Geochemistry And Fluid Inclusion Characteristics Of Pink Tourmaline From Ailao Mountain,Yunnan

In this paper,the pink tourmaline from Ailao Mountain in Yunnan Province is taken as the research object.The basic gemological characteristics,chemical composition,spectral characteristics and fluid inclusions of tourmaline from Ailao Mountain were further studied by means of conventional gemological tests,electron probe,laser denudation inductively coupled plasma mass spectrometry(LA-ICP-MS),UV-Vis spectroscopy,Raman spectroscopy,and microscopic hot and cold table.The geochemistry and inclusion characteristics were investigated.The pink tourmaline of Ailao Mountain is produced in granite pegmatite,with low color saturation and uneven distribution.It has a glassy luster.Some crystal specimens can be seen in hexagonal column and trigonal single-cone clusters,co-existing with albite.The refractive index and birefringence are 1.618?1.642 and 0.018?0.023 respectively,and the relative density is2.98?3.02.The dichroism is weak-medium light pink/pink,and the inclusions are rich in shapes and types.The fluid inclusions are filled in the healing fissures in the form of fences,needles,and flats.There are also separate fluid inclusions,needle-shaped There are few inclusions,solid inclusions include quartz,lepidolite,radial inclusions,iron infiltrate and so on.Most tourmalines have weak pink fluorescence,a few samples have chalky fluorescence,and the surrounding rocks have weak white-strong white fluorescence.The main chemical components of Ailao Mountain pink tourmaline are Si O₂(38.37?39.02wt.%),Al₂O₃(41.45?42.54wt.%),Na₂O(1.75?2.03wt.%),Mn O(0.09?0.72wt.%),rich in Li,Al,and poor in Fe,Mg,has experienced the evolution of schorl?lithium iron tourmaline?elbaite,there are several kinds of elbaite-rossmanite,schorl-elbaite,elbaite-liddicoatite,etc.The isomorphic series,the tourmaline in this area was formed in the late stage of crystallization of granite pegmatite veins.Ailaoshan tourmaline contains high levels of trace elements such as S,Ga,Sn,As,and Sb.Compared with pink lithium tourmaline from other places,the Ga content of tourmaline in this area is higher.There are also Ga and Sr.Certain negative correlation(r²=0.5),Sn and Ta are positively correlated.Ultraviolet-visible light spectrum shows that 520nm is the most important absorption band of pink tourmaline in this area.As its intensity increases,the pink body color of tourmaline gradually deepens.Compared with the pink tourmaline,the purple tourmaline adds a 680nm absorption band,which together with the 520nm absorption band leads to the purple-red color of tourmaline.It is speculated that the chromogenic ion of the pink tourmaline in Ailao Mountain is Mn³⁺.Raman spectroscopy shows that there are[Si₆O₁₈]^12-group vibrations,[BO₃]^3-group vibrations in tourmaline crystals,in addition to hydroxyl vibrations(3500cm^-1,3600cm^-1,3666cm^-1)The fluid inclusions belong to the Na Cl-H₂O system,and there are CO₂ absorption peaks(1358?1390cm^-1)and organic absorption peaks(CH₂/CH₃,C₄H₆and C₂H₆)in the gas phase.