The Salt Lake tribune. [volume] (Salt Lake City, Utah) 1890-current, 1907-05-27
TELLS Of MINES OF
yER|NGT0N CAMP
District Presents Many Very
Interesting Studies to the
Mining Engineer.
EXTRACT OF PAPER
READ In CANADA
Mining Engineer Jennings Tells
of Wonders of Noted
Copper Section.

| The following extract Of paper read
by E. P. jennings. the local well known
! mining engineer. before the Canada
mining Institute last March. appears In
the Mining World:
The Yerington copper deposits in Lyon
county Nevada, forty miles southeast Of
| the famous Comstock lode. present many
interesting features both from commercial
and geological view points. The Mason
| Valley mountains in which the mines are
| located are q small north south range
about twenty-five miles long and three
to six miles wide. with maximum ele-
walton OF $500 feet above sea level and
| 1000 feet above the valley OF the Walker
| river, The core of this range is intru-
sve granite. exposed in the highest peaks
and In the deeper canyons where the ero-
| sion has been greatest. but covered by
| metamorphosed sedmentary strata on
| both the eastern and western slopes. Late
| rhyolIte flows occur along the eastern
base OF the mountain. The intrusive
| granite is coarse grained mixture OF
feldspar. quartz. hornblende and biotite.
| becoming porphyritic In structure near the
| contacts,
Resting on this granite are beds OF
| rock several hundred feet thick. composed
| OF the lime -alumina garnet. grossularite
| graduating into andradite by the partial
| replacement Of the alumina and lime by
| iron. This rock varies in texture from
compact mass TO coarse crystalline ag-
gregate OF a cinnamon brown color. Thick
| beds of white to gray crystalline limo
| stones cover portions of the garnet rock,
| but their original area has been greatly
| reduced by erosion An extensive series
OF metamorphic rocks also occur, whose
! Of the range where they have n nearby
vertical dip and a thickness OF 5000 feet,
This series is uncomfortable with the
garnet and limestone on the western
slope and separated from them by fault
which has dropped this later series into
It's present position. These rocks are not
III :. snl I1,1 tl1 afr
their relation to the garnet-lime series
| Is obscure, In composition they range
| from sllicifed lines TO microscopic as-
gregates of tremollte. lime-siicates and
! blotite. and probably were lime shales
and slates originally.
The eastern foot-hi are covered by
| late flows OF rhyolite that have no con-
nectlon With the ore deposition, The
structure is complicated by a system Of
folding and faulting. older than the gran
ite intrusion. also by faulting after the
| naturalization. Copper ore occurs in the
garnet rock as an impresnation through
out portions OF Its mass and as richer
zones; also as bedded veins in the mar
bleized limestones. The effect of the fold
Ing and fracturing of the strata previous
to the granite intrusion has been TO 10
callze. In q degree, the deposition OF the
ove in the garnet roc. along these frac-
ture zones. giving the deposits sE,os I the ap-
| copyrite disseminated In a garnet or gar
.net-epidote gangue,, which has laminat-
ed structure parallel TO the boundaries
of the fractured zone On either side of
these assures the garnet rock is more or
less impregnated with chalcopyrite, but
separated in some cases by narrow rib
The lower boundary of the ore is the
granite as shown in the Bluestone mine
the contact Is we'll exposed. chalcopyrite
In arnet-epidote gangue resting direct
ly on the barren intrusive rock, The
| marbeliZed limestone which, In places,
| bo
veins filled with oxdiZed copper ore in
a quartz and calcite gansue. At water
depth OF 600 feet, pyite and ehalcopyri,e
begin 10 appear. replacing the oXidized
ore The mines have not been sufficient
" developed TO show the relation OF the
ore in the limestone with the ore OF the
garnet shear zones, but that there is
some connection is very probable. The
chalcopyrite and pyrite which have been
oNidzed and partly leached forming in
the upper enrichment zone, malachite,
azurite and chrysocolla, and covellite as
n coating. or chalcopyrite in the upper
! sulphide zone. Bornite and chalcocite
! occur as secondary sulphdes In few In
stances.
These ore occurrences can be classed as
contact etamorphic deposits. hut diff
fering from the ordinary type in which
the ore occurs as Irregular masses near
the contact: this difference being due to
the existing assures which confined
the re-bearing waters In channels of
local concentrations the garnet is impreg-
mated with low grade copper ore. Where
the assures were more open they were
filled by the molten magma, forming dikes
of granite -porphyry. The mine develop
ments are not OF sufficient extent to
connect the limestone ore bodies with
those contained in the garnet, but II is
! difficult 10 avoid the conclusion that in
| depth the two classes OF ore bodies will
connect forming continuous lode. whose
lower boundary Is the granite and with
its apex in the limestone.
II this view is confirmed by later work.
the deposits will be of great interest as
illustrating the genesis OF ore bodies due
| TO the action OF Intrusive rock masses,
the magmatic waters OF which have min
eralized certain re-eXisting assures. and.
! together with the heat derived from the
imentary beds into garnet rock containing
! more less disseminated orc and other
beds, in a higher horizon, into marble.
and also filling fractures parallel TO the
bedding of this marbeliZed limestone with
copper ore.
II Is not possible at the present time
10 determine how much Of the rock met
amorphsm Is due to the heating effects
of the intrusive and how much TO the in
| PRODUCTION of new compounds by the wa
teTs Of the molten magma, but We can
assume that the ore Is due TO these wa
| ters and that the rock metamorphsm was
! largely caused by the action OF heat. sup
| plemented by the chemical action of the
! water, as the garnet is more OF less i'm
pregnated with ore. showing Its per
| meability to these solutions which un-
! doubtedly contained other mineralizers
that contributed TO the formation of the
garnet
The limestones. which occur at higher
horizon. have probably been altered by the
| action OF heat alone, as they contain
trict is being developed rapidly; one mine
! having 100000 tons OF ore In reserve.
and in two years time IT. Is expected TO
become copper producer on large
scale.