| The Jinchangyu intermediate-acid rock veins in eastern Hebei are developed,mainly including 5 diorite veins from Xiaoheiting,7 granite granulite veins and 1granite porphyry vein from Qingshankou to Yuhuzhai.Most of the veins are exposed with a stable width,and the two ends are extended for a certain distance and then gradually pinched out.Based on petrology,LA-ICP-MS zircon U-Pb chronology,zircon Hf isotope determination and geological and geochemical characteristics,this paper discusses the genesis and tectonic environment of the middle-acid dikes in Jinchangyu,eastern Hebei.The Xiaoheiting diorite dike is north-north-west trending,about 1.5?2km long and 30?40m wide.The U-Pb age of zircon is 2513.3±7.6 Ma,and the emplacement age is the late Neoarchean.The sample has the characteristics of low silicon and rich sodium.It belongs to the peraluminum calcium-alkaline series.The Mg#is relatively high(57.32?59.01).It is rich in light rare earth elements and LILE(Rb,Ba,Sr,etc.),and is depleted in HFSE(Th,U),Ta,Nb,P,Zr,Hf,Ti,etc.),K,P,Ti are strongly depleted,with europium negative anomaly.Isotope analysis shows that the Xiaoheiting diorite dike?Hf(t)=-2.2?2.7,and its magma originates from partial melting of the enriched mantle wedge metasomatized by subduction fluids,and is subject to a certain degree of crustal contamination during the ascent of the magma,may be formed under the island arc structure environment;Yuhuzhai granite porphyry vein zircon U-Pb age is 229.8±1.4 Ma,emplacement age is late Middle Triassic;Qingshankou granite granite porphyry vein is It runs north-north-east,with a length of800-1200m and a width of 30-40m.Granite veins are rich in silicon and sodium,belonging to the peraluminous high potassium calcium-alkaline series,with low Mg#(12.86-19.71).Granite veins are all enriched in light rare earth elements,LILE(Rb,Ba)and HFSE(Th,U,Ta,Nb,etc.),P,Ti,and Sr are strongly depleted,with a negative Europium anomaly.The Yuhuzhai granite porphyry dyke and Qingshankou granite porphyry dyke should have homologous magmatic evolution characteristics.Yuhuzhai granite porphyry vein?Hf(t)=-7.98?-3.48,the magma source area should be the partial melting of the ancient crust of the Mesoproterozoic,and the tectonic environment may be the transition from the post-collision stage to the post-orogenic stage.The magmatic activities in different periods in the study area are related to the migration and enrichment of gold and other minerals.The magmatic activity in the late Neoarchean period may have relatively enriched the gold rich in the hornblende strata of the Zunhua Group,laying the foundation for the formation of the Jinchangyu gold(molybdenum)deposit;the Indosinian magmatic activity may have a negative impact on the mineral resources in this area.The formation of Zn plays a role of providing useful mineral components and providing a heat source to the surrounding rock of the mineral source layer,driving the migration and enrichment of useful elements. |
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