FEATURES OF THE COAL SERIES DEPOSITED IN ERUPTING INTERVALS AND THEIR PROSPECTING PROPOSALS

Liaoning Province is located in the circum-Pacific volcanic belt where diastro-phic and volcanic activities occured repeatedly during Mesozoic and Tertiary, forming several hundreds of volcanic cones and mounds which occupy an area about 7,000km². The total thickness of the volcanic rocks is 3,000 metres. They are classified into the lower Yanshan volcanic rock, upper Yanshan volcanic rock and Himalayan basalt according to the interrelation between their cyclothems of magmatic differentiation and the sediments of erupting intervals. There are usually sedimentary coal series of intervals interbedded in the volcanic rocks developed ia different geological times. The typical occurrence can be seen in some coal fields in Shuangtagou of Nanpiao, Shahezi of Changtu, Wenduhua of Tianshan and Fushun. All of these coalfields, surrounding rocks of central eruption, developed in the marginal belts of volcanos. It shows that the coal accumulation is controlled by the volcanic-structural mechanism. Thus, in origin, these coal series are sharply different from those usually seen in shallow-sea, offshore or inland environments. The coal accumulation in erupting intervals is affected by volcanic mechanism and sedimentation. It formed rapidly and was of the characters of volcanic and sedimentary rocks. Since such coals were generated merely during erupting intervals and their development space was restricted in the marginal belts of central eruption, the coal prospecting should be concentrated on the regions where volcanics developed well, i.e. on Yanshan Depression and Xinganling Foldbelt, which include the upper volcanic rock in the marginal belts of volcanos (Rock Units, No. 16-50, and 35 volcanic cones) about 16,000km², the lower volcanic rock with an area about 2,000km² and the Tertiary basaltic platform about 8,000km². It is necessary to research into the distribution, reserve and buried depth of the coals formed in erupting intervals, especially in Liaoning Province where more coal resources are needed keenly. Effectively mining and utilizing of such coal resources are considered of important economic significance.