Geochemistry and Mineral Matter in Eocene to Miocene Chilean Coals

摘要

In Chile coals are of Triassic, Eocene and Oligo-Miocene age. The sedimentary evolution of the coal basins is linked to the changing velocity of subduction of the Nazca under the South American plate, giving rise to high peat accumulation, which has transformed into coal seams of 1.0 in to 6.0 m thickness. For this presentation, Eocene-Miocene coals from Lebu, Pupunahue (central southern Chile), Pecket and Rio Turbio (Magellan Region) have been analyzed for trace elements (Cu, Zn, Co, Ni, Cr, V, Ge, B, As), vitrinite reflectances and content of mineral matter (LTA characterized by XRD and FT-IR). Trace elements reveal no marked differences between the deposits and do not reach levels of economic interest. B and S contents point to a moderate marine influence during deposition. Mineral matter changes in response to the local sediment input during and posterior to coal formation. Quartz and pyrite dominate at Lebu (R_0 0.70%), a basin isolated from sedimentary supply of the rising Andes. Pupunahue (R_0 0.50%) received more pelitic (illite/muscovite) and volcanoclastic sediment, the latter altering to kaolinite. Coals from the Magellan region (R_0 0.35-0.40%) contain kaolinite group minerals and smectite, similar to the accompanying "Tonstein" horizons. LTA residues show differences in the crystallinity of the kaolinite mineral, changing from a dominantly 1T polytype at Pupunahue to 1Md polytype at Pecket and 7 A halloysite at Rio Turbio. This study makes available for the first time LTA data for the prediction of the combustion and gasification characteristics of Chilean coals. As and S do not reach contaminant concentrations according to present Chilean legislation.