Geochemical Characteristics Of Hydrocarbon Gases In Limu Tin Polymetallic Deposit, Guangxi, And Their Significance To The Study Of Diagenesis And Mineralization

Limu ore area is a typical granite-type W-Sn-Ta-Nb-Sn polymetallic deposit,mainly intruded by Limu granite body.The Limu deposit is located at uplift top of the northern Gongcheng Synclinorium in Haiyang Shan fold-and-thrust belt,which is in the junction part of EW-trending Nanling tectonics and SN-trending Xiangnan tectonics,belonging to the Guanyang-Hexian metallogenic area in the western segment of Nanling tin ore belt.In this paper,the geochemical characteristics of hydrocarbon gases combine with ore-forming geological characteristics,petrogeochemical characteristics and fluid inclusion characteristics to discuss the metallogenic mechanism of Limu W-Sn-Ta-Nb-Sn polymetallic deposit and the relationship between W-Sn-Ta-Nb polymetallic mineralization and magmatic evolution processes.The results show that hydrocarbon gas exists in the all rock samples of Limu ore area.According to the comparative analysis of geochemical and petrogeochemical characteristics of hydrocarbon gases,the magma derived from three stages of Limu composite granites share the same origin and period.In the hydrocarbon gas standardization curves,Jinzhuyuan W-Sn orebody has the most similar morphological characteristics to the third period Jinzhuyuan granite and Laohutou granite.The results of fluid inclusion temperature measurement show that the fluid characteristics of W-Sn mineralization stage in Limu ore area are medium-low temperature,low salinity and low density,which indicates that W-Sn mineralization occurred in the middle-late stage of magmatic-hydrothermal process.It indicates that the material source and origin of the W-Sn orebody is closely related to the third period and the second period rock body,but mainly related to the third stage.In addition,the proportion of each component of hydrocarbon gases is relatively close but still different,in which the proportion of ethane orebody is obviously higher,followed by methane and olefin.This fully shows that in the process of magmatic intrusion,differentiation evolution and mineralization of Limu granite,due to the changes of environmental temperature,pressure,oxygen fugacity,PH and other factors,while the metallogenic elements are enriched and diluted in different stage of magmatic evolution in the process of continuous precipitation and differentiation of crystalline minerals,the macro and micro characteristics of the hydrocarbon gases are regularly changed.It is suggested that the geochemical characteristics of hydrocarbon gases have an indicative effect on the change and migration of ore-forming materials and ore-forming environment during the process of ore-forming evolution of Limu granite.The results show that the geochemical characteristics of hydrocarbon gases are consistent with the conclusions explained by petrogeochemistry,fluid inclusion and other research methods,it is suggested that the geochemical characteristics of hydrocarbon gases can provide certain guidance basis for the study of ore-forming regularity and prospecting model of ore deposits.With the further study of hydrocarbon gas characteristics,it will provide new theoretical basis for the ore-forming mechanism,ore-prospecting regularity and prospecting of metal deposits.