Abstract

Trace element contents (Cu, Zn, Co, Ni, Ct V, Ge, B, As), vitrinite reflectance values and content of mineral matter (low temperature ash (LTA) samples characterised by XRD) have been determined in Eocene-Miocene coals from Lebu (bituminous, Concepcion-Arauco basin), Pupunahue (subbituminous, central-southern Chile) and Pecket (subbituminous, Magellan Region). Trace element concentrations do not differ between the deposits and potential recovery of those from the ash, which does not appear to be of economic interest. Boron and sulphur contents point to a moderate marine influence during deposition. Arsenic and sulphur concentrations in subbituminous coals do not exceed the standards set by the Chilean legislation Sulphur concentrations in bituminous coal are high (> 3%) and they should be blended with low sulphur coals. In the Pupunahue deposit, Pearson's correlation between ash content and Cu (r = 0.42), Zn (r = 0.84), Co (r = 0.87), Ni (r = 0.32), Cr (r = 0.84), V (r = 0.80) and As (r = 0.09) shows an inorganic affinity and an organic affinity between ash content and Ge (r = -0.32), B (r = -0.4) and S (r = -077). The same correlation and affinity are observed in the Pecket mine for Cu (r = 0.50), Zn (r = 0.91), Co (r = 0.58), Ni (r = 0.71), Cr (r = 0.13), V(r = 0.22) and As (r = 0.24); Ge(r = -0.22), B (r = -0.97) and S (r = -0.13) also show an organic affinity. In Victoria de Lebu, the tendency is the same but the data are too reduced for a formal correlation. Mineral matter changes qualitatively and quantitatively in response to the local sediment input during coal formation. Quartz and pyrite dominate at Lebu (Ro = 0.70%), a basin isolated from volcanic emerged ranges to the east (Proto Andes Mountains). Pupunahue (Ro = 0.45%) received more pelitic (illite/muscovite) and volcanoclastic sediment, the latter altering to kaolinite. Coals from the Magellan region (Ro = 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 1 T polytype at Pupunahue to I Md polytype at Pecket. (C) 2000 Elsevier Science B.V. All rights reserved.