TAKU RIVER AREA. 93

In this direction, then, a dispersal of mineralization and lower-grade ore over greater widths
than towards the north-west can be expected. Acid dykes cutting the altered rhyolite occur on
the Banker and Potlatch groups, adjoining the Manville on the north-west. On account of the
heayy overburden covering the low-lying ground in which these showings are situated, and the
limited amount of work completed at the time of examination, no relation between them and
the ore-bodies could be established.

Basic dykes of lamprophyre type cut both the rbyolite and the andesite and are the
youngest rocks of the series. The similarity of these rocks in colour and texture to certain
phases of the andesite make their visual determination difficult when they enter the latter.
The only effect that these basic dykes seem to have on the ore-bodies is to cause their shattering
and impoverishment with included dyke-rock in the areas of intersection. Faulting occurs to
a minor degree, generally along north-south striking planes.

The ore-bodies of type 1 are probably medium to low temperature deposits, formed at an
appreciable depth below the old surface from sluggishly circulating ,solutions. Replacement
probably emanated from the centre of the zones with lateral temperature segregations.. Mineral
deposition is probably related to the concluding period of the batholith intrusion.

ORE-BODIES OF TYPE 2.

The ore-bodies of this type are characterized by a main metallic mineral content of stibnite,
with accompanying pyrite and very minor quantities of galena, in a fine-grained quartzose
gangue. This stibnite occurs in massive granular form in reticulated structure in the vein-
matter, and also as a fine dissemination of minute needle crystals in the gangue-matter. The
pyrite is in fine-grained scattered dissemination through the gangue.

The typical ore-bodies of this type appear to be confined to a diabasice rock, cut by numerous
felsite and small quartz-rhyolite dykes. They seem to favour the area somewhat closer to the
batholith contact than the ores of type 1. The deposits oceur in well-defined replacement shear-
zones along the course of felsite dykes. These dykes have probably formed lines of weakness
in the surrounding country-rock along which the fracturing and shearing has been readily
earried and sustained.

The typical deposits are characterized by a high gold content and abnormally low silver
values. Adulteration with arsenic and copper seems to be practically entirely absent. No
chalcopyrite or copper carbonates were observed in the mineralization. An assay for arsenic
returned nil and that for copper showed a trace. These are important factors in connection
with the possible economic value of this type of deposit from the standpoint of its antimony
content. In the manufacture of pure antimony the presence of arsenic and copper is extremely
undesirable. Zine and lead are also practically entirely absent. From the standpoint of their
antimony content, therefore, the characteristic deposits of this type discovered in the Taku
region are exceptionally pure. Whether the gold content of these ores is related to the stibnite
or to the pyrite is not established.

The antimony market is unfortunately a restricted one and is at present affected by a duty
on the metal recently imposed by the United States Senate. The bulk of the world’s production,
however, comes from the Hunan deposits in China, and the demand is at present reported to be
moderate. The apparent purity of the Taku deposits, coupled with their high gold content, may
offset the handicaps of an antimoniferous ore. Should they be proved to be of important extent,
this type of ore-body may be of economic value. The typical ore-bodies of this type occur on the
Whitewater group on the west bank of the Tulsequah river, about 4 miles south-west of the
Tulsequah Chief.

An intermediate type of. ore carrying minor quantities of stibnite associated with zine
blende, galena, arsenopyrite, and some chaleopyrite, occurs on the Banker and Pottatch group,
adjoining the Manville on the north-west. These occurrences are in quartz-filled fractures, with
lateral dissemination areas, in an altered rhyolitic rock cut by acid and basic dykes. On the
Banker the ores are featured by a high silver content, associated probably with the presence
of some grey-copper mineral; an appreciable gold content is also present in these ores.

The ore-bodies of type 2 are probably of low temperature origin, formed eomparatively near
the surface. The structure indicates that they were formed from rapidly circulating solutions
covering at least two impulse periods. Although the definite genesis of these deposits could “not
be established in the field, they are probably related to the final thermal activities of the
batholithic intrusion and later in origin than the ore-bodies of type 1.