Idaho semi-weekly world. [volume] (Idaho City, Idaho Territory) 1875-1908, 1879-08-15

acteristic mines along its course through
the gold belt. Nearly all the best mines
on the great central zone are either in con-
tact with, or near, great dikcs Of The erup-
tive rocks, such as greensboro, diorite, sy-
enite and porphsry. In most places the
bikes are 4 rliort distance east of the lodes,
or in contact with them, forming The hang
ing walls. The Josephine and Pine Tree
mines on the Mariposa estate, various
places III Tuolumne and Calcveras coun-
lies, Haywards and the Keystone or Spring
Hill mines In Amador county, and other
important mines in I'll Dorado and Placer
counties. are good examples. Grass val
ley, in Nevada county is IN important ex-
ample. Here a great syenitic dixie, or
zone. nf great width, extends north and
south several miles. conformab'e in strike
and dip with the states. In the central
portion of tlris syelitic zone, the Alison
Ranch mine was found, which has pro
duced several millions Of dollars. But
the most remarkable feature of this inter
esting locality Is the metamorphisnl OF the
slate on each side Of the syenitlc dixie, and
the character Of the lodes thai extend east
erly and weste ly from its TANKS. he
states are greatly altered on each side for
Il distance OF half mile or more; then
the meiamorphism rapidly fades out, and
the states become soft and normal In Char
acter. The thanking veins east of the sye-
mite, such as the Empire Hill, Eureka and
Idaho, have an easerly course across the
states. and anortherly dip. They not only
cease 10 be gold bearing, but disappear al
together after crossing the metamorphic
zone. On the west side OF The dixie, the
North Star, Massachusetts Hill, and Gold
Hill lodes trend westerly and dip north,
and disappear in about 1000 feet west of
the dixie. where the unaltercd states are
reached. Continuing north through Yuba
and Butte counties, nearly all The strue
lodesn are similarly associated with erup-
tive tlikes All Of these carry their rich
est ores in chimneys more or less marked,
and all these show "striae" on their walls
coincident in direction with the general
pitch. or downward trend OF the chimncys
The same rule applies to the mines in
the froi-hill zone, and also to the eastern,
or higher mountain zone, extending
through the entire gold-bclt Of the State.
respectfully recommend to geologists
and mining engineers generally the CLOSE
OBSERVATION AND STUDY or THE FACTS IN
THEIR RELATION TO oRE-DEPosITs, that
are embodied in this paper. After doing
SO, If they do not find a great many things
toned in the textbooks, | shall be very
much disappointed, What have stated
| in regard to the mines of California holds
good. in most part, to all mining districts
In the United States. The great mines
everywhere are intimately associated with
the eruptive rocks, in most cases cluster
lug in and around centeis of local pluton-
ic disturbance, and having only a remote
relation to continental uplifts, and de-
preston due to gravity" Many of the
great mines are in geological faults"
The great Comstoek lode in most part has
syenite on one side, and porphyry on the
other The Horn silver mine in Utah
probably the most reinark able deposit of
silvcr-lead ore in the worlds in Il great
geological FAULT" having limestone and
quarizitc one side, and trachytic porphyry
on the other. The limestone and quartz
lite beds are not conformable with the dip
of the lode, the faultcd edges only being
in contact with the ore. The trachytic
porphyry belt that forms the other wall of
the lode is very wide and extends OBJ
lquelY through he mountain range, COW
erina an area of many square miles. The
largest and best mines in l. tile Cotton
wood district are near The TANKS of erup
tive granite. The faulting of the quarlzite
and limestone is due, in most part, to sud
den movements caused by volcanic distur-
Dances. The slow downward movements,
"tlue to gravity" are evident only in places
on the steep sides of the great central dome
Of rlutonic rock.
The question may be asked, how know
this to be eruptive granite? My answer
is First, Near the contact of the granite
with the limestone along the upper end of
grizzly gulch, and other points in the dis
trict numerous fragments of quartZite
and schist are found Embedded in the gran
lite, Of all sizes, from mere pebbles to an
guar blocks several feet in diameter And
these same fragments ale part of the un
deriving beds that belong many hundreds
of feet below the adjacent limestone.
Second The granite is also interlocked
with the nearly horizontal beds of lime
stone and schist BY wedge-like tongues
forced in between the beds, and into riffs
and assures along the line of contact.
The limestone at many points of contact
with the granite, has been changed into
garnetiierous masses; epidote, and other
pyrogenitic minerals are abundant. From
these facts | infer that the granite was
forced up through great geological
fault" in the [ rm of hot pasty mass
that enveloped the fragments torn from
the walls of the tissure; and that the heat
acting upon the waters, that saturated The
broken beds to unknown depth, gave rise
To chemical activities of great and long
continued force. Thus driving hot gases