Research On Metallogenic Regularities Of Cu-Au-Mo Deposits In The Shizishan Ore Field,Tongling, Anhui Province

Tongling region is located in the central part of the metallogenic belt of the middle and lower reaches of Yangtze river, which is rich in mineral resources and one of the seven important ore concentration area. Tongling ore concentration area consists of five ore fields from west to east:Tongguanshan, Shizishan, Xinqiao, Fenghuangshan and Shatanjiao ore field. Shizishan ore field is located in western Tongling ore concentration area, which is the largest ore field. This article selects Shizishan ore field in Tongling, Anhui as the research object, on the basis of the collection and second development of massive data, field geological investigation, key samples and observation of scale structure, we deal with petrology, mineralogy, mineragraphy, elements-isotope geochemistry and high-precision chronology of Tongling region and Shizishan ore field, and summarize metallogenic regularity and metallogenic model. Then we obtain the understanding of the of the full text is as follows:Three kind of intrusive rock types of Shizishan ore field are respectively pyroxene diorite, quartz diorite and granodiorite, using zircon U-Pb dating technology, we get pyroxene diorite diagenetic age is139.6±2.1Ma, granodiorites diagenetic age is140.3±1.5Ma. With comprehensive reported age data and combination of field rock relationship, we think these intrusive rocks are formed by twice magmatic emplacement in Yanshanian period:the first occurred around140～139Ma, mainly be seen in granite diorite magma and pyroxene diorite magma intrusion activities; the second took place in136-135ma, mainly be seen in quartz diorite magma intrusion activities.According to rock geochemical data, the quartz diorite and granodiorite are high-K calc-alkaline rock series, and pyroxene diorite is mainly shoshonite series, rare earth element and lead isotope composition of three kinds of rocks is relatively consistent, indicating the consistency of material source and diagenetic mainly mantle-derived material of crust-mantle mixed source causes. Using the Sr-Nd isotopes, we approximately calculate pyroxene diorite, quartz diorite and granite diorite’s source of mantle material are respectively58.56%,43.04%,43.04%. By comparing three kinds of intrusive rocks and typical geochemical characteristics of adakite rock, we conclude that quartz diorite and granodiorite rock belongs to adakite rock, but pyroxene diorite rock is not.Through the analysis of magmatic rocks’geochemistry, chronology and isotopic data, we speculate that the source of the intrusive rocks in this area and genesis:during Yanshanian period with the oblique subduction of the Pacific plate to Eurasia, dehydration fluid metasomatism the mantle wedge formation of upper mantle partial melting and produce alkaline basaltic magma, a small amount of basaltic magma rising and emplacement, contamination with the earth’s crust formed pyroxene diorite. Most of the basaltic magma invaded lower crust molten formed adakite magma; high temperature produced by melting effect can make the upper crustal granitic magma chamber material formed by partial melting. Most of adakite magma rised fast, emplaced directly to the earth’s crust and contaminated with the earth’s crust, forming quartz diorite, a small number of adakite magma rised to shallow magma chamber and mixed granitic magma, emplaced and formed granodiorite.Ore-forming age of Shizishan ore field is summarized between125～145Ma. It is caused by the mesothermal to hyperthermal mineralization. Isotope research shows that the vast majority of ore-forming material of three types of ore deposits is carried by magma from deep source, main ore-forming elements Cu and Au mainly for mantle source, speculating that Mo is crust-mantle mixed source, mainly the upper crust, the ore-forming hydrothermal fluid is mainly magmatic water, mixed with some meteoric water. Deposits in Shizishan ore field are classified to a uniform Yanshanian magmatic-hydrothermal metallogenic series. According to the ore deposit geological characteristics, ore assemblage and altered mineralization characteristics, shallow ore of Chaoshan and Hucun deposit are contact skarn type, shallow ore of Dongguashan is layer controlled skarn type, deep orebody of Hucun and Dongguashan are veinlet disseminated type. Through the discussion of ore deposit geological characteristics, geochemical characteristics, copper isotope, surrounding rock and mineralization time, we suggest that there is no significant Hercynian SEDEX mineralization in this area, layered sulfide deposits mainly controlled by Yanshanian associated with intrusive magmatic-hydrothermal mineralization, ore-forming materials are from magmatic system. Different formation lithology mutations cause interlayer decollement unconformable surface, as the weak structure surface, it has the strong pump suction effect to ore-forming fluid, making a lot of hot liquid uninstall ore-forming materials near the unconformity surface, this may be the cause of occurrence of stratiform or stratoid ore bodies in particular formation.Analyzed the ore-forming control functions of strata, structure and magma, we think that strata mineralization mainly is beneficial mutations in the lithology and lithologic interface; regional basement tectonics controls the cover layer structure and the distribution of the mineralization, and caprock tectonic control degree of the space position and enrichment of the ore body; magmatic rocks show some metallogenic specificity, intermediate basic pyroxene diorite control the output of gold deposits, and the acid in the quartz diorite and granodiorite are closely associated with copper and molybdenum (gold) deposit, the mineralization have close ties with magma intrusion activities on time, space and material sources.On the basis of comprehensive research on ore-controlling geological factors, time evolution, metallogenic deposits (body) space distribution law and ore-forming material source, forming the metallogenic model of "all-in-one" and "Multi-layer tower type", from the bottom to up are: porphyry ore bodies controlled by rock fractures, stratiform or stratoid ore bodies controlled by multiple layers of layered decollement, irregular shape of lenticular skarn ore bodies controlled by contact zone of rock, hydrothermal vein ore bodies controlled by upper fracture structures, ore bodies controlled by concealed explosive breccia.