Geology and Petrology of Part of Toodyay District, W.A. 125 
{2) The Greenstones. 
(a) Quarts, dolerites.- -The^se are the latest intrusives into the Jimperding 
.Sei'ies. They occur as dykes up to five chains wide, most of which trend a 
little \V. of N., although there are several large dykes with an E.-W. trend. 
The geological map (Plate I.) shows the distribution of these dykes. They 
all belong to the same period of intrusion and no examples of one dyke being 
cut by another were found. This period of intrusion was much later than 
the last orogenic movements in this region and the doleritic rocks show no 
alteration other than those of deuteric character. 
They are variable in grain from line basaltic to coarse gabbroidal, and 
■r)phitic texture is characteristic except where obscured by extensive uralitisa- 
lion of the pyroxene in the more acidic types. 
Pig. 16 . 
Quartz dolerifes 
A. Quarts rare. Both pyroxene and plagiodase are un- 
altered. The ophitic texture is well marked. The i)vroxene 
cleavages are slightly curved and incipient fracturing is notice- 
able. A little primary brown green hornblende is seen in upper 
right in the vicinity of the end pbase fpiaitz. The iron ore is 
ihnenite. 
B. End phase of the (juartz <lolerile magma showing a con- 
centration of quartz and apatite. Pibrous uralite replaces 
pyroxene (ui)])er left) and the idiomor])hic plagiodase is highly 
saussuritised. The ferromagnesian is mainly a brownish prim- 
ary” hornblemle. 
Th(‘ rocks vary from cjuartz-frc(' doh'ritcs made up of slightly browiiisli 
])vroxeuc and plagiodase (Ab;|Anj) with apatite and ilmenite as accessories, 
through (juartz dolerites which usually show considerable uralitisation of 
the pyroxene, to more acidic ty])cs made u]) larg<dy of plagiodase, uralitised 
])yroxf‘ne, ])rimary brown-gr(‘c‘n hornblende, and quartz, with leucoxenised 
ilnnuiite and apatite as abundant accessories. The uralitisation of the pyrox- 
eii(‘ is definitely a deuteric proce.ss in these rocks because there are no later in- 
trusives or ('arth movemt'nts which could have effected thes(‘ changes, because 
it is developed much niort* exttuisively in types in which the end stage (fuartz 
1 as b('(‘n concentrated, and also bc'cause both unaltered and highly uralitised 
rocks occur in the sarru' dyk('. 
