STUDIUL INTEGRAT ROCK-MAGNETIC, TERMO-MINERALOGIC ŞI GEOCHIMIC AL UNOR PORŢELANITE DIN ZONA LUPOAIA (BAZINUL DACIC)

摘要

New examples showing the magnetic properties recorded on various porcelanite rocks, reflecting mineralogical and geochemical changes suffered by the clays within the "coal bearing formations", are presented. The studied rocks are originated in the sequences with Pliocene lignite-clay cyclic alternations from the Lupoaia quarry, located in the western Dacic Basin. As result of the natural spontaneous burning of the coal seam Ⅹ-Ⅺ, in some places, porcelanite-like clays, porcelanites and clinkers have been formed at the expense of the original clays. The heat-affected rocks have shown modified or even newly-formed mineral assemblages. Particularly, the detected thermo-mineralogical characteristics make possible to place the investigated baked clays on a temperature scale with 6 steps, with estimated limits 250... 1200℃. The dependence of the chemical composition of the sediments on their mineralogical evolution is well" expressed by the obtained data. Both the mineralogical and geochemical evolution are clearly reflected by the magnetic properties of the investigated argillaceous rocks. The enhancement of the total natural remanent magnetisation (NRM) intensity (In) and of the initial magnetic susceptibility (k_(in)). measured for the baked clays, is revealed. Some remarks related to the magnetic fabric and to the direction of the total NRM are also presented, by comparing the data obtained on heat-affected rocks and on "fresh" original clays. All these thermo-mineralogical, geochemical and rock magnetic characteristics are integrated by the magnetic anomalies produced by porcelanites. Several profiles have been recorded with a Geometries portable proton magnetometer, and the main results are shortly presented.