1. Institute of Geophysical& Geochemical Exploration, Chinese Academy of Geological Sciences, Langfang 065000,China; 2. Key Laboratory of Geochemical Cycling of Carbon and Mercury in the Earth’s Critical Zone, Langfang 065000,China;
The development of geochemical exploration technologies unaffected by marsh microorganisms is necessary for improving the prediction of wells and exploring natural gas hydrates in mid-latitude permafrost areas. The potential of thermal-release mercury as a new tool for the investigation of gas hydrates in permafrost areas was studied in this paper. The study area, covering 150 km 2, is located in the alpine-arctic swamp landscape of the Qilian Mountain. The sampling density and depth were 1 or 2 points/km 2 and 60 cm, respectively. In total, 300 soil samples were collected and the mercury vapor analyzer was used to measure soil thermal-release mercury. The results indicate that thermal-release mercury anomalies were identified in the gas hydrate deposits. There is maximum thermal-release mercury over the gas hydrate boundary and minimum thermal-release mercury with pinch-and-swell from over the gas hydrate reservoir. The maximum thermal-release mercury is 127.37×10 -9, with the average being 32.59×10 -9, and the threshold of anomaly is 39.24×10 -9. A comprehensive interpretation was conducted based on geological and geochemical survey results. The relationship between the hydrocarbon of gas hydrates anomalies and thermal-release mercury anomalies was further explored. The authors propose a geogas migration mechanism of soil thermal-release mercury in the soil above the natural gas hydrate deposit. The anomalies near the ground surface of the Muli coalfield in the Qilian Mountain were derived from the deep hydrate deposits and fault structures, which were not affected by marsh microorganisms, and they have important reference value for natural gas hydrate exploration in permafrost areas.
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