Electrical image of magmatic system beneath the Xiangshan volcanogenic uranium deposit, southeast China: Linking magmatic evolution and uranium metallogenesis

Abstract

The uranium deposit of the Early Cretaceous Xiangshan caldera (southeast China) represents the world's third-largest volcanogenic uranium deposit. While the hydrothermal system defines uranium mineralization in shallow volcanic-intrusive complexes, we argue that the underlying magmatic system, identified in magnetotelluric data from the Xiangshan deposit, is equally crucial in controlling the origin and migration of ore-forming fluids and driving uranium element transport. As imaged by a three-dimensional resistivity model, a volcanic conduit containing ~4% saline fluid underlies the Xiangshan peak, interpreted to control the formation of alkali fluids that aid the early alkaline uranium mineralization. A deep-seated intrusion also imaged beneath the northwestern Xiangshan caldera likely facilitates the formation of later acidic uranium mineralization and provides the requisite heat flux. Its enhanced conductivity is attributed to graphite liberalization along grain boundaries caused by CO2-bearing volatiles upwelling or igneous carbon injection. The merged zone of the volcanic conduit and intrusion, which is located at a depth of ~10–15 km, functions as a high-level magma chamber. It is fed episodically by low partial melting of lower-crustal rocks and may contain significant uranium concentrations. Essentially, the transport and enrichment of uranium elements are enabled by such a vertical extensive trans-crustal magmatic system, resulting in the emplacement of the shallow volcanogenic uranium deposit. This work is a compelling example regarding the inherited structural control of the magmatic system on volcanic-related uranium metallogenesis.

A Review of Relationship between the Metallogenic System of Metallic Mineral Deposits and Lithospheric Electrical Structure: Insight from Magnetotelluric Imaging

“…The multi-scale electrical structure indicates a giant upper-mantle basaltic magma reservoir, indicated by the conductor DTHCZ beneath the Datong volcanic area, which moves through a lithosphere-scale shear zone, the mid-lower crustal magma chamber CZ3, the crust-scale weak zone, and a conduit (CC1 and CC2) to transport ore-forming magmas and fluids (Figure 7). Other typical results include the Ning (Nanjing)-Wu (Wuhu) basin in eastern China [90], the Shihu-Xishimen gold-iron ore district in North China [91], the Middle-lower Yangtze Metallogenic Belt (including Ningwu, Luzong, Xuancheng, Anqing, Guichi, and Tongling areas) in East China [12,[92][93][94][95][96], the Jiaodong gold deposits in northern China [97], the Liaodong Qingchengzi orefield [98], the Yixingzhai gold deposits (Boqiang Cu-Mo-Au deposits and Nanling W-Sn ore district in China) [45,99,100], the northeastern Jiangxi metallogenic province in southeastern China [101], the Caosiyao porphyry Mo ore district in North China [43], the Beiya Cu ore district in southwestern China [46], the large-scale Hatu epithermal gold deposit in western Junggar, NW China [102], Zhaxikang in the Tethys-Himalaya area in southwestern China [103,104], the Baogutu porphyry copper-gold deposit, the Hongqiling Cu-Ni sulfide intrusions in the Central Asian Orogenic Belt [105], the Xiangshan volcanogenic uranium deposit [106,107], the Narusongduo Pb-Zn-Fe-Cu ore district, and the Qulong-Jima porphyry ore Cu deposit in southwestern China [41,42]. In the Olympic Dam mine and Tennant ore district in Australia [108], the Tsagaan Tsahir Uul Au deposit in southern Mongolia [109], the Norrbotten district in northern Sweden [110,111], and the orogenic gold district in the Red Lake greenstone belt, western Superior craton, Canada [51], the electrical resistivity models obt...…”