Mineralogical And Fluid Inclusion Study On The Malipo Emerald Deposit In Yunnan Province,China

Malipo emerald deposit is located in LaoJunShan metamorphic core complex. It is the first emerald deposit that found in China. But now the emerald mineralogy research hasn’t been systematically conducted, as well as the genetic type for the deposit and the mechanism leading to emerald precipitation are not clear. At this point, it is important to carry out the systematic mineralogy research and fluid inclusion study on the deposit, as it will provide us better understanding of the origin of the emerald deposit and can be used for guiding the exploration of emerald deposit, as well as it is can be used to guide gem identification in Gemmology. Based on the field survey of Malipo emerald deposit, the data gathering, the electron probe research, the Raman spectrum study, infrared spectrum analysis and fluid inclusion research, the understandings and progresses are obtained as following:1. The electron probe results show that the emerald of Malipo mainly contain two groups of trace elements:alkali metal ions and mafic ions. Mafic oxides are given priority to with MgO, FeO, V2O3. The content of V2O3, which act as chromophore, is an order of magnitude higher than the other chromophore-Cr2O3, so we conclude the color of Malipo emerald is mainly caused by element V. Alkali metal ions are mainly Na2O, RD2O, Cs2O, and K2O content is very low, The total amount of alkali metal oxide is about0.40wt%. The trace element characteristics of Malipo emerald are similar to the emerald deposits (Regal Ridge deposit in Canadian and Delbegetey deposit in Kazakhstan)related to the granite intrusion, and it shows none common characteristics with the emerald deposits(Muzo desosit in Colombia) not related to the granite intrusion, reflecting the origin of emerald deposit in Malipo is related to the granite intrusion. And more, characteristics of trace elements can be used to determine the emerald origin.2. IR results show that the structure channel of emerald contain type Ⅰ water, type Ⅱ water and CO2simultaneously, and the absorption intensity of type Ⅱ water is greater than that of the type I water. The existence of the two types of water in emerald can be used to distinguish the natural emerald from the synthetic in Gemology.3.3600cm-1(due to type Ⅱ water vibration) and3610cm-1(due to OH vibration) of Raman shift can be used to distinguish natural emerald from synthetic. The characteristic Raman peaks of emeralds are325cm-1,399cm-1,1070cm-1,686cm-1. The isomorphism of Al do not lead to obvious Raman shift.4. The UV-VIS spectra of430nm and610nm centered wide and strong absorption band is caused by the V3+, and the830nm wide absorption band is caused by Fe2+.5. XRD analysis shows that the characteristic lines of light-colored emerald are8.0076(100),3.2573(112),2.8714(211), while that of dark-colored are8.0093(100),3.2595(112),2.8734(211). The isomorphism of Malipo emerald is octahedral dominated.6. Petrography, microthermometry and Raman research of fluid inclusions in Malipo emerald show that there are three types of fluid inclusions: liquid-rich two-phase aqueous inclusions (type Ⅰ a), gas-rich two-phase aqueous inclusions (type I b),CO2-bearing two-phase aqueous inclusions (type Ⅱ) and daughter-mineral-bearing three-phase fluid inclusions (type III).The mineralization was related to mesothermal-hypothermal fluids of the NaCl-H2O-CO2-CH4±N2system with low salinities. Ore-forming fluid characterized with low salinity (<10wt%NaCl) and high homogenization temperature, which is analogous to the emeralds from Lake Manyara(Tanzania), Lened (Canada) and Mananjary (Madagascar).Combined with the stable-isotope evidence, it is deemed that Malipo emerald deposit has the same origin as the mentioned deposits above, which are related to granite intrusion in origin. It is important for guiding the exploration of emerald deposit on the base of the ascertainment of the deposit origin. The phenomenon of Type Ⅰa and type II fluid inclusions in emerald coexisting in the same fluid inclusions association (FIA) is common, and type Ⅰ a inclusions are homogenized to the liquid phase, type Ⅱ inclusions to the gas phase, and the homogenization temperature of type Ⅱ inclusions agree with that of type Ⅰ a inclusions. The salinity of type Ⅱ inclusions is lower than that of type Ⅰ a inclusions. All these features conclude to that immiscible is responsible for the precipitation of Malipo emerald.