The Mesozoic Tectonic Evolution And Pb-Zn-Ag Metallogeny In The South Margin Of North China Craton

In recent years, many large-medium scale lead-zinc-silver deposits were found in the southmargin of North China Craton such as Shagou, Lengshuibeigou, Laodaizhanggou and so on. Sothere has been wide interest in the types and features of lead-zinc-silver deposits and metallogenicgeodynamics background in this area. Based on the detailed field investigation, this paperconcluded the Mesozoic intracontinental tectonic evolution in the south margin of North ChinaCraton, analyzed the typical lead-zinc-silver deposit clusters, classified the types of lead-zinc-silverdeposits, determined the metallogenic time, studied the mineralizing style and discussed themetallogenic geodynamics background.This paper provided the highly precise zircon SHRIMP U-Pb ages of 115±1.4Ma forTaishanmiao granitic body, 133.5±1.4Ma for Haopinggou granite porphyry body and 112±1Mafor Donggou granite porphyry body. On the basis of the genesis and tectonic setting of granite,Mesozoic tectonic evolution in the south margin of North China Craton were divided into fourstages: post-collisional stage from upper Triassic to middle Jurassic, huge tectonic regimetransformation stage in upper Jurassic, huge lithospheric thinning stage in lower cretaceous andintrocontinental subduction and rifting stage from upper cretaceous to Cenozoic.According to the Re-Os isotopic model age of 116±1.7Ma for the molybdenite in Donggoumolybdenum deposit and ⁴0Ar-³9Ar plateau age of 134.9±0.8Ma in Haopinggou lead-zinc-silverdeposit and 110.1±9.0Ma for hydrothermal altered sericite in Sanyuangou lead-zinc deposit,lead-zinc-silver mineralizing process were divided into two episodes: The first episode includedskarn type and hydrothermal vein-type deposits in 140Ma and the second episode includedhydrothermal vein-type deposits from 130Ma to ll0Ma. The hydrothermal vein-type depositsincluded quartz vein deposits and tectonic altered rock type deposits.Skarn type polymetallic deposit and hydrothermal vein type lead-zinc-silver deposit of 140Mawere located in the peripheral skam belt and the fracture belt of wall rock of upper Jurassicporphyry body. The ore-forming temperature of Skarn type polymetallic deposit was medium tohigh. And the ore-forming temperature of hydrothermal vein type lead-zinc-silver deposit had aH₂O-NaCl system of medium temperature (252～331℃) , medium to low salinity (8.28%～16.43%), medium density, and CO₂ contained. The dD value and d¹⁸O_H2O value of ore-formingfluid are-83‰～80‰and 4.28%～7.65% which suggested the origin of ore-forming fluid wasmagmatic water predominately mixing meteoric water. Sulfur and lead isotope-tracing suggestedthe crustal origin of ore forming materials. Temperature decrease, water-rock interaction, mixingand miscibility of ore forming fluid are the main factors of mineral precipitation.Hydrothermal vein type lead-zinc-silver deposits from 130Ma to 110Ma were mainly locatedin the fracture belt of Xiaoqinling-Waifangshan gold-silver-lead-zinc-molybdenum metallogeniczone. Tectonic altered rock type silver(gold)-lead-zinc deposits had a H₂O-NaCl system of mediumtemperature (147～360℃), medium to low salinity (4.6%～22.71%), medium density (0.52～0.99g/cm³) and CO₂ contained. The composition of hydrogen, oxygen and carbon suggested theorigin of ore-forming fluid was magmatic water predominately mixing meteoric water. Sulfur and lead isotope-tracing suggested ore forming materials derived from the lower crust crystalbasement-Taihua Group. Ore forming mixing, water-rock interaction and temperature decrease arethe main factors of mineral precipitation. The ore forming fluid of Dongchuang quartz vein typegold-lead deposit had a H₂O-NaCl-CO₂-CH₄ system of medium temperature (180～340℃),medium to low salinity (7.0%～22.3%), medium density (0.82～0.98g/cm³) and H₂S contained.The composition of hydrogen, oxygen and carbon and the constituents of ore forming suggested theorigin of ore-forming fluid was magmatic water with the participation of mantle fluidpredominately, mixed meteoric water. Ore forming materials probably came from mantle besidesthe origin of the lower crust crystal basement-Taihua Group. Boiling and mixing of ore forming arethe main factors of mineral precipitation.Lead-zinc-silver mineralizing process in the south margin of North China Craton had a closerelationship with regional geodynamic background. Lead-zinc-silver mineralizing process of140Ma formed in the huge tectonic regime transformation stage of eastern China and was relatedwith syntexis(â… ) type granite porphyry body of upper Jurassic. Lead-zinc-silver deposit of 130Ma to110Ma formed the lithospheric thinning process of eastern China: tectonic altered rock type silver(gold)-lead-zinc deposit of Tieluping deposit clusters and Kangshan ore-field was related withremelting type granite; Dongchuang quartz vein type gold-lead deposit was close to the magmaticactivity with the participation of mantle fluid; and tectonic altered rock type lead-zinc deposit ofFudian deposit clusters was close to A-type granite of Taishanmiao.Key words: tectonic evolution, mineralizing process, metallogenic geodynamics background,lead-zinc-silver deposit, the south margin of North China Craton...