The Study On Mineralogical Characteristics And Geological Genesis Of Tuequoise In The Blue-green Series From Ma'anshan,Anhui Province

Take the blue-green series turquoise in Ma'anshan city of Anhui Province as the research object,using the gemstone microscope,polarizing microscope,electron probe(EPMA),scanning electron microscope(SEM),fourier transform infrared spectrometer(FTIR),raman spectrometer,differential thermal analysis(DTA),whole-rock analysis technique to study the turquoise systematic.The turquoise in Ma'anshan area has two forms:veined turquoise and apatite-preudomorphic turquoise.The mineral assemblage of the veined turquoise can be divided into 3 categories:Turquoise-pyrite–quartz,Turquoise-albite-iron minerals,Turquoise-clay mineral–porphyrite.The apatite-preudomorphic turquoise can exist independently or exist around the veined turquoise,its source of mineralization is consistent with the surrounding veined turquoise.The formation environment of turquoise will affect the structure of turquoise.Observation under polarizing microscope,veined blue turquoise has radial spherulite,apatite-preudomorphic turquoise has spherulite structure?wormy texture or no obvious spherulite structure,as veined green turquoise,it has no obvious spherulite structure.SEM images show that the microcrystals of turquoise are mainly flaky and scaly,with irregular distribution.The density is related to the porosity of turquoise,the denser the turquoise is,the less porosity.Turquoise in this area contains Fe of different contents,it is dominated by Fe³⁺and contains a small amount of Fe²⁺.Cu²⁺determines that the basic color of turquoise is sky blue,and Fe³⁺plays an important role in turquoise color changing from blue to green.The results of differential thermal analysis showed that in the heating process,there were three stages of loss of adsorbed water,crystalline water and structure water during the heating process.During the heating process,because of the loss of water,the samples of turquoise were gradually changed from green or blue to dark brown.The results of IR and raman spectra show that the vibration and frequency of H₂O,OH^-and PO₄^3-groups form the infrared spectra and raman spectra of turquoise.The crystallization of turquoise can affect the characteristics of infrared and raman spectral bands.The better the crystalline degree of turquoise,the more obvious the spectral characteristics,the worse the degree of crystallization,the lack of spectral characteristics or even the loss of the spectral band.The whole rock analysis shows that the content of rare earth elements in apatite-preudomorphic turquoiseis higher than that of the rare-earth elements of the veined turquoise.The rare-earth elements of the turquoise are relatively rich in this area,and the heavy rare earth elements are relatively loss,negative abnormality in Eu.Turquoise is formed by leaching and hydrothermal action.Under the action of low temperature hydrothermal solution and leaching,the ore-forming fluid was formed,which deposited in the crevice of rock and finally formed veined turquoise.When the ore-forming fluid fills the cavity formed after dissolution of apatite or metasomatic apatite will forms apatite-preudomorphic turquoise,then recrystallization at last.