Gas measurement is the most important method and technology for geochemical exploration of concealed ore. It mainly includes mercury vapor measurement, radon and its daughters measurement, geogas measurement, helium measurement, carbon dioxide measurement, sulfur dioxide measurement and hydrogen sulfide measurement. The research work is deeply carried out in the measurement of mercury vapor, radon and its daughters. At present, China has established a relatively mature method and technology system, which plays a certain role in the search for concealed mines. Geogas survey has been carried out in China for more than 3 years. At present, some progress has been made in the study of anomaly formation mechanism and method technology, showing a good development prospect. Because the detection limit of other measuring methods can't meet the needs of prospecting, the corresponding research work is basically at a standstill.
(1) Mercury vapor measurement
Mercury vapor measurement is a relatively mature gas measurement method at present. Its application fields are mainly hidden solid metal mineral exploration, oil and gas resources exploration, hidden and active fault exploration, earthquake prediction research, ecological environment quality investigation, endemic disease prevention and control investigation and other fields. The method and technology of mercury vapor measurement matured in 198s, and it is still in use at present. The progress in recent 1 years is mainly reflected in the development of gas mercury testing instruments and the research of mercury flux observation methods.
(2) measurement of radon and its daughters
radon is an inert gas, and radon has three isotopes: 222Rn, 22Rn and 219Rn, which are the daughters of decay systems of 238U, 231Th and 235U respectively. Radon in the usual sense refers to 222Rn. The main application fields of radon survey are resource exploration, fault structure activity investigation (earthquake early warning research) and ecological environment investigation. According to the difference of measurement principles, many radon measurement methods can be divided. The commonly used radon measurement methods include ionization chamber method, scintillation chamber method, double filter membrane method, balloon method, electrostatic collection method, solid track method, thermoluminescence method, activated carbon passive adsorption method and electret radon measurement method. According to the different measurement methods, it can be divided into instantaneous, continuous and cumulative measurement methods; According to the different measurement time and methods after sampling, it can be divided into three-point method, three-segment method, five-segment method and α -spectrum method. These methods have their own advantages and disadvantages. In practical application, it is necessary to choose the best method to carry out the survey according to the purpose of the survey and the natural conditions of the survey area. In recent ten years, little progress has been made in the development of radon detectors, and most of them still use various radon detectors that were finalized in the 198s. Most research work focuses on the factors that affect the accuracy and precision of radon measurement under different natural and geographical conditions and different measurement methods.
(3) Geogas Measurement
In the 198s, Dr. Kristiansson from the Department of Physics of the University of Rand, Sweden and Dr. Malmqvist from the Exploration Department of Polideng Mining Company put forward the concept of geogas and the hypothesis that geogas flows vertically transport underground material components, and based on the above understanding, passive geogas sampling technology was put forward and developed. Since then, exploration geochemists in many countries (German, Czech, Russian, China) have been working hard to develop fast active adsorption methods to eliminate the defects of lost detectors, improve work efficiency and meet the needs of large-scale regional surveys. Among them, the sampling device developed by Institute of Geophysics and Geophysical Exploration of Chinese Academy of Geological Sciences was awarded the utility model patent of China in 25 (patent number ZL24264226.X). In recent ten years, the focus of geo-gas research has shifted to the study of geo-gas migration mechanism and improvement of methods and technologies. The active geogas measurement technology developed in China mainly captures nano-metal substances free from soil pore gas, and uses 5% aqua regia and foam plastic as the collection media. Geogas method is greatly influenced by sampling season and sampling time; The operation of sampling and analysis is complex, which is not easy to be mastered by untrained personnel; Affected by many reasons, the reproducibility of anomalies is not ideal.