The magmatic differentiation mechanism and metallogenic model of the Yichun granite-type rare metal deposit in Jiangxi Province
Yichun deposit in Jiangxi Province is one of the most important rare metal deposits in South China,which is the largest production base for lithium and tantalum in China,while the Yashan composite rock pluton is a famous rare metal granite in South China.In this paper,based on the previous geochemical data and lithological minerals,it is found that lithium and other rare elements are highly enriched in the topaz lithium mica granites of the pluton.The magmatic differentiation of the deposit gradually increases from melts to melt-fluid coexistence systems.The whole rock SiO2 content,Nb/Ta and Zr/Hf ratios,A/CNK and δEu values of the granites change regularly.Rare metal elements such as Ta and Nb are distributed uniformly in the deposit in the form of disseminated rather than fluid-derived veins or network veins,and are wrapped by the main rock-forming minerals with snowball structures.Mica in each stage has the characteristics of magmatic crystallization,such as flake output,flat boundary,serrated and lobed.It can be concluded that:(1)In the process of crust-mantle magma combination,the metamorphic basement of South China is partially melted to form the initial magma which experienced the evolution process of in-situ high crystallization differentiation;(2)The magmatic hydrothermal fluid rich in rare metals is highly crystallized and differentiated,which makes rare metal elements such as lithium,niobium and tantalum getting more and more enriched in the residual melt,and finally formed the rare metal granites;(3)Each pegmatite crust constitutes an isolated barrier between the magma chamber and the outside wall rocks,making F,B,Li,P,H2O and other volatile components unable to escape.Due to the closed system formed by the overlying pegmatite crust and the sufficient heat provided by the underlying mantle-derived magma,the magma chamber maintained a long-term in-situ differentiation state under the thermal driving mechanism,and finally formed the Yashan lithium-niobium-tantalum deposit.
万方数据
维普
