The Virginia enterprise. [volume] (Virginia, St. Louis County, Minn.) 1893-19??, 1904-01-22

ABOUT ~ per cent OF the area of the
formation has been proven to he
underlaid with ore.e The Mesaba
ore lies in shallow troughs under
n'antel of gravel from a very
little thickness to that of 100 feet.
Sometimes the ore is overlaid with
a layer of rock called taconite,
which layer is occasionally over 100
feet thick. The ore bodies them
selves are from 80 to 200 feet thick
and of considerable horizontal
dimensions, sometimes more than
40 acres.
The earlier practice on the Mes
aba was to explore by test pits,
shallow shafts sunk to the ore or the
taconite, but recently nearly all of
the exploration has been done by
diamond or churn drills. The
churn drill is feature of the Mes
aba range. It is modification of
the familiar we'll drill, an improved
form of which is used in dilling for
oil. 1t consists of chisel drill on
an extensible hollow rod. This rod
is attached by flexible coupling,
which forces stream of water into
the hole and out of perforations
near the attachment to the bit.
This water returns inside the cas-
ing, which is n ordinary gas pipe,
three inches in diameter when in
surface material and two inches in
rock and ore. The drill is manipu-
lated by rope passing several
times over drum driven by a six
or eight horsepower oscillating en-
CINE, and the Jerk" is given by a
man Tightening or stacking the
rope coil. The drill is rotated by
hand, the driller standing on a plat.
form built in the tripod. When
boulders are encountered they are
blasted out with dynamite. This
dynamite is suspended in the hole
and fired by electricity. The cas-
ing is then forced down through
the loosened rock by drive weight,
also operated by the engine, and the
drilling proceeds. The cuttings
from the drill bit are forced up the
casing by the flow of water, and by
examining these the driller deter
mines the character of the rock be-
ing drilled, or the quality of the ore,
if working in ore. A churn drill is
used for the gravel and for broken
rock, as we'll as tor the ore which is
soft and pliable. Three men are
employed on each drill and from
ten to 20 feet day are drilled. The
diamond drill, which has long been
used for exploratory work in other
mining regions, is used here when
hard rock is encountered. The Mes
aba drill is lighter type adapted
to the com paratively shallow work.
A diamond drill consists of a "bit"
| set with black diamonds, or bort,
called on ranges "carbons," and at
tached to hollow rod, which is
rotated under pressure by steam
engine attachment. A stream of
water is forced into the hollow rods.
as with the Churn drill, and this
brings up the cuttings on the out
side of the drill rod and inside the
casing, which is left in the churn
drill hole through the softer mater.
ial. The hollow bit is set with car
bons so as to leave core 1916 OF an
inch in diameter. The size of the
diamond drill hole is / GIG. This
core is taken up from time to time
by core litter, and examined to
ascertain the character of the form
alton being drilled. A diamond
drill will average five feet daily in
fairly hard formation.
"Carbons" cost $45 to $50 karat.
The price now is $50. From IL to 16
karats are used on a bit. Cartoons
vary greatly in durability. They
are usually bought on the judg-
ment Of the operator, a dense and
close grained stone being preferred.
An ordinary bit, then, is worth from
$500 to $500. The carbons are set in
steel ring, and are daily reset, so
as to keep the cutting surface true
and flush. The wear on them is
hardly Perceptible, so that, al
though carbons are occasionally
broken or lost, with proper care a
set of them will last year or more
for continuous work.
The practice on the Nesaba is u.s.
ua1ly to test 40 acre tract by drill
ing tive or Ii holes, arranged in
geo'netrical pattern, so that the size
and shape of the ore body can be
figured out from the results obtain
ed by the drills. When an iron
body has been located it is then
drilled every 100 feet both ways
and carefully sampled at regular