Petrology And Zircon Mineralogy Of The Intrusions In Tongling Area

The Tongling ore-district is an important part of the Middle-Lower Yangtze River Valley metallogenic belt.Mesozoic intrusive rocks and porphyry-skarn copper-gold deposits are widely distributed in the area.This feature makes the Tongling area an ideal place to study the link between magmatism and copper-gold mineralization.In this paper,detailed petrology and zircon mineralogy of the ore-related and barren intrusions have been carried out,with focus on the analysis of the relationship between magmatism and copper-gold mineralization.Petrological studies have shown that the ore-related intrusions host a large number of diorite enclaves and show some disequilibrium textures,such as plagioclase corrosion texture,poikilitic amphibole and acicular apatite,indicating the ore-related intrusions probably formed by mixing of crustal and mantle-derived magmas;Whereas the barren intrusions only show equilibrium textures,suggesting that they maybe from a single source.The petrogeochemical data show that both types of rocks exhibit the geochemical characteristics of metaluminous and high-K calc-alkaline rocks.In chondrite-normalized rare earth element patterns,zircons from ore-related and barren intrusions show subparallel pattern,characterized by heavy rare earth elements enrichment and light rare earth elements depletion,with positive Ce anomalies and negative Eu anomalies.The average values of Ce⁴⁺/Ce³⁺and Eu _N/Eu _N^*of zircons are 322 and 0.69,respectively,for ore-related intrusions,and are 342 and 0.81,respectively,for barren intrusions.The oxygen fugacity estimation results show that the average values of?FMQ of the ore-related and barren intrusions are2.7 and 3.5,respectively.On the zircon Ce⁴⁺/Ce³⁺-Eu _N/Eu _N^*and log?fo₂?-T???discriminant diagrams,the ore-related and barren intrusions in the Tongling area fall into similar areas.The above characteristics,combined with existing data,indicate that the ore-related intrusions have the characteristics of high oxygen fugacity,high water content and mixed crust and mantle sources,while the barren intrusions shows high oxygen fugacity,low water content and crust source characteristics.Comprehensive analysis suggests that high oxygen fugacity promotes mineralization,but it is not the decisive factor leading to the difference in copper and gold mineralization related to intrusions in the Tongling area.