Geochemical Characteristics And The Age Of Diagenesis And Mineralization Of Granite In Yangchun Basin,Western Guangdong

The Yangchun Basin in the west of Guangdong Province is located in the south of the polymetallic metallogenic domain in South China and is one of the five national integrated exploration areas in Guangdong Province.More than 20 large and medium-sized ore deposits,such as Cu,Fe,Pb-Zn and W-Sn,have been found in the basin,and there are many distributions of ore and anomaly spots,indicating that the basin still has good prospecting prospects.The thesis relies on the geological survey project of the China Geological Survey Bureau,?Guangdong Yangchun Copper Polymetallic Mine Prospecting Area Mapping and Technology Application Demonstration Prospecting Research?(No.12120114015801)for scientific research projects.Taking the representative of the 4 granites in the Yangchun Basin(Shilu,Gangmei,Xishan,and Yingwuling)as the research objects,Through geological surveys,systematic sampling and test analysis,the elemental geochemical characteristics and diagenesis and mineralization ages of the four granites were systematically discussed,Combined with previous data of the characteristics of the granites in the Yangchun Basin and the following main results and understandings were obtained:The major elements of Shilu and Gangmei Granite have the characteristic of low Si(The average content of Si O₂ is between 65.91%?65.08%),low alkali(The average content of alkali is between 5.82%?7.08%),high Al(The average content of Al₂O₃ is between 15.78%?15.42%),and high Ca.(The average content of Ca O is between 4.38%?3.17%),high Mg(The average content of Mg O is between 2.08%and 1.39%),belonging to quasi-aluminum to weak peraluminous,Ca-alkaline series rocks;The major elements of Xishan and Yingwuling Granite have the characteristic of high Si(The average content of Si O₂ is between 75.30%?72.01%),high alkali(The average content of alkali is between 8.53%?8.21%),low Al(The average content of Al₂O₃ is between 13.52%?14.12%),and low Ca.(The average content of Ca O is between 0.3%?0.74%),low Mg(The average content of Mg O is between 0.06%?0.58%),belonging to peraluminous and alkaline series rocks.Trace element researches have shown that the spider diagram patterns of Shilu and Gangmei are similar,The loss of Nb and Ta elements in Shilu and Gangmei granites are higher than those in Xishan and Yingwuling granites.However,the loss of Sr and P in Xishan and Yingwuling granites are much higher than those in Shilu and Gangmei granites.Rare earth element researches have shown that the LREE/HREE average value of Shilu and Gangmei granites is 9.02 and 12.28,which is much higher than the average value of 2.58 and 3.17 of Xishan and Yingwuling granites.The average?Eu values of Shilu and Gangmei granites are 0.79 and 0.73,The negative Eu anomaly is not obvious,while the average?Eu values of Xishan and Yingwuling granites are 0.05and 0.08,showing the significant negative Eu anomalies.The REE distribution patterns of Shilu and Gangmei granites are right-dip smooth curves,while the REE distribution patterns of Xishan and Yingwuling granites have a"V"-shaped flat curve with"M"type four grouping effect.Through zircon U-Pb dating,the weighted average ages of the two samples of Gangmei granite is 164.4±1.3 Ma(MSWD=2.1)and 165.3±1.5 Ma(MSWD=2.1),respectively;the weighted average ages of two samples of Shilu granite is 104.4±1.0Ma(MSWD=1.8)and 103.9±0.5(MSWD=1.11),respectively;the weighted average age of the Yingwuling granite is 79.0±0.98 Ma(MSWD=1.6).By the Re-Os isotopic dating of molybdenite,the weighted average age of four samples of Gangmei granite is 163.1±0.7 Ma(MSWD=0.74),the weighted average age of four samples of Shilu granite is 101.88±0.48 Ma.Comprehensive data on granite geochemical characteristics in the Yangchun Basin can be divided into two types of granites:Type I is quartz monzonite and granodiorite associated with the mineralization of thiophilic elements such as Fe,Cu,Mo,and Pb-Zn.Including Shilu,Gangmei,lunshui,Heishigang,Yuanzhuding granites,etc.;Type II is biotite granite closely related to the mineralization of lithophile elements such as W,Sn,Mo,Bi,etc.Including Xishan,Xiaonanshan,Yingwuling,Dajinshan granites,and Shidong Complex,Guangping Complex.The content of Ti O₂,Fe₂O₃,Mg O,Ca O,P₂O₅ and other basic components in type I granites are obviously higher than that in type II granites.The content of Si O₂ and total alkali in type II granites is obviously higher than that in type I granites.According to diagenesis-mineralization chronology data,the granites in the study area was divided into three diagenesis-mineralization periods.The first diagenesis-mineralization period was Middle Jurassic epoch(160Ma±)which is closely related to the Cu-polymetallic deposits;the second diagenesis mineralization period was Early Cretaceous epoch(100±Ma)which is closely related to the Cu-Mo-Pb-Zn mineralization;the third diagenesis-mineralization period was Late Cretaceous epoch(80Ma±)which is closely related to the W-Sn mineralization.The genetic types of the two types of granites indicate that the genetic type of the type I granites belongs to I-type granite,while the genetic types of type II granite are highly differential I-type granites.The analysis of the tectono-environment of the three diagenetic periods indicates that the Middle Jurassic epoch(160Ma±)granites were formed under the collision-extrusion-stretching arc tectonic-environment transition;Early Cretaceous epoch(100 Ma±)granites were formed in a completely stretched-thinning volcanic arc tectono-environment;the Late Cretaceous epoch(80Ma±)granites were go through a highly differentiated crystallization,and the geochemical characteristics affected by the oceanic subduction have changed and formed in the plate tectono-environment.