Abstract:

It is a common phenomenon that gas hydrate occurs with carbonate in Sanlutian of Muli of Qilian Mountains. In order to discuss the formation environment of carbonate, the X ray diffraction analysis, the main-trace element and the carbon and oxygen isotope test of the carbonates were carried out. X ray diffraction results show that the carbonate minerals in the samples are mainly composed of calcite, dolomite and a small amount of siderite. Trace elements and rare earth elements show that the carbonate minerals are formed in the dry and oxidizing environment. δ¹³C_VPDB is -2.3‰ to 3.77‰，and the average value is 2.43‰；δ18OVPDB is -17.90‰ to -10.69‰，and the variation is small. Carbon and oxygen isotopes show that the carbon in carbonate may be influenced by the combined effects of gas hydrate dissociation, dolomite precipitation and lake water pollution, and the possible sources of oxygen may be influenced by the atmospheric rainfall.

Key words: Sanlutian of Muli of Qilian Mountains, gas hydrate, carbonate, mineralogical and geochemicalcharacteristics