Genesis Of The Volcanic-Intrusive Complex And Metallogenesis Of Uranium Polymetallic In The Xiangshan Orefield Of Jiangxi Province

Xiangshan Orefield is at the east segment of Qin-Hang metallogenic belt as the northern boundary of Cathaysia plate and is passed through by Suichuan-Dexing deep fault on the geotectonic map. It is located in the combing site of Yangtze. The Xiangshan volcanic basin is the intersection part of the Gan-hang tectonic volcanic rock’s minerogenetic belt(the important minerogenetic belt of uranium deposits) which is nearly EW trending with the Le’an-Ningdu granitic minerogenetic belt. Since 2005, the geological workers found that a large number of polymetallic ore bodies like Pb and Zn are in the lower uranium deposits.The study lasted for more than 3 years, the author got a batch of new materials and laboratory analysis testing new data through the study of the rock geochemistry and the rock-forming and ore-forming chronology of ore bearing volcano-intrusive complex, and via the comprehensive researches of typical deposit anatomy with metallogenic system. The following results were obtained:1. By using high precision dating technique, the author obtained a series of data of the rock-forming and ore-forming chronology, and defined for the time of magma activities and the evolutive characteristics of ore-bearing volcano-intrusive complex in the ore field. All of above laid the foundation for magmatic setting and the study on the genetic relationship of diagenesis and mineralization. By using an accurate zircon SIMS dating technology, the author obtained some rock ages, they are respectively that the two stages ages of ignimbrite of ore bearing complex in Xiangshan, are 140.7±2.7 Ma, 140.1±1.8 Ma, 138.2±1.6 Ma and 135.6±1.2 Ma, the age of rhyodacite is 135.0±1.8 Ma, the age of porphyroclastic lava is 133.6±1.3 Ma, and the formation time of porphyraceous granite and granite-porphyry are 133.9±1.1 Ma and 133.4±1.2 Ma. The magmatic activity evolutionary sequence reflected by dating data is highly accord with what reflected by geological characteristics.2. Through dating the altered minerals by 39Ar-40 Ar, the high accuracy age of U-Pb-Zn polymetallic mineralization was obtained. The formation time of lead-zinc mine is 137.5 Ma~138.3 Ma, and it is the start of Mesozoic metallogenic activities in the ore field. The metallogenic time of U deposits is 132.6±1.3 Ma and 122.8±1.1 Ma, so it has a two-stage metallogenic feature.3. The properties and origin of ore-bearing rock have been understood. Through field detailed inspection on site and the analysis of rock geochemistry and Pb-Sr-Nd isotope for ore bearing primary rocks-porphyry rhyolitic dacite, porphyroclastic lava, coares granite-porphyry and porphyroid granites in the ore field, geochemical property of ore-bearing magmatic rocks in the study area was summarized, and the genesis and origin of volcanic-intrusive complex magma was revealed. The rock geochemical properties of ore-bearing volcanic-intrusive complex are similar with isotope composition characteristics, rocks appear weakly peraluminous calc-alkaline series, and show the characteristics that rich in K and alkali and poor in calcium and magnesium. Volcanic-intrusive rocks have the same origin, and all of them belong to the same magma chamber, and they originated from middle crust’s melting of extension environment within a plate. In addition, they were intruded by different proportion’s basic magmatism of mantle source, and the basic magmatism of mantle source in the magma chamber increasingly added from early to later stage.4. Action characteristics of mineralization have been summarized. On the basic of many deposit investigations and after analyzing different typical deposits, it is clearly proved that both uranium deposit and Pb-Zn-Ag deposit are volcanic-magmatic hydrothermal deposits, and both of their orebodies occurred in fracture tectonic system of of different order. Uranium ore bodies are produced in vein, thin vein and net vein. Pb-Zn-Ag deposits are produced in parallel thin vein. The country rock aiteration types and characteristics are obviously different between Pb-Zn-Ag deposits and uranium deposits. The range of uranium mineralization and alteration is clearly subject to ore-bearing structure, and had a close link to mineralization. The alteration shows linear distribution and its range is limited and possessed with certain zonation. While Pb-Zn mineralization and alteration is possessed with no zonation. Most of ore-forming fluid and metallogenic material came from ore bearing volcanic-intrusive complex magma, and the salinity of ore-forming fluid was low-mid, and meteoric water had participated in mineralization. The participation of deep(mantle-derived) rich uranium material is the important cause that the mineralization type of Pb-Zn-Ag is different from what of uranium. Mineralization mainly occurred at postmagmatic meso-low temperature stage, it shows that uranium mineralization is two-stage for lasting longer.5. The structure of mineralized system has been preliminary summarized, and the multiple metallogenic model of U and Pb-Zn-Ag deposits in Xiangshan ore field has been put forward. The characteristics what is the structure of material and time and spaces and the conditions that of preservation and transformation of U and Pb-Zn-Ag mineralization in Xiangshan ore field indicate that they belong to the same mineralized system, and both the characteristics and the conditions indicate that the volcanic-magmatic metallogenic system of the ore field moved in different time periods.