The Characteristics Of The Laojunshan Intrusive And Mineralization, Western Henan Province

Laojunshan Intrusive Complex in Luanchuan county of Henan province, is located in the north Qinling tectonic belt and at the junction of the south margin of North China Craton. In recent years, molybdenum deposit(spots)have found in Large-scale Laojunshan granitic batholith and the surrounding rock in contact with host rock, Based on the field investigation, using geology, petrographic, petrogeochemistry and chronology of rock mass; and geology, geochemistry, fluid inclusion and chronology of molybdenum deposit(spots). To summarize metallogenic regularities and establish mineralization model, in order to guide exploration and prospecting effectively, on the basis of research the geological characteristics and the genesis, It can be provide constraint age on molybdenum mineralization.According to the contact relation and the differences of structure, and Laojunshan rock bodies are divided into three intrusive stages, and their lithology are respectively small-prophyry fine-medium-grained biotite monzonite granite, mid-prophyry medium-coarse grained biotite monzonite granite and big-prophyry medium-coarse grained biotite monzonite granite. The three intrusive stages have concentric-ring shape. The main of magma evolution is structure evolution, then composition evolution. Laojunshan Intrusive Complex has transitional characteristics of I-type and S-type. So it is S type granite.The zircon U-Pb ages of the three intrusive stages are 108±1Ma,111±1Ma和109±1Ma from early to late. They demonstrate that Laojunshan Intrusive Complex is the product of the late period of Middle Cretaceous.Laojunshan molybdenum deposit (spots) are hydrothermal ore deposits. It wall rock alteration contains silicification, potassium feldspar alteration, sericitization and pyritization. The compositions of sulfur isotope implying the sulfur of ore-forming materials is characterized by deep-seated sulfur similar to that of meteorite. Hydrogen and oxygen isotopic data show that the ore-forming fluid dominated by magmatic water in the early stage, but in the late stage, it could be produced by mixing magmatic and meteoric water. Re-Os dating of Laojunshan molybdenum deposit gives an isochron age of 114.3±3.4Ma. The Laojunshan Mo deposit was formed at the same time with Donggou,Yuchiling and Tangjiaping Mo deposits, are similar to the epoch formed early cretaceous.Molybdenum deposit and rock bodies have close ages, these ages suggest that the mineralization in the Laojunshan molybdenum deposit was genetically associated to the Laojunshan granite.