Study On Material Components Of Ore In The Xishanwanyangchang Silver Polymetallic Deposit, Inner Mongolia

The Xishanwanyangchang silver polymetallic deposit,lied in mid-west area of Inner Mongolia,is located in the mid-west of north margin of the North China Platfrom.The ore-bodies are lentiform or stratiform occurring in the acidic volcanic rocks of the Lower Cretaceous Bainvyangpan Formation as well as contact zone between the volcanic rock and its footwall rock(Cambrian tonalite).Controlled intensely by fracture structures,the silver polymetallic deposit belongs to epithermal volcanic deposit.Based on the previous works and research results,the study on the material components of ore in the deposit is carried out by applying relevant theory of mineralizing geochemistry and means of the field geological survey,the observation of facieology and mineragraphy,the ore combination analysis,the silver phase analysis and the electron probing analysis,then some results and understandings obtained are as follows:The ore types are mainly veinlet-disseminated sulfide ores,fractured altered rock-type ores and their secondary oxidized ores.There are various types of ore textures,including the euhedral-subhedral granular texture of a variety of minerals,allotriomorphic granular texture,multiform metasomatic texture and the internal texture of some mineral crystals.The ore structures are mainly filled with filling structures,including sparsely disseminated structure,brecciated structure,fine vein structure and massive structure.The occurrence of silver in the deposit is varied,of which Ag occurs maily as visible silver and partly as invisible silver.Visible silver,mainly microencapsulated silver,followed by independent silver minerals,is small in general,and the mineral types are mainly pyroxene,followed by selenite,a small amount of natural silver,silver halide and silver oxide.Most microencapsulated silver is contained in limonite,partly in quartz and potassium feldspar,and a small amount of selenite is wrapped in barite.Independent silver minerals mainly embedded between quartzs and in those fissures.Invisible silver includes metamorphic silver that is contained in copper sulfides,and submicroscopic silver which has the composition more probably of silver sulfide and is contained in limonite,pyrite and galena,related to silver mineralization.The ore-forming process is divided into hydrothermal period and hypergene period.The hydrothermal period consists of three stages: quartz-pyrite stage,quartz-polymetallic sulfides stage that is the main metallogenic stage,and quartz-carbonate-barite stage.The ore-forming fluid in hydrothermal period of the deposit is rich in many kinds of ore-forming elements including Fe,Ag,Zn,Pb,Cu,S,Se.With the alteration of physical and chemical conditions,the complexes of iron,zinc,copper and lead disintegrated and precipitated according to the difference of stability,due to the mixing of cold fluids.The dissociation of sulfur and hydrogen complexes of silver was relatively late,which made silver separate from lead and zinc,resulting in that silver ore is on the top of the lead-zinc ore.Under the condition of supergene oxidation,the leaching of silver and discrete silver in the original carrier minerals can be reenriched with ferrtization of pyrite.