Wall Rock Alteration Characteristics Of JiangXi DaWutang Tungsten Polymetallic Deposit

DaWutang tungsten polymetallic deposit,affiliated to the nine ridge metallogenic belt,located in the southeast of the Yangtze plate edge and the middle of Jiangnan massif.It is same with Shimensi tungsten polymetallic deposit(North district).The tungsten polymetallic deposit gve priority to with veinlet disseminated type and altered granite rock type tungsten ore body in yanshanian granite bead at the top of the inside and outside contact belt.This deposit has many types of alteration,has closely related to alteration and mineralization.In this paper, through the system study of wall rock alterations of the ore deposit,have a preliminary understanding of the process of hydrothermal alteration and mineralization of the ore deposit mechanism.The main completed deposit of wall rock alteration mineralogy,petrology,ateration zoning characteristics,and comb set the alteration of the stage and the element migration characteristics in the process of the alteration,etc.Finally,combining with the existing research to investigate the influence of wall rock alteration for mineralization,then to guide the prospecting exploration.Based on the research in the study area, mainly made the following understanding :(1)Different types of ore body its corresponding alteration zoning characteristics are different.The large quartz vein type ore bodies and veinlet disseminated type ore body of alteration zoning are mainly greisenization zone.Surface type alteration mainly occurs in the rock mass in yanshan period and jinning period inside and outside contact belt of rock mass.Inner and outer contact zone of the alteration types are mainly black scales mica,potassium feldspathization, sericitization, greisenization, and chloritization. Because of the multiphase magmatism,alteration types are superimposed on each other,here let the most developed alteration types in the current rock mass as basis of dividing alteration zone.The alteration zoning is closely related to the lithology of the rock mass inside and outside the contact zone.(2)There are three stages of magmatic activity in the study area,form three phase of the rock mass 。 From morning to night are porphyritic granite and muscovite granite,granite porphyry, I summarize the alteration of rock mass in each period,it has four stages.:1, Alkaline high temperature hydrothermal alteration; 2, Alkaline medium low temperature hydrothermal alteration; 3, Acid high temperature hydrothermal alteration; 4,Medium low temperature hydrothermal alteration.The alteration of the four stages are respectively:1, Potassium feldspathization and black scales mica; 2, Sericitization; 3,Greisenization; 4, Chloritation etc.The main alteration types in different stages are different.(3)Through the study of the migration characteristics of the main elements of the rock before and after the alteration,I know:The content of Na2 O and K2 O increased with the increase of alkali feldspar in the rocks of the potash feldspar,CaO content also increased.The content of SiO2 in the black scale mica is decreased, and the content of Fe,CaO 、 K2 O and Na2 O is increased.The greisenization rocks generally showed the characteristics of SiO2 content reduced.In the rock of silk mica, the content of the mica is increased, which leads to the increase of the content of MgO and Na2 O in the main elements.In various types of alteration, the content of TiO2 is relatively stable.Particular attention is paid to the increasing trend of CaO content in the early stage of alkaline alteration.There are closely relationship between this phenomenon and tungsten mineralization.(4)Through the study of the trace element characteristics of the main elements of the rock before and after the alteration,I know:In the rockof greisenization and protolithionite,W, Cu, Zn and Mo were increased significantly.The amount of move W are the most obvious in greisenization rock,is a few times as many as other altered rocks.And Cu, Zn’s move is mainly changed now black scale mica in the rock.(5)Through the study of the rare earth element characteristics of the main elements of the rock before and after the alteration,I know:The similarity of REE curves of rocks before and after the alteration shows that both may have the same source area.The altered rocks show light rare earth enrichment,Eu negative anomaly.(6)The formation conditions of tungsten by chemical analysis showed that :Tungsten is due to the formation of Ca2+ and [WO4]2- in the hydrothermal combination then form CaWO4.The formation of the study area is the result of tungsten provides the required Ca2+.Geological characteristics, metallogenic location and source of ore-forming materials in Dawutang show that in the early stage of the alkaline alteration, Ca2+ enters into the hot liquid,in the process of alteration, the alkali is slowly depleted.Alteration of alkaline alteration change to the transition to acid alteration,at this point Ca2+ was precipitated out,combined with [WO4]2-,finally, the formation of tungsten.This process are close with greisenization.We can let the greisenization as an indicator of field geological prospecting.