Fig. 7

The preferred 3-D electrical resistivity models. The models, along three profiles (L2000, L4000, and L6000), were obtained with the MODEM inversion algorithm (Kelbert et al. 2014). The locations of MT measurement sites are indicated with black triangles. Distances are along the profiles, from south to north, along longitudes of approximately 98.5 °E, 99.7 °E, and 100.7 °E (see Fig. 1). Black lines correspond to the South Hangai fault system (solid) and to the Bayankhongor Ophiolite Belt (dashed; see Fig. 1), which are related to a major crustal boundary and ancient suture zone. Anomalous features in the upper crust appear coincident with surface fault/suture positions (e.g., F1, F2, and F3). Fault/suture extension in the subsurface (dashed grey lines) is speculated, and is intended only to illustrate down-dip features. The locations of several prominent mineralized zones are marked (BMB: Bayankhongor Metal Belt; TTU: Tsagaan Tsahir Uul and Saran Uul). They are coincident with low-resistivity anomalies in the shallow upper crust (M1 and M2). Highly resistive features in the north are attributed to a continental block north of the ophiolite belt and suture zone (Hangai; R1, R2, and R4). Conductive features C3 and C4 are of unknown origin. Geological units, and their contacts, are labeled on profile L4000 from the congruent cross-section of Osozawa et al. (2008). Villages are labeled as in Fig. 1. Note that the crust is believed to be 45 km to 50 km thick. Horizontal dashed lines denote the approximate depths of the upper crust, midcrust, and lower crust