Geochemical Characteristics And Genesis Of Zhangcuo Fluorite Deposit In Shaowu,Fujian Province

The Zhangcuo fluorite deposit is located in the southwestern of the Banling-Yucuodun-Xinping-Daping-Zhangcuo fluorite ore belt in Shaowu,Fujian Province.It is one of the typical fluorite deposits in the study area.Previous geological work is mainly basic geological mapping and low level of mineral exploration work,the research on geological characteristics of fluorite deposits and metallogenic conditions is relatively late,and little has been mentioned about the genesis of fluorite deposits.Therefore,in this paper,the fluorite ore in Shaowu,Fujian Province,is taken as a typical deposit,and the geology of the area,the spreading pattern of the ore body,the alteration of the surrounding rocks and the mineral assemblage are analyzed by combining the geochemistry of trace elements and rare earth elements with the study of fluorite inclusions and other tests,and the source of the ore-forming material,the ore-forming fluid environment,the evolution of the ore-forming fluid and the genesis type of the deposit are analyzed in depth.The main results and understanding are as follows:1.The fluorite deposit of Zhangcuo is located in the fracture of the Late Jurassic porphyroid medium-fine grain syenogranite body.The deposit is mainly controlled by the north-east fracture zone;the fluorite ore body has the phenomenon of expansion and reduction along the trend and tendency.The ore structure is mainly automorphic and subhedral granular structure.The ore structure is mainly blocky,banded and brecciated.The alteration type of the surrounding rock is single,mainly silicification,chloritization and kaolinization.2.The distribution patterns of trace elements of different types of fluorite are basically the same,indicating that the ore-forming fluid has a uniform source area.According to the similar partition pattern of trace elements between fluorite and ore-bearing surrounding rock,it is inferred that its mineral formation is related to surrounding rock.3.The distribution pattern of rare earth elements of both the surrounding rocks and fluorite samples is right-leaning LREE enrichment,and Eu show a clear"V"shape,which is a negative Eu anomaly;the results of laser Raman spectroscopy show that the ore-forming fluid is mainly H₂O and the presence of reducing gas H₂,which together indicate that the deposit was formed in a reducing environment.The Y/Ho-La/Ho diagram of the fluorite shows a more obvious negative correlation,indicating that the fluorite ore-forming material should be of the same fluid source,and it is not contemporaneous;the Tb/Ca-Tb/La relationship diagram indicates that the fluorite ore in this area is the product of hydrothermal genesis.4.The fluid inclusions of fluorite are mainly gas-liquid two-phase inclusions.The temperature of ore-forming fluid is between 120℃～180℃and 200℃～280℃,and the salinity of ore-forming fluid is mainly between 0.18%～0.35%and 0.53%～2.41%,suggesting that there are two ore-forming stages in the process of fluorite mineralization.The density is 0.70～0.95g/cm³.The ore-forming fluid belongs to the medium-low temperature,low salinity,low density,NaCl-H₂O fluid system.5.In theδD-δ¹⁸O projection map of fluorite,the data projection point falls in natural hot water,far away from the primary magmatic water and metamorphic water,so the source of the ore-forming fluid is inferred to be mainly the underground hot water formed by atmospheric precipitation after heating.6.The Zhangcuo fluorite deposit is a fault-controlled thermogenic deposit.F may be derived from hydrothermal leaching of granite,while Ca may be derived from plagioclase in granite.