the former, more capital, more experience, more complicated machinery
and richer material are required than for the latter. The placer miner
throws the dirt into the water, which then does the work; whereas the
pulverizing of rock is a nice operation, requiring constant attention.
Quartz requires a mill and water-power; placer dirt is washed in a
simple sluice. Dirt containing ten cents in the cubic yard may pay the
hydraulic miner, but the quartz miner must have a hundred times as much
in a cubic yard of vein stone, or he cannot work. The placer gold, when
freed from the baser material surrounding it, is much of it in coarse
particles, which are easily caught by their specific gravity; the
quartz gold must be reduced to a fine powder before it be set free from
its gangue, and with the fineness of the particles increases the
difficulty of catching them.
Auriferous quartz lodes are often found by accident. Not unfrequently
it happens that a rich streak of pay-dirt in a placer claim is followed
up to the quartz vein from which it came. While miners are out walking
or hunting, they occasionally will come upon lodes in which the gold is
seen sparkling. Some good leads have been found by men employed in
making roads and cutting ditches. The quartz might be covered with
soil, but the pick and shovel revealed its position and wealth. In
Tuolumne county in 1858, a hunter shot a grizzly bear on the side of a
steep _canon_, and the animal tumbling down, was caught by a projecting
point of rock. The hunter followed his game, and while skinning the
animal, discovered that the point of rock was auriferous quartz. In
Mariposa county, in 1855, a robber attacked a miner, and the latter saw
the rock behind his assailant sparkle in the sunlight, at a spot where
a bullet struck a wall of rock. He killed the robber, and found that
the rock was gold-bearing quartz. In Nevada county, several years ago,
a couple of unfortunate miners who had prepared to leave California,
and were out on a drunken frolic, started a large boulder down a steep
hill. On its way down, it struck a brown rock and broke a portion of it
off--exposing a vein of white quartz which proved to be auriferous,
induced the disappointed miners to remain some months longer in the
state, and paid them well for remaining. Science and experience do not
appear to give much assistance in prospecting for quartz lodes.
Chemists, geologists, mineralogists and old miners, have not done
better than ignorant men and new-comers. Most of the best veins have
been discovered by poor and ignorant men. Not one has been found by a
man of high education as a miner or geologist. No doubt geological
knowledge is valuable to a miner, and it should assist him in
prospecting; but it has never yet enabled any body to find a valuable
claim.
_Distribution of Gold in Quartz._--The rich quartz-veins of California
extend from Kern River to the Siskiyou, are found on hills, in _canons_
and in vales. They are at least two thousand feet above the level of
the sea, and not more than ten thousand feet above it. Their course is
generally from north-north-west to south-south-east, and they dip
steeply to the eastward, sometimes being nearly perpendicular. They
differ in thickness from a line to sixty feet. Quartz veins are very
numerous in most of the mining districts, so the task is not to find
the veins, but rather to find those which are gold-bearing. It is
supposed that nearly all large veins come to the surface of the
bed-rock or "country;" but many of them are covered with soil and thus
are hidden. Hidden veins are called "blind;" those plainly visible on
the surface are called "croppings veins," because their position is
shown by the out-croppings. Experience has not ascertained whether
large or small veins are more likely to contain gold. It is found in
both. The porous quartz, or that containing many cavities, is more
frequently found auriferous and richly auriferous, than the very
compact quartz. The best gold-bearing veins are usually yellowish or
brownish in tinge, near the surface at least; but very rich specimens
are found in white and bluish-white rock. Most quartz veins in
California contain a little gold; the metal seems to have been
distributed most lavishly, but unfortunately in nine-tenths of the
veins, the proportion of metal is too small to pay. Most of the large
veins are supposed to run for miles upon miles, though they can rarely
be traced clearly on the surface for more than a furlong. The
auriferous veins vary much in richness. No vein is wrought for more
than a few hundred feet. Beyond that, it is either too poor to pay, or
the vein is hidden. Some persons have supposed that there is one great
gold-bearing quartz vein running along the side of the Sierra Nevada,
from Mariposa to Plumas county, and that many of the richest claims are
really in this one vein; but this a supposition which cannot be proved
now. Sometimes a vein seems to spread out and divide into a number of
smaller veins, all of which afterward unite again. These points of
junction, and the narrower places in the vein, are usually richer than
other parts of it. When two veins cross each other, one may be
auriferous on one side of the intersection and not on the other; but in
this case the other vein will be auriferous on both sides. It is as
though they were streams, one rich, the other barren, and that after
meeting, the wealth of the one was divided between them. It is a
general rule that metalliferous veins running parallel with the strata
of the bed-rock or country are not extensive. In fact they are rather
deposits than veins, and though often extremely rich are soon
exhausted, while the lodes which run across the stratification, run far
and deep, and have a regular and straight course and dip. Lodes lying
between two different kinds of rock, are usually richer than those
which have the same kind of rock on both sides. Thus it is said that
the richest veins of auriferous quartz in California, have been
discovered at the intersection of trap and serpentine, and the richest
places in veins are where they cross from one kind of bed-rock into
another. The richest part of a lode of auriferous quartz is almost
invariably on the lower side of the vein, near the foot-wall. All these
are facts to be remembered by the prospector as a guide, and an
assistance to him in his search for a rich gold-bearing vein. If the
lode is covered with earthy matter, he may sometimes trace its course
by the difference in the color of the dirt and stones over it from that
elsewhere. When the prospector finds dirt and stones on a vein,
evidently disintegrated portions of it, he should wash some of the dirt
in a pan, and if he finds no gold, there is a strong presumption that
the vein is barren.
_Prospecting Quartz Rock._--After finding a gold-bearing vein, the
question arises whether it will pay. Great sums are lost in gold-mining
countries by injudicious investments in mills and machinery to work the
auriferous rock, and persons going into the business should be
particularly careful not to commit this great error. The business of
quartz mining has great profits, but also great pecuniary dangers
connected with it. It is rarely that all the rock of a vein will pay
for working. In some lodes, the vein-stone will average one hundred
dollars to the ton, for all the stone found in a certain part of the
lode, but beyond that the rock may be poor or worthless. Picked
specimens may be worth several thousand dollars to the ton, but perhaps
not more than a ton of such specimens has been obtained in the best
lode ever opened in the state. The most profitable lodes are those
which have a large supply of rock, easily to be obtained, and all of it
yielding something above the cost of working. The common method of
ascertaining whether rock will pay, is to pulverize a little of it and
wash it in a horn spoon. In taking out the quartz rock in large lodes,
it is important to take out only that which will pay, and to determine
this, the superintendent of the quarry-men must occasionally test the
vein-stone. He takes several little pieces of it, average specimens,
places them on a hard, smooth, flat stone, about a foot square, on
which he crushes them with a stone muller four inches square, and then
by rubbing with the muller he reduces them to a fine powder. He has a
horn spoon, made of a large ox-horn, with a bowl about three inches
wide, and eight inches long, being merely one-half of the horn in its
natural shape. With this spoon he washes out the powder in water, and
if he does not find a speck of gold or a "color," as it is called, in a
pound of the rock, he infers that it will not pay. The three principal
quartz mines in the state are those of Fremont in Mariposa county, of
the Allison company in Nevada county, and of the Sierra Butte company
in Sierra county. The first has produced $75,000 in a month, the second
$60,000, and the third $20,000, but the average is probably thirty per
cent. less, and the expenses about thirty per cent. of the total
product. The average yield of the Fremont rock is fourteen dollars to
the ton, of the Sierra Butte rock eighteen dollars, and that of the
Allison company, according to report, has for more than a year at a
time been one hundred dollars per ton. The cost of working quartz rock,
including quarrying, crushing and amalgamating, is in the best mills
from five to ten dollars per ton. The width of the vein, the softness
of the rock, the amount of work done, and the skill and industry of the
workmen, all are items of great importance in estimating the cost of
quartz-mining. It is a business which the owner of the mill ought to
understand. The cost of quarrying common quartz rock is about two
dollars per ton, that is, for mill-owners that understand the business
and superintend the labor themselves. When given out by the job, it
usually cost more. When quartz is crushed in a custom mill, that is, a
mill built to crush for all applicants, the cost is rarely less than
five dollars per ton, and in Washoe, the price was at one time thirty
dollars per ton; but in the large mills, where many tons are crushed
every day, is about two dollars per ton.
_The Divining Rod._--In prospecting for auriferous quartz, use is
sometimes made of the divining rod, a practice not without credit with
some good miners. The rod is a fork of a green hazel-bush, shaped like
a V, with the arms about a foot long. The prospector holds the end of
an arm in each hand, with the point of the V directed forward
horizontally, and as he walks along, the point turns down whenever he
comes over a metalliferous vein, metallic body or water. It is supposed
that very few persons can use the divining rod effectually; for most
men it refuses to turn. It is used in nearly every civilized country,
especially by miners, and is generally considered superstitious,
because it is employed by ignorant people, and because there has been
no generally accepted scientific explanation of the manner in which a
stick could be influenced by a metal hidden under ground. A scientific
explanation of the principle of the divining rod has been offered to
the world, by Baron Reichenbach, (see page sixty of his _Odic-Magnetic
Letters_, translated by John S. Hittel).
_Quarrying Quartz._--The quarrying of quartz rock differs little from
the quarrying of other metalliferous vein-stones. The lode descends
steeply, and the excavation must follow its course. Sometimes the
quartz is so soft that it may easily be loosened with the pick. The
harder rock is blasted. Soft quartz is that which is penetrated by
numerous cavities, though the lumps between the cavities may be very
hard. Some quartz on exposure to the air crumbles into sand, though
hard when first taken from the vein. In narrow lodes, some of the
wall-rock must be cut away to get room for the workmen. In wide lodes,
that part of the vein-stone which does not pay is left. Sometimes the
gold from the lode penetrates a little way into the foot-wall, and in
that case the quarrying must extend beyond the vein stone. The quartz
loosened in the vein, must either be hoisted perpendicularly in a
bucket with a windlass, or be hauled out through a tunnel. The common
method is to hoist the rock with a windlass. Most of the veins are in
such places that shafts are more easily dug than tunnels. After the
excavation has extended twenty or thirty feet below the surface, it is
usual to dig a perpendicular shaft, so as to strike the vein sixty or
seventy feet below the surface, and from this point the miner or
"drifter" works upward, and as he loosens the rock it falls to the
bottom of the shaft, where it is put in the bucket to be hoisted to the
surface. Our quartz mines are generally in dry hills, so that they are
not troubled much by water; but there are a few shafts where
steam-pumps are constantly at work to carry off the water.
Occasionally the miners find small quantities of auriferous quartz
which are so easily broken up, and the pieces of gold in which are so
coarse, that after the rock has been pounded a little in a mortar, the
metal can easily be picked out with the fingers.
_Arastra._--Quartz is pulverized either in an arastra, or Chilean mill,
or by stamps.
The arastra is the simplest instrument for grinding auriferous quartz.
It is a circular bed of stone, from eight to twenty feet in diameter,
on which the quartz is ground by a large stone dragged round and round
by horse or mule-power. There are two kinds of arastras, the rude or
improved. The rude arastra is made with a pavement of unhewn flat
stones, which are usually laid down in clay. The pavement of the
improved arastra is made of hewn stone, cut very accurately and laid
down in cement. In the centre of the bed of the arastra is an upright
post which turns on a pivot, and running through the post is a
horizontal bar, projecting on each side to the outer edge of the
pavement. On each arm of this bar is attached by a chain a large flat
stone or muller, weighing from three hundred to five hundred pounds. It
is so hung that the forward end is about an inch above the bed, and the
hind end drags on the bed. A mule hitched to one arm will drag two such
mullers. In some arastras there are four mullers and two mules. Outside
of the pavement is a wall of stone a foot high to keep the quartz
within reach of the mullers. About four hundred pounds of quartz,
previously broken into pieces about the size of a pigeon's egg, are
called a "charge" for an arastra ten feet in diameter, and are put in
at a time. The mule is started, and in four or five hours the quartz is
pulverized. Water is now poured in until the powder is thoroughly mixed
with it, and the mass has the consistence of thick cream. Care is taken
that the mixture be not too thin, for the thickness of it is important
to the amalgamation. The paste being all right, some quicksilver (an
ounce and a quarter of it for every ounce of gold in the quartz, and
the amount of gold is guessed at from the appearance of the rock) is
scattered over the arastra. The grinding continues for about two hours
more, during which time it is supposed the quicksilver is divided up
into very fine globules and mixed all through the paste (which is so
stiff that the metal does not sink in it to the bottom), and that all
the particles of gold are caught and amalgamated. The amalgamation
having been completed, some water is let in three or four inches deep
over the paste, and the mule is made to move slowly. The paste is thus
dissolved in the water, and the gold, quicksilver and amalgam have an
opportunity to fall to the bottom. At the end of half an hour, or
sooner, the thin mud of the arastra is allowed to run off, leaving the
precious material at the bottom. Another charge of broken quartz is now
put in and the process is repeated, and so on. The length of a "run,"
or the period from one cleaning up to another, varies much in different
places. In the rude arastra a run is seldom less than a week, and
sometimes three or four. The amalgam having settled down between the
paving stones, the bed must be dug up and all the dirt between them
carefully washed. In the improved arastra the paving fits so closely
together, that the quicksilver and amalgam do not get down between
them, but remain on the surface, and can readily be brushed up into a
little pan, and therefore cleaning up is much less troublesome and is
more frequently repeated than in the rude arastras; besides there is a
greater need of frequent cleaning up in the improved arastras, because
the amount of work done within a given time is usually greater.
The arastra is a slow instrument, but in some important respects it is
superior to any other method of working auriferous quartz. It grinds
the quartz well, is unsurpassable as an amalgamator, is very cheap and
simple, requires no chemical knowledge or peculiar mechanical skill in
the work, requires but little power, and very little water--all of them
important considerations. In many places, the scarcity of water alone
is enough to enable the arastra to pay a larger profit than any other
method. Again, if a miner finds a rich spot in a lode, he may be
doubtful as to the amount of paying rock which he can obtain. Such
cases very frequently happen in California, and the arastra is just the
thing for the case; for then if the amount of paying rock is small,
nothing is lost, whereas the erection of a stamping-mill would cost
much time and money, and before it could get into smooth operation the
rich rock would be exhausted, and the mill perhaps become worthless. No
other simple process of amalgamation is equal to that of the arastra;
and it has on various occasions happened in California, that Mexicans
making from fifty to sixty dollars per ton from quartz, have sold out
to Americans who have erected large mills at great expense, with patent
amalgamators, and have not been able to get more than ten or fifteen
dollars from a ton. The arastra is sometimes used for amalgamating
tailings which have passed through stamping-mills.
_Chilean Mill._--The Chilean mill has a circular bed like the arastra,
but much smaller, and the quartz is crushed by two large stone wheels
which roll round on their edges. In the centre of the bed is an upright
post, the top of which serves as a pivot for the axle on which both of
the stones revolve. A mule is usually hitched to the end of one of the
axles. The methods of managing the rock and amalgamating with the
Chilean mill, are very similar to those of the arastra. The Chilean
mill, however, is rarely used in California; the arastra being
considered far preferable.
_Stamps._--Nine-tenths of the quartz crushed in California is
pulverized by stamps, of which there are two kinds, the square and
rotary. The square stamp has a perpendicular wooden shaft, six or eight
feet long, and six or eight inches square, with an iron shoe, weighing
from a hundred to a thousand pounds. The wooden shaft has a mortice in
front near the top, and a cam on a revolving horizontal shaft enters
this mortice at every revolution. When the cam slips out of the
mortice, the stamp falls with all its weight upon the quartz in the
"battery" or "stamping-box." The rotary stamp has a shaft of wrought
iron about two inches in diameter, and just before falling this shaft
receives a whirling motion, which is continued by the shoe as it
strikes the quartz. The rotary stamp is considered superior to the
square, its advantage being that it crushes more rock with the same
power, that it crushes more within the same space, and that it wears
away less of the shoe in proportion to the amount of rock crushed.
There are usually half a dozen square stamps or more, standing side by
side in a square-stamp mill, and these do not all fall at the same
moment, but successively, running from the head to the foot of the
"battery." The quartz is put in at the head of the battery, and is
gradually driven to the foot. The rotary stamps sometimes stand side by
side, and sometimes in a circle. The battery of both rotary and square
stamps is surrounded by wire gauze, or a perforated iron plate,
allowing the finely pulverized quartz to escape, and retaining the
coarser particles. Quartz is crushed wet and dry. In wet crushing a
little stream of water runs into the battery on one side and escapes on
the other, carrying all the fine quartz with it.
_Separation._--After pulverization comes the separation of the gold
from the rocky portion of the powder. The means of separation are
mechanical or chemical. The chemical process is amalgamation; the
mechanical are those wherein the gold is caught on a rough surface with
the aid of its specific gravity. The chief reliance is upon
amalgamation, and in some large quartz-mills mechanical appliances are
not used at all for catching the particles of gold, but only for
catching amalgam.
The mechanical appliances used in quartz-mills in separating the gold
from the pulverized rock, are the blanket, the sluice, and the raw
hide.
The blanket is a coarse, rough, gray blanket, which is laid down in a
trough sixteen inches wide and six feet long. The pulverized quartz is
carried over this by a stream of water, and the particles of gold are
caught in the wool. The blanket is taken up and washed, at intervals
depending upon the amount of gold deposited. In some mills where a
large amount of rock is crushed, and where the powder is taken over the
blanket before trying any other process of separation, the washing
takes place every half hour. In mills where the pulverized quartz is
exposed to amalgamation first, the blanket may be washed three or four
times a day. The washing is done in a vat, kept for that especial
purpose.
The sluice used in quartz-mills is similar to the placer board-sluice,
but the amount of matter to be washed is less, and there is no dirt to
be dissolved, and there are no larger stones, and therefore the sluice
is not so large, so strong, or so steep in grade, as the placer-sluice,
and the riffle-bars are not so deep. In some quartz-mill sluices there
are transverse riffle-bars. If the quartz has much iron or copper
pyrites, the sluice is used to collect this material and save it for
separation at some future time. The pyrites ordinarily contains, or is
accompanied by much gold, which it protects from amalgamation. This
separation of the pyrites from the pulverized rock is called
"concentrating the tailings," and the material collected is called
"concentrated tailings." In the sluices of some quartz-mills cast iron
riffle-bars are used; cast in sections about fifteen inches square, and
about an inch deep. Much study has been devoted to the subject of
making these riffle-bars in such a manner that the dirt will not pack
in them, but will always remain loose, and keep in constant motion
under the influence of the water running over them; but the object has
never been fully attained. Quicksilver is used in nearly all
quartz-mill sluices.
The raw hide used in separating gold from the pulverized quartz is a
common cow hide, laid down in a trough with the hairy side up, and the
grain of the hair against the course of the water. The gold is then
caught in the hair. Sheep hides have been used in the same manner,
recalling to mind the Golden Fleece. The hides, however, are inferior
to the blankets for this purpose, and are never used in the best mills.
The methods of amalgamating are numerous. Among them are amalgamation
in the battery, amalgamation with the copper plate, amalgamating bowls,
and patent amalgamation of many kinds.