| 试论“江南古陆”两侧二叠纪煤变质作用与海泡石成矿作用的关系 |
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| DISCUSSION ON THE RELATIONSHIP BETWEEN PERMIAN COAL METAMORPHISM AND SEPIOLITE MINERALIZATION BESIDE THE "JIANGNAN OLDLAND" |
| There are two coal series: Liangshan coal measure (early Permian) and Longtan coal measure (late Permian) underlying and/or overlying the sepi-clite-bearing strata (early Permian) respectively, and accumulating beside the "Jiangnan Oldland".The study of metamorphism of coal measures is available in assessing the sepiolite resource.The degree of coalification in this area may rover the coal rank from bituminous coal to anthracite (Ⅰ to Ⅳ stages), except brown coal (0 stage), whereas the series of the sepiolite phase-transformation is sepiolite-steven-site-talc. These two series are closely concordant each other in the regional distribution, the lower degree zones of coalification (lignite to fat coal) are related to sepiolite, higher ones (maggie to anthracite) to talc, and medium ones (coking coal to lean coal) to stevensite, talc and illite districts.Coal seams occurring in sepiolite districts have their own special mace-ral groups. The exinite as an important prospecting criterion is present in sepiolite areas and has concordant relationship with the degree of sepiolite phase-transformation during coalification progress. Thus, the sepiolite may occur Mg-clay layers wherever the maceral groups in underlying or overlying coal seams contain much more exinite.Similar to coalification, the main control factors for sepiolite phase-transformation are temperature, pressure and time, of which, temperature is an essential factor. In this paper, palao temperature for forming sepiolite is determined by the coal metamorphic "law". The preservation of sepiolite in strata depends on the geothermal condition of palaobasin during burial history. According to the author's calculation, the palaotemperature for forming lower degree of coalification, especially for fat coal (Ⅲ stage) may serve as the critical temperature (130℃)for forming sepiolite, above the temperature sepiolite would disappear. The important and accurate mean to be used to analyse the paleotempe-rature is the vitrinite reflectance measurement. So there is a probability of sepiolite prospcting districts wherever the vitrinite reflectance R° is less than 1.00%. According to Kaweil diagram (1975), that value (R°<1.00%) just responds to the paleotemperature of<120℃.At the end of this paper, the Permian palao-temperature map is reconstructed by coal metamorphic data. It shows that all of the occurence of sepiolite are distributed definitely within temperature rang of 120℃. Therefore, it is reasonable to consider that the temperature for preservation of sepiolite in strata must not higher than 120℃. |
| CHEN Shan-qing,YANG Zhen-qiang,LIN Jin-ming.1991.DISCUSSION ON THE RELATIONSHIP BETWEEN PERMIAN COAL METAMORPHISM AND SEPIOLITE MINERALIZATION BESIDE THE "JIANGNAN OLDLAND"[J].Acta Geoscientica Sinica,12(3):31-46. |
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