54

ECONOMIC GEOLOGY

its value to such great depths. The ore-body has the shape
of a flattened pipe with an average thickness of 10-12 feet.,
a maximum of 33 feet, and a width of usually less than 600
feet, though in places of 1000 feet. It is in a bed of chloritic
schist which is probably altered calcareous clay. The bed is
vertical, and the pipe of ore lies along it at an angle of 45°
to the horizontal. The ore consists of sulphides, especially
pyrite, pyrrhotite, and arsenopyrite, with a little chalcopyrite,
 and a matrix of siderite, quartz, dolomite, and calcite,
with some carbon and fragments of the chloritic schist.
The gold is rarely seen as it is present in the arsenopyrite.
The ore was foliated after the mineralization, and the sparse
vein-quartz is barren. There is no evidence of much earthmovement,
 such as faulting, and no pug along the ore. The
lower levels are quite dry and the lode has no deep-seated
minerals, such as tellurides or tourmaline, There is also no
clear evidence of the infiltration of solutions, and the ore
has maintained its value as deep as it has yet been followed.
This lode was probably a placer containing alluvial iron
oxide and fine-grained gold ; when the sediments were foliated
into chloritic schist, the iron minerals were converted into
sulphides, and the gold dissolved and redeposited with the
arsenopyrite. This view is consistent with the continued
richness of the ore in depth, its mineral character and microscopic
 structure, and absence of infiltration channels.