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HITTEL
ON
GOLD MINES
AND
MINING.
QUEBEC:
PRINTED BY G. & G. E. DESBARATS.
1864.
HITTEL
ON
GOLD MINES
AND
MINING.
_Chief Industry._--Mining is the chief industry of California. It
employs more men and pays larger average wages than any other branch of
physical labor. Although it has been gradually decreasing in the amount
of its production, in the profits to the individuals engaged in it, and
in its relative importance in the business of the state, it is yet and
will long continue to be the largest source of our wealth, and the
basis to support the other kinds of occupation.
_Metals obtained._--Our mines now wrought are of gold, silver,
quicksilver, copper and coal. Ores of tin, lead, and antimony in large
veins, beds of sulphur, alum and asphaltum; lakes of borax and springs
of sulphate of magnesia, are also found in the state, but they are not
wrought at the present time, though they will probably all become
valuable in a few years. Platinum, iridium, and osmium are obtained
with the gold in some of the placer mines, but are never found alone,
nor are they ever the main object sought by the miner. The annual yield
of our gold mines is about forty millions of dollars, of our quicksilver
two millions of dollars. Our silver, copper and coal mines have been
opened within a year, and their value is yet unknown. All our other
mining is of little importance as compared with the gold.
_Gold Mines._--Our gold mines are divided into placer and quartz. In
the former, the metal is found imbedded in layers of earthy matter,
such as clay, sand and gravel; in the latter it is incased in veins of
rock. The methods of mining must be adapted to the size of the
particles of gold, and the nature of the material in which they are
found. In placer mining, the earthy matter containing the gold, called
the "pay-dirt," is washed in water, which dissolves the clay and
carries it off in solution, and the current sweeps away the sand,
gravel and stones, while the gold, by reason of the higher specific
gravity, remains in the channel or is caught with quicksilver. In
quartz mining the auriferous rock is ground to a very fine powder, the
gold in which is caught in quicksilver, or on the rough surface of a
blanket, over which the fine material is borne by a stream of water.
About two-thirds of our gold is obtained from the placers, and
one-third from the quartz.
A mine is defined and generally understood to mean "a subterraneous
work or excavation for obtaining metals, metallic ores or mineral
substances;" but this definition does not apply to our placer mines,
which are places where gold is taken from diluvial or alluvial
deposits. Most of the work is not subterraneous; it is done in the full
light of day. In some of the claims the pay-dirt lies within two feet
of the surface; in others it lies much deeper, but all the
superincumbent matter is swept away.
Water is the great agent of the placer miner; it is the element of his
power; its amount is the measure of his work, and its cost is the
measure of his profit. With an abundance of water he can wash every
thing; without water he can do little or nothing. Placer mining is
almost entirely mechanical, and of such a kind that no accuracy of
workmanship or scientific or literary education is necessary to mastery
in it. Amalgamation is a chemical process it is true, but it is so
simple that after a few days' experience, the rudest laborer will
manage it as well as the most thorough chemist.
It is impossible to ascertain the amount of gold which has been taken
from the mines of California. Records have been kept of the sums
manifested at the San Francisco Custom House, for exportation, and
deposited for coinage in the mints of the United States; and there is
also some knowledge of the amounts sent in bars and dust to England;
but we have no account of the sums carried by passengers to foreign
countries and coined elsewhere than at London, or used as jewelry, or
of the amount now in circulation in this state. According to the books
of the Custom House of San Francisco, the sums manifested for export
were as follows:
In 1849, $4,921,250; in 1850, $27,676,346; in 1851, $42,582,695; in
1852, $46,586,134; in 1853, $57,331,034; in 1854, $51,328,653; in 1855,
$45,182,631; in 1856, $48,887,543; in 1857, $48,976,697; in 1858,
$47,548,025; in 1859, $47,640,462; in 1860, $42,303,345; in 1861,
$40,639,089; a total of $551,603,904 in twelve years.
The exportation of gold commenced in 1848, but we have no record of the
sums sent away in that year. Previous to 1854 very large sums were
carried away by passengers, who gave no statement at the Custom House;
since that year, the manifests show the exportation correctly within a
few millions. I am entirely satisfied that the total gold yield of
California has been not less than seven hundred millions of dollars;
but I have not room here to state the reasons for this opinion. My
estimate is considerably less than that of most business men of the
state, and less than that made by Hunt's _Merchants' Magazine_. There
was undoubtedly a regular increase in the annual yield of the mines
from 1848 to the end of 1853; and there has been a gradual decrease
since the beginning of 1854--a decrease perhaps not very regular but
still certain. Since 1854 considerable sums exported from San
Francisco, and included in our tables, came from mines beyond the
limits of California, such as the mines in Southern Oregon, in the
eastern part of Washington Territory, in British Columbia, and in
Nevada Territory; and while the California gold yield has been
decreasing, these extraneous supplies have been increasing. Several
millions must be deducted from the annual shipments since 1858, for
foreign gold. The gold yield will undoubtedly continue to fall, but to
what point and at what rate no one can know. I believe that in 1870,
the yield will not exceed thirty millions of dollars.
_Placer Mines._--Placer mines are divided into many classifications.
The first and most important is into deep and shallow. In the former
the pay-dirt is found deep, twenty feet or more beneath the surface; in
the latter, near the surface. The shallow or surface diggings are
chiefly found in the beds of ravines and gullies, in the bars of
rivers, and in shallow flats; the deep diggings are in hills and deep
flats. The pay-dirt is usually covered by layers of barren dirt, which
is sometimes washed, and sometimes left undisturbed, while the pay-dirt
is taken out from beneath it through tunnels or shafts. So far as our
present information goes, we have reason to believe that no gold
country ever possessed so large an extent of paying placer mines, with
the pay-dirt so near the surface, and with so many facilities for
working them as California. In Australia the diggings are very deep and
spotted, that is, the gold is unevenly distributed, and the supply of
water for mining is scanty. In Siberia the winter is terribly cold
during six months of the year. In Brazil the diggings were not so
extensive nor so rich as in this state. Here we have numerous large
streams coming down through the mining districts, very large bodies of
pay-dirt, and a mild climate.
After dividing placers into deep and shallow, the next classification
will be according to their topographical position, as into hill, flat,
bench, bar, river-bed, ancient river-bed, and gulch mines. Hill
diggings are those where the pay-dirt is in or under a hill. Flat
diggings are in a flat. Bench diggings are in a "bench" or narrow table
on the side of a hill above a river. Benches of this kind are not
uncommon in California, and they often indicate the place where the
stream ran in some very remote age. Bars are low collections of sand
and gravel at the side of a river and above its surface at low water.
River-bed claims are those beneath the surface of the river at low
water, and access is obtained to them only by removing the water from
the bed by flumes or ditches. Ancient river-bed claims are those of
which the gold was deposited by streams in places where no streams now
exist. Gulch claims are those in gullies which have no water, save
during a small part of the year. A "claim" is the mining land owned or
held by one man or a company.
The placer mines are again classified according to the manner in which,
or the instruments with which they are wrought. There are sluice
claims, hydraulic claims, tunnel claims, dry washing, dry digging, and
knife claims. In 1849 and 1850, the main classification of the placers
was into wet diggings and dry diggings, the former meaning mines in the
bars and beds of rivers, and dry diggings were those in gullies and
flats where water could be obtained only part of the year or not at
all. That classification was made while nearly all the mining was done
near the surface, before the great deposits of pay-dirt in the hills
had been discovered, and before ditches, sluices, and the hydraulic
process had been introduced. The class of mines then known as the "dry
diggings," and which for several years furnished nearly half of the
gold yield of the state, are now, with a few unimportant exceptions,
exhausted, or left to the attention of the Chinamen.
The purpose of all placer miners is not to catch all the gold in the
dirt which they wash, but to catch the greatest possible quantity
within a given time. It is not supposed that any process used in gold
mining catches all the metal. Part of it is lost; in some processes a
considerable proportion. The general estimate in California is, that
one-twentieth of the gold in the dirt which is washed is lost. Many of
the particles are so very small as to be invisible to the naked eye,
and so light that their specific gravity does not avail to prevent them
from being carried away by the water like sand. The larger pieces will
sink to the bottom and resist the force of the water; the smaller the
particles, the greater the danger that it will be borne away. Many
devices have been tried to catch all the gold, but none have succeeded
perfectly, and some which have caught a portion of what escaped from
the ordinary modes of mining, have been found to cost more than their
yield. The miner does not grieve about that which he cannot catch. He
is not careful to catch all that he could. His purpose is to draw the
largest possible revenue per day from his claim. He does not intend to
spend many years in mining, or if he does, he has become thriftless and
improvident. In either case, he wishes to derive the utmost immediate
profit from his mine. If his claim contain a dollar to the ton, and he
can save five dollars by slowly washing only six tons in a day, while
he might make ten dollars by rapidly washing fifteen tons in a day, he
will prefer the latter result, though he will loose twice as much of
the precious metal by the fast as by the slow mode of working. The
object of the miner is the practical dispatch of work, and his success
will depend to a great extent upon the amount of dirt which he can wash
within a given space of time. He regrets that any of the gold should be
wasted, but his regret is because it escapes from his sluice and his
pocket, rather than because it is lost to industry and commerce.
_The Sluice._--The board-sluice is a long wooden trough, through which
a constant stream of water runs, and into which the auriferous dirt is
thrown. The water carries away the clay, sand, gravel and stones, and
leaves the gold in the bottom of the sluice, where it is caught by its
gravity and by quicksilver. The board-sluice is the great washing
machine, and the most important instrument used in the placer mining of
California. It washes nearly all the dirt and catches nearly all the
placer gold of the country. It was invented here, although it had
previously been used elsewhere; it has been more extensively employed
here than in any other country, and it can be used here to more
advantage than elsewhere. It is not less than fifty feet long, nor less
than a foot wide, made of boards. The width is usually sixteen or
eighteen inches; and never exceeds five feet. The length is ordinarily
several hundred and sometimes several thousand feet. It is made in
sections or "boxes" twelve or fourteen feet long. The boards are an
inch and a half thick, and are sawn for that special purpose, the
bottom boards being four inches wider at one end than the other. The
narrow end of one box therefore fits in the wide end of another, and in
that way the sluice is put together, a long succession of boxes, the
lower end of each resting in the upper end of another, and not fastened
together otherwise. These boxes stand upon trestles, with a descent
varying from eight to eighteen inches in twelve feet. It is therefore
an easy matter to put up or take down a sluice after the boxes are
made, and it is not uncommon for the miners to haul their boxes from
one claim to another. The descent of a sluice is usually the same
throughout its length, and is called its "grade." If there be a fall of
eight inches in twelve feet, the sluice has an "eight-inch grade," and
if the fall be twice as great, it is a "sixteen-inch grade." The grade
depends upon the character of the pay-dirt, the length of the sluice,
and its position. The steeper the descent, the more rapidly the dirt is
dissolved, but the greater the danger also that the fine particles of
gold will be carried away by the water. The tougher the dirt, that is,
the greater its resistance to the dissolving power of the water, the
steeper, other things being equal, should be the sluice. A slow current
does not dissolve tough clay, and that is the greater part of the
pay-dirt, so rapidly as a swift one. The shorter the sluice, other
things being equal, the smaller the grade should be. There is more
danger that the fine particles of gold will be lost by a short sluice
than by a longer one, and to diminish this danger, the rapidity of the
current must be reduced by a small grade. The greater the amount of
dirt to be washed, other things being equal, the steeper should be the
grade; for a swift current will wash more dirt than a slow one. In many
claims the pay-dirt is full of large stones and boulders, weighing from
one hundred to five hundred pounds each, all of which must be carried
away through the sluice. Some are sent down whole, and others are
broken into pieces with sledge hammers before they are thrown into the
box. These require a swift current and a large body of water. The
larger the supply of water, the steeper the sluice is made, other
things being equal. Of course economy and convenience of working
require that the sluice should be near the level of the ground, and as
that may be steep or level below the claim, the grade of the sluice
must to some extent conform to it. There are thus a multitude of points
to be taken into consideration in fixing the grade of a sluice; but a
fall of less than eight or more than twenty inches, in a box of twelve
feet, would be considered as unsuitable for the board-sluice. Sometimes
the upper part of the sluice is made steeper so as to dissolve the
dirt, and the lower part has a small grade to catch the gold. The
clayey matter of ordinary pay-dirt is fully dissolved in a sluice two
hundred feet long with a low grade, so the use of the boxes beyond that
length is merely to catch the gold. There are claims however in which
the clay is so extremely tough that it will roll in large balls more
than a quarter of a mile through a steep sluice with a large head of
water, and come out at the lower end scarcely diminished in size.
The gold is caught in the sluice-boxes by false bottoms of various
kinds. It would not do to leave the smooth boards, for the water would
sweep all the gold away, and the boards themselves would soon be worn
through. The most common false bottom is the longitudinal riffle-bar,
which is from two to four inches thick, from three to seven inches
wide, and six feet long. Two sets of these riffle-bars go into each
sluice-box, the box being twice as long as the bar. A set of
riffle-bars is as many as fill one half of a box. They are wedged in,
from an inch to two inches apart; the wedging being used, because the
bars can more readily be fastened in their places, and more easily
taken up, than if nails were used. Before the work of sluicing
commences, all the boxes are fitted with riffle-bars, and the bottom of
the sluice is therefore full of holes from one to two inches wide, from
three to seven inches deep, and six feet long. These are the places in
which the gold, quicksilver, and amalgam are caught. Quicksilver is
used now in nearly all the sluices, and is the more necessary the
smaller the particles of gold. The large pieces of the metal would all
be caught by their specific gravity without the aid of amalgamation.
The sluice-boxes having been made, and set up with the proper grade,
the water is turned in. The boxes are made of the rough boards as they
come from the saw, and the joints are not waterproof, but the leaks are
soon stopped by the swelling of the wood, or by the dirt. The stream of
water in the sluice is at least two inches deep over the bottom. The
height of the sides of the boxes is from eight inches to two feet. The
sluice usually runs through the claim, and the auriferous dirt is
thrown in with shovels, of which from four to twenty are constantly at
work. A man will throw in from two to five cubic yards of dirt in one
day. The water rushing over the dirt as it lies in the box, rapidly
dissolves the clay and loam, and then sweeps the sand, gravel and
stones down. The first dirt in the box goes to fill the spaces between
the riffle-bars. After the sluicing has been in progress a couple of
hours, some quicksilver is put in at the head of the sluice, and it
gradually finds its way downward, most of it stopping, however, near
where it is put in.
_Amalgamation._--There are a few metals, including gold, silver, copper
and tin, which, with quicksilver, form a peculiar chemical union called
amalgamation, a process of great importance to the gold miner. When a
piece of gold or silver is placed in mercury, the latter metal
gradually penetrates through it, destroys the coherence of its
particles, and form with it a mass like dough. A lump of gold as large
as a bean will be soaked through in three or four days; with silver and
copper the process is slower, but they are affected in the same manner.
Amalgamation, though a union of a solid with a liquid, differs much
from a solution. In the latter the union is mechanical; in the former
it is chemical. In the latter the solid is reduced to particles of
impalpable fineness; in the former it is not. An ounce of salt will be
dissolved in, and nearly equally diffused through, a pint of water; but
if an ounce of gold be thrown into a pint of quicksilver, it will,
after forming an amalgam with the quicksilver, remain at the bottom. We
have no texture so fine that it will strain salt out of water; but the
particles of gold are so coarse in amalgam that they can easily be
strained out by means of buckskin or tight cloths. However, a little
gold will remain in the quicksilver--about the fiftieth part of an
ounce of gold in every pound of quicksilver; and the only method of
obtaining this gold is by retorting.
Quicksilver is used in gold mining for catching the small particles of
metal; the large ones are caught by their weight. But many of the
particles are so small that they are almost invisible to the naked eye,
and when in moving water they float. Miners frequently show visitors
the fineness of their gold by putting some of the dust in a vial with
water, and upon shaking, the particles of metal can be seen floating
about in the clear water. Riffles, and all the devices to get the
benefit of specific gravity, are of little use to arrest this
"float-gold," so amalgamation is employed. If a bit of quicksilver is
put in the way of the fine gold, the two metals unite at once and make
a larger bulk, which can be caught.
There is no such attraction between gold and quicksilver as there is
between the magnet and iron; but when the two former metals once touch,
an amalgam is immediately formed, and if the proportions of the metals
be about even, they in time make a hard mass. Some gold does not
amalgamate readily; in various diggings of Siskiyou county, the gold
has a reddish coating, which prevents amalgamation. Grease or resin in
the water used for washing, is also unfavorable. So is cold. Heat is
favorable, and therefore less gold is lost in summer than in winter.
Quicksilver that has been once used is considered better than that
fresh from the flask.
No tinned iron or copper vessel should be used for holding or panning
out amalgam, or dirt containing amalgam; since quicksilver forms an
amalgam with tin and copper, and will stick to the sides of a tinned or
copper pan.
In most sluices, the quicksilver is put in above the riffle-bars at
various places along in the boxes, with a confidence that the great
specific gravity of the metal will prevent it from being lost. The
greater the quantity and proportion of fine gold, the greater the
importance of the quicksilver.
The best method of catching very fine gold by amalgamation is to cover
a large copper plate with mercury, and let the dirt and water, in a
thickness of not more than a quarter of an inch, pass over it slowly.
There are various methods of covering copper plates with quicksilver.
The first thing, in every case, is to wash the copper with diluted
nitric acid, so as to remove all dirt and grease. The quicksilver may
then be rubbed on with a rag; or, still better, it may be dissolved in
nitric acid, and the liquid nitrate of quicksilver may be applied with
a rag. The nitric acid will attack the copper, and leave the
quicksilver as an amalgam on the surface of the copper. This is the
most common process, but the nitrate of copper continues for a long
time to come up through the quicksilver and interfere with the catching
of the gold. When the nitrate of copper appears--it is a green
slime--it should be scraped off and the place rubbed over with
quicksilver. When a plate is once covered with mercury, the operation
need never be repeated; but more mercury must be sprinkled on as the
gold collects and forms a solid amalgam. The plate is usually three
feet wide and six feet long, and is set nearly level. In very large
sluices the stream should be divided so as to run over different
plates. The slowness of the current and the shallowness of the water
are important, for with a swift current or deep water many of the
particles of float-gold may escape without touching the quicksilver.
Wherever a speck of gold has fixed itself on the plate, there others
will collect about, evidently preferring to fix themselves in a
neighborhood rather than in a waste place. The more gold there is on a
plate, the better it is considered to be. The seasons for cleaning up
are usually determined by the danger of theft. Miners do not like to
leave their gold out in quantities so large as to attract thieves. The
amalgam is sometimes half an inch thick, and is usually, at cleaning-up
time, a hard mass, which must be loosened by heat. The plate is put on
a fire, and when it gets so warm that the hand can scarcely bear it,
the amalgam is softened and loosened, so that it can be scraped off
readily. The plate is then sprinkled anew with quicksilver, and is
ready for use again. Mercury does not amalgamate with copper so readily
as with gold or silver. A copper plate, the sixteenth of an inch thick,
may be used for at least five years, and perhaps for ten; whereas a
gold plate of equal thickness would, if exposed to the action of
quicksilver in the same manner, fall to pieces in a few weeks. After a
time the quicksilver pervades the copper, and gives it a silvery
whiteness all through on the under side. It is said that a solution of
cyanuret or prussiate of potash, is used instead of nitric acid in
applying mercury to copper plates, and that it is still better, there
being then no trouble with the green spots of nitrate of copper.
A good amalgamated copper plate is considered as serviceable as a bed
of quicksilver of equal size, and it is very much cheaper and more
convenient to manage.
The dirt and water should be admitted to the copper plate, by falling
first through a sheet-iron plate, pierced with holes half an inch long
and a sixteenth of an inch wide. Some miners place this sheet-iron
plate immediately over the copper.
Very soon after the water and dirt commence to run in the sluice, all
the spaces between the riffle-bars are filled with sand, gravel and
dirt; which, however, present many little inequalities of surface,
sufficient to catch all the particles of gold larger than a pin-head.
The largest gold is caught near the head of the sluice; and the farther
down the sluice, the finer the gold. In some sluices, where the
pay-dirt contains much coarse gold, the quicksilver is introduced from
thirty to sixty yards below the head, so as to catch only the fine
particles of metal.
_Cleaning up._--The separation of the gold, amalgam, and quicksilver,
from the dirt in the bottom of the sluice, is called "cleaning up;" and
the period between one "cleaning up" and another is called a "run." A
run in a common board-sluice usually lasts from six to ten days.
Ordinarily the sluice runs only during daylight, but in some claims the
work continues night and day. Cleaning up occupies from half a day to a
day, and therefore must not be repeated too often, because it consumes
too much time. In some sluices the cleaning up does not occur until the
riffle-bars have been worn out or much bruised by the wear of the
stones and gravel. Cleaning up is considered light and pleasant work as
compared with other sluicing, and is often reserved for Sunday. At the
time fixed, the throwing in of dirt ceases, and the water runs until it
becomes clear. Five or six sets of riffle-bars, a distance of thirty or
thirty-five feet, are taken up at the head of the sluice, and the dirt
between the bars is washed down, while the gold and amalgam lodge above
the first remaining set of riffle-bars, whence it is taken out with a
scoop or large spoon, and put into a pan. Five or six more sets of bars
are taken up, and so on down. Sometimes all the riffle-bars are taken
up at once, save one set in every thirty-six feet, and then the work of
cleaning up is dispatched much more rapidly.
The quicksilver and amalgam taken from the sluice are put into a
buckskin or cloth, and pressed, so that the liquid metal passes
through, and the amalgam is retained. The amalgam is then heated, to
drive off the mercury. This may be done either in an open pan or in a
close retort. In the former, the quicksilver is lost; in the latter, it
is saved. The pan is generally preferred. Often a shovel or plate of
iron is used. Three pounds of amalgam, from which the liquid metal has
been carefully pressed out, will yield one pound of gold. The gold
remaining after the quicksilver has been driven off by heat from the
amalgam, is a porous mass, somewhat resembling sponge-cake in
appearance.
_Riffle-Bars._--The riffle-bars are usually sawn longitudinally with
the grain of the wood, but "block riffle-bars" are considered
preferable; the latter are cut across the tree, and the grain stands
upright in the sluice-box. The block riffle-bars are three times more
durable than the longitudinal; and as the latter kind are worn out in a
week in some large sluices, there is a considerable saving in using the
former. The block riffle-bars are only two or three feet long.
In some small sluices the riffle-bars are not placed in the boxes
longitudinally, nor in sets; but one bar near the head runs downward at
an angle of forty-five degrees to the course of the box, not touching
its lower end to the side of the box, but leaving an open space of an
inch there. Just below this open space another bar starts from the side
of the box and runs downward at right angles to the course of the first
bar, and an open space is again left at the end of this bar; and so on
down to near the lower end of the sluice, where there are longitudinal
riffle-bars in sets as described in the preceding paragraphs. The
consequence of using this kind of riffle-bar is, that though much of
the water and light dirt runs straight over the bars, the heavier
material runs down from side to side in a zigzag course. Near the head
of the sluice is a vessel, from which quicksilver falls by drops into
the box; and it follows the course of riffle-bars, overtaking the gold
which takes the same route. These zigzag riffle-bars are nailed down.
In all sluices, men must keep watch to see that the boxes do not choke;
that is, that the dirt and stones do not collect in one place, so as to
make a dam, and cause the water to run over the sides, and thus waste
the gold.
There are small sluices, from which all stones as large as a doubled
fist are thrown out. For this purpose the miner uses a sluice-fork,
which is like a large manure-fork or garden-fork, but has tines which
are blunt and of equal width all the way down; the bluntness being
intended to prevent the tines from catching in the wood, and the
equality of width to prevent the stones from getting fast in the fork.
In some sluices, the "block riffle-bars"--that is, bars cut across the
grain of the tree--are set transversely in the boxes, and about two
inches apart.
Another device is, to fill the pores of such riffle-bars with
quicksilver. This is done by driving an iron cylinder with a sharp edge
into the surface of the bar, then putting mercury into the cylinder,
and pressing it into the wood. The quicksilver, thus fastened in the
wood, catches particles of gold, which must be scraped off when the
time for "cleaning up" comes.
_Double Sluices._--Sluices are sometimes made double--that is, with a
longitudinal division through the middle, so that there are two
distinct sluice-boxes side by side. Two companies may be working side
by side, so that it will be cheaper for them to build their sluices
jointly. In some places the amount of water varies greatly; so that in
the winter there is enough to run two sluices, and in the summer only
one. And there are companies which wish to continue washing without
interruption; so they wash first on one side and then on the other, and
clean up without any interruption to the process of washing.
Another device for saving gold in sluices is the "under-current box."
There is a grating of iron bars in the bottom of a box, near the lower
end of a sluice; and under this grating is another sluice, with an
additional supply of clean water, and with a lower grade. The grating
allows only the fine material to fall through; and the current of water
being moderate, many particles of gold, that would otherwise be lost,
are saved. Sometimes the matter from the under-current box is led back
to the main sluice.
_Rock-Sluices._--Large sluices are frequently paved with stone, which
makes a more durable false bottom than wood, and catches fine gold
better than riffle-bars. The stone bottoms have another advantage--that
it is not so easy for thieves to come and clean up at night, as is
often done in riffle-bar sluices. But, on the other hand, cleaning up
is more difficult and tedious in a rock-sluice, and so is the putting
down of the false bottom after cleaning up. The stones used are
cobbles, six or eight inches through at the greatest diameter, and
usually flattish. A good workman will pave eight hundred square feet of
sluice-box with them in a day; and after the water and dirt have run
over them for an hour, they are fastened very tightly by the sand
collected between them. In large sluices, wooden riffle-bars are worn
away very rapidly--the expense amounting sometimes, in very large and
long sluices, to twenty or thirty dollars a day; and in this point
there is an important saving by using the stone bottoms. They are used
only in large sluices, and they generally have a grade of twelve or
fourteen inches to the box of twelve feet.
_Hydraulic Mining._--After the board-sluice, with its various adjuncts
of riffle-bars, stone bottoms, copper plates, and so forth, the next
instrument of importance in the gold-mining of California, is the
hydraulic hose, used to let water down from a considerable height, and
throw it under the pressure of its own weight against the pay-dirt,
which is thus torn down, broken up, dissolved and carried into the
sluice below. The sluice is a necessary part of hydraulic mining. The
hose is used, not to wash the dirt, but to save digging with shovels,
and to carry it to the sluice.
The hydraulic process is applied only in claims where the dirt is deep
and where the water is abundant. If the dirt were shallow in the claim
and its vicinity, the necessary head of water could not be obtained.
Hydraulic claims are usually in hills. The water is led along on the
hill at a height varying from fifty to two hundred feet above the
bed-rock, to the claim at the end or side of the hill, where the water,
playing against the dirt, soon cuts a large hole, with perpendicular or
at least steep banks. At the top of the bank is a little reservoir,
containing perhaps not more than a hundred gallons, into which the
water runs constantly, and from which the hose extends down to the
bottom of the claim. The hose is of heavy duck, sometimes double, sewn
by machine. This hose when full is from four to ten inches in diameter,
and will bear a perpendicular column of water fifty feet high; but a
greater height will burst it. Now, as the force of the stream increases
with the height of the water, it is a matter of great importance to
have the hose as strong as possible; and for this purpose, in some
claims, it is surrounded by iron bands, which are about two inches
wide, and are connected by four ropes which run perpendicularly down.
The rings are about three inches apart. The "crinoline hose," thus
made, is very flexible, and will support a column of water one hundred
and fifty or two hundred feet high. The pipe at the end of the hose is
like the pipe of a fire-engine hose, though usually larger. Sometimes
the pipe will be eight inches in diameter where it connects with the
hose, and not more than two inches at the mouth; and the force with
which the stream rushes from it is so great, that it will kill a man
instantaneously, and tear down a hill more rapidly than could a hundred
men with shovels.
One or two men are required to hold the pipe. They usually turn the
stream upon the bank near its bottom until a large mass of dirt tumbles
down, and then they wash this all away into the sluice; when they
commence at the bottom of the bank again, and so on. If the bank is one
hundred and fifty feet high, the mass of earth that tumbles down is of
course immense, and the pipemen must stand far off, for fear that they
will be caught in the avalanche. Such accidents are of daily
occurrence, and the deaths from this cause probably are not less than
threescore every year in the state. Often legs are broken; still more
frequently the pipemen have warning, and escape in time. When men are
buried in the falling dirt, the water is used to wash them out. In some
claims, the pipe will tear down more dirt than the sluice can wash; in
other claims, the sluice always demands more dirt than the pipe can
bring down. In the latter case, blasting may be used to loosen the
dirt, or the miners may undermine the bank, leaving a few columns of
dirt for support; and then these being washed away by the pipe, the
whole bank comes tumbling down.
In hydraulic claims, all the dirt is washed; in all other kinds of
claims, such dirt as contains no gold is thrown to one side, or
"stripped off." "Hydraulic mining" is the highest branch of placer
mining; it washes more dirt, and requires more water, and a larger
sluice, than any other kind of mining. The number of men employed in a
hydraulic claim, however, is usually small, from three to six, the
water doing nearly all the work. In some claims a man is constantly
employed with a heavy sledge-hammer in breaking up large stones, so
that the pieces may be sent down the sluice. One man attends to the
sluice, and sees that the dirt does not choke up in the sluice, or in
the claim above it.
The quantity of dirt that can be washed with a hydraulic pipe depends
upon various circumstances--such as the supply of water, the height of
its fall, the toughness of the dirt, and the amount of moisture in it.
More can be washed in winter than in summer, because the dirt is then
moister, and requires less water to loosen and dissolve it. The
quantity of water used in a hydraulic claim is from forty to two
hundred inches. With one hundred inches, at least thirty cubic yards
can be washed in ten hours, on an average; and three men can do all the
work. If there were a cent's worth of gold in each cubic foot, the
thirty cubic yards would yield eight dollars and ten cents per day, or
two dollars and seventy cents to the man, exclusive of the cost of
water. But, as a matter of fact, nearly all the hydraulic claims pay
more than that, and they will average at least three cents to the cubic
foot, and many of them yield five cents. The water usually costs twenty
cents an inch per day, so that one hundred inches would cost twenty
dollars. Allowing for the water at that rate, a claim in which thirty
cubic yards could be washed in a day with one hundred inches of water,
and in which the dirt contained five cents to the cubic foot, would
leave a net pay of six dollars and sixty-six cents to each man per day.
One hydraulic company, of whose labors I have a note, washed two
hundred and twenty-four thousand cubic feet of dirt in six days, using
two hundred inches of water, and employing ten men. The wages of the
men amounted, at four dollars per day each, to two hundred and forty
dollars; the water cost three hundred dollars; and the waste of
quicksilver, and wear of sluice, perhaps one hundred dollars more,
making a total expenditure of six hundred and forty dollars: and the
gold obtained was three thousand dollars, leaving a clear profit of
twenty-three hundred and fifty dollars. The dirt contained one cent and
a fifth of gold in a cubic foot. The greater the amount of water used,
the greater the proportionate amount of dirt that can be washed, and
the greater the proportionate profits. It is far more profitable to
have a large sluice than a little one, if the water and dirt can be
obtained in abundance.
Usually, in a hydraulic claim, the dirt is washed down to the bed-rock;
but in some places the washing stops far above the bed-rock, because
there is no outlet for the water.
_Blasting._--In some hydraulic claims, the dirt, in dry seasons, is
blasted, so as to loosen it. A drift or hole is cut into the bottom of
a hill, one or two hundred feet high, and a number of kegs of powder
(from twenty to two hundred) are introduced, and they are fired with a
slow match. The explosion makes an earthquake in the vicinity; and the
ground is loosened to such an extent that there is a great saving of
labor. The breaking up of the dirt and the exposure to the air are
supposed to facilitate the washing greatly.
More water is required for piping down banks than for washing the dirt;
and often the sluice is almost idle for want of dirt, while the water,
after being thrown against the hillside, runs away without doing any
service at washing. Blasting, therefore, by loosening the earth,
enables the hydraulic miner to have an abundant and regular supply of
dirt in his sluice, at an expense much less than the cost of manual
labor to dig the bank down with pick and shovel.
_Tail-Sluice._--The tail-sluice is a large sluice made for rewashing
the tailings or dirt which has previously passed through other sluices.
It is placed ordinarily in the bed of a ravine or creek through which
tailings run, and it receives no attention for weeks or months at a
time, save to keep it from choking. The sluices emptying into it
furnish both dirt and water, and in the dirt there is always a large
amount of fine gold, as is plainly proved by the fact that some of the
tail-sluices have paid large profits to their owners. Tail-sluices are
always large, long and paved with stones; and sometimes they are
double, so that one side may be cleaned up while the other continues
washing. In a branch of the Yuba there is, or was not long since, a
tail-sluice twenty feet wide.
_Tunnel-Sluice._--A tunnel-sluice is a sluice in a tunnel. It sometimes
happens that a considerable body of water runs out through a tunnel;
and in such case, a sluice at the bottom of the tunnel offers the
easiest method of getting out and washing the dirt. The tunnels are
never cut level, but with a slightly ascending grade, so that the water
will always run out. The grade is so low, that transverse riffle-bars
must be used; for with longitudinal riffle-bars or stones, there would
be too much danger of choking. These tunnel-sluices, because of their
low grades, require much more attention than any other kind of sluices.
_Ground Sluice._--All the sluices hitherto mentioned and described have
wooden boxes, but the ground-sluice has no box: the water runs on the
ground. The place selected for the ground-sluice is some spot where
there is a considerable supply of water, a steep descent for it, and
much poor dirt. The stream is turned through a little ditch, which the
miners labor to deepen and enlarge, and when it is deep they prize off
the high banks so that the dirt may fall down into the ditch. This is a
very cheap and expeditious way of washing, but it is not applied
extensively. It is used to the most advantage for washing where the
water is abundant for only a few weeks after heavy rains, and where it
would not pay to erect large sluices. A few cobble-stones should be
left or thrown at intervals in the bed of the ground-sluice to arrest
the gold, for if the bed were smooth clay, the precious metal might all
be carried off. Quicksilver is not used in the ground-sluice. After the
dirt has all been put through the ground-sluice, it is cleaned up in a
short board-sluice, or a tom.
_Long Tom._--The tom or long tom, an instrument extensively used in the
Californian mines in 1851 and 1852, but now rarely seen, is a wooden
trough about twelve feet long, eighteen inches wide at the upper end,
and widening at the lower to thirty inches, with sides eight inches
high. It is used like a board-sluice, but has no riffle-bars, and at
the lower end its bottom is of sheet-iron, perforated with holes half
an inch in diameter. This sheet-iron is turned up at the lower end, so
that the water never runs over there, but always drops down through the
perforated sheet-iron or riddle, into a little riffle-box, containing
transverse riffle-bars. A stream of water of about ten inches makes a
"tom-head"--or the amount considered necessary for a tom--through the
tom, which has a grade similar to that of a board-sluice. The dirt is
thrown in at the head of the tom, and a man is constantly employed in
moving the dirt with a shovel, throwing back such pieces of clay as are
not dissolved, to the head of the tom, and throwing out stones. From
two to four men can work with a tom; but the amount of dirt that can be
washed is not half that of a sluice. The tom may be used to advantage
in diggings where the amount of pay-dirt is small and the gold coarse.
The riffle-box contains quicksilver, and as the dirt in it is kept
loose by the water falling down on it from the riddle above, a large
part of the gold is caught; but where the particles are fine, much must
be lost.