Ore Characteristics And Occurrence Of Silver Of The Erdaokan Silver Polymetallic Deposit In Heilongjiang Province

Erdaokan silver deposit is 10 kilometers south of Heibaoshan Town,Nenjiang County,Heilongjiang Province.That is located in the east of Xingmeng orogenic belt.It is the first newly discovered silver deposit in Duobaoshan ore district.The deposit occurs in the Devonian Niqiuhe formation.The direct host rocks of deposit are tuff,limestone,carbonaceous slate and altered andesite.The magmatic rocks in the mining area mainly include granitoid and medium-basic intrusive rocks.The occurrence of diabase,diabase-porphyrite and quartz diorite porphyrite is closely related to the ore body.The NE and NW fault structures mainly controll the ore deposit in the mining area.The ore body and intrusive rock are distributed along the NW structural belt.At present,erdaokan silver deposit mainly have NO.I and NO.II.orebodies.Ore bodies are vein and dyke likely.The average silver grades of two orebodies are 315.63g/t and 550.71 g/t.The ore type of the deposit is mainly tectonic breccia type.The size of breccia ranges from several millimeters to more than ten centimeters.The breccia is mainly composed of altered andesite,sub-volcanic rocks and carbonate.The ore minerals mainly include magnetite,hematite,pyrite,chalcopyrite,sphalerite,galena,marcasite,pyrargyrite,stephanite and argentite.The supergene minerals include coronadite,pyrolusite,goethite,etc.The gangue minerals mainly include quartz,calcite,feldspar,etc.The ore structure mainly include brecelated,massive,veinlike and miaroliticlike structure.The ore texture mainly consists of metasomatic texture and crystalline texture,followed by the exsolution texture and crushed texture,as well as,the framboidal texture of pyrite and thezoned texture of magnetite.Through the analysis of mineral micro area,include scanning electron microscopy,electron probe microanalysis and LA-ICP-MS in-situ trace element test,we found the main silver bearing minerals are independent minerals of silver,include pyrargyrite,stephanite,argentite,of which silver accounts for 59.39%-85.04%.The proportion of silver in pyrite,chalcopyrite,sphalerite,galena,manganite and pyrolusite is less than 5%.Silver mainly occurs in the independent minerals of silver,and distribution state of silver minerals include inclusion silver,intergranular silver and fissured silver.Secondly,silver occurs in pyrite,chalcopyrite,sphalerite and galena in the form of isomorphism and submicroscopic inclusion,and in manganese minerals such as coronadite and pyrolusite in the form of ion adsorption.The characteristics of trace elements in pyrite from different depths show the Ag is more enriched from the deep to the shallow part of the ore body.Based on the analysis of mineral fabric and mineral micro area,the metallogenic process can be divided into three stages: sedimentary stage,hydrothermal stage and epigenetic stage.the hydrothermal stage is the main metallogenic stage and the epigenetic stage has secondary enrichment.The hydrothermal mineralization stage is divided into three stages: Quartz oxide stage,sulfide stage I and sulfide stage II.Sulfide stage I is the main mineralization stage of silver.The mineral assemblage and the component of mineral electron probe indicate that the ore-forming hydrothermal solution is a low-temperature system,and the deposit is a low-temperature ore-forming one.The trace elements of pyrite reveal the enrichment,migration and sedimentation laws of Mn,Ag and other ore-forming elements in the ore-forming hydrothermal solution.The deposit has experienced the functions of boiling,mixing and filling.On the basis of the study in this paper,it is preliminarily inferred that the deposit is a epithermal silver deposit..