The Vazante Underground Mine, Brazil — An Example of Controlled Water Table Drawdown in Karstic Areas

The Vazante Zinc Mine is located in the Vazante District of the Minas Gerais Province of Brazil. The zinc ore is mined from underground operations and is located in a well-developed fracture zone in karstic dolomites belonging to the Vazante Group. The mine has an installed pumping capacity of 16000 cubic meters of water per hour and pumps an annual average of 6300 cubic meters per hour. In April 1999, the underground mining operations intercepted a karstified structural zone causing a flood on the order of 5000 cubic meters per hour, which, in turn, affected the local dolomite groundwater table. The accelerated lowering of the water table caused damage to surface installations due to the generation of a doline of approximately 1000m in diameter and up to 0.4m deep. Since this incident, more than 821 new sinkholes and dolines have been observed in the vicinity of the mine, and Votorantim has intensified its hydrogeological studies. The currently implemented monitoring scheme and data management system have greatly assisted the mine in minimizing risks and impact to the environment.