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ORES OF GOLD
ve lanes ;
Some of the mines are in rocks silicified hE shear sands
others were probably bedded rerruginous rocks containing
altered to ironstone and quartzite. T ot of Upper Palxo-
the ores disappear to the N. beneath a shee lance, by tracing
Zoic sandstone. Survey by the torsion nae, the course
the buried granite and basic rocks, werd oo Gold-bearing
of any northern extension of the goldfie inners Sorice
focks outcrop further N. in Pilbara with a San similar to the
Ad conglomerg tog that have been describe ld in these con-
Banket of the Transvaal ; the alluvial ge of the West
glomerates Suggests the pre-Cambrian ag
Australigy ores
51
SEerion B. SECONDARY ORES AND ENRICHMENTS
Mz. Morgay, QUEENSLAND—The early development of
gold Mining wag hampered by the belief that gold would
20t be found fur below the surface. This view was
Suggested by the rapid decrease in value of many
gold oreg when followed downward. This fall in grade
'S In many cages due to secondary enrichment (cf. p. 31)
Which hag concentrated near the surface gold that had been
Spread through a great vertical range of lode. This secondary
orichment jg Most marked in countries which have remained
Soe sea-level for long periods of time, such as West Aus-
tralia apg Southern India, In some of these fields the
deeper Part of lodes which are rich at the outcrop are too
low grade to Pay. An extreme case was that of the London-
derry Mine of Coolgardie. A hole 2% feet deep, 6 feet long,
and 5 feet wide showed £30,000 of gold; the claim was
sold for £180,000, and floated as a company in London
for £700,000." “Tp pocket” (Rickard, Eng. and Min,
Fourn,, I6 April, 1808) “did not continue even one foot
lower,” The vein below was repeatedly explored, but without
Success,
. Secondary enrichment on a greater scale has formed some
Mportant mines, such as the Mt. Morgan Mine in Southern
Queenslang. The mine was opened on a hill 400 feet high,
S0mposed of 4 mass of quartz so cavernous and stalactitic that
It was described by Jack as the sinter of an ancient geyser,
Festing on slate and quartzite, Hot waters had leached the
