Mineral
Geology of Mitkoff Inland.
. . . . By H. F. ERWIN . . . . •
There, is. a. metamorphich
romplex belt which lies near the
coast range batholith and con
sists of injections of gneiss,
crystalline schist, marble, phyl
lite and schistose green s’
This belt extends the full length
of Mitkof Island in a Northwest
and Southeast direction. This
formation is evidently of Meso
r/ic age.
From Point Frederick in a
southerly direction to Ideal
Cove is an intrusion of Crystal
line scist in many places 60 feet
vide. There is very little indi
cation of any mineral showing
in this area.
Between Dry Stream ana
Blind Slough, extending some
distance northwest up the high
er elevations there are intru
sions of greenstone, graywhack
and slate; the formation being
well mineralized. Pannings from
many of the creeks in this local
ity reveal colors in minute form,
gold, Agentite, (silver) copper
pyrites and Iron pyrites. There
are many other kinds of miner
als which can bo determined on
ly by a laboratory test. There
are some indication of Barite
on the higher elevations. Bar
ite generally occurs as replace
ment deposits in limestone beds.
The formation of this local
ity would be a likely place for
the prospector to look over care
fully.
Kupreanof Island
A description of the formation
of this island and its minerals
vs fully described by Theodore
Chapin in his report on the
Geolcgy and Minerology 1929
Bulletin No. 800, which is here
with quoted in part:
“The Middle Devonian rocks
contain altered volcanic flows
fxnd tuffs, black slate, gray
whack, and conglomerate, all of
which carry mineral deposits of
value. The altered volcanic
flows and breccias, which com
prise the lowest members of the
series, contain shear-zones de
posits and appear to be favor
able locality to prospect '->*> liv ^
type of ore depo it.
“The overlying rnc;noer> of
the Middle Devonian appeal ‘.o
be the most highly mineralized
rocks of the Ketchikan region
and contain deposits of various
types. The contact and sheav
zone deposits of Kasaan Penin
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p
p
sula, Karta Bay, and many oth
er localities occur within this
formation. The black slates
and associated tuffaceous sed' -
ments are favorable for the de
position of gold-bearing quart/
lissure veins. In the vicinity cf
Hollis on Twelvemile Arm, vein ;
of this type are prevalent. The
sediments are cut by a larg'
boss of quartz diorite and by as
sociated porphyry dikes and
veined with many quartz fissure
veines which in places have
bordered or cut the porphyry
dikes mineralizing and replac
ing them. This area has yielded
consideiable ore from several
small mines and offers possib
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