present within the survey area. It should be noted that terrain corrections were not undertaken to the gravity data; this may have produced cleaner datasets. The surface ERI data showed more and clearer anomalies than the micro-gravity data and were not as affected by above-ground structures. However, the made-ground nature of the site made it challenging to obtain equivalent electrode contact resistances across each profile, with the resistive anomalies mostly due to different made-ground material rather than the target mine access shaft itself. The modelling also showed the target depth was likely to be too deep to be successfully imaged with ERI profiles. The mine shaft ERI profile produced the clearest geophysical anomaly of the target shaft of the whole study albeit with a 12 % robust inversion model error. Unfortunately reciprocal measurements to estimate the noise levels were not collected due to time constraints, but the TIGRE internal stacking values showed a 1.34 % average point error estimate (Table 1). The prominent low anomalies present in the ERI profile E5 model inversion were probably due to modelling artifacts. Other potential low anomalies present could be due to relict metal mine tracks still present (cf. Fig. 12a) or due to heterogeneities off to the side of the profile. The mine shaft micro-gravity profile also showed an anomalous low, with respect to background values, but not at the same location as the ERI resistive high anomaly (cf. Fig. 13). This could be due to another mine shaft that was not on the given mine plans, anecdotal evidence suggesting a variety of previous unrecorded mining occurred on site. The mine shaft gravity profile did not detect an anomaly at the ERI anomaly location (i.e. at 24m) for reasons which are, at present, not
present within the survey area. It should be noted that terrain corrections were not undertaken to the gravity data; this may have produced cleaner datasets. The surface ERI data showed more and clearer anomalies than the micro-gravity data and were not as affected by above-ground structures. However, the made-ground nature of the site made it challenging to obtain equivalent electrode contact resistances across each profile, with the resistive anomalies mostly due to different made-ground material rather than the target mine access shaft itself. The modelling also showed the target depth was likely to be too deep to be successfully imaged with ERI profiles. The mine shaft ERI profile produced the clearest geophysical anomaly of the target shaft of the whole study albeit with a 12 % robust inversion model error. Unfortunately reciprocal measurements to estimate the noise levels were not collected due to time constraints, but the TIGRE internal stacking values showed a 1.34 % average point error estimate (Table 1). The prominent low anomalies present in the ERI profile E5 model inversion were probably due to modelling artifacts. Other potential low anomalies present could be due to relict metal mine tracks still present (cf. Fig. 12a) or due to heterogeneities off to the side of the profile. The mine shaft micro-gravity profile also showed an anomalous low, with respect to background values, but not at the same location as the ERI resistive high anomaly (cf. Fig. 13). This could be due to another mine shaft that was not on the given mine plans, anecdotal evidence suggesting a variety of previous unrecorded mining occurred on site. The mine shaft gravity profile did not detect an anomaly at the ERI anomaly location (i.e. at 24m) for reasons which are, at present, not
Apedale%20NSG_v3_full.docx