Investigation of Some Phosphatic Nodules from Dandaragan, 81 
Western Australia. 
ORIGIN OF THE NODULES. 
In his original description of the Dandaragan phosphate deposits in 
1907 W. D. Campbell (5) stated that the phosphate nodules were “ copro- 
lites,” presumably accumulations of animal excreta, bones and teeth. Simp- 
son’s subsequent investigations in 1912 (4) showed that the so-called bones and 
teeth were in reality fossil wood, and it was not until December, 1943, that 
undoubted bone fragments were recognised and identified from these deposits 
(6). Simpson seems to have retained the term “coprolite” for the nodules, 
however, and this name apparently remained unchallenged until the last few 
years. As a result of field investigations in the Dandaragan District in 1941 
Matheson in an as yet unpublished report (7) expressed the view that the 
nodules are of inorganic origin and quoted the supporting opinion of Teichert 
that the use of the term 6 coprolite” bed should be discontinued. 
Evidence available from the present investigation is, in the writer’s 
opinion, strongly in favour of the view that these nodules have been formed 
by inorganic chemical action. The nodules are composed of grains of quartz, 
glauconite, felspar and iron ore — all normal components of the enclosing 
greensand — which are cemented together by phosphatic material to form 
separate rounded, relatively compact bodies lying within beds of more or 
less consolidated glauconite, quartz, felspar, etc., grains intermixed with 
some chalk. This suggests that nodules have been formed by deposition of 
calcium phosphate (collophanite) around grains of quartz, glauconite, etc., 
within the original greensand, and that gradual accumulation about these 
primary centres of deposition has resulted in larger and larger concretions. 
It is probable that in many cases original interstitial chalk has been replaced 
by the cementing calcium phosphate, whilst the frequent presence of phos- 
phatised wood fragments within the nodules themselves suggests that wood 
fragments have often formed the nuclei for the growth of nodules. 
No clue as to the source of the original phosphoric acid responsible for 
the precipitation of the collophanite was afforded by this microscopical investi- 
gation of the nodules, though it may be hazarded that this material was 
probably dissolved out of original organic remains either from within 
the enclosing beds or from an adjacent, possibly higher horizon. 
SUMMARY AND CONCLUSIONS. 
A number of specimens of phosphatic nodules from Cook’s Deposit, and one 
from Minyulo Deposit, Dandaragan, have been examined microscopically and 
their mineral content figured and described. Unfortunately the material avail- 
able for examination from both deposits is probably not truly representative 
but is slightly more ferruginous than the average nodules. 
Micrometric analyses were made to determine the relative proportions 
of the essential minerals present, viz., quartz, collophanite, glauconite, iron 
ore and felspar, in several specimens, and the results tabulated. All speci- 
mens contained appreciable quantities of glauconite, iron ore and felspar. 
Taking the average mineral composition of specimens from Cook’s 
Deposit, the partial chemical composition was calculated. These figures 
were compared with those of a complete chemical analysis of a composite 
sample of nodules from Cook’s Deposit, and they showed tolerably good 
agreement. 
As a result of this investigation it can be said that most if not all of the 
iron oxide and alumina obtained from chemical analyses of coarser fractions 
from sizing tests of Dandaragan phosphate rock occur within the nodules 
