Annual report EL 4870 Fish River, Tolmer project 1987

Abstract

An INPUT survey over the Tolmer area, commissioned to Geoterrex in April, 1987 it was carried out during the first two weeks of July. Approximately 69 flight lines for 968 line-kms were flown, followed by infill lines for about 80 km. After each flight, the tracking camera films were developed and the analog charts were sorted and annotated. As the charts are on thermal paper, which tends to fade with time, it is recommended to take a more permanent photocopy as soon as the recordings become available. After locating the charts in relation to the navigation photo strips anomalies were selected and marked on flight-line overlays at 1:25,000 scale. The data quality has been excellent throughout the survey; efficient work from the ground crew allowed the revision of the complete survey and the selection of infill areas one day after the end of the last flight. During the survey, the manager of Tipperary Station was kept informed of the whereabouts and purpose of the aircraft. The preliminary results are based on the field evaluation of the anomalies. The plots on the 1:25,000 maps are approximate only; more accurate are the anomaly locations on the colour photographs set. Three models were followed during the field interpretation: two indicating horizontal surface conductors (thin sheet and half-space) and one indicating a sub-vertical conductor. Only the 'vertical' anomalies were plotted on colour photographs. Spatially close anomalies were grouped in 'areas', generally reflecting a particular geological environment. A total of 61 areas was thus defined. Unfortunately, none of them indicates the expected occurrences of graphitic schist beneath the sandstone cover. A test flight was carried out over a known graphitic conductor in the Rum Jungle area, in order to compare the amplitude and persistency of the anomalies. The areas fall broadly into four categories: 1) Conductors in exposed Burrell Creek Formation ('basement'). 2) Conductors along faults. 3) Conductors in Tolmer Group. 4) Conductors in Cambrian Volcanics and/or Cretaceous. The anomalies that occur in Cretaceous are generally located near the edge of a cliff; they could indicate the presence of a thin layer of Antrim Plateau Volcanics in the pediment between Cretaceous and Proterozoic Sandstones. Some anomalies appear to line up or coincide with rivers and billabongs. Several Input conductor anomalies have been defined which are considered to warrant ground follow-up. No ground radiometrics are planned due to the absence of the unconformity within the license; no Burrell Creek sediments outcrop within the tenement.