Preliminary results of spectral induced polarization measurements, Wadi Bidah District, Kingdom of Saudi Arabia

Abstract

Laboratory spectral induced polarization (SIP) measurements on 29 carbonaceous schist samples from the Wadi Bidah district show that most are associated with very long polarization decays or, equivalently, large time constants. In contrast, measurements on two massive sulfide samples indicate shorter polarization decays or smaller time constants. This difference in time constants for the polarization process results in two differences in the phase spectra in the frequency range of from 0.06 to 1 Hz. First, phase values of carbonaceous rocks generally decrease as a function of increasing frequency. Second, phase values of massive sulfidebearing rocks increase as a function of increasing frequency. These results from laboratory measurements agree well with those from other reported SIP measurements on graphites and massive sulfides from the Canadian Shield.

AEMIP robust inversion using maximum phase angle Cole–Cole model re-parameterisation applied for HTEM survey over Lamego gold mine, Quadrilátero Ferrífero, MG, Brazil

“…The initial models for the other parameters were defined manually. In this work, the initial values for 𝜙 𝑚𝑎𝑥 was 300 mrad, similar to the phase range based on the analogous lithologies presented in Smith et al, (1983), and 𝜏 𝜙 and 𝐶 started from 0.001 s and 0.5, respectively.…”

“…Using the AarhusInv code (Auken et al, 2015) and with the configuration for the AeroTEM HD system described in Table 1, also using the parameters presented in Table 2, we simulated four scenarios considering the increment in the 𝜙 𝑚𝑎𝑥 value of the second layer from 10 to 500 mrad, i.e., gradually making the intermediate conductive layer more polarizable and analyzing how well the RO and MPA inversions recover the true model by 1D smooth inversions. The parameters values for each parameter presented in Table 2 were decided based on the values achieved in the preliminary inversion results for the AeroTEM HD data, based on the laboratory petrophysical frequency-domain IP measurements presented in Smith et al, (1983) for similar lithologies in a greenstone belt environment in Saudi Arabia and also data from borehole information for the resistivities values. In particular, in Smith et al, (1983) phase values between 100 and 350 mrad were measured in the frequency interval between 100 and 1000 Hz.…”

“…The parameters values for each parameter presented in Table 2 were decided based on the values achieved in the preliminary inversion results for the AeroTEM HD data, based on the laboratory petrophysical frequency-domain IP measurements presented in Smith et al, (1983) for similar lithologies in a greenstone belt environment in Saudi Arabia and also data from borehole information for the resistivities values. In particular, in Smith et al, (1983) phase values between 100 and 350 mrad were measured in the frequency interval between 100 and 1000 Hz. A standard deviation of 5% was assigned to each gate of the forward response, but no perturbation was introduced, to focus only in the understanding of the differences responses between RO and MPA models, not considering any other effect in the synthetic data, like noise level and couplings.…”

“…Carbonaceous and graphite schists, associated with gold mineralization within disseminated metallic sulfides, occur in the mine area, which might be responsible for the IP effects in the AEM data. Indeed, the frequency-domain IP measurements conducted in the laboratory by Smith et al, (1983) on similar lithologies (from a greenstone belt environment in Saudi Arabia) show significant IP effects over the whole measurement range from 0.06 to 1024 Hz.…”

Geophysical surveys at the Getchell and Preble disseminated gold deposits, Humboldt County, Nevada

“…The observed changes in amplitude and phase as a function of frequency result from conduction and polarization processes that produce the IP effect in rocks. These changes in amplitude and phase are commonly plotted on logarithmic scales (Smith et. al., 1983).…”