Geological And Geochemical Characteristics Of Lamprophyre And Its Origin In The Xikuangshan Mining District, Central Hunan

Abstract:The giant Xikuangshan deposit located in central Hunan, is the largest antimony deposit in the world, and is called as Capital of Antimony. Although a lot of researches have been carried out on this deposit, lamprophyre in this area is scarcely studied. The origin of lamprophyre, and its relationship with antimony mineralization are still unclear. Applying petrologic, mineralogical and geochemical methods, geology and geochemistry of the lamprophyre in the Xikuangshan mining district are systematically studied in this dissertation. Based on the above, the origin of lamprophyre is ascertained, and the relationship between lamprophyre and antimony mineralization is also revealed.The studied lamprophyre displays a typical lamprophyric texture, and its phenocrysts mainly consist of biotite and plagioclase, thus, it belongs to kersantite, and can be classified into the alkali basalt series.The lamprophyre in this study is characterized by LILEs-rich, HFSEs-depleted, high-concentration REEs and right-inclined chondrite-normalized REE pattern. Sr and Nd isotope studies reveal that the ε Sr(t) values vary in the rang of75.37-92.91, and its ε Sr(t) values change between-0.71and-8.33. Both trace elements and Sr-Nd evidences reveal that the studied lamprophyre is probably derived from an enriched mantle magma generated by partial melting, and crustal contamination can be negligible.Zircon is common in the studied lamprophyre, these zircon grains predominately are of magmatic origin and were captured from the neighboring strata during lamprophyric magma ascending. Zircon U-Pb isotopic dates mainly fall in830Ma,800Ma and730Ma, which coincide well with those age data for the Precambrian strata in the adjacent Xufeng Range, and reveal that there exist Precambrian clastic basement deeply lying in the Xiangzhong Basin. The lamprophyre formed under the geodynamic setting of crustal extension, and its emplacement depth at least reaches5kilometers.The lamprophyre in the Xikuangshan mining district emplaced at about128Ma, slightly earlier than the late antimony mineralization (124Ma), but obviously later early antimony mineralization (156Ma). It is concluded that the lamprophyre is not the eastern boundary of antimony mineralization in the Xikuangshan mining district and there still exists prospecting potential in the east of the lamprophyre.