The Late Jurassic Magmatism Of Ore Bearing Rock Mass In Laiyuan,hebei Province And Its Relation To Metallogeny

The genesis of the Mujicun Cu(Mo)deposit and Dawan Mo deposit,as two typical deposits in the Late Jurassic in Laiyuan country,Hebei Province,is related to diorite porphyrite body and rhyolite porphyry body respectively.Combined with the previous research results,the geological survey in field about Mujicun and Dawan mining area was carried out,and the petrology,geochronology and geochemistry of diorite porphyrite and rhyolite porphyry are analyzed.Furthermore,the magmatic activity of ore-bearing rock in late Jurassic and its relationship with mineralization are preliminarily discussed.Based on the comprehensive geological researches,the Late Jurassic rocks in this region are mainly diorite porphyrite and rhyolite porphyry,occurring as the ore-related rocks of Mujicun Cu(Mo)deposit and Dawan Mo deposit,respectively.Geochemically,the diorite porphyrite is characterized by high content in Si O₂,low content in Fe O,Ti O₂ and Mg O,and belongs to quasi-aluminum and high-k calc-alkaline series.It is also characterized by enrichment in Ba,U,La and Sr,and depletion in Rb,Th,Nb,Ta,Zr and Ti.The rhyolite porphyry shows characteristics of high content in Si O₂ and K₂O,low content in Ti O₂,Fe₂O₃,Fe O,Mg O,Ca O,Na₂O and P₂O₅,and the composition ranges from peralkaline to slight peraluminous,belonging to shoshonite series.Compared with the diorite porphyrite,the rhyolite porphyry shows features of enrichment in Rb,U,Zr and Hf,and relative depletion in Sr and Ti.The chondrite-normalized REE patterns of these two types of rocks are both exhibiting features of enrichment in light rare earth elements.The diorite porphyrite exhibits weak positive Eu anomalies,whereas the rhyolite porphyry has negative Eu anomalies.The analysis of ore-forming elements tells us that Cu and Mo in Mujicun deposit are concentrated in the alteration zones of potash feldspathization and quartz-sericitization in diorite porphyrite.However,in the Dawan deposit,the Mo is mainly enriched in the silicified zone in rhyolite porphyry.In this research,the zircon U-Pb dating indicates that the diorite porphyrite in Mujicun deposit is formed at 139.8±3.3Ma.The molybdenite Re-Os isotopic dating shows that the Mo mineralization in Dawan deposit occurred at 139.0±1.5 Ma.The previous studies tell that the Mujicun Cu(Mo)deposit was formed at 142.95Ma and the Dawan rhyolite porphyry was emplaced at 140.47Ma.The time difference between diagenesis and mineralization is small,which are closely related,and belonging to Late Jurassic.Therefore,according to the comprehensive analysis of diagenesis and mineralization,and it suggests dioritic and rhyolitic mamgas underwent emplacement and crystallization to form diorite porphyrite and rhyolite porphyry in transitional tectonic setting from compress to extension during the Late Jurassic.During the post-magmatism,magmatic hydrothermal fluids enriching large monunt ore-forming material give rise to distinct minerlization at interior and contact zone of plutons.The ring alteration-mineralization system characterized by diorite porphyrite at the center was formed in the Mujicun ore district,whereas ring-like alteration-mineralization system exhibiting rhyolitic porphyry at the center was taken place at the Dawan ore district.