Characterization of primary geochemical halos for the Hetaoba volcanic-related uranium deposits in Duolun County, Inner Mongolia

Primary geochemical halo is a powerful tool for exploring blind deposits. However, primary geochemical halo studies have seldom been conducted on hydrothermal uranium deposits. This study conducted primary geochemical halo studies on the Hetaoba volcanic-related uranium deposit in the Guyuan–Hongshanzi uranium-polymetallic metallogenic belt based on the 780 core samples with 20 elements analyzed from 13 boreholes. Staged factor analysis (SFA) of the centered log-ratio (CLR) transformed data showed that an ore-related elemental association is F1 (U–Mo–As–Pb–Cd–Sb association). However, scatter plots and anomaly maps based on the thresholds determined by the concentration–number (C–N) fractal model showed that the extent of sulfide-rich zones was larger than that of uranium mineralization, and some sulfide-rich zones were accompanied by low uranium content, although uranium mineralization was always accompanied by sulfide enrichment. Furthermore, uranium minerals were distributed along the metal sulfide edges and even encased them, suggesting that uranium mineralization may have occurred later than the sulfide precipitation. Zoning patterns of indicator elements (from top to bottom) for ore bodies at shallow (AZS₁) and greater (AZS₂) depths determined by Gregorian’s method are Bi–Zn–Cd–Mo–Sb–Cs–Pb–Hg–U–Sc–Be–Li–W–Cu–As–Tl–V–Co–Cr–Ni and Cr–Ni–Sc–Be–W–V–Co–Sb–As–Bi–Cu–Pb–Mo–U–Hg–Zn–Cd–Li–Tl–Cs, respectively. These results are significant for mineral exploration. Sulfide-rich zones may provide favorable space and reducing agents for uranium mineralization and can serve as an auxiliary indicator for uranium exploration. More importantly, strong Hg anomalies at relatively greater depths may represent favorable traps for uranium deposition. Consequently, Hg can serve as a near-ore indicator of uranium exploration at relatively greater depths. In addition, AZS₂ front-halo elements may suggest the superposition of two metallogenetic stages and exploration potential in the up-dip of the fault zone.