_To the Editor of the Scientific American:_
Nearly every person interested in geology sets up a theory of his own
with regard to the carbonate deposits of Leadville, immediately on
arriving in this famous district. There is, however, but one theory
which has been generally adopted by scientific men, formulated by
W. S. Keyes, General Manager of the Chrysolite Iron and Little Chief
Mines, and substantiated by the mute testimony of the fossil remains
that fix the geologic data. The theory is substantially as follows:
A shallow sea overspread this entire region. An even bed of limestone,
dolomitic, was formed by the myriads of shell-fish that subsisted in
this shallow sea. From some natural convulsion the waters flowed off,
leaving the sedimentary deposits. Subsequently the porphyritic rock
flowed over the surface in a pasty mass, covering the limestone. There
then followed two processes of ore making. The first was through the
mineralizing action of heated and ore depositing waters, coming up out
of the depths, and impregnating and permeating the hanging and foot
walls of the contact. No free oxygen was contained in these waters;
neither did they carry any chlorides or chlorobromides, wherein
consists the present richness of Leadville's ores; but in the first
process the ore was entirely in the form of sulphurets.
The second process was initiated by the uplifting of the mountain
ranges to their present height, at which time the diorites, those ore
indicators of the globe, uprose through the sedimentary strata.
Thus was the original surface of deposit bent and folded, and not
unfrequently entirely broken. The surface waters carrying free oxygen
and free carbonic acid now penetrated along the contact, and oxidized
the sulphurets, which formed free sulphuric acid, giving rise to
the sulphates and sulpho-carbonates. The irresistible law of gravity
distributed these sulphates, these oxides, and these carbonates in
vast bonanzas, that have been the wonder of the world. The fossil
trilobites of this region identify it with the silver lead districts
of Nevada, Utah, and Mexico. It is not anomalous, but simply richer
than its sister regions to the West and South.
The output of ore from the Leadville mines last year (1879) aggregated
122,483 tons, which represents a value of $11,477,046. That is to say,
there was an average yield at $90 per ton, or just $31,443.96 each
day. On the first day of May of the present year (1880), the returns
from thirty-seven of the leading mines gave a total daily output
of 8991/2 tons of ore, yielding, at the low average of $90 per ton,
something like $80,955 per day. The world's history of silver mining
in the past shows nothing like this for so young a camp. Scarcely a
month passes without opening up some new and vast carbonate deposits.
The territory has not even been thoroughly prospected; and the future
yield of the royal metal will far eclipse its past production.
It might not be uninteresting in this connection to give something
regarding the sampling and milling of ores. One of the most complete
concerns engaged in this business anywhere in the country is that of
Augustus R. Meyer & Co. This establishment has grown with the growth
and development of this carbonate district. The business was first
established as long ago as the year 1877 (before Little Pittsburg was
dreamed of). A little log house, a relic of seventeen years previous,
was found sufficiently ample for the needs of the business of that
period. However, it was not long before additions had to be made
and new buildings erected. In the year 1879 the present company was
incorporated with a capital stock of $50,000, and every preparation
that money and business sagacity could effect was made to meet the
demands of the prosperous era, that has built a mining metropolis
10,240 feet above the sea level, at the base of the great continental
divide. As at present constituted the premises of the company comprise
seven and one-half acres of ground, upon which six buildings have been
erected, including ore houses and crushing and sampling buildings.
During the busy season of summer from thirty-five to forty men are
employed, who alternate their work in two shifts, day and night. At
this season it frequently happens that the ore houses, which hold
1,500 tons, are insufficient for the accommodation of the mineral sent
from the mines to be crushed, and large quantities have to be stored
outside. In sampling ores from the various mines about Leadville this
establishment pursues the most careful methods. The different ores are
first deposited in large bins holding from 25 to 100 tons. One-tenth
of each load is taken and run through a Dodge crusher, which well
adapts it for the furnaces. A fifth of the tenth already indicated is
put through heavy rollers, and one half of this finely crushed ore is
subjected to the Bucking hammer and powdered to an eighty-sieve grade.
One sample of this powder, consisting of a fourth, is given to the
miner, two samples are kept for reference, and the other is sent to
the assayer, who takes his "assay ton," upon which the company buys
and sells. The capacity of the works are all the way from 80 to 150
tons per day. For samples, $7.50 is charged for silver and lead per
ton, and $10 per ton for gold; but in large quantities a less charge
is made. In job crushing, the market value of silver is allowed, with
from five to ten per cent. deducted. The Meyer works enjoy an excellent
patronage from the best mines of the camp, including such as the
Chrysolite, Carbonate, Vulture, Duncan, Matchless, Climax, Morning
Star, Crescent, and J. D. Dana, some of which have all their crushing
done at these sampling works.
[Illustration: AUGUSTUS R. MEYER AND COMPANY'S ORE MILL.]
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