| The Guojialing granites are mainly formed in Early Yanshan Period, and distribute in Zhaoyuan City (Shangzhuang, Beijie and Congjia), Penglai City (Nanwang, Qixia and Guojialing) and Zetou of Wendeng City in the east. Generally, they are appeared as discontinuous strips with an area of about 514 square kilometers, and belong to the main ore-controlling range of gold deposit in Jiaodong area. This paper thoroughly carrys out a study on petrology, geochemistry and significance of the Guojialing granites, which is helpful to further study deep ore-forming mechanism so as to guide the prospecting work of gold in depth.Based on the field geological observation and laboratory study, this paper analyzes comprehensively mineral association, petrology and geochemistry characteristics of the Guojialing granites. According to the substantive relation between petrochemistry characteristics and tectonic environment, this paper chooses certain geochemical discriminant parameters and diagrams, by which it researches thoroughly the geochemistry characteristics of the Guojialing granites.The geologic achievements obtained in this research as follows:(1) The Guojialing intrusive rocks belong to this series of monzodiorite-quartz monzonite-granodiorite-monzonitic granite. Generally, they appear as porphyaceous and granular texture, contain a little of amphibole and biotite, and distribute widely.(2) Geochemical characteristics of the Guojialing granites include that K2O/Na2O is generally less than 1,σis between 1.79 and 3.24, A/CNK is averagely between 0.77 and 1.1, DI belongs to medium to high level and SI is more lower; lithophile elements enrich and high field strength elements loss, the curves corresponding with each unit appear as right-leaning trend, and no obvious difference as a whole; light rare earth enrich and high rare earth loss, the distribution curves are right-leaning, and no obvious EU valley.(3) The Guojialing granites are formed by crystallization differentiation after the mix of magma from mantle and crust, and belong to granitoid of syntectic and plutonic type. They belong to intrusive series of double evolution including texture and composition, and are characterized as periodicity, progress gradually, and the certain cyclicity, and the evolutionary time is difference.(4) The tectonic environments forming the Guojialing granites include that volcanic arc caused by the subduction of oceanic crust, continental collision and extensional continental margin of back-arc.(5) By studying, emplacement mechanism of the Guojialing granites belongs to the heat-light-balloon-expansive pattern of frequent pulsation and flow from small to big area along the compressive zone of NEE direction.(6) The Guojialing granites provide heat source and mineralizer for gold mineralization of Jiaodong region, and tensor-shear expansion spaces formed in the process of tectonic emplacement have a good control over the enrichment, superposition and relocation of the gold. In a word, for Jiaodong gold deposit, the Guojialing granites are the direct rock series of ore source. |
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