Characteristics And Genesis Of Igneous Rocks Of Dongliang Gold Deposits In Eastern Hebei

The Dongliang gold deposit located in the eastern Hebei, which is identified as a middle post subvolcanic hydrothermal type gold deposit in recent years. It has developed the Tiaojishan volcanic rocks and diorite, quartz monzonite porphyry and granite porphyry in late Jurassic. In order to identify the geological and geochemical characteristics of igneous rocks, and the relationship with gold deposits, the study used radioisotope geochronology, geochemistry and zircon Hf isotope methods to make a study of their ages, geochemistry, magma source characteristics and so on,which achieved the following results and understanding:（1）LA-ICP-MS zircon U-Pb dating data of the andesite, diorite, quartz monzonite porphyry and granite porphyry yielded ages of 170.2±1.4Ma, 156.4±1.0Ma,151.25±0.63 and 154.5±0.49, they were the products of Middle-late Jurassic.（2） SiO₂ content of andesite is 60.73% 62.21%, and the total alkali content（ K2 O + Na2O） is 5.16%⁸.6%. K2 O / Na2 O ratios is 0.14³.36, ∑REE content of andesite in Dongliang is 86.73 × 10-6 162.10 × 10-6, the LREE were riched,（La/Yb）N=6.31²3.22,the average value is 13.68, LREE/HREE=6.41¹4.41, the average value is 10.51, δEu=0.84¹.21; The deposits is enriched in LILE, such as:Rb, K, Ba etc. The loss of high field strength elements Ta, Nb, Ti etc, which belongs to calc-alkalic series- high potassium rock series.（3） While SiO₂ content of granite porphyry is 76.13%⁷7.22%, and the total alkali content（K2O + Na2O） is 8.13% 8.26%, and the value of A/CNK is more between 1.11 1.22, which belongs to weak peraluminous rock high potassium calc-alkaline series. The ∑REE contents were 33.10×10-6 44.7×10-6, with the intense fractionation of REE,（La/Yb）N=7.48¹4.26, LREE/HREE=9.96¹9.79,the average value is 13.74, δEu=0.29⁰.36; It shows a strong negative Eu anomalies.The deposits is enriched in LILE, such as: Rb, K, etc. and Ba, Th, U, and the loss ofhigh field strength elements Ta, Nb, Ti, etc, which shows the the characteristics of I type granite porphyry（4） Zircon Hf isotope studies shown that the εHf（t） values and TDM2 ages of two granite porphyry samples were-14.8^-6.7,-15.9^-7.2 and-16.0^-7.9, 1642²155Ma,1667²211Ma and1703²216 Ma, respectively, which are representatives of the Paleoproterozoic crustal reservoir.（5）The Middle-late Jurassic granites in the eastern Hebei, including the Dongliang granite porphyry and volcanics of Tiaojishan are under the tectonic settings of crustal thickening and the subduction of ancient Pacific plate with Eurasian plate, which cause mantle magma intrusion and the partial melting of lower crust, and then the acidic magma rising to the shallow magma chamber and formed by fractional crystallization.