Electrical resistivity models reveal mineralization and fault systems in the Valley of the Lakes, south-central Mongolia

Abstract

The Valley of the Lakes, south central Mongolia is located between the uplifted Hangai Dome and the Gobi Altai Mountains , within the Central Asian Orogenic Belt . It includes many interesting features, including t he South Hangai f ault system that represents an ancient suture zone and terrane boundary . This zone is possibly an extension of the Mongol Okhotsk suture that resulted from the closur e of the Mongol Okhotsk Ocean The adjacent obducted Bayankhongor Ophiolite Belt is possibly the longest continuous ophiolite belt in the world. This region is important because it is associated with the Bayankhongor Meta l logenic Belt that is an economic ally significant zone for ore extraction in Mongolia , including important sources of gold and copper.

Electrical resistivity is a key parameter for mineral exploration. Because faults and suture zones are regions of fractured, weakened crust they often have circulating fluids that act to i ncrease their electrical conduc tivity . Additionally, econom ic mineralization is commonly associated with a conductive signature from associated sulfide minerology. We present magnetotelluric data acquired in a n array across central Mongolia (Comeau et al., 2018; K äu fl et al., 2018; Becken et al., 2018; this abstra ct volume) volume). The magnetotelluric data we re used to generate 3 D electrical resistivity models of the shallow crustal structure, which was previously poorly understood. Because the cratonic upper crust is highly resistive (>1000 ohm m) the low res istivity (<30 ohm m) South Hangai f ault system is easily detected . It is revealed to be a major crustal scale structure. A clear transi tion in crustal electrical properties wa s observed across the suture zone and may reflect both the rheological and petrological d iff erences across accreted terranes Furthermore, a nomalous, low resistivity zones in the crust are spatially associated with the surface expressions of known mineralization and resource extraction projects. By combining our electrical resistivity results with other geological and petrological data we attempt to gain insights into the potential mineral resources of this unique region and their origin