Geological Report AP 1739 Central Mount Wedge and South Siddeley Range 1967

Abstract

The survey of AP 1739 was carried out between May 30th and June 8th 1967. It formed part of an exploratory visit to the Mt Doreen locality and the western end of the Stuart's Bluff range area. geological reconnaissance mapping completed during the present survey. Both the Stuart's Bluff and Siddeley Ranges are dominantly sandstones and quartzites. These form the lower member of a large basinal or synclinal structure on the northern side. These sediments are continuous with those of the eastern Stuart's Bluff ranges. The conditions which allowed the exposure of the quartz-haematite bodies in AP 1738 are repeated in AP 1739, and a small strip of basement complex foots the sandstone scarp before being covered by superficial dsposits at lower 1evels. The quartzites and sandstones are extremely resistant to erosion and thus are a major factor in the geomorpho1ogical development of the area. The sandstons dip to the north and north-east at angles up to 3 degrees. The southerly turn of the strike, in the western Stuart's Bluff Range seems to be due to a flexure in the arm of the syncline The sandstones, quartzites and the older basement rocks show strong west to north-west cleavage. In four localities in the basement rocks and at one place in the sandstones the rocks are remarkedly brecciated and capped by gossan. This seams to indicate that pyritic bodies occur in the hypogene zone at depth. The gossanous exposure in the Stuart's Bluff area has a patchy distribution covering 30 to 40 acres. It is situated close to the foot of the sandstone capping and has poor relief. In the southeast Siddeley Range the gossan is about this size whilst those to the north west cover only 10 acres. All the gossan outcrops have poor topographic expression and limited exposure. Both ranges are flanked on northern and southern sides by alluvial soil derived from themselves. These superficial deposits merge into aeolian types often with dune character.