New-York tribune. [volume] (New York [N.Y.]) 1866-1924, 1880-08-07
MINING IN COLORADO.


ROUND MOUNTAIN AND THE PLATA VERDE
TIE FEATURE or THE LasDscAP&-AS EXAMiNA'
TON OF THE PLATA VERDE NINA WISE PLAN
OF oPERATIoNs-TuE BEST MILL OF IT'S KIND
AND WHAT 1T Is EXPECTED TO ACCOMPLISH
lFROM srAFF CORRESPONDENT OF THE TRIBUNEJ
SILVER CLIFF Col, July 21.-Northeast OF the
town of Silver Cliff and about nile distant, Round
Mountain raises its head like immense sugar
loaf about l. 200 feet above the surrounding IOol-
hills. The southern contact OF the granite tongue
which described In former letter rs extending
into the trachytic formation from the northwest
runs across the further side of this mountain so that
the broken rock. mixed with the soil on
its northern slope for decliyity for IL
Is vory steep. is granite while tlat on
it's summit and southern side Is porpbyry.
Round Mountain is one Of the best known land
marks in all this country. Its great height when
compared with the surrounding hills, its peculiar
shape and its bald top aud sides make it easily
recognized wherever 1t can be seen. Ii IL To Silver
Cliff what Mount Davidson is to Virginia City, OF
Bear Butte to Fort Meade in the Black Hills.
Looking at Round Mountain from the streets OF
this camp its sides seem to DO covered with a thin
growth OF grama grass except at Il point about
hundred feet from tho Summit, where on the right
or cast side of the mountain, great mass OF
trachyte rock sticks out like an enormous wart
stained and blackened by the suns and storms OF
thousands of years. Above and around this great
blowout of porphyry a few stunted evergreen
trees hardly bigger than shrubs which cling to the
barren rocky soil with tonaclty that Is wonder
full
VISIT TO THE NINE.
On the side Of Round Mountain, facing Silver
Cliff and about six hundred feet below its summit,
there are two large excavations from which great
al
out upon the hill side These operations about
a quarter of mile apart, and at about the same
altitude. Each is reacbod by road cut across the
face of tine mountain at sharp incline,
that leading to the eastern excavation start
Ing from the foot of the hill far to the
west and vice versa, that the two roads cross
each other about 200 feet below the two mines.
forming great &" X" on the front of the bill. The
excavation at the right Is the Plata Verde mine. i
do not at this moment recall the name OF the claim
to tine left, but 1t is unmportant, since, ~ have
been informed, very little valuable ore has been
found in it, aud no work is now being done upon it,
When came to climb the mountain to visit tho
Plata Verde mine found that what seemed to be
its smooth sides covered with thin grass was really
thickly with broken pieces of trachyte rock
after getting above the wash" and even this
drift" was chiefly composed of the Same material,
ground up into gravel by long-contnued atrition.
The Plata Verde mine was discovered and 10
catedD within week after Mr. Edwards first
founo horn silver in the Racine Boy, and from the
first was considered one of the best mines in the
new camp. Aside from the fact that the BODY OF
ore which was disclosed as explorations were prose-
cuted was larger and richer than In many other
claims its situation as have described it, well up
on the mountain side, made it popular with the
miners who had been accustomed to look for rich ore
in such localities rather than beneath the surface in
gently sloping foothills Its position is also much
more favorable for the cheap mining and handling
of ores than that of any other mine the chloride
belt The customary dispute in regard to title took
place over the Plata Verde, but, believe was set
tied before the present company came into posses
sion of it,
THE MANAGEMENT OF THE PROPERTY.
The mine Itself. when 1t is reached. Is simply
great quarry Of the prevalent porphyry trachyte
of the country. stained as elsewhere with streaks
of rel oxide Of Iron black oxide OF manganese md
i'm some places with green chloride of silver The
cut extends INTO the mountain should think, hOri
zontaly fifty sixty feet and, owing to the sharp
ness of the angle with which the hillside rises,
makes depth" the miners say or goes
beneath the surface, with great rapidity.
The width of the main cut is also,
| should think, about fifty feet, but the
ground on each side of it has been carefully pros
pected, and the breadth of the body of richer rock
has been proved to be about 200 feet. The length
of the claim is 800 feet and the mass of rich ore
now opened is nearly in the middle OF il. Ii is my
Judgment after seeing many other mines and learn
ing their average daily production, that the Plata
Verde Company could easily remove 100 tons of ore
a day without crowding the mine interfering
with the necessary prospecting works but it is
impossible for to form any estimate of the
amount of ore in sight. / could simply say chat it
is very great.
Careful assays Of the rock show that a cOnserva-
tive estimate of its grade would be from fifteen TO
twenty ounces of silver to ton. and it is more
likely to be nearer the latter than the former figure.
The ore shipped from the mine before the present
company acquired it was selected and probably
yielded rs much az seventy-fve of silver to
ton If it were wise or profitable to do so. large
quantities of hgh-grade ore could now
DO sorted out but this is an expensive
operation, and the policy of this and other
companies on the chloride belt will probably
be to send to the mill all rock, just it is qulrred
out which viii yield enough silver to pay for min
ing and milling 1t will be more profitable to do
this than to sort the ores because the lean rock
mixed with that which il richer has to be taken out
and the expense OF mining ii has to be paid whether
it is milled not. To tins must be added the cost
of sorting, all of which must be subtraeed from the
yield of the selected ore before any profit be
alized.
For example, suppose the superintcndent of a
mine in the chloride belt takes out 100 tons of ORE
the average yield of which is $40 ton, besides u |
streak of richer rock mined at the same time. and
thai it will cost just that amount TO mne and mill |
It, of which 81 ton must be paid for mining. If |
lie the whole hundred tons through the mill he
neither makes nor loses anything while he will |
have silver bullion enough to pay all expenses. If
he sorts il he NAV get fifty tons that will produce
S15 ton, or $3.50 Out of this sum he must pay
$500 for mining 90 tons 1850 for milling fifty tons