Genesis of the Huashitoushan Fluorite Deposit, Beishan, Inner Mongolia: Constraints from Trace Elements, REE and H-O Isotope Geochemistry of Fluorite

The Huashitoushan fluorite deposit is a newly discovered fluorite deposit with medium-large potential resources in the eastern part of the Beishan metallogenic belt. The orebodies are located in the outer contact zone of the Suosuojing biotite monzogranite and are controlled by NE and NS faulted structure. The host rock is mainly quartz sandstone and siltstone with limestone lens of Xishuangyingshan Formation. On the basis of studying the geological characteristics of the Huashitoushan fluorite deposit, carry out the studies of trace element, REE and H-O isotope geochemistry. The results show that 9 fluorite samples showed strong enrichment of MREE relative to LREE and HREE, and the standard partition curve showed an "inverted V" shape. Positive Eu anomaly (1.11～1.25) and negative Ce anomaly (0.90～0.95) indicate a weakly oxidizing environment with the same source of ore-forming fluids and lower temperature. In addition, the characteristics of La/Ho-Y/Ho of the fluorite samples Indicate that the ore-forming fluid may be a contemporaneous and homologous F-rich fluid. The δD_V-SMOW values of the 5 fluorites ranged between −109.7‰ and −99.4‰ (average value is −104.3‰), while the δ¹⁸O_V-SMOW values ranged between −3.1‰ and −1.9‰ (average value is −2.3‰), which indicating that the ore-forming fluid is a mixed hydrothermal solution of atmospheric water and magmatic water. The characteristics of Tb/La-Tb/Ca also indicates that the Huashitoushan fluorite deposit is magmatic hydrothermal. Moreover, only Sb in all fluorite samples is enriched compared to wall rock(Xishuangyingshan Formation, Beishan Oregenic Belt and Crustal), while other elements are depled, which indicating that the fluorite deposit belongs to the category of medium-low temperature deposits. The REE standard distribution curves of two biotite monzogranites show a right inclination, and LREE is strongly enriched relative to HREE. Combined with the geological characteristics of the deposit, it is believed that the Huashitoushan fluorite deposit was formed in a weakly oxidizing environment with lower temperature. The ore-forming fluid is a mixed hydrothermal solution of magmatic water and atmospheric water, the ore-forming material F is mainly derived from biotite monzogranite, and the Ca mainly comes from the Xishuangyingshan Formation. Therefore, it can be inferred that the Huashitoushan fluorite deposit is a medium-low-temperature hydrothermal, structure filling type deposit.