Geology

		Charles Darwin Reserve lies in a typical, but uncleared, wheatbelt valley. Although virtually flat, with relief usually measured in a few metres, Charles Darwin Reserve is very diverse. It is comprised of 15 major land system types. Most of the property sits on ancient Yilgarn granite. The Yilgarn Craton (continental block) is over four billion years old and represents one of the oldest pieces of continental crust on the planet. This extremely old landscape is highly weathered and has eroded to a flat plain with few topographical features. The region is one of vast sand plains, low ridges of laterite or granite bedrock, breakaways and extensive natural salt lake systems. A small gold mine, located in the north-east corner of the property is still operating, but does not impact on Charles Darwin Reserve's conservation values. The geological history of the Yilgarn Craton has been reviewed by
Phil Commander et al. (The Geology, Physiography and Soils of Wheatbelt Valleys. Phil Commander, Noel Schoknecht, Bill Verboom and Peter Caccetta). Their aim was to better understand the hydrology and processes of salinisation of the cleared and farmed valleys of the wheatbelt landscape.

Recent revision of the geology In April 2006 the Western Australian Geological Survey announced a significant revision in their geological understanding of the ancient (Archean) rocks of Western Australia (GSWA Record 2006/8). It is now thought possible that the area of rocks on which Charles Darwin Reserve is situated, referred to as the Youanmi Terrane, represents the nucleus on which the younger rocks of the State were built. It seems likely that the initial formation of the area occurred more than 3,050 million years ago, and it is thought that there may be even older components.
The map shows this nucleus. Volcanic and sedimentary rocks are shown in green and granites are shown in red. A 14 km thick sequence of sediments and volcanic rocks intruded by large masses of granitic rocks has been mapped by the Western Australian Geological Survey (1976-1979) in the vicinity of Charles Darwin Reserve. These range in age from possibly 3,010 million years to 2,620 million years old.

Geology and gold mining

In the Retaliation gold mining area in the north-east of Charles Darwin Reserve there is a sequence of volcanic and sedimentary rocks. Poorly exposed basalt lava flows occur at the base of the sequence. These are followed to the north-east by a single banded iron formation horizon and metamorphosed sedimentary-felsic rocks (ie feldspar and quartz rich ash, dust and fragments blasted out of volcanoes and deposited in water or onto land) which host the gold mineralisation. These are further followd by a 5 km sequence of basalt flows, each about 50 m thick, which are well exposed. The sequence is younger to the north-east. These rocks were probably folded when granites intruded some 2,764 million years ago. There was a subsequent intrusion of more granites around 100 million years later.

Explorers were expected to report on the natural resources of the country, including the geology:

12. To render the expedition as extensively useful as possible, I would urge you, in the interests of science, to make and preserve such specimens in natural history as may come within the reach of yourself and party, especially in the departments of botany, geology, and zoology, which may be greatly enriched by productions of country not yet traversed. Surveyor - General’s instruction to John Forrest, 13th April, 1869, in Forrest, John, Journal of proceedings of an exploring expedition in search of the late Dr Leichhardt and party, undertaken, by order of the Government of Western Australia by John Forrest, Government Surveyor, 1869, in  Explorations in Australia  Sampson Low, Marston, Low, & Searle, London 1875 

Forrest’s journal, like Gregory’s before him, reports little of the geology, however, and the region around Charles Darwin Reserve remained undescribed until Harry Woodward was appointed Government Geologist.

In his first annual report of 1888-89, Harry Woodward describes a visit made from Berkshire Valley (near Moora), via Jibberding on Lake Goorly and Ninghan, to Mt Kenneth (Fields Find area) and onwards to Bandgera (Badja) and Peterwanngy (probably Pindar):

Jibeding is on the edge of a large salt lake, probably part of Lake Moore, as similar flooded salt country (with here and there a protruding mass of granite) extends to the Ninghan Range. This range is a lofty group of hills rising between Lakes Moore and Monger, and attaining its greatest elevation (about 4,000 feet above sea level), in a big mass of dolomite sandstone, called Mt Singleton, or Ninghan.  The rocks in the rest of the range are slate, quartzite, hornblende rock, granite, and amygdaloid, with ferruginous jaspery quartz veins and hematite lodes, which latter should, I think, be tested for copper and silver.

There are several isolated ranges to the North, North-East, and North-West beyond the Lake; which would, in all probability be worth prospecting.

In June 1911 Woodward again travelled through the area from Moora to Paynes Find via Juadong, Jibbiding, Ninghan and Coodingnow. HP Woodward 1912: Payne’s Recent Gold Discovery Near Coodingnow, Yalgoo Goldfield. Geological Survey Western Australia Miscellaneous Reports Bulletin No 48, Series IV, No 19.

Woodward produced the first report on the geology near the Charles Darwin Reserve area in August 1915, following an inspection of gold workings south of Mt Singleton (Bonnie Venture Group) and south-west of Mt Gibson (Crusoe Group). He had travelled from Yalgoo by car accompanied by the Inspector of Mines. He considered the area south-west of Mt Gibson to be an extremely promising looking tract of country. HP Woodward 1915: Certain Mining Centres at the South End of the Yalgoo Goldfield. Geological Survey Western Australia Miscellaneous Reports Bulletin No 64, Series IV, No 54.