14

of gold a ton. The best ore consists of massive, fine-grained pyrite with
free gold. Rarely the ore contains small nests of scheelite and specimens
have been found containing small amounts of chalcopyrite and galena.
The fine-grained nature of the ore is in marked contrast with the coarse
pyrite of the veins. Where replacement is less intense the ore consists
of silicified limestone with streaks of minute pyrite crystals and local
bunches of ankerite or dolomite. Some impure, shaly, limy bands at the
ends or edges of the ore-body are replaced by coarse pyrite crystals. The
ore-body at Island mountain is at least 300 feet long and in one or two
places is 9 feet wide. It extends for about 300 feet up the dip above the
main tunnel. Its downward extent has not yet been determined. It is
not so irregular in shape as might be expected of limestone replacement
bodies, probably for the reason that the limestone occurs in uniform narrow
beds. Several bodies of this type are exposed in the workings of the Cariboo
Gold Quartz mine. The largest body so far found there has a maximum
thickness of 18 inches. The grade and general appearance are identical
with the ore in the Island Mountain mine. At the Cariboo Gold Quartz
mine the limestone appears to have been more silicified than at Island
mountain and a few limestone beds have been changed into quartz beds.
None of the siliceous replacements so far as is known contains more than
a trace of gold.

ORIGIN OF THE DEPOSITS

In discussing the origin of the deposits the veins and replacements
will be dealt with separately. In regard to the veins it will be necessary
to take up first the origin of the vein fractures.

Uglow (pages 39, 40) believed that the rocks of the Cariboo series were
folded and intruded by quartz porphyry sills prior to the deposition of the
Slide Mountain series of late Paleozoic age. Further, that during the
deformation the A veins were formed from the materials coming from the
intrusives from which the sills were derived. Later settling caused cross
range faults and these were healed with quartz and sulphides to form the
B veins. Much later, possibly in Jurassic time, there was further defor-
mation and settling forming northeasterly trending faults and crushing of
the quartz veins (pages 39, 40). Close examination of the veins has shown
that those occupying transverse and diagonal fractures, that is the so-called
B veins, do not lie along faults in the sense claimed by Uglow.

The earliest quartz mineralization seen in the gold belt is in the
form of narrow bed veins formed mainly or entirely by replacement of
narrow bands of rock. These are known to be early because they are
folded with the strata. Other bands of silicified clastic sediments are very
similar to these veins, but they are clearly silicified rock bands and not
quartz veins. They are cut cleanly by transverse quartz veins and the
silicification shows no relation to them, suggesting that the silicified rock
bands are decidedly earlier than the veins cutting them. Some beds of
limestone, too, have been converted largely to quartz for lengths of hun-
dreds of feet and some of these bands may have been silicified at this
early date. It may be that some of the veins paralleling the strata or A
veins may also have been formed early, but the writer has no information