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county. Here mines have been worked uninterruptedly since
1851. It is true there have been periods when the interest waa
more than usually depressed, and several of the mines, wUch
are now regarded as among the best, were thought to be ex*
hausted and were abandon^ for the time being, out in many
instances where work was resumed new bodies of gold-bearing
quartz were opened up, which proved rich and valuable. The
veins in this district, and particularly those which have been
most productive, are noted for their narrowness, as well as for
the richness of the quartz. They are encased in a hard met-
amorphic rock, and the expenses of mining are, as a general
thing, higher here than anywhere else in California, amounting
as they do in some instances, to from $20 to $26 per ton. Within
the last fourteen years the total production from the quarts mines
of Grass Valley District has been not far from $28,000,000. The
most prolific vein has been that situated upon Massachusetts and
Gold Hills, which alone has produced more than $7,000,000
worth of gold during this time, from a lode which will average
only a foot or fourteen inch/» in width.

The gold bearing rocks at this place are mostly highly met-
amorphic schists or sandstones passing into diorite or greenstone
syenite. These greenstones seemingly crystalline, are probably
only highly altei^ sedimentary rocks, containing a lai^ amount
of protoxyd of iron with sulphuret of iron. In some parts of

Digitized by


B. Silliman on the Grass Valley District. 237

the district, slaty rocks occur, more or less talcose or chloritic in
character ; masses of serpentine also abound, forming at times
one wall of the quartz veins. This serpentine is probably met-
amorphic of the magnesian rocks last named. The red soil,
Been almost everywhere in the Grass Valley district, has its
origin in the perozydation of the iron contained in the green-
fitoues and diorites, and set at liberty by their decomposition.

The line of contact between the gold-bearing ana metamor-
phic rocks of Grass Yalley, and the mnites of the Sierra Ne-
vada is met on the road to the town of Nevada, about half a mile
before coming to Deer creek. The talcose and chloritic slates
are seen to the north, in the direction of the Peck lode, and in
the slate districts of Deer creek.

The dip and strike of the rocks in the Grass Valley region is
seen to vary greatly in different parts of the district. Follow-
ing the course of Wolf creek, a tributary of Bear river, it will
be observed that the valley of this stream — which is Grass Val-
ley — as well as of its principal branches, follows in the main the
line or strike of the rocks. In the absence of an accurate map
of the region, it may not be easy to make this statement evident
But all who are familiar with the chief mines of this district,
will recall the fact, that the course of the veins in the Forest
Springs location, at the southern extremity of the district, is
nearly north and south — N. about 20^ E. — with a very flat dip to
the east, while at the Eureka mine, on Eureka hill, about rour
miles to the northward, the course of the vdn is nearly east and
west, with a dip to the south of about seventy -eight degrees.
Again, commencing at North Gold Hill and following the course
of the famous vein which bears the names of Gold Hill, Massa-
chusetts Hill and New York Hill, we find the veins conforming
essentially to the southerly course of the stream with an east-
arly dip. The North Star, on Weimar Hill, has likewise the
same general direction of dip. Near Miller's ravine, at El Do-
rado mill, Wolf creek makes a sudden bend to the left, or east,
leaving the Lone Jack, Illinois, Wisconsin and Allison Banch
mines to the west. All these last named mines are found to
possess a westerly dip, showing the existence of a synclinal axis
running between the base of New York Hill and the mines hav-
ing westerly dips last named, along which probably the veins
will, if explorea in depth, be found "in basin." The dip at
Lone Jack is about 80° W., at Allison Banch it is about 45*^ W.
Just below the Allison Banch mine. Wolf creek again makes a
sharp turn to the lefl, nearly at a right* angle, and then resumes
its former course with the same abruptness. A mile lower down,
where it strikes the Forest Springs locations, we find the Noram-
bagua inclosed in syenitic rocks, dipping at a very low angle
to the east, a dip seen also at still less angle in the Shamrodc,

Digitized by


236 B. Sittiman on the Grass Valley DUtrict.

vet farther south. There is probably a saddle or anticliDal axis
below the Allison Banch mine, due to the elevation of the syen-
itic mass, which, it seems probable, sets in at the sharp bend in
the stream, before alluded to, and where the ravine trail joins
it. The stream probably runs pretty nearly in the basin of the

The rocks on the east side of Wolf creek, and above Forest
Springs locations, dip westerly. Such is the case at Kate BLayes,
and with the veins on Osborn Hill. The middle branch of the
creek sweeps around to the east, forms its junction with the north
fork, and tne veins explored there near its upper waters, as at
Union Hill, the Burdett ground, Murphy vein, Lucky and Cam-
bridge, all dip southwest or south, conformably to the Idaho
and Eureka, and at a pretty high angle. The Eureka vein
going west, faults in the W hiting ground, and having previously
become almost vertical has, west of the fault, a northerly dip at
a high angle. At the Coe ground, this northerly dip is also
found at an angle of about 50^. At Cincinnati Kill the vein
dips southerly, in a direction exactly opposite to that of the
North Star, there being a valley between the two, and a saddle
or anticlinal between Cincinnati and Massachusetts Hills.

These facts, which, by a more detailed statement, could be
easily multiplied, seem to warrant tha conclusion that the course
and dip of the Grass Valley vein is especially conformable to
that of the rocks, and that the streams nave, in general, exca-
vated their valleys in a like conformable manner.

The quartz veins of Grass Valley District are not generally
large. Two feet is probably a full average thickness, while
some of the most productive,. and those which have given, from
the first, a high reputation to this region, have not averaged
over a foot or possibly eighteen inches in thickness. There are
aome exceedingly rich veins which will hardly average four
inches in thickness, and which have yet been worked at a profit,
while at the same time there are veins like the Eureka which
have averaged three feet in thickness, and the Union Hill vein
over four feet The Grass Valley veins are often, perhaps usu-
ally, imbedded in the inclosing rocks, with seldom a fluccan or
clay selvage or parting, although this is sometimes found on one
or both walls. The walls of the fissures and the contact fisboes
of the veins are often seen to be beautifully polished and

The veins are, as a rule^ highly mineralized and crystalline,
and afford the most unmistakable evidence of an origin from sobi-
Hon in water, and not the least evidence of an igneous origin.
Chaloedonic cavities and agatized structure are very conspicu-
ous features in many of the best characterized and most produc-
tive of the gold-bearing veins of this district. These inaisputa-

Digitized by


B. SUUman on the Grau Valley District. 830

ble evidences of an aqueous origin are seen in Massachusetts
Hill, Ophir Hill, Allison Banch, Elate Hayes and Eureka.

The metallic contents of Grass Valley veins vary extremely,
some carry but very little or no visible gold or sulphurets, al-
though the amount of gold is found in working in mill to be satis-
factory, and the sulphurets appear on concentrating the sands
fh>m crushing. This is the case in the Lucky and Cambridge
mines^ for example. But in most cases, the veins of this dis*
trict abound in sulphuretet, chiefly of iron, copper and lead, the
sulphuretted contents varying greatly in the' same vein; zinc
and arsenic are found also, but more rarely< The most noted
example of arsenical sulphurets are in the Norambagua and
on Heuston Hill; lead abounds in the Union Hill lodes (as
galena,) and the same metal is found associated with the yellow
copper in parts of the Eureka mine. The gold when visible is
very commonly seen to be associated with the sulphurets — this
was particularly the case in Massachusetts Hill ; wnile in Bocky
Bar and Scadden Flat, on the same vein, the gold is found some-
times in beautiful crystallized masses, binding together the
quartz and almost destitute of sulphurets. Mr. William Watt
informs me that in working some seventy thousand tons of rook
from Massachusetts Hill vein, the average yield of gold was
about $80; but at times this vein was almost barren^ while
again the gold was found in it so abundantly, especially where
it was thiuf that it had to be cut out with chisels. It is matter
of notorietv that in the Gold Hill vein (continuation of the vein
in Massacnusetts Hill) portions of the lode were so highly
charged with gold that the amount sequestered bv the miners
in a single year exceeded $60,000. On the other hand, in the Cam-
bridge and Lucky mines, yielding about $86 to $60 of gold to
the ton^ the precious metal is seldom visible. In the Eureka,
where the average yield of gold in 1866 was $60 per ton, it
seldom exhibited what may be called a " specimen " of ^old.

The structure of the veins in Grass Valley varies, in different
portions of the district, especially in respect to the distribution
of thepvrites and of portions of the adjacent walls. On Eu-
reka Hill, the veins p<»sess a laminated structure parallel to the
walls, enclosing portions of the diorite or talcose rocks, forming
closures or joints in which the .vein splits easily. On these sur-
&ces of cleavage minute scales of gold may often be detected
by close inspection. The sulphurets are also seen to be ar-
ranged in bands or lines parallel to the walls. In many other
cases, this kind of structure is found to be wholly absent, while
the sulphurets and gold appear to follow no regular mode of
distribution. In a few mines the sulphurets are arranged very
distinctly in bands of zones, parallel to the walls, forming *' rib-

Digitized by


340 B. SiUitnan on ilte Grass Valley DistricL

bon qaartz.'' This is especiallj distinct in the Norambagua,
where, as before mentioned, the sulphurets are arsenical, and the
gold very finely disseminated.

The average amount of gold in the Grass Yalley veins is be-
lieved to be considerably in excess of what is found in most
other portions of California. In Allison Banch, Massachusetts
Hill, Kocky Bar, Ophir Hill, and Eureka, this average has prob-
ably reached $50 to the ton. In many other mines it has been
considerablv less, but on the whole, $30 may not be far from
the general average for the whole district ; meaning of course,
the amount actually saved by milling operations.

The loss of gold is very various, out is probably nearly al-
ways greater than owners are willing to confess — if indeed they
know, which is doubtful. It is certam, in one well known mine,
my own samples of quartz sands, and sulphurets from ''pans,"
assayed respectively $23 and $57 per ton — a result which was
later confirmed, quite independently, by the researches of a very
competent mining engineer. In other cases, as at Eureka and
Norambagua, my own researches show the loss in the tailings
to be very small, not exceeding seven dollars to the ton in the
latter, and less than that in the former.

The gold in many of the Grass Valley mines is very easily
worked, being clean, angular and not very small, hence it is
readily entangled in the fiber of blankets, together with a con-
siderable portion of sulphurets, naturally leading to the method
most commonly in use in Grass Yalley for treatment of the gold

What may pi^/perly be called the Grass Valley method of amal-
gamation consists in the use of heavy stamps, seven hundred
or a thousand pounds, crushing usually two tons, sometimes two
and a half tons of ore each in twenty-four hours — through
screens not exceeding No. 6, rarely so fine. Amalramating
in battery and copper aprons are usually omitted. In some
mills, murcurial rimes are placed in front of the discharge, but
commonly the whole body of crushed stuff is led at once over
blankets, which are washed out every few minutes into tanks
where the free gold and sulphurets are allowed to collect pre-

?aratory to being passed through the '' Attwood amalgamators."
'hese simple machines are designed to bring the gold into
thorough contact with mercury contained in little vats sunk in
the surface of an inclined table, over which the stuff is fed to the
vats in a regulated manner by a stream of water, while iron
blades slowly revolve in the vats to cause a mixture of the
sands and quicksilver. By this apparatus, at the Eureka mill
ninety per cent of all the gold is obtained which is saved from
the ore. Bevond the amalgamators, the sands are carried over
amalgamated copper sluices, and are put through various ore-

Digitized by


B. SiUiman on the Grtass Valley District 241

saving processes with a view especially to concentrating the
sulphurets. These processes vary much in different mines. In
some mills, especially the Ophir, much more elaborate mechani*
cal apparatus has lately been introduced — with what results still
remams to be seen, it is certain that if the method of treat-
ment just sketched seems imperfect, (as it undoubtedly is,) it is
the method which has hitherto yielded the large returns of gold
for which Grass Valley has obtained its well-deserved renown*
As the development of the district goes forward, cases will oc-
cur of veins containing gold in a state of very fine division, to
which other methods of treatment must be applied. Such ex-
amples indeed already exist, and the problems which they offer
will be met by the use of other systems of amalgamation, or by
suitable modifications of the existing system.

The sulphurets occurring in the Grass Valley District are
usually rich in gold — some of them remarkably so. In quan-
tity they probably do not on an average amount to over one per
cent of the mass of the ores, although in certain mines they are
found more abundantly. For a long time there was no better
mode known of treating them than the wasteful one of grind-
ing them in pans and amalgamating. In this way rarely was
60 per cent of the gold saved. After many abortive efforts, at
length complete success has been met with in the use of Piatt*
ner's chlonnation process. Mr. Deetken, now connected with
the reduction works of the Eureka mine, is entitled to the credit
of having overcome the difficulties which formerly prevented
the successful use of this process in Grass Valley, a more detailed
description of which will be found in our notice of the Eureka

Of the length of the productive portion of quartz veins and
the depth at which they commence to become productive, Grass
Valley offers some instructive examples.

The North Star vein, on Weimer Hill, has been proved pro-
ductive on a stretch of about one thousand feet, while the propor-
tion of gold has gradually increased with the depth, from an aver-
age of twenty dollars in the upper levels to nearly double that
in the lower levels. The limits named are rather those of ex-,
ploration than the known extent of the productive ore. In the
vein on Massachusetts and Gold Hills, on the contrary, the dis-
tribution of the '' pay " has been found much more capricious,
being at times extremely rich, and again with no apparent reason
yielding scarcely the cost of milling. The Eureka mine offers
the most remarkable example, however, of a steady increase
firom a non-paying amount or gold near the outcrop to one of un-
common productiveness. An opinion has found advocates, and
has been perhaps generally accepted by most writers on the sub-
ject of gold-bearing quartz veins, that they were richest near the
Am. Joue. Sci.— Skcond Series, Vol. XLIV, No. 181.— Seft., 1867.

Digitized by


343 B. amiman on the Grass Valley District.

sarfiuse and in depth became gradnall j poorer. There is noth*
ing in the nature of the caee, as it seems to me, to justify such a
ceneralization, more than there is to sustain an opposite opinion,
if we accept &cts as a guide, we find in California that the
deepest mines, for example, Hayward's Eureka, in Amador,
1,200 feet, North Star, 750 feet on the slope, Princeton, in Mari-
TOsa county, 800 feet, Eureka (Grass Valley) 400 feet, AUiscm
Ibinch, 626 feet, etc., as a rule have an increasing amount of gold.
If the Allison Banch, the Princeton mine, and some others ap-
pear to be exceptions, the answer is, we may reasonably expect
the same yariations of productiveness in depth which are known
to exist in linear extent. The Princeton, alter an excellent run
of good ore, became suddenly poor, at a depth of over six
hundred feet, in 1866 ; but I am informed by Mr. Hall, the
present superintendent, that the good ore came in again in a
short distance. Mr. Laur, the French engineer, whose papers
on California mines is often quoted, cites the Allison Banch
mine in evidence of the theory of a decreasing amount of gold in
depth, but it is in proof that since the date of Mr. Laur^ visit
(lo62-8), this mine has been at work on ores which have yielded
over one hundred dollars value, its present suspended activity
being due to causes quite unconnected with the intrinsic value
of the mine. The rich "chimneys," or productive zones of ore
ground, are known to be of various extent in quartz veins, from
a few feet to many hundreds of feet, and it is impossible to as-
sign any valid reason why we may not expect the same changes
in a vertical direction which we find in a horizontal. As the
ore-bearing ground or shoots of ore have in many, if not in
most cases, a well determined pitch of the vertical, it is self-evi-
dent that a vertical shaft, or incline at right angles to the vein
must, in descending, pass out of the rich into poor ground, at
certain intervals, ana it is perhaps due to ignorance of this
fact that miners have abandoned sinking because they found the
" pav " suddenly cease in depth, when a short distance more
would probably bring them into another zone of good ore. The
experience of every gold mining district offers examples in illus-
tration of these remarks. In quartz veins containing a consider-
able amount of sulphurets, it is evident that the outcroppings
should offer mach better returns to mining industry than will
follow after the line of atmospheric decomposition has been
passed, because above this line nature has set free the gold for-
merly entangled in the sulphurets, leaving it available for the
common modes of treatment, with the added advantage often
times that the particles of free gold formerly distributed through
a considerable section of the vein, are found concentrated in a
limited amount of ore. It is easy to reach the conclusion in
such cases, that the amount of gold in the vein is less in depth,

Digitized by


B. Silliman on ih% Grass Valley District S48

after the real average amount is reached, while in faot it ia neither
greater nor less ; but the metal is no longer available bj com-
mon methods of treatment

The Eureka mine. — From the date of its location, February 7,
1867, to the close of 1868, the mine proved only a source of ex-
pense to its owners, and its history is instructive as suggesting
that shallow sur&ce explorations, in gold mining, may be as un- '
satisfactory as they are known to be in other mining enterprises.
So late as 1868, it is said, that five thousand tons of quartz
taken above the drain level, or thirty* feet from the surface,
yielded in mill less than ten dollars per ton in gold, not return*
ing expenses. A shafl sunk to a depth of about fifty feet af-
forded quartz, however, which yielded about fifteen dollars per
ton, and the amount of gold rapidly increased to twenty-eight
dollars at one hundred feet Between the one hundred and two
hundred feet levels the average yield was about thirty-seven
dollars per ton, and between the two hundred and three hundred
feet levels the average has been about fifty dollars per ton,
rising to sixty-four dollars in the last four months of 1866.

There are in fact two distinct veins in the Eureka mine, sepa-
rated from each other by a mass of greenstone or metamorpnic
sandstone, about twenty-eight or thirty feet in thickness. The
smaller of these veins is on the south and has not been explored,
but is a well-defined vein at the points where the shaft and cross
cuts have exposed it The greenstone forms the hanging wall
of the main vein, and is particularly regular and smooth, in
some places beautifully polished. The foot wall consists in
some parts of soft serpentine, and when the vein pinches it ap-
pears to be from swelling of the foot wall. No other mine m
this region has such a structure as the Eureka, so far as I know,
and there is very much in the peculiarities here described to
fiivor the highest confidence in the permanence of this great ore
channel, botn in depth and extent

It is interesting to analyze a little more in detail the returns
of this mine, as illustrating a point already alluded to, viz — its
progressive increase of gold with an increase of depth.

From October, 1865, to December 81, 1866, the quantity of
quartz crushed was twenty-four hundred and forty-five tons,
yielding an average of $38.87 per ton, and costing to mine and
reduce $18.61.

From January 1st to June 1st, 1866, the crushing was forty-
seven hundred and three tons, averaging $42.68 per ton, at a
cost of $12.62 per ton.

From June let to September 30, 1866, the amount of quartz
crushed was forty-two nundred twenty-seven and three-fourths
tons, giving an average yield of $60.38 per ton, at a cost of
$16.78 per ton.

Digitized by


244 Z Gaffield on the action of Sunlight on Glass.

For the whole year ending September SO, 1866, the total
crushing was eleven thousand three hundred and seyenty^fiye
and three-fourths tons, yielding a general average per ton of
$47.15, at a mean cost per ton of $18.76.

The net profits for the year ending September 80, 1866, were
$868,042.18. The ratio of costs of mining to the gross product
' was, for the three periods named above, respectively, 40}, 29}
and 26} per centum. In the mining costs are included all
charges for dead work, machinery, etc. The profits of the Eu-
reka mine have^ therefore, for the period named, averaged in
round numbers from sixty to seventy-four per cent of the gross
product of the mine. The earnings are divided every twenty-
eight days, making thirteen annual dividends.

The bullion of the Eureka mine is about 860-thou8andtli8
fine, worth $17.57 per ounce. This value is, of course, slighdy
variable, say within five-thousandths.

Art. XXVTLL—TTie Action of Sunlight on Glass; by Thomas


The great attention now given to all the phenomena connected
with li^ht and heat may awaken some interest in the experi-
ments m which I have been engaged for the past four years on
the subject named at the bead of tnis article. Perhaps I cannot
better commence my essay, than by <]^uotinff from the " Proceed-
ings of the Natural History Society," (vol. ix, p. 847) an account
F'ven before that Society^ of ray experiments m 1868, and after
had been engaged in them only a few months.

" He believed that his experiments in connection with the
aubject were original as to their method and their extent, al-
though it had long been observed in Europe that colorless or
light-colored plate-glass had turned to a purple hue by exposure
to intense sunlight. One case* is cited of a change to a gold
color; and one experiment recorded by Dr. Faraday,! some
forty years ago, proving that a light purple changed to a darker
hue after eight month^s exposure.

"Other experiments are on record showing the action of glass
of different colors as media in the transmission of light and of
heat; but none^ with the iibove exception, showing the effect
produced on the glass itself.

" An experience of some twenty years in the window-glass
business had only presen.ted a few isolated cases of supposed
change of color from this cause, which were attributed to some
obvious defect In an article of inferior manufacture ; but, within

Online LibraryJohn AlmonThe American journal of science and arts → online text (page 79 of 102)