(iKOUKJY AND Petrology of Part of Toodyay District, W.A. 12!^ 
IV. DCONOMIO DKOLOGY. 
Gold and tlie refractory minerals andaliisite and sillimanite are the only 
minerals of economic importance which have been noted in this area. 
(1) The gold deposits occur in the vicinity of Yinni<ling Creek in the south- 
west('rn corner of tlie area mapped and have be('ii described by Blatchford 
(1932), Forman (1935), and Prider (1934, p. 73), and require no further descrip- 
tion here. Tlie aurift^rous deposits appear to be gem^tically related to tlu' 
younger non-foliated granite of the south-west part of the Area. 
(2) Refractories — {a) *S'?7/iwan?Ve.- -Refi’actory clays derived from tlu' 
alteration of sillimanite schists of the Jimperding Series have been workc'd 
at (lackline for some years (Simpson, 1935, ]). 11 : Matheson, 1938, p. 13). 
The sillimanite content of these clays is estimated to vary from 5 to 10 jx'r 
C('nt of th(' rock. 
In tl.(' 'Foodyay area, the metamorphism of the Jimperding Series has 
been effectc'd umler sillimanite zone conditions. Although sillimanite occ‘urs 
in the mir*ac('ons schists throughout tlu' area, the best sillimanite deposits- 
not('d during tht' survey were in the country lying to the north-west of Key 
Farm hom('st('ad, wlu're there has been a thickening of the incompetent mica- 
sillimanit(' schists during folding. Although rapid variations in the silli- 
manite' conte-nt are' noticeable, the average sillimanite contemt o\('r com- 
paratively wide* bands is high and in certain bands u]i to 10 fea't wiele', the 
sillimanite (mainly fibrolite;) forms up to 70 pov vont of the re)ck. This mate'i’ia l 
constitutes a \'aluable ore' provided the small nuiscovite-biotite cejutemt can be' 
se'paratc'd. I^^xperime'ntal work in this connection is at j>re>se'nt in progre'ss. 
{h) Aadalvsife . — This minen-al is elevelope'd in the uppe'rmost band of 
mie-a scliist in the south-we'ste'rn corner of the are'a. Tliere eloes not a])])e'ar, 
in the area ma})])e'el, to be' any natural concentration of this mine'ral, suflicie'nt 
to constitute* an economic proposition. Howe've'r, in the westerly exte'nsie)ii 
e)f the anelalusite' mica scliists, a mile or so west of the eelge* of the mappe-d are'a, 
in the* lu'adwaters of Mortigup Brook, considerable deposits of white* wc'athere'el 
anelalusite schist witli abundant anelalusite are expose'el. Tlieso eleposits ai'c 
be'ing e'xple>ite*d at the^ preseait tinier by a loe-al company. 
V. SUMMARY AND (’0NCLUS10N8. 
A e-onfe)rmable^ se'ries e>f metamorphic re>cks lias bex'n describeel. It 
inclueles both sexlimemtary anel igneous type-s. The former incluele inte'rbe'elde'd 
sillimanite*- anel anetalusite-mica schists, extre'inely ]iure' ejuartzite's, and 
eice^asiemal e-ale^are'oeis sanelstone's, now re'pre'sentevl by e^alc-silie'ate* reie'ks. 
All these rocks lie within the sillimanite zeme*. Rare biotite'-pIagie>e*lase seJiists 
have* be'em noteel, in erne instance etarrying a e*onside'rable amount of ge'elrite 
and cummingtemite. This biotite-ge'elrite-cummingtonite-plagioe-lase' schist is 
consiele're'el te> n'sult probably from the re'gional me'tamorjihism eif a somewhat 
eleilomitic clayey se'elimemt. 
Interbe'eleled with the se'elime'nts there are* basic, igneeius roe^ks now 
iepre>se'nttHl by schistose plagioclase amphibe>lite*s, which have be'e'u derivt'd 
by re-gional me'tameirphism, uneU'r sillimanite' zone conditions, from tholeiitie: 
roerks which may have be'e'ii eiriginally sills e>r flows. Thc'y are oleUr tlian thei 
iirst granite intrusiem anel have bee'n folde'd along with the associateel sedimeaits. 
Wide'i- bands of granite* gne'iss have^ re'sulte'd from tlie intrusion of granitic 
magma into the' above rocks. The pe'rioel of intrusion coincided with tlu; 
ore)ge*nic jicriod, wlu'n the pre-existing rocks wore a!te*re>el te> their pre'se'iit 
state. The granite*, a porphyritic microe*line type, was intrude'el unde'r stre'ss 
anel ]ire'sents a fhixiemal structure, which in the uppe'r, more narrow banel is 
