The Salt Lake tribune. [volume] (Salt Lake City, Utah) 1890-current, 1906-02-26
ONTARIO LODE DEPOSITS.
Walter P. Jenney Writes Fourth Arti-
Gle in Interesting Series.

The last OF a series Of four articles was
recently published In the Mining and
Scientific Press on the ore deposits OF the
Ontario lode, In Utah, written by Walter
Z. Jenney. and In commenting upon the
same the Press says:
The explanations offered are fun OF
interest, because they may prove applice
BILE TO other regions. His cross-section OF
the Ontario lode should invite invcstiga-
ton. because the extent to which occur
renee of ore Is affected by change OF wall
rock has long been one of the funda-
mental problems Of mining geology. In
this case rich ore, from three to eight
feet wide. persisted from near the surface
20 a thousand feet. at which horizon the
lode became less productive, the impov-
erishment coincIdlng with change OF
formation, for while both walls were
qUartzitc down 20 100 feet, the foot-wall
became shale at that point.
Nice Question Involved.
"Coincident with this condition. the lode
widened until it was as much as 30 feet.
but tho streaks OF rich ore within this
large width were so far apart that they
became less profitable TO mine. This con-
ditiou began where the foot-wall was
shale and became emphasized when the
hanging also became shale. with limestone
on the foot, that Is, tho lode follows a
fault-fraCtUrc showing a diSlocntlon of
rot less than 80 feet which is approx
matcly the thickness OF the shale beds. II
ls nice question whether the enrich
ment down 90 100 feet was Influenced d.
rcctly by the nature OF the quartzite and.
similarly. whether the iWpovcrishment
deeper down wos due to any quality In
the shale
Lode Flattens in shale.
rs 1t not possible that the structural
conditions explain the latter. and sec
ondary action the former Thus, II will
have been noticed that the lode f0ttens
I'm the shale beds. because II was easier
for the fracture 10 travel along. rather
than right across. the lamlnatlon; Instead
yNsfg Ilf=
width OF shattered rock which prepared
the way for large mass OF scattered ore.
In the quartzite, the fault-fTacturc cut al
most at right angles across the bedding
OF that hard, close-Gralned rock and made
n narrow assure which tended to restrict
ore deposition within narrower limits
These conditions are often reproduced on
smaller scale. where n fair width. four
or fvc feet of medium grade ore gives
place. either I'm strike or dip TO n narrow
scam of rich STUFF. Such cases are usually
due 10 Change OF structural conditions.
Lodes Richest Near Outcrops
",Furthermore, we usually expect to see
gold and silver lodes richest within a GER
tain depth from their outcrop because
the teaching Of the upper part-oftsn
eroded portion-ot tho vein Yields sou-
10 the original metal content OF the ore;
In fact, Dr. Jenuey recognizes this. for
ne mentions q zone of oSldation followed
by one OF secondary deposition WHY,
then, lmpute tho poverty of the vein he
low, this horizon to the effects OF the wall
rock?
The evidence for tho influence OF the
enclosing rock upon the distribution of
ore Is much stronger I'm the case OF the
contact deposit which follows the stratum
OF sort gray limeatone-25 to 20 feet thick
that occurs some distance above tho
quartzlte. In this regard the vertical
section OF the Daly-West mine is partic-
NlaflY instructive. Ore Is found along the
Ontario-Daly nsSure, and apparently Il 4
81 Ntrba fl,.,
hanging wall is black lime gray lime
upper qunrtzite. cherry limestone or
Ontario quartZitc,' throwing doubt on
tho agency OF any particular formation in
producing conditions especially favorable
10 It's deposition. 1t must be pointed out
however. that the foot-wall Is quartzite
throughout this section, while the horses
inside the vein are torn from the hang
ing,
Geological Features,
But the selective action of the mineral
solutions Is clearly suggested by the con-
TACT formation which follows the gray
llme. producing fiat ore-measure which
appears TO have been fed by the various
fractures that were produced by the
faulting Of the region. II appears true
that the gray lime afforded a soluble
stratum In which the ore was deposited
may properly inquire whether structural
conditions were not as decisive as the |
chemical composition OF the rock This /
gray lime Is particularly fragile and |
orlttle rock. says DR.. Jenney; these char
actellStlcs caused IL to be so crushed and J
shattered as to influence the deposition OF |
ere