AN APPROACH ON THE GENESIS AND THE ENVIRONMENT OF THE SILICEOUS COAL BALL IN THE COAL SEAM OF FENGJIANGXI COAL FIELD

There is a great deal of siliceous coal balls containing fossil such as Pteridophy-ta in the coal seam of the Upper Permian Lungtan upper series in Fengjiangxi Coal Field of Shaoyang,Hunan Province. There coal balls with the shape of lens or ellipsoid occur in the upper part of the fourth coal seam. In the section there are several layers, and in the plane they are distributed continuously or discontinuous-ly and distinguished clearly from the wall rocks. Authigenic quartz and calcedony are the main coal balls-making substances, and carbonaceous fragmental phytolite conies second. SiO₂ content of the coal balls is 85.35%, with 11.4% of burning loss. And the coal balls also contain trace elements, such as Zr, B, Ni, Co, Cu etc.. This coal ball was formed in the diagenetic process. It was related to the pouring of SiO₂-rich old river water into the peat bog during the end of the fourth coal seam deposition. In the early period of the diagenetic process, pH of the peat bog decreased, the colloidal solution of SiO₂in association with humus hemigel formed better homogeneous embryonic concretion of colloform.After a series of diagenetic changes, the coal balls were formed. The evolution of its formation has three stages: 1. Gel stage in the early period of the diagenetic process. 2. Coal ball-making stage in the middle period of the diagenetic process. 3. Stage of coal ball change in its form, nature and quality in the late period of the diagenetic process. This kind of coal ball was formed in the platform stage,and underwent the formation of all the structures in Diwa (geodepression). The siliceous coal ball is a fine symbol of the coal seam correlation and an im -portant basis for discussing the environment of the incoalation.lt assumes both practical and theoretical significance in the geological exploration of coal field and the development of coal mine.