Minp:ralogy of the Donnybrook Sandstonp::s, 
Western Aesthalia. 
213 
ot* finding workable ('oal seaiUH in the district, and with the oceiirrenee of 
gold have been summarised ])y (Jibb Maitland (lt)39) but actually there is 
little detailed knowledge either ol’ the sandstones or oi‘ the I’re.-Cambrian 
complex, whi(di lies to tile east, north and soulli of tin* sandstones (Figure 
1). Tile Fre-( 'ambrian is represimted predominantly by gneisses at Donny- 
bi’ook, and, in the valley ot' the Freston Fiver, tlu'i’e an* numerous iiegmatitc* 
dykes some ol' which i-arry lai’gi* crystids of beryl and tourmaline; garneti- 
f'erous gn(‘iss(*s, associated witii mica schists, an* also common. (tranite 
occui's fartliei- to tin* east. 
The soils oNci'lying the l-lonn^du’ook sandstones are gmierally sandy, 
torming sand-plains. In phu-es, howe\'(*r, the ciay in some parts of the forma- 
tion is suffii'icnt to give a loamy soil with a ('lay sub-soil evidently well suited 
to the reiiuinauents of Jarrah [Kn(uihjitl.H>< )nitr(jiKi(ta) which provides timb(‘r 
for the mills near Donnybrook and Nannu]). Tlu' sand-plain, lying as it does 
in a region of .'f)-40 inch annual i-aini'all may constitute a, distinct type jn 
the sand-j>lains of Western Australia, and the investigation given below was 
begun several years ago when the writer was examining the heavy minerals 
ot sandplain soils gfuierally. Tin* iH'sults 1‘or sonn* otln*!' types of sand- 
plain hav(' already Inam publislu'd. 
MlXFHALOdV OF TIIF DONNYBROOK SANDSTONF8. 
The specimens (*xamined fall into two groups, actual ro('k specimens, 
and soils d(‘rived from the W('atlu*ring of tin*, sandstoin‘s. 1die sandstones 
were examin(*d by thin section as well as by ('oiua'iitrating tin* hea\'y minerals. 
The sandstoiu's were ci’ushed until a larg(* (|nantity of the material 
passed an 85 F>.S. sie\’(* (approximately 70 l.M.iM.), the linest }>articles were 
wasln'd out, tin* sample dried, and about lO to 15 grams were* separated in 
bromoform. Tin* soils ^yvr^' si(*ved in a similai' way and the ('lay grade* of 
material wusIkmI out before bromol'oi’m separation. A few ot‘ the sands 
were treated with IICl io remo\'e feri'uginotis coatings tVom the grains, ])ut 
most of tln'iu wvw white or almost white in the natural staff; so that acid 
treatment was untn'cessary. Tin* heavy residues were not Wf'ighed so that Jio 
percentage ligures art* availabh*, but it was found that the residues Avert* 
fairly large and would ha\-e, in all })robability, l)(*en at least 1 pf*r cent, of 
the sand separated. Beforf* momiting, inagn(‘tit(* AA^as r(*moA'ed from each 
r<‘sidue. 
In thin sf'ction tin* Dojinybi'ook sandstone is s(*('n to be a medium to 
tine-grained rot-k ('onsisting of al)oui 75 pt'r ('('iit. (piart/; tin; r(*mainder is 
felspar, both oHgoclasf* and inicrot-lim*, kaolitiite or other (day mineral sup- 
plying tin* binding. Tin* (piart/ grain*; an* rounded to suh-angidar in shape 
and oft('n show re-growth at. tin* edges; such grains W(*r(* also I'ound in some 
of the soils directly (h'l'ived from the sandstones. The fels[)ars in the sand- 
stones are someAA'liat kaolinised. 
Tin* heavy mirnwa] ass('ml)lag(*s contain the following minerals: — mag- 
netite, ilmenite, leu('ox(*ne, zircon, tourmaline, rutile, splu*ne, epidote, zoisite, 
garnet, amphibole, chlorite, anatase, nionazite, kyanitc*, sillimanite, staurolite, 
spinel, and muscoA’it(‘. The suites are rather similar throughout as is shoAvn 
in Table 1, Avhere the relative abundance is indicated. 
Notes on Individual Minerals. 
Magnetite, ilmenite, and leucoxene require no comment except to state 
that all are rather abundant in the residues, particularly magnetite and 
ilmenite. 
