The potential application of the decrepitation method of fluid inclusions to the exploration of deep-seated gold deposits in the Jiaojia gold belt, Shandong Province

Abstract：The decrepitation method of fluid inclusions was used in former Soviet Union and China in the 1970’s and 1980’s to help mineral exploration. This method can be used in combination with other measurements in mineral exploration. Previous studies of the decrepitation method have shown that the decrepitation intensity (frequency) near the ore body is high and will decrease gradually with the increasing distance from the ore body, which is believed to be caused by strong hydrothermal activity and relatively high abundance of fluid inclusions around the ore body. Hence, positive anomalies are likely to occur in/around the ore body. Samples were collected from 8 drill holes along No. 112 and 144 exploratory lines in the Jiaojia gold deposit in northwestern Shandong Peninsula, and quartz separates from the samples were analyzed by DT-4 acoustic decrepitometer developed by Prof. Xie Yihan of the Institute of Geology and Geophysics, Chinese Academy of Sciences in Beijing. The results show that the unaltered granites in the Jiaojia gold deposit exhibit high decrepitation frequencies and their decrepigrams (decrepitation curves) have a pronounced peak with normal distribution in the temperature interval of ca.360~450℃ and a sharp peak at 573℃ which is the phase transition temperature of α/β-quartz. With the increase in alteration intensity, the decrepitation frequencies decrease from the K-feldspathization zone through the pyrite-phyllic alteration zone to the gold ore. The decrepigrams of gold ores in the mineralization center become weak-waved curves or nearly horizontal lines with very low decrepitation frequencies, and negative steam aureoles occur around the gold ore body. Hence the unique decrepigrams and negative steam anomalies can be applied to gold exploration in northwestern Shandong peninsula.