Geology and Petrology of Part of Toodyay District, W.A. 83 
4 .— THE GEOLOGY AND PETROLOGY OF PART 
OF THE TOODYAY DISTRICT, 
WESTERN AUSTRALIA.* 
By Rex T. Prider, Ph.D., B.Sc,, F.G.8. 
(Df'pavtment of Geology, University of Western Anstraiia). 
R('ad 12tb August, 1941 : Published 14th March, 1944. 
(’ONTENTS. 
Page 
T. — Introdvcuton 84 
II. — Geological Structure of the Area ... ... ... ... ... ••• 85 
ITT. — Petrology ... ... ... ... ... ••• ••• .•• ••• ••• 88 
A. — The Jimperding Series ... ... ... ... ••• ... 88 
( 1 ) Quartzites ... ... ... ... ... ... ■ ■ ■ ■ - ■ 88 
(а) Upper quartzite ... ... ... ... ... ••• 90 
(б) The lower quartzites ... ... ... ... ... 91 
(c) The origin of the quartzites ... ... ... ... 92 
(^) The fabric of the quartzites ... ... ... ... 94 
(2) Calc-silicate rocks ... ... ... ... ... .•• ... 94 
(3) Mica schists ... ... ... ... ... ■■■ .■• ••• 97 
(а) Sillimanite schists ... ... ... ... ... ... 98 
{h) Garnet-plagioclase-biotite schist ... ... 99 
{r.) Gedrite-cummingtonite-plagioclase schist ... ... ... 100 
{d) Andalusite schists ... ... ... ... ... ... 101 
(4) Hornblende schists (plagioclase amphibolites) ... ... ... 104 
(5) The Granite Gneisses and the associated xenoliths ... ... 107 
{a) Upper Granitic Gneiss ... ... ... ... ... 108 
(i) Biotite-microcline granite gneiss ... ... ... 108 
(ii) Microcline granite gneiss ... ... ... ... HI 
(hi) Biotite-oligoclase granite gneiss ... ... ... Ill 
(б) Xenoliths in the Upper Granitic Gneiss Ill 
(i) {Schistose plagioclase amphibolites ... ... ... Ill 
(ii) HornVdendic schlieren... ... ... ... ... 11.2 
(hi) Biotite granulite xenoliths ... ... ... ... 112 
(iv) Eulysitic rocks ... ... ... ... ... 113 
(c) Conclusions regarding the origin of the Upper Gneiss ... 114 
(^^) Lower Granitic Gneisses ... ... ... ... ... 114 
(c) Xenoliths in the Lower Granitic Gneiss ... ... ... 115 
(i) Eulysitic rocks ... ... ... ... ... 115 
(ii) Calc-silicate rocks ... ... ... ... ... 118 
(iii) Cordiei’ite-anthophyllite rocks and related types ... 118 
(iv) Amphibolite xenoliths ... ... ... ... 119 
(f) Hybridisation of the Lower Granitic Gneiss ... ... 122 
Ig) Conclusions regarding the origin of the Lower Gneiss and 
the associated xenoliths ... ... ... ... ... 123 
B. — The Younger Igneous Inirusives ... ... ... ... ... ... 124 
(1) The granites 124 
(а) The normal granites ... ... ... ... ... ... 124 
(б) Garnet-muscovite granites ... ... ... ... ... 124 
(c) Pegmatites, garnet aplites, and later quartz veins ... 124 
(2) The greenstones ... ... ... ... ... ... ... 125 
(а) Quartz dolerites ... ... ... ... ... ... 125 
(б) Ultrabasic intrusives ... ... ... ... ... ... 128 
(i) Metamorphosed ultrabasic sills ... ... ... 128 
(ii) Serpentines ... ... ... ... ... ... 128 
IV'. — Economic Geology 129 
(1) Gold 129 
(2) Refractories ... ... ... ... ... ... ... ... 129 
(a) Sillimanite ... ... ... ... ... ... ... 129 
{b) Andalusite ... ... ... ... ... ... ... 129 
V. — Summary ano Conclusions ... ... ... ... ... ... ... 129 
VI, — Acknowledgments ... ... ... ... ... ... ... ... 131 
Vll. — L lst of References 132 
Western Australia. 
k 30/48. 
