Passive seismic HVSR surveying for groundwater exploration at the Chilalo Graphite Project, Tanzania

Summary Passive seismic HVSR surveying is increasingly being used for investigating the thickness of soft sedimentary cover deposits sitting over hard and fresh bedrock, and for direct drill targeting of paleochannels for groundwater and brine resources. A detailed passive seismic HVSR survey was carried out at the Chilalo Graphite Project in SE Tanzania to assist with defining the thickness of alluvial deposits on the margins of the Mbewmburu River system. These alluvial sediments have the potential to host significant groundwater supply in paleochannels filled with porous coarse clastic material which can to be used for supporting a graphite ore processing. The HVSR data were acquired by local field operators, and then processed and depth converted using a Vs of 370m/s, with the modelled bedrock surface ranging in depth from <4m to 28m. The gridded bedrock depth highlighted two paleochannel features of variable depth within the river valley. One bore was drilled along the margin of a paleochannel and had encouraging water flow, and several water bores have planned to test the thick paleochannel deposits for groundwater potential. Drilling is ongoing at the time of writing and results are pending. The objective of this presentation is to demonstrate the successful application of the passive seismic HVSR method in assisting with hydrogeological studies by providing modelled bedrock surfaces which can be used for direct drill targeting, budgeting and volume estimations, and identifying potential aquiclude clay layers which could affect the hydraulic connectivity and recharge of the groundwater resource.