Final report on exploration for EL 1633 Hatches Creek

Abstract

RC 9 area photographs taken in 1963 were used and were much better than the earlier (1949) series, of photographs. General examination of the margin of the elliptical-shaped dome failed to show any area where a contact, unconformable or otherwise, was revealed, because the last few metres of ground below the rim of definite Hatches Creek Group sediments were invariably concealed by scree. However, examination of creek sections, particularly in the west, east and south, showed numerous steeply-dipping bands, 5-30 mm thickness, of thin-bedded silicified quartz sandstone, similar to that in much of the Hatches Creek Group and with strikes changing in conformity with those of the Hatches Creek Group surrounding the dome. Interbedded with the quartz sandstone bands are weathered fine-grained igneous rocks apparently similar to those in a valley in the eastern part of EL 1633 and also in numerous other valleys between sandstone ridges in the Davenport Range; the inclusion of these 'valley rocks' in the Hatches Creek Group has not been disputed, and they have been mapped as acid and intermediate type extrusive rocks of that Group. The sandstone bands within the dome cannot be mapped without a detailed survey and/or use of enlarged air photographs, but the prevalence of the bands is indicated in RC 9 photographs- where major faults cut the bands the quartz breccia shows as white patches on the air photographs. Floaters of greisen were found in Nia Nia Creek, at localities near the stream's exit from the dome. Granite previously mapped in the north-east of the dome is on a different stream system and although no outcrops of granite or greisen were found along Mia Mia Creek, or its tributaries, their presence is clearly indicated. Radioactivity was tested both from the air and on the ground, by means of a GRS l0lA Scintillometer, but no anomalous zones were detected. After comparing results on the ground with those obtained on the same instrument carried on a helicopter, several flight lines were surveyed (Figure 2), from a height of 40 feet above the terrain and a speed of 45 knots. The detecting instrument responded well to changes in rock types. The extrusive rocks gave uniform total counts about 40 per cent higher than uniform counts obtained on quartz sandstone ridges and bands, but no anomalous readings were recorded. The same order of separation and magnitude was found by ground prospecting both within and outside the domed area. Conslusions; (a) There is a need to revise part of the published Frew River 1:250,000 Geological Sheet.

(b) No significant radioactivity was recorded.