Tonopah bonanza. [volume] (Butler City [i.e. Butler], Nev.) 1901-1909, 1904-06-25
SOME ORE
DISPOSITIONS
The Occurrence and Types
of Ore Deposits.
Valuable Mines Occur In Rocks of
Almost Every Description and
Geological Age.

ries of ore deposition are that of
replacement of the original rock
mass by ore, or in%fltration of mineral
into spaces of discision. This occurs
in vein-like zones, or in masses of
irregular form, where the country
rock has been subjected to crushing
and in some instances to shearing.
In the former case the ore deposit
will have no particular form, but ex-
list as a deposit of irregular size and
form, or there may be several de-
posits occurring along a common
direction, either vertically or hori-
zontally, or both, for a considerable
distance, and having an apparently
common origin or genesis. In such
deposits, there generally occur many
pieces Of unaltered or only slightly
altered country rock. In some in
stances the fragments of country
rock have a rounded appearance, due
to the alteration and disintegration
Of the outer portion Of the fragment.
Where there has been much sheariug
the deposit will probably have a
banded structure. These bands oc-
cur in zones which vary in width.
The zones are not confined for con
siderable distances between defined
walls. In n part OF the deposit
the vein may be considered a assure,
say four feet wide between well de-
fined walls. The ore is removed and
the vein has every appearance Of
being Identical throughout, but fifty
feet away it may be found that the
naturalization has extended beyond
the planes Of the walls" and the
assured zone is much wider. Zones
Of this kind are sometimes many feet
in width and croscutting is necessary
in the operation Of a mine of this
character. A third type is one in
which the mineral has replaced the
country rock without any consider.
able crushing or movement Of the
rock mass, although there Is gener-
ally present n or more assures.
Instances Of tins character are seen
where states have become silicifed
and constitute gold bearing veins.
Another type is found in the material
filling a ~pre-existing assure. These
are Of comparatively rare occurrence
and do not represent as d rule large
deposits or veins. Beside the above
there are many other types or mod
flied forms Of those mentioned, but it
may be safely asserted that it is
necessary 10 see the ore in place,
together with It's geological relations
to make it possible to classify the
type Of deposit or vein to which it
belongs. "A hand specimen rarely
conveys a safe indication of the type
Of deposit to which it belongs, even
by the use Of a magnifying glass.
The angle of capitalization is con
slant in mineral species, whether
formed from ascending thermal
waters or by "infltration, " or
otherwise, and this angle can rarely.
II ever, be correctly read or ascer-
tanned by employing a simple magni-
lying glass, particularly il the crys-
tails are imbedded in a mass OF ore.
Instruments called goniometers are
employed for this purpose. The
simplest kind are held in the hand,
and consist of a graduated semi circle
TO which is attached an adjustable
index, which marks the angle of any
crystal placed in the proper position
IN the instrument. A more accurate
instrument, known as the rejecting
goniometer, is also employed. The
best Instruments of this class have
two telescopes. The measurements
are made with great care and pre-.
clsion. 1t is not q fact that no mines
OF value occur in eruptive rocks, such
as diorite, diabasc, etc. The reverse
Is rather the case. Most important
mines are directly associated with
eruptive rocks, but ores occur in
rocks of almost every description.
Valuable mineral veins occur in rocks
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