Pre-Yanshanian Magmatism And Its Mineralization In The Miaoershan-Yuechengling Area, Northern Guangxi Province

The Miaoershan-Yuechengling area is located in the border region between Northern Guangxi and Southeastern Hunan. Many W-Sn deposits occurred in the contact zone between the complex pluton and the adjacent strata, forming the most important metallogenic belt in the western Nanling. It is also an ideal place to research pre-Yanshanian magmatism and its mineralization. Based on the previous researches, We selected Niutangjie and Youmaling tungsten deposits as the research goal. These two deposits are all located in the southern margin of the Miaoershan-Yuechengling granitic complex, the extent of their research is still in a very low level, especially, little work has been done on the ages of ore-forming and related granite.Niutangjie tungsten deposit belongs to bedded skarn-related scheelite deposit. The mineralized intrusion, which occurs as small stockwork. is spatially and temporally associated with the scheelite deposit in the orefield. Petrologically, it is fine-grained two-mica granite. Based on LA-ICP-MS zircon U-Pb ages, the Niutangjie granitic pluton emplaced at (421.8+2.4) Ma, similar to the adjacent Yuechengling pluton. Wi--th the use of Sm-Nd isotope analysis techniques in the scheelite for the first time, we acquired the Sm-Nd isochron age (421+24Ma). Although the data error is larger, but it still clearly shows the mineralization epoch is coupled with the emplacement of the magmatism within the error range. Zircon εHf(t) values and Hf two-stage model ages range from-6.5to-11.6and1.79to2.11Ga, which propose the granite was derived from the Mesoproterozoic crustal materials. The εNd(t) values of the scheelite samples range from-13.06to-13.26, which mean the ore-forming fluid are also derived from the ancient crustal materials.The mineralization types of the Youmaling tungsten deposit are diverse, and the main type is stratoid skarn-type scheelite in outer contact zone of the granite. In this study, we carried out a comprehensive research including zircon U-Pb dating; petrology and geochemical studies on the granite related to the tungsten deposit. Petrologically, it is medium-fine grained two-mica granite. LA-ICP-MS zircon U-Pb chronology indicates that the granitic pluton emplaced at212-215Ma, during the Indosinian period. Chemical analyses show that the granite has high SiO2(SiO2=73.73%-78.68%), high alkalies(ALK=6.99%-8.36%), low Ca and Ti (CaO=0.13%-0.96%, TiO2=0.05%-0.27%), and is weakly-strongly peraluminous (ACNK=1.03-1.28); The granite also displays low total REE contents (ΣREE=61.39X10"6-161.22xl0-6), with strong negative Eu anomalies (8Eu=0.04-0.20), and is enriched in Rb, Cs, etc. LILEs; Th, U, Ta, etc. HFSEs and ore-forming element W (averaging6.55ppm), depleted in Ba、 Sr. These characteristics are similar to the typical highly fractionated S-type granites in Nanling region. Our petrological and geochemical data suggest that the granite has the ability to provide material for formation of tungsten depositThe above studies once again have shown that the Caledonian and Indosinian magmatism indeed existed in the western Nanling region and these two pre-Yanshanian magmatic rocks are tungsten ore mineralization host rock.