Mineralogy of the Donnybrook Sandstones, 211 
Western Australia. 
15.— MINEEALOG-Y OF THE DONNYBROOK 
SANDSTONES, WESTERN AUSTRALIA. 
By JlOROTHv Carroll. 
Read 13th May, 1941; Published 7th August, 1942. 
INTRODUCTION. 
Sandstones, Permian or Triassie in age (Maitland, 1939), outcrop along 
the w-estern edge of the Darling Plateau in the vicinity of Donnybrook 
(Lat. 33° 10' S. Long. 116° 10' E.) about 130 miles south of Perth, Western 
Australia. 
It has been supposed on lithological grounds that these sandstones, 
known as the Donnybrook sandstone (Saint-8mith, 1912), are a remnant of 
the Collie Coal Measui'e Series Avhich are Permian (Maitland, 1939, p. 185), 
but there is as yet no sut)porting palaeontological evidenc<‘ although farmers 
in the district have discovered fossil footprints, not yet identified, in the 
u])per part ot tlie tormation. Beyond some lithological resemblance to the 
(Mai Measure series at (k>llie and the occurrence of some poorly developed 
thin beds of coal, there is nothing to show that the Donnybrook sandstone 
Jormation is of the same age as the Collie beds; however, both ajipear to be 
of estuaiine or lacustrine oi’igin and to have l)eeu laid down on an uneA'en, 
eioded surtace of the i ^re-Cambrian complex. There is apparently no con- 
tinuity betwc'en the two formations. 
The Donnybrook sandstone formation varies from coarse, unevenly 
graded and bedd(‘d sandstone with pebble bands near the base, to fine-grained, 
e\enly bedded, ripple-markcfl sandstones with clay t>artings towards the top. 
Ihe beds dip at about 4° to the south-west. The thickness is not definitely 
known, but Imres ha\-e penetrated it to a depth of 200 feet (Maitland n 
183). ' ^ 
Ihe Donnybrook sandstone J.orms fiat-topped hills, covered bv laterised 
sandy soils, to the M'est, north and south of Donnybrook. Laterih^ (duricrust) 
above the sandstones is distinguishable from that formed from the Pre- 
Cambrian rocks by its abundant (]uartz grains. 
i be disti ibut.ion ol the Donnybrook sandstone, is shown in Figure 1 
where the formation is seen to overlap tlie edge of the Pre-Cambrian shield, 
indicating that the sandstones were in part laid down on an eroded surface 
of Pre-Cambilan rocks (Forman, 1936, p. 4). The Pre-Cambrian rocks 
immediately to the north-west of Donnybrook are at a much higher level 
than the sandstones. A range of sandy hills, known to be underlain in some 
])arts by sandstone, occurs to the south-south-west of Figure 1, suggesting a 
continuation of the formation in this direction. The contact of the sandstone 
with the Pre-C ambrian just west of Nannup, about 30 miles south of Donny- 
hrook, is similar to that at Donnybrook. Economically these sandstones are 
of importance, tor the fimu’, evenly-laalded types jirovide an ensily- worked, 
durable building stone. 
In 189/ gold was dlscoATU’ed in the Donnybrook sandstones which were 
worked until 1906, yielding about 850 ounces of gold from 1,650 tons. The 
gold is thought to have been derived from small (luaiitities in the surrounding 
Pre-Cambrian rocks (Maitland, [). 181) and to have been deposited from 
solution in the sandstones. An unsuccessful attempt was made about ten 
years ago to recover gold from the Pre-Cambrian rocks near where the old 
mines are situated in the sandstones. 
j 327/42. 
