Tonopah bonanza. [volume] (Butler City [i.e. Butler], Nev.) 1901-1909, 1907-08-31
UNsoLvED PROBLEM.
impregnations of Copper in Purely
SedimentaTy Rocks.

w hot q lew pTODlemS IN
economic geology that are as yet un-
solved, and are open for speculation.
One of these is the occurrence of i'm
~pregnations Of copper in purely sedi-
mentary rocks uncOnnected with any
visible or probable volcanic source or
manifestation. Where did the copper
come from, and how did it get where
we find it? When we find copper IN
igneous or metamorphic rocks we at
tribute its origin, as of other metal
liferous veins, to hot solutions asso-
ciated with igneous or metamorphic
agencies; but when such impregna-
tions, or copper ores, occur in purely
s~edimentary rocks without any obvi-
Gus connection with volcanic or meta
morphic agencies, we are somewhat
nonplused to account for their origin.
Down on the ella river, in Arizona,
at a locality appropriately named
Copper mountain, we have seen an
area impregnated with copper, usual
ly in the secondary form of copper
carbonate, with some copper glance,
or chalcocite. As these deposits oc-
cupy a highly volcanic center, which
was probably once a large crater, and
in which all the rocks are of igneous
or volcanic origin, we readily at.
tribute the copper to .emanations of
hot springs and fumaroles in the last
stages of dying vulcanism. But when
VIC find in the Green river beds Of
Wyoming or of eastern Utah deposits
of similar copper underlying large
areas, and lying evenly between beds
of s~edimentary rocks like a coal
seam, with no trace of any ancient or
modern volcanic agency in the vicin-
ity,'or for hundreds of miles from the
spot, we are at a loss TO account for
the copper.
We have generally assumed that
ultimate or original form Of copper
to be copper sulphide. or copper py-
rites, put in these sedimentary de-
posts tn ereis no trace of sulphide.
The ores are all of a secondary char
acter, such as ~carbonates, oxides, or
ch~alcocites. There are no assures or
assure veins in the vicinity. and the
strata lie as evenly horizontal and
u%ndisturbed as they were when laid
down by the waters of the vast ter.
, tiary lake that M covered thai
Green river area for thousands Of
square miles.
= Again, we find in various regions
the sedimentary red beds of the Jur;
Trias, stained or impregnated witt
copper, sometimes sufficiently so al
: to constitute a workable ore. In SOM
I cases organic remains are abundan
in these rocks, and may have consti
tuted a precipitating agency for cop
per solutions; but whence came thos
solutions? There is no reason to be
lieve that they percoiated from vol
canic rock that have long since bee
removed. In some cases. as in Ne'
Jersey, such sedimentary impregna
I tions have been accounted for on tn
/, hypothesis of hot springs ascendln
/, from beneath and probably from
deep-lying volcanic laceolite, or sui
terranean igneous magma. But !
that region there are trappean Is
neous rocks not far distant, ais
, carrying copper Such a hypothes
:, would hardly apply to a field lii
J. that of Green river.
Can It be possible that certain sea
or other large bodies of water, coul
locally be SO charged with copper 81
buttons. derived from some unknoN
sulphide source, as to be capable
being precipitated by organic or 9TH
agencies to such an extent as subs
quently to form beds of workable co
" per ore? It is an open question
invite geological discussion.-Arth
Lakes, in Mining Reporter.