Research On The Characteristics And Metallogenic Regularity Of Marine Volcanic Type Ore Deposits In The Northern Qilian,Qinghai Province

The northern Qilian orogenic belt locates among the northern China plate,Tarim plate and middle Qilian-Qaidam plate.It locates at the middle of Qinling-Qilian-Kulun giant polycyclic composite orogenic belt,it is an important nonferrous metal orogenic belt in China.Because of its huge prospecting potential,northern Qilian has attracted sustained attention among the related study in recent years.This paper based on Langlike,Yinaocao and Honggou copper deposits as research object.On the basis of field and mining geological work,I carried out systematic indoor research like analysis and test the samples collected from deposit,discussed mineralization and alteration characteristics,studied geochemical characteristics of the rocks and ores deposit and finally revealed the diagenetic epoch and metallogenic regularity.1.Petrogeochemistry:This region develops one NWW-trending fault belt,which plays a controlling role in magmatic activity and mineral distribution in this region.These three typical deposits all belong to marine volcanic type ore deposits,the geochemical characteristics react differently.The similarities are summarized as(1)Rb,Ba,Sr,Th and K are relatively enriched(2)no obvious negative anomaly of Eu.Meanwhile,the differences are summarized as(1)Langlike belongs to low potassium calc-alkaline;(2)Yinaocao belongs to peraluminous calc-alkaline series;(3)spilite of Honggou have both arc calc-alkaline basalt and mid-ocean ridge basalt geochemical characteristics at the same time;(4)study of S and Pb isotope show metallogenic material come from earthcrust with mantle contamination to some degree.2.Alteration zoning and mineralization characteristics:The mineralization alteration if Langlike is sericitization,sericite-quartz alteration,chloritization and epidotization with zoning.From the center of volcano channel to its edge are actinolitizationepidotization zone,silicification zone and sericitization-chloritization zone respectively.Sericite-quartz alteration has close relationship to mineralization.The main alteration of Yinaocao is sericitization and sericite-quartz alteration,which have close relationship to mineralization.Carbonate lithification and sericitization are secondary alteration.Honggou has sericite-quartz alteration,silicification and so on.Silicification has the most relationship to mineralization.3.Thermochronology:The Zircon U-Pb age of Langlike copper deposit is 463.5±1.4 Ma formed in oceanic crust subduction environment;Yinaocao is 424.3±5.4 Ma formed in residual ocean basin sedimentary environment;Honggou is 443.0±6.6 Ma formed in passive terrestrial rift environment.These ages all stand for their diagenetic age.Shows these deposits are mainly formed from Ordovician to Devonian.Apatite fission track age is 26?85Ma.The history of Uplift and denudation in this region reflects the northern Qilian uplifted slowly and affected by strike-slip faults at the same time.4.This paper established the metallogenic model of marine volcanic type copper deposit in northern Qilian area.Magmatic fluid includes basement metamorphic rock series,lower neutral lava and upper basic volcanic rocks of Precambrian migrated and erupted upward along the magmatic hydrothermal channels,carried a lot of oreforming material fluid then formed enriched sulfur-copper region.Because of the leaching effect of water cycle,the ore-bearing hot brine formed ore bodies in a particular location.Together with diorite porphyrite intruded into upper,surrounding rock overlaid and reconstructed the mineralization process.Finally the upper volcanic sedimentary rock system completed the following mineralization by exhalative sedimentation.