An in situ bioseismicity experiment 3.6 km beneath the surface at NELSAM

Instrumentation has been designed and constructed for performing in situ biogeochemical experiments in a borehole, DAFBIO, situated at 3.6 km beneath the surface of South Africa in the Natural Earthquake Laboratory in South African Mine, NELSAM, site at Tau Tona gold mine. At this location, which lies within the Pretorius fault zone, several boreholes contain 3-component accelerometers, seismometers, strain-meters and a gas mass spectrometer. Characterization of rock cores and formation fluids from NELSAM suggest that sulfate reducing microbial communities are present. Periodic release of H2 from the fault zone has been correlated with blasting induced seismic activity from along this fault zone. As blasting can also cause anomalous N species in the environment the instrument was designed to measure N and S species as well as collect dissolved gas and microbial samples. The instrument is designed to circulate fluid and automatically collect samples from inside a stainless steel, straddle packer that has isolated a fracture within the Pretorius Fault zone, 18 meters from the wall of the laboratory. Because of the deformation within the borehole an inflatable packer is used. HPLC pumps circulate fluid through peek tubing the from the straddle packer a flow cell that monitors the temperature, conductivity, pH and utilizes ion specific electrodes (Pasco, Scientific and RMS, Ltd.) to measure NH4+, NO3- and HS- concentrations. An autosampler (Gilson) has been converted into a fraction collector that periodically injects 20 mL of fluid into 160, inverted, sterile, Ar-filled, high pressure Balsch tubes. Fluid is replaced into the straddle packer from a sterile, 10 L, anaerobic, Nalgene reservoir with an Ar headspace by a second HPLC pump. Because of the high ambient air temperature, the flow cell, autosampler and reservoir are housed inside a cooler (ST Gebaudetechnik GmbH) that maintains a constant 10oC environment. Because of the remote location of the NELSAM site, the system was designed for minimal maintenance requiring only replacement of the Balsch tubes and data downloads from the ion specific electrodes every week or two.