92 REPORT OF THE MINISTER OF MINES, 1929.

The mineralization of the chief ore-bodies discovered are of two main types :—

1. Copper, zine, lead, and iron sulphides carrying appreciable gold and silyer values, in a
barite-calcite-quartz gangue.

2. Antimony and iron sulphides, with very minor quantities of copper, lead, and zine, but
carrying decided gold values, and practically negligible silver contents, in a quartz gangue.

It is possible that these two types of mineralization may merge along the margin of the
zones to which they are confined. This is indicated on the Banker and Potlatch groups, north-
west of the Manville, where a small amount of stibnite is associated with a characteristic zine-
blende-galena mineralization. On the Banker there is also an occurrence of high silver values
possibly associated with a grey-copper mineral.

ORE-BODIES OF TyPE 1.

The mineralization of the Tulsequah Chief and Manville ore-bodies belongs to type 1. In
these deposits zinc-blende, chalcopyrite, pyrite, with minor quantities of galena, occur in very
fine-grained texture. The mineralization is partly massive and partly finely disseminated. The
massive sections of the ore-bodies are generally confined to the central portions of the zones and
gradually grade to a fine dissemination near the walls.. A massive mixture of fine-grained
chalcopyrite and pyrite, with a few indistinct bands of very fine-grained zinc-blende, frequently
occupies the centre of the zones. With the bands of zinc-blende gradually increasing in width,
this central portion of massive chalcopyrite and pyrite gradually grades on both sides into a
dense dissemination of very fine-grained zinc-blende with a minor admixture of fine-grained
chalcopyrite and pyrite, which gradually diminishes in density towards the walls. A decided
banded or relict structure is characteristic of these ore-bodies. :

These occurrences are characteristic replacement ore-bodies in shear-zones. In places,
generally in the central portions of the zones, the sulphides haye totally replaced the sheared
rock. Towards the walls the replacement is more or less incomplete, with a dispersal of
mineralization in the sheared rock near the walls. Two main directions of fracturing occur, one
striking north-easterly and the other north-westerly.

The geological features and mode of occurrence of the Tulsequah Chief and Manville ore-
bodies-are similar. The shear-zones occur in what appears to be an interformational sheet of
altered pyritized rhyolite in an andesitiec country-rock of dense texture. The formation has
been subjected to comparatively gentle folding along north-south striking axes. On the
Tutsequah Chief the shear-zones strike north-easterly and on the Manville the zone strikes
north-westerly. Whether the Manville shear penetrates the andesites to any extent could not
be established. On the Tulsequah Chief, however, the shear-zones are confined to the light
cream-coloured rhyolite and are delimited by the surrounding grey-coloured andesites. On this
property the rhyolite appears to plunge in a northerly direction, a feature that gives hope for
continuity at depth of the ore-bodies in that direction beyond the vertical projection of their
surface pinching at the margin of the rhyolite and andesite contact.

On the Tulsequah Chief a very dense-textured and siliceous dyke of dacite type, cutting both
the rhyolite and the andesite, may have an important influence on the ore-bodies of that property.
No. 2 ore-zone lies in contact with, or closely adjacent to, this dyke on its east side. No. 1 ore-
zone strikes at an angle of about 25° to the dyke on its west side and abuts on to it a short
distance south of the surface pinching of the zone. Although the age of this dyke in relation to
the ore-deposition may be debatable, it would appear from its mode of occurrence to have
preceded the formation of the ore.

It would seem that on the Tulsequah Chief the stresses have been readily transferred
through the rhyolite and then faded against the buffer of tenacious dacite in contact with the
dense and tough andesite. The same medium of stress confinement would also have a damming
influence on circulating mineral-bearing solutions and prevent a dispersal of values in the area
within the scope of that confinement. The probabilities on the Tulsequah Chief are, then, that
within the confined northward area of the rhyolite and conforming to the northerly plunge of
the sheet, higher-grade ore over more restricted widths should occur than to the southward.
In the southerly horizon the tendency would be for a dispersal of values over greater widths,
and consequently a lower-grade ore.

On the Manville no dacite or acid dyke was observed associated with the ore. The rhyolite
area, however, appears to spread or fan out in the low-lying ground towards the south-east.