Typical Jadeite-bearing Rocks-minerals-geochemical Characteristics And Gemological Significance

In recent years, jadeitite have been found at more than ten places in the world. As changing geological environment and deepening study, more jadeitite origins will be discovered around the world in the future. Academia considers that jadeite-bearing rocks that contained more than60%jadeitite minerals are being called jade (FeiCui), It is located in the Sagaing strike-slip fault zone, near plate sutures, formed under effects of low temperature, high pressure and metamorphism, which revealed that the geological significance of the ancient plates tectonic characteristics, the indicating significance of further searching the rare and precious jade, the academic and the commercial value of researching the jadeite minerals. Therefore, jadeites always attract the attentions by geological scholars and gemologists.So far, in China, the jade deposit has not been found yet, but the jadeitite-bearing rocks appeared in many places. This article took the typical jadeitite-bearing rocks from Dabie mountains, Myanmar and Guatemala as samples to view specimens and observe rock slices under the microscope, through whole rock analysis, electron microprobe analysis (EMPA), X-ray powder diffraction analysis, infrared spectrum (X-Ray) analysis, laser LA-ICP-MS and other modern testing means, precisely measure and systematacially analyze the characteristics of geology, mineralogy, petrology and geochemistry for domestic and foreign typical jadeitite-bearing rock deposits. After comparative researching, the article, for the first time, discussed emphatically the geological significance and the gemological significance of jadeitite-bearing rocks in China.The petrology characteristic shows that the samples from Dabie mountains exist prevalently coronal structure. It consists of two parts, the kernel and reaction margin. The kernel is the jadeite’s malcrystalline existed inside the coronal structure. Reaction margin can be subdivided into the inner zone and outer zone. The fine-grain of albite and smaragdite is closed to the inner zone. The albite’s end-members reduced from the inner zone to the outer zone. The outer zone near the quartz side is the metamorphosed reaction margin of naferon amphibole. The coronal structure indicates that fluid takes part in the process of metamorphisms. The researching on mineralogy characteristics shows that the major mineral components for the rocks from Dabie mountains are jadeite, quartz, garnet, plagioclase, rutile, etc. Quartz and rutile occur in the the jadeite and garnet as inclusion forms. The rocks in Dabie mountains are different from those in Burma and Guatemala, contain lower Na, Al, and higher Fe, belong to the high-Fe specie. The molecular weight of jadeite end-member is73.4680.83, mainly project on the jadeite area in the pyroxene triangular diagram, a small amount project on the boundary of omphacite area near the jadeite area. On the whole, the jadeitite-bearing rocks from Dabie mountains are closed to pure jadeites. The chemical composition of metamorphosed pomegranate is almandine mainly, which consists of Spe0.20-1.20, Pyr17.54～27.31, Gro7.60～8.54, and Alm61.14～72.51(mol%). The amphiboles mostly are the naferon amphibole among the alkaline amphibole, the others are the crossite and waldheimite among the calcium sodium amphibole. The albite’s end members are Ab86.01-100%and An0-13.73%.The geochemical features testify the characteristics of rare-earth trace elements. The jadeitite from Dabie mountains, Guatemala and Myanmar is under the influence of the protolith’s chemical composition. The protolith is different, so is REE. By constrast, the total REE of Dabie mountains’ is highest than any other else, its distribution curve presents the mode of LREE’s concentration (high left) and HREE’s loss (low right). LREE/HREE>1. but the enrichment degree of LREE is different. δEu in each origin is slightly different. In the jadeitite-bearing rocks and jadeite mineral from Dabie mountains,δEu>1.By using the clinopyxene-johnstonotite geologic thermometer to calculate the temperature and the pressure for the Dabie mountains’jadeitite-bearing rock, you can see the temperature is855-1119℃, the pressure is2.8GPa or higher. According to temperature-pressure formula’s estimating, the formation temperature of jadeite minerals in the Dabie mountains jadeitite-bearing rocks is about1800℃, pressure is more than6G Pa. The formation temperature and pressure of amphibole-plagioclase is separately400-500℃and over0.2GPa.Finally, under contrastive analyzing and researching on the domestic and foreign typical jadeitite-bearing rocks in the side of petrology, mineralogy and geochemistry characteristics, combined with the metallogenic geological conditions in our country, the article discussed why jades can not be formed in jadeitite-bearing rocks in China, and analyzed the gemological significance of jadeitite-bearing rock resources in China.