{18 
ECONOMIC GEOLOGY 
area of pillow lavas. The ore-bodies have replaced the sedi- 
ments at the contact with the quartz-porphyry. The ore 
occurs in shoots, of which over 30 are known ; a few are in 
the quartz-porphyry and the lavas, but most are in the sedi- 
ments. The Hollinger Mine, which is now one of the world’s 
great mines having up till 1923 produced £15,350,000 worth 
of gold, consists of a belt of Keewatin lavas which have been 
sheared and crushed into schist; nodules of unsheared rock 
can be found which show the variolitic structure. The in- 
trusion of quartz-porphyry was followed by the deposition 
of many lodes which are sub-parallel to it, but some- 
times cut across it. The lode material is mainly quartz, 
much of which encloses lava debris. A little poor ore has 
N 
FD. 
5 5 
no _ Fr 
¥ 
v 
ol. 
Fre. 13.—TuE Dome Mine, PorcupiNg. 
The section across the country north of the Dome Mine, Porcupine 
Goldfield, Canada, S, gently folded sedimentary beds, slates, and 
quartzites, overlying conglomerates. Both are intruded by quartz. 
porphyry, P. The Dome Mine, D, with the ore-bodies {black} occurs 
along a fault, F, separating the sedimentary beds from the pillow 
lavas, p.i., which form an extensive area south of the mine. 
been found in the quartz-porphyry. According to Spurr 
the quartz-lodes are intrusive vein-dykes; but to the author 
they appear due to the saturation of a crushed mass of rock 
by solutions which deposited the quartz along the main 
channels of circulation. 
That the ore formation was deep-seated is shown by the 
abundance of tourmaline in part of the Dome Mine and the 
abundant tellurides including hessite (silver-telluride), altaite 
{lead telluride), and sylvanite and petzite (gold-silver tel- 
furides). The tellurides in the Hollinger Mine were sparse 
‘n the upper levels, but abundant 800 feet deep. 
THE GorprieLps or West AUSTRALIA—West Australia 
consists of a plateau which rises from the coast by a mountain 
scarp to the height of about 1800 feet, and after extending