Characteristics And Mineralization Of The Madi Alkali Feldspar Granite In Eastern Hebei Province

The author participated in the projects of “Hebei Xinglong county rubidium and other rare metal ore precheck”and “Study on rubidium mineralization system in Husshi,Xinglong county,Hebei province”which were carried out by his work unit-the eighth Geological Brigade of Hebei Province Geology and Mineral Bureau,in 2016.This thesis is based on the above projects.Based on sufficient collection of previous research results and according to a large number of field geological investigation and indoor data research and summary,the author study the regional geological background,collect rock samples for structural mineralogy of microstructure,and carry out electron probe,rock chemistry,microelement chemistry,rare earth element chemistry and zircon U-Pb chronology analysis on the basis of microscopic petrology.It identified the main rubidium minerals and content,and rock/ore structure characteristics,also accurately determined of rock types and the age of diagenesis and mineralization,which in order to provide theoretical foundation and construction guidance for the exploration of the super-large rare metal deposit.Regarding the Madi rare metals mineralizing granite as the research object,from the external characteristics to the internal mechanism of action,The auther tries to interpret the following six scientific problems:(1)Geological characteristics and accurate nomenclature of the Madi rare metals mineralizing granite;Through a large number of field geological investigation,it is considered that the Madi rock mass is a complex body which was made up of at least two intrusions.The rock type belongs to alkali-feldspar granite,and the main mineral composition is quartz,albite,potassium feldspar,and a small amount of lepidolite.The rock mass is also the ore body,including the main mineralization types of rubidium,niobium and tantalum,lithium and pyrite mineralization.Generally,the mineralization phenomena was obvious on the top and edge of the rock mass.(2)Distribution of rare metallic elements in rock-forming minerals;Through electron probe analysis,rubidium was mainly enriched in potassium feldspar and mica.The content of rubidium in potassium feldspar and mica increased progressively from early to late,and the petrochemical compositions presented a trend of enriching in fluorine,rareand alkali elements.(3)Geochemical characteristics of rare metal granite;Through the analysis of main,trace and rare earth elements,the chemical composition of rock is characterized by high silicon,enriching in alkali(rich in sodium),poor in calcium and magnesium,belong to peraluminous calc-alkaline series.Large ionic lithophile elements such as Rb,Th,U,and high field-strength elements Nb,Ta,Zr,Y,and Yb elements are significantly enriched,while Ti,Ba and Sr are relatively depleted and the normalized trace elements diagram with strong negative europium anomaly and "tetralogical effect".(4)Diagenetic age of rare metal granite;U-Pb isotopic chronology suggests that the formation of Madi rock mass was around 160 Ma.Accorded with the large-scale early magmatism of yanshan in the western section of malanyu,the formation of Madi rare metal granite is an important part of yanshanian diagenesis and mineralization events in the complex anticline area of malanyu in Eastern Hebei.(5)Experimental demonstration of rubidium distribution;By the electron probe analysis,the major contained rubidium minerals and their percentage contents were determined,then selected semi-quantitatively the major contained rubidium minerals,and counted the weight percentage of the major contained rubidium minerals in the whole rock.The results showed that rubidium mainly existed in potash feldspar and lepidolite,while the content of rubidium was very low in other minerals,and the overall distribution rate of rubidium in potassium feldspar was higher than that in lepidolite.(6)Discussion of diagenetic-metallogenetic mechanism and deposit model;Regarding the mechanism of diagenesis and mineralization as the strong interaction of melt and fluid.(which is the permeable magmatic fluid mineralization),Rubidium and other rare metals mineralization is the result of multiple favorable factors coupling,namely,the "Small magma(rich in volatile,rare element and alkali)-metamorphic crystalline basement(which provided channel)-sedimentary cover of overlying Changzhougou group(which is the barrier layer)" ternary structure,is the key factor of mineralization.