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ORES OF GOLD 
43 
Settlement of the country after the volcanic activity. The 
ores are Middle or Upper Kainozoic in date, and have not the 
Secondary enrichments common in older lodes. 
New Zealand, in addition to gold-quartz veins in slates, 
has two goldfields in volcanic rocks with fracturing of a 
different pattern from that usual in the plateau eruptions of 
the Rocky Mountains ; it is however similar to that at Gold 
Field, Nevada, which as shown by F. L. Ransome (U.5.G.S., 
Prof, Pap., 66, 1919, p. 196) was torn across by intersecting 
fissures without fault movements. In the Hauraki Gold- 
field in the North Island Kainozoic andesites and dacites were 
traversed by a network of ruptures along which were deposited 
Quartz, calcite, pyrite, chalcopyrite, blende, galena, and gold. 
When the fissures were full the solutions were forced into the 
country and formed replacement lodes 50 feet, and at the 
800 feet level, even 100 feet wide. Owing to the saturation 
of the country by the solutions the ore-shoots were remarkably 
Persistent to the depths of 1000 feet, and they have been 
worked to the depth of 1900 feet (cf. J. M. Bell, Tr. Austr. 
LME, 1911, pp. 548-79; and P. C. Morgan, Bull. Geol. Surv. 
N.Z, 1924, No. 26). The Thames Goldfield, on a peninsula 
E. of the Hauraki Gulf, illustrates the formation of a gold- 
field where the fracturing and ore deposits are shallower. 
The andesites there have been intensely altered hydro- 
thermally to the depth of 500 feet, and traversed by veins 
of quartz with rich pockets of ore where the main veins are 
joined by small quartz stringers. 
PNEUMATOLY TIC OrEs—CRrIPPLE CREEK, AND PASSAGEM, 
BraziL—Cripple Creek, in the red pre-Cambrian granite 
of Pike's Peak, Colorado, represents the pneumatolytic 
goldfields. Itisin the pipe of a Middle Kainozoic volcano and 
Pneumatolytic agents are shown by the characteristic mineral 
being telluride of gold, by the abundance of fluorite, and the 
alteration of felspars into kaolinite (cf. p. 169). The volcanic 
breccia in the pipe has been so silicified that its original nature 
IS recognizable only under the microscope. The breccia was 
cut by dykes of basalt, andesite, and phonolite, and has been 
torn by fractures due to shrinkage of the cooling rocks. The 
lodes are later than the dykes, which contain chimney-shaped 
ore-shoots ; the ascent of the solutions was doubtless aided 
by the reheating due to the intrusion of the dykes.