Santa Fe new Mexican. [volume] (Santa Fe, N.M.) 1898-1951, 1900-08-31
C0CHITI DISTRICT
An Accurate Description Of Its Geo.
logic Formation and Its Min
eral Resources.
ARTICLE BY W. c. WYNKOOP


come in Treating the Ore Found at
Bland and Vicinity-Developed
Properties.
w. c. Wynkoop, manager of the Co
chiti Reduction and Improvement Com
pany at Woodbury., six miles below
Bland, has a very interesting illustrat-
ed article in the Engineering and Min
ing Journal of this week on the Cochiti
mining district, which Is of Importance
and of great interest because it Is writ
ten by mine expert who is thorough
ly familiar with the district and it's re-
sources. Mr.. Wynkoop says:
THE Cochiti district, New Mexico, is
a comparatively new mining district,
situated in direct line thirty-five
miles due west from Santa Fe, in the
Jemez range of mountains. The mines
are located on the eastern slope, at an
elevation ranging from $500 to 5000
feet. The known good ore-bearing veins
are confined to an area about three by
four miles in extent, though veins,
which, so far as known, are barren of
good ore, are found on every side out
side of the small producing area. Three
parallel canons about one and a half
miles apart, having general range
slightly west of north, extend through
the district. They are from 500 to 500
feet in depth, and are bounded by ver-
tical cliffs or precipitous sides. The
topography gives good opportunities to
study the geology of the region. All the
country is volcanic, and the prevailing
rock is pOrphyritlc andesite. In few
| nlanaC Ia n Vn1fCturha1. I1xy ~ &c
brecciated or a congloMerate. Nowhere
in the region are the underlying rocks
visible; local authorities say the over
flow took place at about the close Of the
Jura-Trias; Bandolier says the under
lying rocks are Cretaceous, but am in
clined to think, without any other ba-
sis for the opinion than their corre-
spondence with the similar and near
by of the San Juan region in Colo
rado, that they are Tertiary; this, too,
is the age ascribed to them by the eth
nologists, who are just now deep in a
discussion trying to demonstrate that
man lived on earth during the Tertiary
age, basing their claims on evidence of
human work found in volcanic rock in
this region.
There are at least two volcanic over
flows here; the older one is the andesit-
ic, and it is in this only that the veins
are found. The younger one, covering
the andesite, Is tufa, and Is very mod
ern. 1t is in this that evidences of hui
man life are claimed to have been
found The ethnologists, I think, have
made an error by ascribing this later
rock to the wrong age. Among other
evidences of the late deposition of the
tufa Is the fact that it is found covering
VI to- oh otnr
worn boulders and ore float, clearly de-
rived from the disintegration of the an
desites and their accompanying rocks.
I'm the upper or portion of the dis
trict nearest the range, the tufa has
been mostly eroded, but in lower por-
tiOns 1t still caps some of the noun
tains, covering the veins which out
crop on the mountain sides below.
After the deposition of the andesite the
country was faulted and fractured, and
dikes were formed, and there were con-
siderable changes of elevation, while
denudation formed deep sedimentary
deposits. which extend easterly to the
Rio Grande river, fifteen miles distant.
The periods of elevation were gradual,
and extended over long periods of time,
until a late one. which was probably
contemporaneous with the tufa over
flow, which was rapid as geological
time is measured.
1.-THE dikes are generally of soft
gray, acid porphyry, with occasionally
one of diorite or trachite. Following the
first period of dixie formation, there was
second one, the dikes Of that period
following the first and adjoining or cut
ting them. The second series are small
er than the first, and are composed, so
far as I have seen, of basalt, or phono-
lite. Running parallel to and within a
few feet of the main dikes are many
small veins of white quartz, barren of
ore. The largest dikes are about 100
feet in width, narrowing in places to a
few feet, and again widening to more
than 100 feet. All of them throw off
spurs running at acute angles to the
main dixie, and extending hundreds or
even thousands of feet. The ore Is en-
tirely a replacement of the dixie ma
terial. In some places the replacement
has been complete, and in others par
tial in the latter the replacement may
nave been all adjoining one WALL or in
streaks or pockets or bodies anywhere
in the vein. Porphyry horses" are
found in all the workings, and frequent
ly chunks of quartz will be found to
nave a core Of porphyry around which
The ore is deposited in streaks, forming
handsome samples Of banded structure.
"The quartz deposits are peculiarly
characterized by fracture planes (hav-
ing no better name for them) parallel
and from a few inches to a couple of
feet apart, which run almost at right
angles to the strike of the veins. Some
times these planes form very distinct
boundaries to the ore. Rich or pay ore
will be cut off by them, the rock ad-
joining being barren; at the next, OF
some other plane, the ore may reappeal
as suddenly as 1t disappeared. These
barren spots sometimes extend for a
distance of 100 feet or more. Practical
ly all of the ore of the district carries
from IS to IS per cent silica. Silicious
rocks characterize the entire region
Opals (mostly wood, but occasionally
precious one), chalcedony and brilliant
but small quartz crystals are abundant
Analysis of the ore shows 1t to be
an arsenical pyrite, though the amount
of sulphur and arsenic present Is very
small, generally to 2 per cent of thu
former, and from trace to 0.5 per cen
of the latter. Copper and lead arr
found only in traces Manganese Is oc
casionally plentiful, but does not ap
pear to be a constituent Of the good ore
Anthony Is more rarely found, and Il
always an accompaniment of higl
values. The ore of smelling grade
ranging in value from $50 to $50 or NOR
per ton, is generally found in lenticula
bodies, extending longitudinally from ;
| few to 100 feet or more, and vertical!
| the same distances. These pay streak
vary in thickness from few inches tt
10 feet, and are often so solid that tn
ore requires no sorting. Generally tn
low grades are formed by the dissent
nation of specks Of high grade through
an otherwise practically barren quartz
"All of the ores carry gold and silver
the relative proportions varying IN ar
ferent properties. On the vein which
have been developing the values are s
per cent silver (valuing 1t at GO cent
per ounce and 40 per cent gold. thoug
it is not unusual to find places wher
the value Is almost entirely gold. In
few properties gold largely predomi
mates. The. quartz, as might be expect
ed from its composition, Is exceedingly
hard and costly to drill. but as rule