A Study Of The Meng Ya A Skarn Type Pb-zn Deposit In Tibet And Its Geological Significance

In the Meng Ya A lead-zinc deposit,the skarn is very developed,and the predecessor has confirmed that the deposit is a typical stratified skarn type lead-zinc deposit,but there are many deficiencies in the skarn research in the deposit.Including the skarn petrology characteristics,mineral characteristics,typical skarn garnet geophysical characteristics,the characteristics of the garnet ring and typical skarn mineral pyroxene,and other aspects of the study are still inadequate.In this paper,a series of work was carried out through sufficient field geological survey,collected samples,collected data,microscopic observation and identification of rock and rock and obtained the analysis data,which filled some vacancies in skarn research in this area,including skarns in Meng Ya A The basic geologic characteristics of the skarn,the petrology of skarn,the mineralogical features of skarn and the trace elements of rare earth,with a view to providing reference for the study of deposits in this area.And ultimately get the following important understanding and conclusions:The skarns in the study area have obvious zonation characteristics from the perspective of the scale,including horizontal and vertical.Horizontal direction of the rock from the inside to the outside is alteration quartz porphyry ? angle rock ? garnet skarn ? diopside-garnet skarn ? marble ? silicified limestone ? limestone distribution law,in the vertical Rock mass to a certain degree of stratification,a layer also showed a certain zoning.And its mineral assemblage is complete,undergoes a complete skarn period from the dry skarn to the final skarn of the wet skarn to the oxide stage,forming a typical skarn system.The basic characteristics of the garnet mineral in the study area show that the crystallinity of the garnet is high and the crystal development is good,which shows that the physical and chemical conditions of garnet formation are suitable for the formation of garnet.Garnet itself is difficult to dissolve minerals,in the case of little change in the environment can maintain its original characteristics of the original mineral.Part of the low degree of crystallization,the development of poor garnet shows that with the evolution of garnet,the environment has also been a corresponding change,it is deduced that garnet has experienced many stages of formation.The formation of garnet in the early,in addition to the basic conditions to meet,its ore-forming materials and adequate mineralization space;with the mineralization and space consumption,the formation of garnet tends to crystal small and incomplete,and observed under the microscope.Part of the mineral in the early mineral fissures in the formation of the phenomenon is consistent.The location of Andradite tends to the lower part of the rock.Grossular's content increases from deep to shallow location but the content of andradite is reduced.It is not hard to infer these two reasons.On the one hand,the mineralization of garnet consume the ore-forming materials which from the deep source hydrotherm.The temperature and pressure change,so the garnet's endmember change.The other hand,the influx of new hydrotherm make the concentration of ore-forming elements increase in early hydrothermal solution.Garnet crystallises continuously that shape into girdle structure.The number of girdles and the content's fluctuation of Fe may stand for the number of hydrothermal influx during the garnet's formation.Material consumption of lower part of garnet crystallize.Grossular's endmember increases in the core of early rising hydrotherm.With the new hydrothermal influx and consumption reduce from the lower garnet,andradite increases in the girdle around upper garnet,In this cycle,the content of Al and Grossular is high in the central part of the girdle and it's low in the edge part.It can explain the formation of Garnet girdle.From the characteristic of garnet girdle,we can infer that the formation of skarn is in a turbulent environment.The temperature and pressure of mineralization in a definite range but they are different.Hydrothermal material concentration is affected by the new hydrothermal influx and hydrothermal dissolution,data is fluctuant.The rare earth element characteristic of garnet show that the garnet in this area is magmatic and it support the content of andradite is affected by temperature and pressure in different burial depth.Y/Ho indicates garnet form in a dynamic environment.Mineralogical characteristics of augite and wollastonite indicates there is no contradiction with the above conclusion.