Geological and geotechnical assessment of some derelict barite fields in the Abakaliki Basin, Nigeria

The proliferation of abandoned surface excavations and subsequent derelict of ore fields not only contribute to land degradation and landscape disruption but also result in loss of economic deposits, dearth of mining data and generation of unprotected spoils with known potential to contaminate ground and surface water sources. This study adopted field description and measurements, laboratory analysis and numerical simulations techniques to evaluated some abandoned barite fields in Nigeria with the aim of factoring geological and geotechnical issues that render excavations derelict. The modes of occurrence, structural styles and lithofacies constitute a complex and highly varied geologic setting for ore incidences and lead to significant errors in interpreting their geophysical signatures and obtaining reliable ore quantity estimates. Ore grades vary widely and groundwater flow is driven by structural dips and topographic gradient with the ores and intrusive rocks forming as seals. The extraction of the permeable barriers using surface excavations leads to modification of hydraulic gradient distribution around the excavations leading to groundwater incursion and associated slope failures. The use of diversion ditches, sump and pump technique and slope unloading will achieve stable excavations. Unreliable reserve estimates, ore grade migration, groundwater invasion and resulting slope distress are the major impediments that render surface excavations derelict. Optimum location of excavations should be preceded by exploratory drilling and analysis of groundwater flow regime.