Studies On Petrology And Zircon U-Pb Geochronology Of Mesozoic Intrusive Rocks In Guichi-Qingyang Region,Anhui Province

Lower Yangtze region is an important copper, iron, gold polymetallicmetallogenic belt in China and the mineralization in this region is closely related withMesozoic intrusive rocks. Guichi-Qingyang region is located in the junction ofAnqing-Guichi, Luzong, Tongling ore concentration area where the Mesozoicintrusive rocks as the research object of this paper widely developed. In the paper, wepresent petrology, petrography, mineralogy, LA-ICP-MS zircon U-Pb geochronologyfor the intrusive rocks in the area, with the aim to precisely determine the lithologyand formation age of these rocks; With the mineral chemistry analysis of plagioclase,hornblende, biotite in the intrusive rocks combined with the zircon thermometer andtrace elements analysis，we got detailed thermodynamic evaluation of the formationconditions of these intrusions and were in able to find out the diagenetic process andits relationship with mineralization. The main research results are as follows:1. There are two kinds of intrusive rocks outcrop in Guichi-Qingyang area,Maotan Moyite with the intrusive age of126.2±3.3Ma~127.8±1.3Ma andDianmenkou Diorite.2. Dianmenkou intrusive pluton’s diagenetic process experienced two stages ofmineral crystallization, the first stage of crystallization of139.1±1.3~144.0±2.2Maand the depth of17~19km with the conditions of temperature and pressure forT=781±13℃, P=0.57±0.06GPa; the second stage of crystallization happened at theage of125.3±3.1Ma, and at the depth of about8km with temperature and pressureconditions for T=741±12°C, P=0.24±0.06GPa, the magma were rising at thespeed of0.05mm/y.3. By using LA-ICP-MS methods to analazed geochemical characteristics ofREE for the zircon sample, we found that most of the zircon showed relatively loss inLREE, while enrichment in HREE. They were chareterized as left assault type, andCe has the positive abnormal, while Eu has the negative abnormal. Thecharactereristics analysis of REE of zircon indicated that both of the two kinds ofintrusion rocks were corned from the partial melting of crustal material.4. Dianmenkou intrusive rock’s diagenetic age can be match with the age whencopper, gold mineralization occurring (145to135Ma) within the overall framework of the mineralization age in lower Yangtze metallogenic belt, but its diagenetic processconstraints metallogenic capacity.