SUBJECT TO
REVISION.
[TRANSACTIONS OF THE A3lERICAN IKSTITUTE O F BIINING ENGINEERS.]
Features of the Occurrence of O r e at Red M o u n t a i n , O u r a y
County, Colo.
BT
T. E.
SCHTVARZ, DENVER;
COLO.
(Annual Meeting. February, 1905.)
THE lwblicatiou of the rel)ort 119 Mr. P. L. Ransomel was
~velcomeclby many engiilecrs \vho ha(1 mined in the heart of
the Sit11 Jn:in conntrg, braved its long a~icl snowy winters,
clinlbecl its lofty peaks, run the gauntlet of its snow-slides, nlid
stnclied its l)roblems of geology, while niaking c1ivi;lrncls for
their English or American clients. This r e l ~ o r thelps one to
nnclerstand why the bonanzas occurreel, aucl why the inevitable
borrasca presents itself where least esl~ectecl.
The Red Mo~ultnindistrict of Ooray couatj, n very,l~rocluctire bectioll fro111 1884 to 189.3, occupies consic1er:tlle space ill
the report mentioned. Tht: character of the ore-occurrence,
being dishinctive 2nd preseubiug rilany fetttures not esisting
elsewhere, has been deserving of' special st~iiclg. It, is to be
regretted t1hnt.Mr. Ransonle 11-as nilable t,o ul~serrethe conditions unclergrouncl, its all t,he priucipal properties, hallJr of
which I ogenecl nud cleveloped, were clo'secl nt the time of his
investigation; I t 11% been my privilege t o have contributed
a fen. 1:)rief papers,' recorcling my observa.t,io~~s
iu developing
these properties; ancl it is the object of' tlle present paper t,o
present certaiu sections of the
Girl mine, which t,hrow
nclditio~~al
light on the geology of the sect,ion and make t h e
iivnilnhle clnta n ~ o r ecomplete. The muin Yankee Girl chimney
or '' stock" was the most ~~rocluct,ire
for the first 500 ft. in
depth of a119 chimney in the clist,rict,.
Mr. R:ti>some describes these ore-bodies as upright stocks,
referring to tllenl :IS follo~rs:3
' A Bcport on the E e o ~ ~ o ~ iGeology
lie
of tile Silrertot~&~ccccl.rcingle,Chlornilo, Bulletin
No. 182, by F. L. Ransome, U. S. Geological Surrey.
The Ore-Deposits of Red i\Iountnin, Ouray County, Colo., Z'I.(L~LS.,xviii., 139145 (ISSO-90). Also ssri., 10.5!;-1059 (1SYG).
Op. cit., p. 107.
.
[1I
l L I ti 9 evident from tlle descriptiolls given of the Red JIountain stocks, that the
term 'chimney' applied to thew is so~uewliat misleading. They are not simple
vertical pipes of ore extending fro111 tlie surface to indefinite depths, but are
separate bodies of irregular, lenticular, or spindle-shaped fortu, often completely
enclosed by conntty-rock, but linked with ~~eigllboring
stocks by tisaures which
are uften small and \vIlicll carry little or no ore."
I c:~nuot agree \\lit11 Mr. R.nusome in the use of t,he term
stock ;" and I regn.rc1f G cl~illlney"as much more expressive nud
suggestive of the lilaill fe;tt,ilres of t,lle occiirrence. I t seems
to m e the former tern1 applies 110 better to tlie Reel R/Iountuin
ore-bodies t1in.n to those of t,he R:~ssicko r Bull-Domingo nines
of Custer couuty. One of t.he features of the ore-bodies of ICed
Mouut:tiu is t.his T ~ ~ persist,ence
~ J J
in ilel1t.11, proven in the Ytillkee Girl, Congress, Genesee-V:~ntlerl:tilt.,Silver Bell, nut1 Glisto~l'
mines, to,the clepths attained. I do not, recn.11 L: single iustance
of n chiml~eyon tlie above-named properties where the terms
Irut~iculixr" or sl~i~lclle-sh:~~pel
" woilld apply as descril:)t.ive
of t,be form of the ore-bodies. Their formation by replacernellt
of the breccia is well proreu, and t,l~emerging of the ore, I\-Ilich
occurs m:~seive ancl rluitc fkee from silica or wast,e, into the
country-rock on nearly all sicles is cliaritcteristic. I t is true
they were somet.imes very erratic :~ucl dilticult to fol.lom, especially in the upper levels, owing to t.he absel~ceof any clefined
slip or fracture leacling to th6 ore-bodg, or cot~nect.ingtnlo o r
Inore chimneys.
I u opening a new level, the ore-break;" or belt of altered
breccia i n which t,he chiluueys occurreel,' nrus first 1oc:~ted.
111 this area t,here might l ~ e
some one fracture-pl;tue, perl1:~ps
very obscnre, which if fi~lloweclwoulcl leacl to a chimney; biit
as such planes rarely had bile same course 011 two successive
levels, the fiuiliug of the quartz " or siliceo~isenvelope of the
shoot was, iu the upper portiolls of t h e ore-l~oclies,the first
notice of their prosimit,y. T h e difficulty of fi,llo\ving the
" pa^ " was increased by the utter uncet.t:~i~ityot' the l.)ositiou
of the areas of llli~ssireandesite. (See Fig.' 1.) These ~velldefined nlnsses enclosed no ore-l~oclies,:tl~il were very untllll:~tory, both vert.icallg a n d 1i.orizontnlly. IVIiethc~~
~ L I I ~of
: these
shonlil be properly clescribecl as intriisive clikcs, I I - I ; I \ , ~ tlever
fully satisfied myself, alt.hough they possess 11early it11 t l ~ ecl1:lrcL
,
.
Trcins., xxri., 1056-1(l.j9 (1S91i).
[21
-
acteristics of n clike. Their course 011 the surface is more
ne:trly east and west than the course of the general frnct.uring,
which is placed by Mr. Ransome at N. 20' E. This was well
illustrated by the Gustou chimney, \\~llicllin its course i n the
Fro. 1.
Scale 80 fi:=l inch
+ + + +
YANKEE G I R L MINE
Showing Ore-Break at the
Second Level, and portions of
containing-walls, asdetermined
by development in the lower
West lVull-
PLANOF YANKEE
GIRL~ I I S E SHOWING
,
ALSO
THE
POSITION
OF CENTERS
OF
Cn~nrs~ri.
Guston-Robinsou ore-1)renk " follo~vsa frnvture between the
third and fourth levels clirectly through one of these dike-like
nlnsses which extends up the mountain from the Guston into
the Little Annie claim. Esccpt in the above-mentionecl instance I (lo not Bno\v of ally ore-body crossing or euterii~grock
of this cl~arncter.
37(!
.
.
,
OCCURRENCE O F ORE. AT RED R I O U S T A I S , COLORADO.
While Mr. Ranso~llerefers t,o t,he occnrre~lceof t , l ~ e sareas
~
of 11l:assive andesite nud to iutrl!sive dikes in t,llis section, their
relation t o em11 other ancl to. the ore-l~oclieais not ment,ionecl.
I presutne,,ho~vever,these feat,ures vill Le cooerecl by t,he fort,llcoming report by Mr. Wllit,nl;lu Cross upon t,he geology of this
dist.rict.
Oue of the clist,iuct,irefeatures of these chimneys is t,he silicified n~lclesite enrelolle, wliich, as in the Nntiona,l Bell,e, Congress, Gnston, Robinsoa, :t~lcl White Cloud mines, project,^ in
lllassive knolls of " quartz" nbore t,he surrounding surface, aacl
ma.rks t,lleir outcrop. This s i l i c e o ~ ~nlntris
s
of the ore-bodies
is 1:lrgest near t,he surface, ilecressing in size izucl hardness ~rritll
dept,ll, until i t finally ceases to be a11 eurrelope of t,lle chimuey;
ancl the enclosing rock becomes comp:~~r:~tirely
soft, altered anclesite. 1t.s occurrence seems to Le. parallel n~it,llt,hn,t of t,he
Iligher-grade ores, which ~vo~llcl
indicate t,l~ntit was a feat,ure
of the zone of secouclnry enrichmeut.
T h e n c c o m p a ~ g ~ isketch
~ l g of t,heYankee Girl chinlnegs, given
in Fig. 1, shows the ~~osit,ion
of the center of eacll ore-chinlaey
on the iliflerent lcrels coverecl 1)y t,lle notes, anil of the bounding-fi~cesof massive nuclesite, which enclose the ore-break.
T h e development on the successive levels was not su6cient to
s110~17 the li~ilitsof the ore-l~renkat all
t,lierefore, the
position of t,he antlesite ftlces is outlined ouly so f i ~ rus it, has
been practicttlly disclosed 11.): clrifts. It. \rill be 01~servec:lthat
t h e several chimneys grad~lnll.):a11prc1aclithe largest, or Y i ~ n k e e
Girl chimney, i n . tlepth. T h e Orpllna B o j ancl the Yaukee
Girl chimneys joiuecl ljet,~reenthe sisth ancl sevent,l~levels, as
sho\vn in Figs. 1 and 3. On t,he sist,h level, just above t.he
~ ~ e : ~ ,horizont:\l
rly
clay-seam, ~ v h i c his referred to by Mr. Ransome," nlist,inctly solitl body of ore occurred connecting these
two chimneys for nearly 6 ft. in lleigllt nucl 60 ft. in leugth.
T h e r e nrns 110 fault,ing on this flat seam, as has been st,ateh, but
tliere nrns a very mttrkecl change in the character and pracle of
t,he ore. After the Pi~.nBeeGirl ore-hody l~asseclbelow it,, t,he
stromeyerite, which occurs above, censecl entirely, a~iclmassive.
Jjornite occurs, which is riare above this point.
Referring again to this cross-frgcture, I see no reason for
. '
O p eit., p. 21s.
[ .iI
L
I
1I
i
\
nssumii~gthat it is icle~lt,icnln1it.h the f'nult-111ane \vhich occurs
below t,he seventh level of the C4uston mine, as stated by Mr.
, R:~nsome.~ The evidence wa's that it a~lteclntedthe ore-cleposition, ancl in fact there are but slight iudiciltions anywhere in
the mine of clisplacemeut,~or fracturing after the ore mas depositecl.
I t is iaterest.ing to note the illcreasing percentage of bisnluth
in the ores of the upper levels (from 300 ft.. to 500 ft. in depth)
of the mines ou t,he line of the main fracturing, fronl those on
the south a.ucl highest iu elevation to those on the uorth and on
lower ground. I11 t'he Congress mine oil the esbreme south
ancl near the cliricle, t,lle ores a,re a,Imost elibirely e1lnrgit.e.
Proceecliag down the \7nlley the Hitdson itud St. Lanlreuce
ores show appreciable quantities o f bismuth, which increase in
the Geuesee-VnnderLilt, Gustou, nncl Silver Bell mines, iu the
order nameel. T h e latter propert,y proclucecl massive boclies of
ore high in bismutl~,ancl carrying from 500 to 1,000 oz. of
silver per ton. The ores of tile Yankee Girl mine are not iucluded in this compnrison, being to the west of the niaiu fracturing mentioneel; however, t.11e-j carriecl little of the bisnluth
minern,ls.
Fig. 2 gives the sect.ions of the main chinlney of the Yaukee
Girl miue fro111 the surface to the ~ e v e u t l level,
l
aud shows the
orebody itself, t,he altered audesite nncl siliceous euvelope filling the ore-break, nncl the bouncling-faces of massive nndesite
11etn7een nrhich t,he chimneys occur.
There are therefore many features of t h e ore-occurrence in
this section, which should be more fully stnclied and which
might be disc;ussed with profit.
T h e Yankee Girl chimney is, ns Mr. R,ansorne points out, a
notable instance of secol~daryenrichment. On the tlleory of
descencliug acid-solutions, t.lx seam referreel to as occurring
just below the sisth level, eviclently induced n conceutr~tiouof
silver-values above that point, a t the same time allo~vingthe
col~per-valuesto pass through i t and enrich t h e ore-body below,
sncl accounted for an entire cl~angein the nliueralogical character of the ore.
Whnt were the ores of the upper portions of the Yankee Girl
Op. tit., p . 10s.
[$I
. ..
.. .
nucl Guston cl~imneys,previous to the scoring away to the present level ? They showecl low-grnrle leacl-ores nt surface, followecl
by illcreasing l?ercenta.ges of col>per,the tlisal:~pearanceof leacl, ,
ancl t,l~emarkecl occurrence of the rich silver, copper anci bismuth cornhiuations. I s it not probable that ennrgite esist,ecl in
higher horizons, as it forms the ore of the chim~leyson higher
ground to the sonth ? I n the Nntioilal Belle mine, it occurs as
i~ principal mineral in au ore-body 75 by 60 ft. in men, and nppears in a11 the ~vorkiugsas tbe sulpliicles occur in clepth. l u
the Congress mine i t is the ore to the lowest. level (450 ft.), and
it, occurs also iu the upper ~vorkingsof the Genesee-TTanderbilt
mine.
The paper by Mr. Walter Harvey Weed,' explni~~iug
the occurrence of ent~rgitein the Butte mines, as a seconclary procluct
clepositecl by a,scending alkaline-solutions, is very interesting in
this connection, nncl ninny of the features of the Red Monntaiu
chimneys seen1 in accorda~lce~ ~ i this
t h theory.
I desire. therefore to call speciitl attellt,ion t,o t,he following
features of the occi~rrenceof ore in the Red Mountain district,
viz. :
1.' That the ores have occurred iu persistent chimneys, t,o
which the tern1 " stocks" does not well ap1:dy.
2. Tllnt in the upper zones-from 300 to 500 ft.-\\-ell definecl fracture-planes, bouncling a.u ore-body or connecting two
or more of them, were not mnch in evideuce. The wet fissures
fillecl wit,h clay clescribecl by R.ansome becanle markecl features
only n.it,ll deptl~.
3. The masses of blue, blockg, unalterecl mclesite, reseml y and
bling dikes, outcrop on t.lie surface wit11 a ~ p p r o s i ~ a t e east
west courses, a.nd 11iaL-ean angle from 70 to 90° ~vit,hthe course
of t,he ge~lera.lfract,uring.
4. The siliceous envelope of the chimneys is a markecl feature on the surface and in the nyper levels, gracludly' clist~ppeizring with clepth.
5. E ~ a r g i t ~
occurs
e
but slightly in the Yankee Girl a.nc1Gust,on
chimneys, while i t is t,he ore of the chimneys to the south on
higher ground.
'
Ore-Deposition and Vein-Enrichment by Ascending Hot Waters, Trmu.,
xxxiii., 747.
i