Study On Genetic Mechanism And Metallogenic Background Of Mafic Rocks In Longlin-Xilin,Western Guangxi

The tectonic site of the western Guangxi is located at the junction of the Yangtze paraplatform and the southwest margin of the South China fold system,and belongs to the Guixi depression of the Youjiang Regeneration Site in the South China paraplatform,the layered,layered and irregular veins intruded mafic flow and dikes are well cropped out around the Longlin-Xilin area of Western Guangxi.The study for the petrogenesis of the mafic dikes will better understand the tectonic-magmatic significance of this region.This paper focuses on petrology,mineralogy,element geochemistry and isotope geochemistry of the mafic dikes.By systematical geologic-geochemical studies on the Longlin-Xilin area of Western Guangxi,we analyzed in detail of the petrogenesis and source region characteristics.The following conclusions have been obtained:1.The main rocks in the Longlin-Xilin area are dominated by diabase,and the geochemical data indicate that the diabase belongs to the alkaline basalt series with low Si O2 and high Ti O2,Mg O,LREE-enriched characteristics,they have Ti/Y= 579~742,(La/Yb)N=6.70~10.24,Nb/U=23~33 and Nb/La=0.80~0.94,thus,the geochemical features of dikes akin to the Emeishan large igneous province(ELIP)high-Ti basalts.2.The Nb and Ta elements were slightly negative in the Longlin-Xilin area,and enrichment of Rb,Sr,Ba,significant loss of Zr,Hf and Y,indicate such a melt formed from the partial melting of plume mantle source experiencing the weak crustal contamination.3.The low 87Sr/86Sr(t)(from 0.705023 to 0.705782)and high ?Nd(from +0.7 to +1.0)of the Longlin-Xilin area,akin to ELIP high-Ti basalts and the aother high-Ti mafic rocks of Western Guangxi,suggest that the Longlin-Xilin mafic dikes most likely represent a part of outer zone of the ELIP plume magmatism.4.Combine the regional tectonic relationships between the mafic dikes and the fine-disseminated gold deposits as well as the extensive evolved carbonate platform uplifting,we further conclude that the ore-forming process of gold deposits likely resemble to that of Nevada's Carlin-type gold deposits in US,the interaction between the Emeishan plume and Paleotethyan subduction zone induced the regional gold deposits.