Mineralization of the Bayankhongor Metal Belt and the South Hangai suture zone, Mongolia: Insights from 3-D electrical resistivity models

The Bayankhongor Metal Belt passes through the Valley of the Lakes, south-central Mongolia, between the Hangai Dome and the Gobi-Altai Mountains. It is an important region because it is associated with significant mineral occurences, including important sources of gold and copper. Adjacent to this is the South Hangai suture zone and the Bayankhongor Ophiolite Belt. This is an ancient suture zone and terrane boundary that resulted from the closure of a paleo-ocean, marked by obducted ophiolites, and is possibly the longest continuous ophiolite in the world. Magnetotelluric data were used to generate 3-D electrical resistivity models of the upper crustal structure, which was previously poorly understood. The cratonic upper crust is highly resistive and thus the low-resistivity fault/suture system is easily detected. It is revealed to be a major crustal-scale structure. A clear transition in crustal electrical properties was observed across the zone and may reflect both the rheological and petrological differences across accreted terranes. Furthermore, other anomalous low-resistivity zones are spatially associated with the surface expressions of known mineral occurences and resource extraction projects. By combining electrical resistivity results with geological and petrological data we attempt to gain insights into the potential mineral resources of this unique region and their origin.