Santa Fe new Mexican. [volume] (Santa Fe, N.M.) 1898-1951, 1900-10-02
THE CHAMA PLACERS
A Device That Is Now Used with
Success to Catch the Black
Sand,
MANY EXPERIMENTS MADE
U%ndercurrent Devices with Screens Which
Size Down to One Fourteenth Of an
Inch-The Amalgamation Idea a
Failure and Discarded.
Mining and Scientific PresS.)

Mining and Scientific Press.)
The river dredge placer machines Of
fer better facilities for saving the gold
silica and black sand than 9TH
ei placer machines, on account OF their
compactness, quantity of dirt and
and nature of their machinery. AS so
many dredging plants are not a paying
it would be we'll to look into
the concentration of these sands, for
when some cheap and efficient means OF
saving the values they contain is found
no doubt many otherwise valueless
placers will be dividend paying PROPOSE
lions.
DREDGING ON THE CHAMA.
In 1S9S-99 I was dredgemaster for the
New Mexico placer syndicate on the
Chama river, in Rio Arriba county,
where an experimental dredger was
built, and many tests were made with
various devices for saving the values or
the river placers of that district. Ordi-
AIRY sluice boxes with different design
ed rifles, and loaded with quicksilver,
were first tried with no success; failure
revealed the fact that the bright-look-
ing gold was covered with a transpar-
ent siliceous coating, making the parti-
cles look twice their actual size. Forty
assays were then made from the river
material, ranging from the surface to
20 feet in depth, giving an average of Az
per cent free gold, 40 per cent in m
nation with the silica and 20 per cent in
combination with the black sand. There
was 1.158 per cent black sand of the
material as it came from the buckets;
| and extracting it with magnets was
tried with the result that only the mag
netic iron was caught, and assays from
this showed but a slight trace of gold.
The amalgamation idea was discard
ed, and the boxes were provided with
cocoa mating, expanded metal and de-
vices with un~dercurrents. These gave
little satisfaction, as the interstices
would quickly fill up, letting the values
run over and causing too frequent shut
downs.
CONCENTRATING.
All who are experimenting in this
class of mining seem to be working in
the same channel, viz, to saw the black
sand by a single o~peration-that is, by
dumping the whole mass into a box,
sluicing off the coarse material and
saving the valuable silica and black
sand, as in washing gold: but I find the
gravity of the silica too near that of the
black sand to allow of such rough work.
The Chama river people have been car
rying on experiments in this line with
undercurrent devices for the past ten
must use screens, which, by sizing to
one-fourteenth of an inch, will take off
four-fifths of the material as it m
from the buckets, giving their machines
much lighter work. BY leaving their
concentrates run 10 to 80 per cent of the
reddish silica, so manifest in the Cha
ma, and which is the silica that carries
the gold, they obtain a concentrate as
saying from s35 to $50 per ton. While
engaged with them I built a revolving
burlap concentration that worked we'll:
the interstices would catch the reddish
silica, black sand and fine gold, and, as
t. revolved. the concentrates were
washed into a hopper, leaving the bur-
lap clear to be filled anew as it came in
contact with the s~luicing material. AS
before stated, they were looking for a
device to do away with screening,
which would condemn that class of ma
chinery, as it could not handle such a
vast amount of material; besides, the
large bOulders would not let it do good
work and would knock 1t out quickly.
Therefore, it was set aside to make
screens can be used, I do not know of
another machine so efficient as one with
a revolving burlap. I once tried bump
ing tables to bring a 6 per cent black
sand concentrate to 60 per cent, and
found they were too slow and took up
too much space to adapt them to placer
work, as wer also devices that required
stopping and cleaning up every few
hours.
MODIFICATION.
AS all placers have a popularity of
their own, and necessary smelter facili-
ties for treating the concentrates vary
with locality, a slight modification may
be required; but, in general, screening
t1n H.
through a series of revolving screens,
n running the fine material over one
OF more revolving burlap machines, ac-
cording to amount handled and fineness
required. to be determined by values in
the silica and smelter facilities, Is (from
what data I can collect from the expert
ments of others and those Of my OWN
the best arrangement for extracting the
silica and black sand of