PHYSICO-CHEMICAL FEATURES OF FLUIDES, WHICH FORMED APOHYPERBASITE, AND APOCARBONATE JADES

Abstract

The relevance. The deposits of two formation types (apohyperbasire and apocarbonate) were discovered in the jade province of Siberia, the largest in Russia. Their bodies are usually formed on the contact of serpentinized rocks and dolomite marbles with the aluminisilicate rocks. It is necessary to identify the genetic differences in jade of various formational accessories that allows making a conclusion on the sources of the fluid phase and answering the actual question about the oxygen source in the minerals forming the jade. The main aim of the research is to justify the physiochemical conditions of jade formation with the help of a critical summary of the world’s material on the geochemistry and petrology of jade. Objects: Kavoktinskoe deposit of apocarbonate jade and Osipinskoe deposite of apohyperbasite jade. Methods. Chemical composition of the rocks was determined by photometric, atomic absorption, potentiometric and flame photometric methods. Trace element analysis was done by inductively coupled plasma mass spectrometry. The isotopic compositions of oxygen and carbon were analyzed by laser fluorination, and carbon and oxygen in carbonates – by the method of decomposition with orthophosphate acid. The isotopic composition of hydrogen in hydroxyl-containing minerals was determined by the method of Vennemann, O’Neil. Results. It was found that apogiperbasitic jades were formed under the influence of magmatic and metamorphic fluids released during the deserpentization of rocks; and in apocarbonate jade occurrences, the fluid is meteoric water saturated with carbon dioxide formed during decarbonization of dolomite. The order of formation of mineral paragenesis during the expansion of metasomatic zonation on the contact of rocks of various compositions was considered. It was shown that the uniformity of the mineralogical types of jade of a various genesis depends on composition of the hydrothermal solution, and P–T conditions of the process. Apocarbonate jade belongs to the low-temperature facies of magnesian skarns by the mineral paragenesis. As a result, the following metasomatic zoning is formed: dolomite marble – calcite marble with jade – tremolite skarn - pyroxene – amphibole – clinocyoisite skarn – amphibolites. The deposits of apohyperbasite jade have the different metasomatic zonality: microantigorite serpentinite – tremolithite – jade – tremolite – quartz-diopside-clinocyosite rhodingite – cyosite-amphibole rock. The temperature varies in the range of 300–450 °C, the pressure is 2000–3000 bar. These data allow us to create a model that properly describes the characteristics of the physicochemical processes of both apocarbonate and apogiperbasitic jade formation.

Keywords

• jade
• geochemistry
• isotopes
• physicochemical forming conditions
• eastern siberia