Daily inter mountain. [volume] (Butte, Mont.) 1881-1901, 1900-06-19
MINE HORSES
AND BRECC|A

Written for the Mining and Scientific
Press by j. P. Wallace: Large isolated
masses Of country rock, when enclosed
in a vein m wholly or partly surround
ed by ore, are called horses. Horses re-
suit in many cases from an irregular
%fracturing of the country along the line
OF assuring, whereby large angular
masses are torn from either wall. The
walls in many assures are often very ir-
regular and cracked Mineralized solu
tions at a later period find their way
into these cracks and enlarge them by
dissolving out certain rock constituents,
and in their stead depositing metallic
and earthly minerals called ores. AS a
result of this process of replacement, the
barren rock mass is completely de-
tached from it's resting place, is included
within the vein and becomes a horse.
Sometimes instead of a single assure
there are two nearly parallel assures
formed within a few feet or yards OF
each other, and these continue for vary
ing distances and then come together to
form but one crevice; a large sheet or
slab of country rock is thus enclosed by
h assures, and, when the latter are
subsequently filled with ore, the slab be-
comes in mining parlance a horse. IN
other cases the assure is split up for a
short distance into several arms, ana
these surround different horses OF
ground. The presence OF horses IN a
vein may occasionally be accounted for
by loose boulders rolling into a assure
from the surface; but such occurrences
are probably rare, because the great ma
jority of vein creNiceS were rlglnally
narrow cracks, and not gaping assures.
Veins which LAY been much faulted
commonly enclose horses. Horses are
often met with at the junction OF SO.
W. pS'
with a true vein, the country at such in
tersections being usually much broken.
Horses Of country rock are not conhned
to fissure veins; they occur in gasn
veins, bedded veins and contact deposits.
Ore deposits in limestone furnish many
examples of horses surrounded by ore.
Horses differ much in size and shape;
thew NAV be several hundred or only a
few feet in length and of almost any
shape; the width may be sufficient to al
most block up the vein, or 1t may spilt
the vein into two or more branches, the
latter surrounding the barren block and
again uniting beyond it. Several horses
but little removed from each other also
produce irregularities in the ore body.
A single horse is sometimes divided by
numerous ore seams, which traverse II
in many directions, and not
the whole body is transformed into a
mass of ore.
The fact tina a vein is horse-rldden
does not initiate against ITS true lssule
character nor it's Ore-bearlng quailtieS,
hut the presence of horses often adds to
the expense of development n occa-
sions great inconvenience. Many sucn
veins are excellent ore producers, anu
although often lacking the old orthodox
requirements of a true assure, nalhely,
we'll defined, smooth, corrugated anu
s,ickensided cheeks, they are neVertne-
less true veins.
Rraccia in veins is a cemented mass VI
numerous. small. angular rock mag
nenlts. Horses and breccia are 10 De us.
tin gllished: a horse is a single large oouy
and breccia is an aggregation Oh many
small fragments. Either may occur IN
vein without the other or poth may We
associated in the same vein. Breccla oc-
~ Mostly in veins bounded by hard,
brittle rocks which have been subjected
tn violent shocks or explosive FORCES
Fissures resulting from such FORCES gen,
erally have shattered and Imperfect
wa lis. with much loose material pel"eel
them. Subsequent movement on one
wall against the other crush THIS mate
rial into innumerable pieces, ana uhese
are gathered into expanded portions o.
tine vein, commonly known as moot
which extend downwards at varying an
giles to different depths. Although ven
ibreccia may occur Independent OF as
placements, it's presence is generally III
dicative of movement; but the amour
of brecciation is not always IN proper
ton to the amount of movement. Whel
the are loosely adherent. nav
ing many open spaces between thefn
annie room is afforded for the entranc
of hot mineral-bearing waters. ines
slowly percolate through the mass, anu
by an interchange of elements betWee1
the waters and rock fragments, the lat
ter becomes more or less minerallZed an
the open spaces filled with quartz an
metallic minerals. All brecciasa are not or
bealing: when made up of unusuall,
small pieces of ground-up material. tn
mass packs very closely n chokes tn
openings, so that no passages are lei
for the mineralized waters. Such place
in a vein are consequently barren OF Ore
The same vein may yield in one shoe
barren. and in another shoe productlV
breccias. While other brecciated vein
may be wholly unmineraliZed. AS a ruiz
brecciation is conductive to ore depos1
ton. Veins of this character are of FIRE
uuent occurrence. and are general
looked upon with favor. Veins Whic
have once been filled, but not with brec
cha. are at a later period OCCASIONAL
rent asunder and their contents reduce
by fault movements to a breccfated cor
dition. Breccia thus formed may be sim
ple or complex, that is, made from a sir
gle gangue stone, such as quartz, or ne
and different material furnished by tn
last movement may be mingled with thu
already present.
Brecciated ore deposits occur SOM,
times in the form of isolated chimneys
upright zones of crushed country roc
Brecciation is made possible in sue
cases by the occurrence of a network
short, crossfraeture lines, limited
diameter anywhere from 10 to so or 1
feet, but extending vertically to consi
cradle depth. Gouge matter and stri'
tons are present in some instances. al
these suggest prior movements with
tho maSc Gaoara1lv ore zonaS of th