Mineralogical Research And H-O Isotopic Characteristics Of Lailishan Tin Deposit In Yunnan Province

Lailishan tin deposit is the well-known tin deposits in western Yunnan.In this paper,the author conducted a study of the features of cell parameters and infrared spectroscopy of quartz,cassiterite and pyrite with different ore-forming stages in Lailishan tin deposit of Yunnan Province,by using X-ray powder diffraction and infra-red spectroscopy,so as to discuss the causes of minerals and deposits and ore-forming liquid source,and provide practical significance for prospecting.The results show that the hydrothermal mineralization period of tin deposit can be divided into four stages,which is mica-pyrite-topaz-granular cassiterite phase(?),mica-quartz-pyrite-columnar cassiterite phase(?),quartz-pyrite-radial cassiterite phase(?)and fluorite-quartz-pyrite-sphaerolitic cassiterite phase(?).Stage ? is the main metallogenic stage.From stage? to ?,the values of a0,c0,V0 and the c0/a0 ratios of the cell parameters in quartz all have a decreasing tread,Axis ratio of the rate of change in quartz is from 0.77307 to 3.49688;the absorbance of each absorption peak of the infrared spectroscopy in quartz tends to increase.The authors speculated that quartz maily exists substitutional impurities in stage ? and ?,such as Al3+and Fe3 +,exists substitutional impurities and interstitial impurities,which is complicated,in stage ? and exists interstitial impurities in stage ?,such as Na+,K+.Moreover,the composition of hydrogen and oxygen isotopes in quartz shows ore-forming fluid is a mixture of magmatic and meteoric water,which implies initial ore-forming fluid derives from magma.With the evolution of hydrotherm,meteoric water mixes into hydrotherm along the tectonic fissures,which makes the isotopic composition of hydrogen and oxygen shifts to atmospheric water.The values of a0?c0 and V0 decrease firstly and then increase in cassiterite with the evolution of the ore-forming stage,and is smallest in the main metallogenic stage,which is consistent with the changes of the total amount of impurity elements in cassiterite with different ore-forming stage.It reflects that changes of cell parameters in cassiterite are mainly affected by mixed impurity elements in lattice rather than temperature.The characteristics infrared spectral of cassiterite at different ore-forming stages are similar and belong to the deformation spectrum.It reflects the characteristics of cassiterite-sulfide hydrothermal deposits.The absorption peak intensity of cassiterite in the main mineralization stage is the mximum.The lattice parameters and infrared spectroscopy of cassiterite have the prospecting significance.From stage? to ?,The shapes and positions of the absorption peaks of the infrared spectra of pyrite at different stages are similar,but the absorbance ratio A4/A2 of characteristic peak in pyrite gradually increases which shows that the infrared spectrum of pyrite is mainly affected by temperature.