| Baiyun gold deposit,a superlarge deposit in the north of Qingchengzi ore concentration area,is located in baiyunshan village,fengcheng city,Liaoning province.The ore bodies are in Gaixian Formation of Liaohe Group and controlled by strata,and the main mineralization categories are silicon potassium altered rock type and quartz veins type.In this paper,based on the achievements and data of past scholars,the author studied on the geological characteristics of deposit,isotope chronology and lithogeochemistry of the igneous rocks in the area,the mineral composition of K-feldspar and pyrite of the mineral,also summarized the ore-forming physicochemical conditions and deposit genesis.At last,the author built a magmatic hydrothermal deposit metallogenic model for Baiyun deposit.The ore bodies,which appear in bedded or veined,are in the sillimanite bearing mica schists strata or in the lithologic interface of sillimanite bearing mica schists and marble,and controlled by the ductile shear zone and fracture zone.The orebodies are closely related to quartz porphyry and granite porphyry,and they are in a same Magmatic hydrothermal system:silicon potassium altered rock type ores formed by contact-infiltration metasomatism in occurrence flat fault,while quartz vein ore formed in the opened fracture as ore-bearing fluid injected.A series of basic-acid wide composition spectrum dykes such as gabbro,lamprophyre,diorite prophyry,granite prophyry,quartz prophyry and monzonite porphyry are well developed in Baiyun gold deposit area and their generate sequence is gabbro-granite prophyry-quartz prophyry-diorite prophyry-lamprophyre-monzonite porphyry.Zircon U-Pb isotope dating shows that the dykes can be divided into Proterozoic,Indosinian and Yanshanian.The geochronology of the dykes are 1252.7±8.8Ma,218.6±0.4Ma,218.5±2.9Ma,229.0±1.0Ma,164.4±0.4Ma.In addition,the Shuangdinggou pluton composed by center phase,main body phase and marginal phase,with development of magma mingling.The ore related dykes show magma mixing ingredient variation characteristics.The granite prophyry in Baiyun gold deposit are related with main body phase of Shuangdinggou pluton,while the quartz prophyry are related with center phase.We concluded that granite porphyry,quartz porphyry and Shuangdinggou pluton are formed from the same magma system,and genesis with the orebodies of Baiyun gold deposit:the magma system provided ore-forming energy and matter,and orebodies,granite porphyry and main body phase may constitute a series of continuous evolution.Silicon kalium altered rock not only is the main ore type but also is the directly surrounding rock in baiyun gold deposit,in which K-feldsparization developed widely.The hydrothermal alteration of potassium feldspar is blue purple,composed by microcline and perthite,uaually paragenesis with quartz and pyrite.There is a big difference between Hydrothermal feldspar and protogenetic feldspar,Hydrothermal feldspar K2O content of 15.02?16.83%,Al2o3 content of 17.66?18.92%,SiO2 content of 64.11?65.50%,while the same constituents in protogenetic feldspar are 46.56?66.39%,19.02?36.79%,SiO2 15.02?16.83%,that means hydrothermal alteration fluid concentration of K and Si,on the other hand,Al?Fe?Na?Mg are moved during the process of alteration.The mineralization temperature is 298?.Pyrite mineral composition shows,Co/Ni averages of 1.94,S/Se is 0.12x104?1.78×104,with a mean of 0.5 ×104,the characteristics of all besides figures of As-Co-Ni and 5Fe-?S proved that pyrite are for hydrothermal origin.In conclusion,we argued that the baiyun gold deposit is magmatic hydrothermal type gold deposit that related to Indosinian magma activity. |
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