the host rock, typified by epidote and chloritization. Tests of mineral compositions, mechanical parameters, nuclear magnetic resonance, porosity and slaking characteristics were conducted on granite specimens on three different types of alteration. The results show that the amounts of montmorillonite and chlorite present in the altered granite are the main controlling factors forporosity, water absorption and dilatancy, and weaken the mechanical parameters of rocks. Under wet conditions, the granites which are intensely altered, slake into fragments rapidly nearly losing their entire bearing capacity. The porosity and slake-durability index of granites are also found to strongly correlate with point load strengths. Based on the experimental results, suggestions and recommendations are made concerning the construction and mining around altered granites in drives and stopes of altered granites. The results of this work have a significant bearing on the safe implementation of mining activities in highly geologically-altered rock masses.