Research on Metallogenesis of Gold Deposits in the Wulongou Ore Concentration Area,Central Segment of the East Kunlun Mountains,Qinghai Province

Author:Zhang Yuting

Supervisor:Sun Feng month

Database:Doctor

Degree Year:2018

Download:156

Pages:261

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The eastern Kunlun orogenic belt,located in the northeastern margin of the Qinghai Tibet Plateau,is an important part of the Central Orogenic Belt.The evolution of the geology has created rich mineral resources,for example,gold,salt and copper polymetallic mineral deposits.Wulonggou gold metallogenic district is located in the middle East Kunlun orogenic belt.At present,a series of gold deposits,like Hongqigou-Shenshuitan(large),Baidungou(medium),Xintuo-Haxiwa gold deposit(small),have been found in the Wulonggou region,which has great potential for gold mineralization.Based on the collection and collation of previous data,combined with the metallogenic geological background researches,using magmatic petrology and geochemistry,metallogenic chronology,and fluid inclusions methods,this paper 1)analyzes the geological characteristics,2)discusses the metallogenic material source,nature,origin and evolution of ore-forming fluid,and metallogenic age,3)determines the origin type of ore deposit,and 4)further constructs the practical prospecting model of the Hongqigou-Shenshuitan,Baidungou and Xintuo-Haxiwa gold deposits.The main results are as follows:The study of the geological characteristics of the typical deposit shows that:1)the ore hosting lithologies of the Hongqigou-Shenshuitan gold deposit are mainly dominated by the Jinshui gneisses and Indosinian magmatic rocks(e.g.,mafic dykes).Under the control of the NW trending fault,the intermediate-basic swarms are developed in the mining area,often associated with the ore body in space.The main types of ore are fractured zone type(oxidative fracture zone type and structural fracture zone type)and altered rock type.The wall rock alterations consist of silicification,sericitization,chloritization,carbonation,and kaolinization.Hydrothermal mineralization period include gold-arsenopyrite-quartz stage,gold-pyrite-quartz stage and carbonation stage;2)the ore body of the Baidungou gold deposit is located in quartz diorite and granulite,controlled by the north-west fault zone.The ore type is tectonic altered rock type,and the alteration of surrounding rock includes silicification,sericitization,chloritization,carbonation,and kaolinization.Hydrothermal mineralization consists of the gold-arsenomarcasite-pyrite-quartz stage,gold-pyrite-quartz stage,polymetallic sulfide stage and carbonate stage;3)the ore bodies of the Xintuo-Haxiwa gold deposit are constructed in the granodiorite in the fracture zone,controlled by NW fault zone.The ore types are tectonic altered rock type and quartz vein type.The alteration of surrounding rock includes silicification,sericitization,chloritization,carbonation,and kaolinization.Hydrothermal mineralization consists of gold-pyrite-arsenopyrite stage,gold polymetallic sulfide stage and carbonation stage.Gold mineralization has a close spatial correlation with the mafic dikes,which often with body arranged in parallel,or become the wall rock in the East Kunlun area.Zircon U-Pb dating results indicate that they formed in the early Indosinian,in details,1)the Shuizhadonggou appinite dikes formed at 248 Ma,2)the Heishigou diabases formed at244 Ma,and 3)the Xiaogangou diabase dikes formed at 263 Ma,slightly earlier than the mineralization time.The source region of these dykes is the mantle wedge metasomatized by subduction fluids.The activity of early Indosinian mafic dikes provided a channel for subsequent mantle-sourced fluids and gold rising.The subduction and dehydration of oceanic crust provided sufficient mantle fluids for large-scale gold mineralization in the post collisional extension stage.Besides the early Indosinian basic dyke swarms,the surrounding rocks of ore body also contain a series of intermediate to acid magmatic rocks.The formation time of the Baidungou quartz diorite is 242 Ma,and its source area is related to the crust-mantle mixing during the subduction process.The formation time of the Huanglonggou diorite porphyrite is 218 Ma,most close to the era of the ore body,which was considered as the product of the partial melting of delaminated lower crust.It is believed that the deposit was formed in the post collision extension environment associated with the late Indosinian lithospheric delamination.In the main stage of the Hongqigou-Shenshuitan metallogenic processes,the quartz δ18O value is 10.1‰4.4‰.Corresponding to the main metallogenic stage,the fluidδ18O is between 6.310.6 and the delta D is between-74.6 and-105.7,and has the characteristics of mantle derived primary water.Its 206Pb/204Pb is 18.2518.62,207Pb/204Pb is 15.5815.95,and 208Pb/204Pb is 38.1838.60,a mixture of mantle lead and orogenic belt lead.Aboutδ34SV-CDT values,most of them are between 08 per thousand and 25 per thousand,forming a significant peak with the characteristic of normal distribution,with an average of 3.5 per thousand.The source is presumed to be a basic magmatic rock.Quartzδ18O values of the XinTuo-Haxiwagold deposit range from 15.6‰19.6‰.The main mineralization stage of quartz fluidδ18O values are between 6.3‰10.5‰,delta D is between-85.3 and-101.9,which has the nature of evolved mantle-derived primary water.Its 206Pb/204Pb,207Pb/204Pb,and 208Pb/204Pb values are 18.2518.62,15.5815.95,and38.18-38.60,respectively,a mixture of mantle lead and orogenic belt lead.Itsδ34SV-CDT-CDT are between 412 per thousand and define a peak at 6-8 per thousand,which shows a normal distribution characteristic of an acid magmatic rock.The isotopic study of these deposits indicates that the deep geological activities have played a dominated role in the generation of the gold mineralization.Homogenization temperature,salinity and fluid pressure of main stage for fluid inclusions in the Hongqigou-Shuizhadonggou gold deposit concentrated in 260320℃,4.008.00 wt.%NaCl,and 75130 MPa,respectively,corresponding to the depth of7.049.50 km.Homogenization temperature,salinity and fluid pressure of main stage for fluid inclusions in the Baidungou gold deposit concentrated in 230300℃,4.008.00wt.%NaCl,and 70100 MPa,respectively,corresponding to the depth of 6.779.10 km.Homogenization temperature,salinity and fluid pressure of main stage for fluid inclusions in the Xintuo-Haxiwa gold deposit concentrated in 220280℃,3.006.00 wt.%NaCl and65 to 100 MPa,respectively,corresponding to the depth of 6.508.25 km.From north to south,the uniform temperature and salinity are decreasing,and the mineralization depth shows a transition from deep to shallow gradient.The ore-forming fluid is H2O-NaCl-CO2system.The main ore forming fluid is in a medium temperature range.Fluid miscibility is the main precipitation mechanism of gold.The main driving force of the ore-forming fluids is late Indosinian deep magmatic tectono-thermal events.Mineralization regularity:in the Wulonggou ore district,the main ore-controlling fault XI mineralization belt has the characteristics of dextral normal faults.In the horizontal direction ore-body thickens when striking to the south,while in the vertical direction ore-body thickens when it steepens.The Wulonggou ore district has a large number of mafic swarms marked mineralization center,from the mine to the north and south sides of mineralization elements gradually transition from gold to gold and silver lead zinc polymetallic mineralization.In conclusion,the main material sources of gold mineralization in the Eastern Kunlun are the mantle,and the specific patterns are as follows:in the process of subduction of the Paleo Tethys during the late Variscan to Indosinian,it formed a series of regional faults,large shear zone and secondary folds and faults of a cracked ore control structure.At the same time,the ocean crust experienced dehydration,and the fluids metasomatized the overlying mantle wedge,leading to the invasion and formation of ore district mafic dyke swarm along these structures.After the closure of the Paleo Tethys Ocean in the Middle Triassic,the fluids enriched in the mantle wedge were separated from the source during subsequent post collisional extension,and then the deep source gold in the mantle is brought to shallow mineralization.In the process of upward migration,the fluids gathered with metamorphic water,meteoric water and other sources,and they suffered continuous extraction of surrounding rock and intrusive rocks in the ore material.When carrying a large amount of ore-forming fluids into the favorable tectonic area,the tectonic environment change induced the changes of physical pressure and chemical condition,during which,fluid unmixing happened and eventually prompted gold material precipitation,thus forming gold deposits.