Gilpin observer., 1900-05-17
STAMP MILL METHODS.
Comparison of Systems In Use In Colorado
and California.

There is constant comparison and
discussion of what for convenience
may be termed distinctively California
and Colorado stamp mill practice-in
the former state the heavy quick-drop
stamp and shallow mortar; in the lat
ter the light slow-drop stamp and deep
mortar with high issue. The Gilpin
county slow-drop mill, n 500-pound
stamp, dropping sixteen inches thirty
times n minute, with deep mortar, an
amalgamator as well ms a crusher. is
typical of Colorado practice: the quick
drop 11O0-pound stamp dropping six
inches 100 times n minute, a coarse
crusher, is typical of California prac-
tice. But as the Gilpin county bump
er now divides the work in many n
Colorado mill with other vanners or
concentrating tables. so the slow-drop
stamp now has considerable company
of rapid drop.
The question is not one of eXped
iency nor policy. but of results: wheth-
er it be Clear Creek or Gilpin county,
Colorado. or Nevada or Tuolumne
county. California. the mllman aims
to constantly suit the ore. and 1t is TO
be recognized that the gold ores of
the two sections differ greatly. The
ores of California, until considerable
depth is reached, are mainly quartz
and schists containing free gold; this
the heavy stamp cracks rather than
crushes. The surface ores of Colorado
are not entirely dissimilar, but the on
idized part of the Colorado vein eX-
tends downward Il comparatively
short way-often less than 100 feet
while the oXidizcd area of the Cali
fornia vein is often found extending
al IL Il 4.
sulphide ores of Colorado are deemed
by millmen to need fine crushing and
introduction of amalgamated plates
inside of the mortar for successful ex-
traction of gold by amalgamation.
though this fine crushing entails II
greater amount of shines, which fire.
quently carry off so much gold.
The California ore. which rarely
carries more than four per cent. sui
phurptS, admits of Il coarSer crushing.
and consequent less dependence on
amalgamation in the mortar. The
tendency in California is toward in
creased stamp duty. now. reaching IL
maximum of 5.5 tons per stamp per
twentyfOur hours. The present Col
orado tendency is toward an increase
rather than decrease in the number
of heavy rapid-drOp stamps. IL is
noticeable that whenever an old mill
is torn out at Black Hawk or else
where, and II new mill put in, the new
battery Is of considerably greater
weight than the old.
With intent of amnlgamation. some
of the mills in Gilpin and Clear Creek
counties. Colorado. have two plates in
side the mortar-onc back plate and
| one front plate-put just below the
discharge screen. The inside plates are
generally arranged so that their upper
edges are level with the pulp in the
mortars, from one and one-half to two
inches above the surface of the dies
with the mortar the rear plate is
usually twelve inches and the front
plate six inches wide. The outside
plates are the same width as the NOR
tar-four feet seven inches: they vary
in length from six to sixteen feet.
In California practice the rear
plate is nine to ten inches wide of the
same length as the mortar; the front
plate is four and one-half inches wide
and of the same length as the mortar
This plate is inclined from 10 to 10
degrees; the rear plate inclined about
40 degrees, depending on the shape of
the mortar. An apron plate two or
three feet wide Is interposcd between
there being drop of two or three
inches from the apron plate 20 the
table plate. The plates are fastened
TO solid wooden tables with raised
sides. about six inches high. In Cal
ifornla the table plates have an in
clination of one ana one half or two
inches per foot, the apron plates an
average inclination OF one and one
half inches. In Colorado, where, as
noted the ores are more heavily sui
phuretted these have an inclination of
of from two to two and one-half
inches per foot. II is this difference in
sulphides that occasion the differences
noted above In stamp mill practice
throughout. ns herewith detailed. in
the two states.
Colorado millmnD. working con
tinuously In one locality and never
travelling around. would he as much
surprised nj some things In California
mn practice as n California millman
similarly circumstanced were he to
spend half an hour In some Colorado
stamp mills.
only he said. as in everything else con
ncctcd with the treatment of ore. tbnt.
from n commercial standpoint. that X
the best process that pays The best.
VI course, taking even this criterion,
there Is manifest room for improve
mcni The two types discussed in this
article ar" considered distInctivcly
superior to some that might he cited.
not for invidlous or dIspnraglns com
pnrson, bul by way of illustration. ny
some Australian mill characteristics.
crude design for mortar, the cam
shafts not driven direct by betting, but
run by tooth gearing, fifteen or twenty
stamps actunicd by II single cam shaft
80 genred. the tnppcts fixed and ad-
Justcd by scrcw-thrcads cut on the
stem, eighty drops per minute consid-
cred rapid work. chilled iron shoes and
dies instead of steel. and other char