Mine - Mining of Minerals
sometimes ask where we get our rock and do we truck it
in from somewhere. I
point to the mine shaft and tell them, “right over
there!” They are usually surprised that it is being
mined on site. Another
question asked is, “How do you mine it? Do you go down
there and dig it out?”
Morefield mine is an underground hard rock operation.
The pegmatite lays like a near vertical vein but
in the case of pegmatite, a granite intrusive with no
ore metals like lead, copper, zinc, gold or silver, it
is called a dike. Igneous
sheet-like intrusions are called dikes if steeply
inclined or called sills if the dip is low to flat.
The Morefield dike dips at about 80 degrees to
the northwest and varies from 6 feet to 15 feet in the
areas that have been mined.
To the southwest toward
Butler’s Road, it thickens to as much as 30 feet wide and
little is known about the dike below the immediate
surface and nothing is known about the pegmatite at
greater depths. The
U.S. Bureau of Mines drilled through the pegmatite in
their deepest hole at 238 feet below the surface.
operation is a typical drill, blast, haul system but we
are mining in a most basic manner with the least
In 19 years of mining, we have had a very good
safety record with the exception of one serious accident
relating to falling.
Our safety record has been aided by using simple
is pretty hard to hurt ones self with a shovel! It is
hard to believe but we have moved almost 1926 tons with
is roughly equal to 100 dump truck loads!
is done with a Gardner Denver S58 airleg drill sometimes
called a ’jackleg’.
Holes are drilled 6 feet deep in the face of a
tunnel-like opening and vary from 1-3/8” to 1-1/2”
for blastholes and 2” for holes creating a ‘free
face’ to which other holes can break. (The
‘tunnel-like opening’ is really called a ‘drift’
in our case. In
mining terminology, tunnels pass through hills; adits
pass into hills; drifts follow veins; and crosscuts
cross geologic structure or serve as access drifts.)
Our drifts are about 8 feet high by 6 feet wide;
we drill up to 35 holes six feet deep and use 1-3/4
cases of explosive, 42# each per 5 feet of advance.
We use both stick powder and ANFO prills what are
blown into the holes with compressed air.
The photo shows a miner drilling the initial
holes for a “burn cut” in a new face.
The object is to shoot loaded holes around 3-5
larger empty holes to collapse them and create a
cylindrical hole which becomes the free face toward
which all other holes break.
loading of holes is done by hand.
Holes in the burn cut must be loaded fully.
Once we get an area opened with successive
drilling and blasting, we can drill wider spaced holes
and load them lightly to try and break the rock in
larger pieces good for the collecting areas. Some
holes may be shot together with the same delay and other
rows may be shot with successive delays giving time in
milliseconds for the broken rock from the first holes to
clear before additional holes detonate.
In the photograph, detonating cord can be seen
connecting holes. The
detonating cord is initiated with a single electric
employees leave the mine and are accounted for before
blasting and allowing time for smoke to clear, the
workplace is inspected and then it is washed down with a
hose and then the heading is scaled or ‘barred down’
to remove loose rock from the roof (back) and walls
an unfortunate matter that blasting creates fines or
sand and knowing how much explosive to use requires
judging ever-changing conditions.
We start the burn cut in simple pegmatite off to
one side of the pegmatite core and amazonite zone.
Everything in the burn cut is pulverized. We then
work our way over into the rare mineral, mica, and
amazonite zone shooting as lightly as we can.
It is during this part of the mining that we may
drill into a cavity, a vug or “pocket”, hopefully
with crystals. When
we hit a cavity, the drill lurches forward which is a
telltale sign and yellow to red mud colors the drill
is the gem miner’s dream; big pockets with lots of
following photographs show opening two vugs on the 60
foot level northeast and southwest.
removal of rock broken by blasting is called
“mucking” Almost all of the rock mined from 1985
until summer 2001 was done with a shovel and
18 inch gauge mine rail was installed so the shaft
bucket could be lowered onto a flat car then pushed back
to the face and the freshly broken rock.
This eliminated the wheelbarrow.
most recent improvement in mucking is the installation
of an air-powered two drum slusher that pulls a large
scraper blade back and forth.
It rides up over the muck pile and then drags
rock to a drop point. At the drop point, rock
accumulates until it is drawn through a chute on the
next level and directly into the shaft bucket.
This method is being used in the sill removal
project between the 45 foot and 60 foot levels.
all cases, the bucket is pushed or trammed to the shaft,
the hoist cable is attached, hoist signals are given and
the bucket is pulled to the surface.
At the surface, the bucket is stopped mid air,
the gin pole boom is swung to the dump point and the
load of fresh pegmatite is dumped onto the stockpile.
Removal Project-45 Foot Level Northeast
sill removal between the 45 foot northeast and the 60
foot level northeast is an interesting project.
This is an area of high grade amazonite,
zinnwaldite mica, topaz, and rare minerals.
It is approximately 7 feet thick.
There are two possible outcomes.
The first would be to back fill the volume of the
removed sill with concrete.
This would allow track to be re-install track and
re-establish the 45 foot level for access.
Then the 60 foot level drift would be advanced
under the new concrete sill and normal mining continued.
This method if mining is called underhand
second method would be to leave the removed sill and the
lower 60 foot level as an open stope.
A timber floor would be installed on the 45 foot
level and the hanging wall of the dike bolted with resin
and fiberglass rockbolts for ground support.
It would be possible then to see the
amazonite/complex pegmatite from the roof of the 45 foot
level to the floor of the 60 foot level, a height of 23
two methods are shown in the cross section.
Bottom Rehabilitation and Examination
of the 100 Foot Level
work is also taking place during the fall of 2015 to
examine and explore the 100 foot level.
This level of the mine has not been completely
dewatered or explored since it was abandoned by the U.S.
Bureau of Mines in 1949.
Water for the sluice boxes or flumes has come
from this level since mining began again in 1985. Over
the years of abandonment, rock and earth around the
surface collar of the shaft has fallen in and the bottom
of the shaft has been filled with as much as 20 feet of
debris. This debris will have to be removed to below the
floor of the 100 foot level.
The shaft was originally sunk to a depth 115
will be installed dewater the 100 foot level and to keep
it dewatered. Approximately
8500 gallons of ground water enter the mine over a 24
hour day. All
of the work in the shaft is wet and water from upper
levels rains down the shaft. A sump pump will pump water
from the floor into a 200 gallon holding tank where a
booster bump will pump the water the 100 feet to the
walls of the 100 foot level and the shaft walls have
been coated with a layer of brown iron oxide deposited
by an iron bacteria making it impossible to see the
minerals without making a fresh exposure. This is a
bacterium that seems to derive its energy from
converting ferrous iron to the ferric state.
the level is dewatered and 3 feet of mud is removed near
the shaft, the level can be entered and inspected
firstly for safety, loose rock, and the toe of the rock
pile that now partially fills the Bureau of Mines stope.
Safety is paramount; the shaft at 100 feet down
is like being in a gun barrel and any falling object
becomes a projectile.