Lake Vermont geophysical investigations

Abstract

Detailed gravity surveying and high resolution seismic profiling have been used in the Lake Vermont area in central Queensland in an attempt to establish structural control. There are two coal seams of interest, the Leichhardt seam, 2?3 m thick, varying in depth from subcrop to 80 m, and the Vermont seam, 5?7 m thick, varying from subcrop to 130 m deep. They are cut by a series of faults trending N-NW with throws up to 15 m, and a less frequent pattern of faulting oriented E-NE. A micro-gravity test survey along three lines in 1984 attempted to identify areas of faulting in these coal seams. A pattern of anomalies was correlated across the lines in the expected strike direction of the faults, but specific structures could not be modelled. Following another phase of drilling a short seismic reflection survey was shot over the same test area in late 1986. The shallower Leichhardt seam was not able to be resolved but the deeper Vermont seam was well defined. The seismic verified structures interpreted from drilling, altered the interpretation of some structures detected by drilling and found additional features missed by the detailed drilling programme.