LA-ICP-MS Zircon U-Pb Ages and Lithogeochemistry of Basic Dykes in the Guoluolongwa Au Ore Field, Qinghai Province, China
详细信息
- 责任者：Yue Weihao (College of Land Resource Engineering ; Kunming University of Science and Technology ; Kunming 650093 ; China) ; Gao Jianguo
- 刊名：Journal of Mineralogy and Petrology
- 出版年：2013
- 卷期：33(3)
- 页码：p.93-102
- issnNo：ISSN1001-6872
- isbnNo：CN51-1143/TD
摘要
Intruded in metamorphic rocks,basic dykes are well developed in the Guoluolongwa gold ore field,Qinghai Province,with gray-green and dark gray color,and with compact lump structure and residual diabase and gabbro and porphyritic textures.The main minerals compositions are plagioclase,pyroxene,hornblendes and carbonate minerals,with titanite,zircon and apatite(less than 1%)as accessory minerals.Phenocrysts are composed of plagioclase and highly altered pyroxene.Complex matrix consists of mainly plagioclase,pyroxene,chlorite and accessory minerals.Rocks are strongly altered evidenced by tremolite actinolitization,chlorite epidotization and carbonatization.The major components in the rocks are consistent with carbonate alteration features with low w(SiO2)(44.1% to 48.5%),high w(MgO)(8.3% to 12.28%)and w(CaO)(8.84%to 10.9%),consistent with the basic rocks and carbonatization features.Zircon grains in the basic dykes are rare and small with organized oscillatory zoning feature of magmatic origin.LA-ICP-MS dating reveals forming ages of 416.2Ma±3.5Ma(MSWD=0.25,N=6)and 487.5Ma±4.0Ma(MSWD=0.92,N=3)respectively.The older ones among the zircons are of better psephicity,which are probably inheritance or captured zircons.Therefore,the age of 416.2Ma±3.5Ma should represent the crystallization age of basic dykes and is in accordance with the crystallization age of Qingshuiquan diabase and volcanic rock of the Nachitai Group.The determined age indicates that Guoluolongwa gold deposit ore-bearing strata can be classified in Nachitai Group,and the basic magmatism has no direct genetic link with regional Indosinian orogenic type gold deposit.Basic dykes are with relatively lower rare earth(ΣREE=51.35×10-6 to 101.4×10-6)and enriched in LREE,Eu and Ce anomalies are not obvious.Meanwhile,theses basic dykes are rich in large ion lithophile elements(K-Rb-Ba-Sr)and depleted in high magnetic field strength elements(Nb-Ta-Ti-Y),in accordance with the characteristics of island arc calc-alkaline series,and it may be attributed to the subduction of oceanic crust and the extension of back arc during Early Paleozoic.