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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