Dizhi lixue xuebao (Feb 2024)
Characteristics of hydraulic ore-bearing structure: A case study of hydrothermal tungsten and uranium deposits in South China
Abstract
Objective Hydraulic fracturing is a vital deformation and fracture mode in the whole crust-lithosphere range. The related structures are also critical ore-bearing structures of some hydrothermal deposits. Clarifying the main characteristics and identification marks of hydraulic fracturing ore-bearing structures aids in conducting detailed structural analyses of ore fields. Methods The article introduces the formation mechanism of hydraulic fracturing structures and classifies the hydraulic ore-bearing structures into two types, namely, hydraulic fracturing and hydraulic spreading. Taking typical hydrothermal tungsten and uranium deposits in South China as examples, the study, based on detailed field investigations, analyzes the essential characteristics of hydraulic fracturing ore-bearing structures, including the Shimensi tungsten deposit, Xingluokeng tungsten deposit and Zoujiashan uranium deposit. Results The study suggests that hydraulic fracturing ore-bearing structures are characterized by complex shapes (arc-shaped, branched, radial, chrysanthemum-shaped, etc.), relatively small scale, predominantly tensional macro-mechanical properties, variable trends and dips, indistinct directionality with dominant orientations in only local areas, and often accompanied by hydrothermal crypto-explosive breccia. Meanwhile, five typical marks of the hydraulically fractured ore-bearing structures have been identified, including arc bifurcation or irregular shape, overall small scale, multi-directional occurrence, uneven distribution, and associated hydrothermal crypto-explosive breccia. Conclusion After comparing and analyzing the similarities and differences between hydraulic fracturing ore-bearing structures and stress-induced ore-bearing fracturing, the study concludes that hydraulic fracturing ore-bearing structures are relatively limited in development. In contrast, hydraulic spreading fracturing ore-bearing structures are relatively common. There is no apparent correlation between the hydrothermal alteration zoning and whether the ore-bearing structure is due to hydraulic fracturing or stress-induced fracturing. Tensional structural features exhibited by compressional genesis structures during the mineralization period are attributed to overpressure from mineralizing fluids rather than changes in regional tectonic stress fields. Although the ore-bearing structures of compressive origin show tensional macro-mechanical properties during the metallogenic period, some result from the overpressure of ore-forming fluids rather than the change in the regional tectonic stress field. [ Significance ] As an important ore-bearing structure type, hydraulic fracturing enriches the connotation of ore field structure. The coupling effect between the extensional fracturing of fracture ends caused by hydraulic fracturing and ore-forming fluids is an essential mechanism of structural control of the ore-forming end effect, which will enhance the theory of structural ore control and contribute to breakthroughs in prospecting strategies.
Keywords
