Multi-stage tectonic superposition, ore-controlling mechanisms, and prospecting potential analysis of the Lianhuashan fluorite deposit in southwestern Guizhou Province

Objective Recently, a new hydrothermal fluorite deposit has been found in the Lianhuashan area on the northwestern margin of the Youjiang Basin, southwestern Guizhou. The fluorite deposit, which is controlled by faults, shows high ore grades and is preliminarily estimated to reach a medium−sized deposit. However, it is difficult to prospect the fluorite orebodies in the Lianhuashan area, largely due to the complex structural styles and fault systems. Therefore, this study aims to clarify the ore−controlling regularity of these complex structures and to guide future exploration.

Methods To achieve this, we conducted detailed field geological survey and structural analysis, systematically observing fold geometries, fault properties, joint development characteristics, and orebody occurrence states, and analyzing the multi−stage deformation sequences and their relationships with mineralization in the context of the regional tectonic evolution.

Results Systematic studies indicate the following: ① The mining area exhibits significant superimposed structures, with typical reverse "S"−shaped folds and complex fault systems; ② The deposit is mainly controlled by NE−trending faults and tension joints in the hinge zone and southeastern limb of the Lianhuashan anticline; ③ The F₁₉, F₂₁, and F₂₂ are the main ore−bearing faults and show the features of multiple−period activities. In general, the study area had undergone at least three−stage tectonic activities. The first stage (D₁) was driven by nearly north−south compression, which led to the development of nearly EW−trending folds in the Lianhuashan and a series of sinistral thrust faults. The second stage (D₂) involved the NWW—SEE compression, which resulted in the development of the Lianhuashan anticline with a reverse S−shaped fold, and NE and NW−trending faults accompanied by intense dextral thrust activities. During the third stage (D₃), the nearly NW—SE extension caused the reactivation of pre−existing faults and formed a large number of tension joints within the fault zones and folds. The fluorite ore bodies hosted in NE−trending faults show the feature of coaxial veins growing inward, suggesting that the tensile spaces controlled by bearing−ore faults play a key role in the ore−bearing fluid transport and precipitation.

Conclusions Combined with regional research results, we consider that the tectonic framework of the Lianhuashan area is controlled by the shortening deformation in different directions, and the reactivation of pre−existing faults caused by the extension in the Late Yanshanian period provides the favorable space for mineralization. Superposition structures are the key ore−controlling factors in low−temperature hydrothermal deposits within the Youjiang Basin, which may be one of the most important mechanisms of large−scale mineralization.