Deep source region and fluid pathways of gold deposits in the northwestern West Qinling orogenic belt of China

Abstract Relatively little is known about mineral deposits associated with the closure of the Paleo-Tethys Ocean. The West Qinling orogenic belt in central China has experienced a series of subduction–collision orogenic events due to the closure of the Paleo-Tethys Ocean, hosting abundant polymetallic mineralization deposits during the early Mesozoic, particularly in the Tongren–Xiahe–Hezuo area (along the northeastern margin of the Tibetan Plateau), which is a key gold mineralization belt in China. However, the origin of Au-bearing materials and the processes of fluid transport from their deep source region across kilometer-scale expanses of the continental crust remain unclear. Our study combined magnetotelluric (MT) imaging with a deep seismic reflection profile along the same survey to explore the crustal structure beneath the gold mineralization belt. MT imaging reveals a prominent high-conductivity zone (<20 Ω·m) at depths of 18–50 km beneath the Tongren–Xiahe–Hezuo area. This high-conductivity zone corresponds to the front of the subducted continental crust and is interpreted as the deep source region of Au-bearing fluids, potentially linked to devolatilization processes associated with Triassic slab subduction. Additionally, subvertical conductors in the upper crust that connect with the inferred source region may represent pathways for the upward migration of Au-bearing fluids, consistent with the spatial distribution of surface gold deposits. Interpretation of the MT data together with complementary seismic reflection profiles suggests that the West Qinling orogenic system provided the conditions necessary for the formation of the source region and auriferous pathways, ultimately contributing to the development of gold deposits in the Tongren–Xiahe–Hezuo area.