93

In the main belt, the veins have, as a rule, well-defined walls of quartz
diorite and are composed of parallel bands of quartz and molybdenite
occasionally associated with orthoclase and pyrite. In many places well-
formed quartz crystals project into cavities in the veins. In the country
rock immediately adjacent to closely spaced veins, are minute veins of
quartz, sericite, biotite, epidote, and pyrite, and from these veinlets small,
irregular areas of the same minerals project into and replace the minerals
of the country rock. The replacement does not seem to extend more than
an inch or so in the case of some of the well-marked fissures. Away from
the fissures molybdenite is present very sparingly, if at all, and most of the
pytite lies in the country rock adjacent to, rather than in, the fissure.

In many of the openings, quartz veins lie alongside black dyke rocks;
in others they cut across them at a low angle. The veins also occur
associated with pegmatite and cut across an aplite dyke. The fractures

\ eecupied by the veins evidently were formed after the intrusion of the

dykes.
In studying the arrangement of the bands of mineral in the veins it
was found that the orthoclase when present lies on the outside. This is
followed toward the centre by bands of molybdenite and these by bands
of quartz, proving that the minerals formed in the order, orthoclase, molyb-
denite, and quartz. The relative order of deposition of the pyrite is not so
clearly indicated, but the mineral when present seems to lie near the out-
side of the vein, so that quite possibly it is earlier than the molybdenite.
From the examination of one thin section of the altered quartz diorite
occurring near the ore, it was concluded that pyrite was later than the
other secondary minerals in the replaced rock. As far as could be discovered
then, the order of deposition of ore and gangue minerals was as follows:
quartz, sericite, biotite, and epidote formed first and replaced the country
rock near the fissures. These were followed by pyrite. Before the replace-
ment by pyrite ceased the main fissures were being filled by molybdenite
and quartz, these two crystallizing in the order named. Calcite was seen
in one place only, where it was evidently one of the latest minerals. In
the outcrop in the creek bottom northeast of the main belt an exposure
(Figure 13, locality 5) about 30 by 40 feet consists of very much fractured
quartz diorite traversed by numerous, irregular quartz veins, most of them
under one inch in thickness and trending in all directions, but with a general
direction nearly at right angles to that of the fissure veins described above.
The manner of arrangement of the minerals in each of the individual
veins and in the adjoining country rock is the same as in the case of the
main belt.

In the upper few feet of many of the ore-bodies, the quartz is stained
brown with limonite, and yellow powdery molybdite is found coating the
molybdenite crystals and lying in seams in the quartz. The molybdite and
limonite ave evidently the results of the alteration by surface waters of
molybdenite and pyrite. The alteration was observed to extend to 4 feet
below the surface. Since the yellow oxide carries only 40 per cent of
molybdenum as against 60 per cent in the sulphide, there has been consider-
able impoverishment of the ore by weathering. Underground work is
necessary to prove whether this has given rise to secondary enrichment

below.
_5172—7

a

a i be te a a a

Yeates sts

SS RES ORS ICE ~ neo

Seer eon

OP rel wah Lele 0 ove rolD