## 2 Materials and Methods
### SIP Data Collection at the Field Scale  
We collected SIP data along seven lines using different measurement setups from which we present three representative lines (P1, P2 and P7 in Table 1). Line P1 has an orientation NE-SW, and it is located outside the graphite quarry along a forest road (see Figure 1a), where the graphite is not observed at the surface but is expected to be located in the subsurface. Lines P2 (with an orientation NE-SW also) and P7 (perpendicular to P2) are located at the quarry where graphite content is observed at the surface (see Figure 1a) but its extension at depth is unknown. The topographical features of the quarry and the dense vegetation of the study site influenced the orientation of the IP lines. Profile P1 and P7 measurements were collected with 64 electrodes and a spacing of 5 m and 2 m between them, respectively, whereas measurements in P2 were collected with 32 electrodes with a separation of 10 m between them. To increase the resolution of our investigation, a second measurement, which we refer to as P2b, was conducted at P2 with 64 electrodes and 2 m electrode separation (with both profiles P2 and P2b centered on the same point). All electrodes are made of stainless steel and have a diameter of 10 mm. We used the DAS-1 (from Multi-Phase Technologies, LLC) to collect FDIP data. SIP measurements were collected in the frequency range between 0.1 Hz and 225 Hz in all profiles. However, data collected above 25 Hz revealed noisy pseudosections and were excluded from the analysis. We used a dipole-dipole configuration [43] using the eight measuring channels available in the DAS-1. Thus, voltage measurements are collected in eight adjacent potential dipoles for each current dipole, always ahead of the current dipole to avoid contamination of the data caused by remnant polarization of the electrodes. For the 10 m and 2 m electrode separation profiles, we used coaxial cables to connect the electrodes and the measuring device to minimize distortion of the data associated with cross-talking between the cables [18; 19; 44], with the shield of the coaxial cable running together into a ground electrode (as presented in [PERSON] et al. [24]). To obtain a broader frequency spectrum and enhance the spectral resolution, in-situ IP spectra were collected with a 4-electrode array at three selected points, referred to as Z1, Z3 and Z5 (Figure 1a), using the PSIP unit (from Ontash & Ermac, NJ, USA). This electrical impedance spectrometer is commonly used for laboratory investigations [39]. Those in-situ spectra were collected with a single quadrupole using stainless steel electrodes with a separation of 50 cm in a Wenner configuration. We collected data at 58 frequencies between 0.1 Hz and 20,000 Hz, with a distribution of eleven measurements per decade. In the case of the imaging dataset, we filtered the raw data independently for each frequency (0.1-25 Hz) by removing readings that diverge significantly from the expected smooth change in the pseudosections. After the first filtering, we removed quadrupoles not found in all frequencies, as required to resolve for inversion results with relatively the same frequency in the 0.1 Hz and 25 Hz range. For the inversion of the filtered datasets, we used the smoothness-constrained least-squares algorithm CRTomo by [PERSON] [45], which allows \begin{table}
\begin{tabular}{c c c c c c} \hline
**ID** & **SIP (Hz)** & **Profile Length** & **Electrode Spacing** & **Configuration** & **Direction** \\ \hline P1 & 1–225 & 315 m & 5 m & DD & NW-SE \\ P2 & 0.1–225 & 310 m & 10 m & DD & NW-SE \\ P2b & 0.1–225 & 126 m & 2 m & DD & NW-SE \\ P7 & 0.1–225 & 124 m & 2 m & DD & NE-SW \\ Z1, Z3, Z5 & 0.1–10,000 & 1.5 m & 0.5 m & Wenner & - \\ \hline \end{tabular}
\end{table} 
Table 1: Measurement setup in terms of the name of the profile (ID), frequency range of the spectral induced polarization (SIP) measurements, profile length and electrode spacing in meters, and electrode configuration (DD—dipole-dipole).