The Salt Lake herald. [volume] (Salt Lake City [Utah]) 1870-1909, 1905-12-31
ALTA, Its Geology Ore Occurrence and Naturalization xaM

Alta camp or Little Cottonwood min
ing district. being at the dawn Of a
modern method era, and promising so
We'll to attract worldwide attention
as a famous mining camp, data
concerning its geological history and
economic relations to mineral industry
in the light Of modern deductions, are
OF great interest, especially in the
fact that so little Of a technical ma
ture has been written on the district.
Geologically speaking, the bearing
strata OF Alta dates from the very
foundation layers OF the earth's crust
and its main ore bodies are but lit
tie removed from the granite or basal
formation, and, indeed, important ore
occurrence exists both in and at gran
lie contact with quartzite and lime
stone. The stratigraphy Of Little Cot
tonwood canyon, from its mouth to
Alta at the head of the gulch, is as
regular as the leaves of a book, and
presents a simple anti-ciinal fold with
a general north and south axis greatly
eroded both at apex and west limb.
Practically no mining is done on the
valley slopes of the Wasatch range,
primarily because the limestone or
ore-bearing strata is erOded almost en-
tirely away 10 a great depth below
the slopes Of Great Salt Lake val
ley. -~...'.... .....-...
To reach the mining region Of the
range it is necessary to go up the
narrow gorge OF Little Cottonwood
creek, passing through some six miles
OF apparently barren granite, which
constitutes the core Of the range struc-
ture. Just below Tanners fat the first
sed1mentary rocks (the lower quartz
ites) are seen browning. the granite
and dipping regularly toward the head
OF the canyon. Four miles above or
near Alta, the limestones that lie on
the -quartZites reach the bottom of the
canyon, and .ereafter the canyon,
which here broadens to quite an ex-
tsnstve open fat, is entirely in lime
stone and upper quartize, and this Sc
r1es OF strata constitutes the mining
region.
The thickness Of the total limestone
strata, as exposed, is probably in the
neighborhood of $500 feet, and is as
sumed to be Of lower and upper car
boniferous, The lower strata. or that
which lies on the quartZite, is OF a
blue and white banded structure, and
on this strata rests some hundreds of
feet in thickness of Columbus quartz
lite, on which is several hundreds OF
feet in thickness Of upper limestone.
The upper lime stratas are also inter
laid with black and shaley lines.
This upper mass Of limestone is q
regular series Of distinct layers, the
thickness of the separate bands vary
ing from two feet TO dozens OF feet,
and the whole sloping from 81 to 40
degrees into the north side Of the can
yon, or TO the northeast.
The limestone is traversed by numer-
Gus diorite dykes. and is extensively ifs
sured, and it is these dyke contacts
in some few instances, but mostly the
assured region of sedimentary strata,
that bear the ore bodies. At the ex-
IRENE head of the main gulch there is
an intrusion or denuded laccolite Of
granite and granodiorite OF consider
able extent, in contact with lime
stone.
The Columbus quartZite referred to
corresponds in geological age TO the
Ontario quartZite of Park City, While
the Flagstaff and Continental lime
stones ybeaFaa similar relation to the
Silver King limestone Of the same
camp. The same system Of diorite
dykes extend from Park City to Alta.
The erosion Park City in the vi
cinity or the mines has been deeper,
stratigraphloalIy considered, than at
Alta, and the strata that mas been
mined in at Alta represents that which
is erodea at Park City. Accordingly.
broadly speaking. mining at Alta has
only been prosecuted TO barely the
same photographic depth as the out
crops Of ore deposits at Park City.
The distance separating the main ore
regions Of Alta and Park City is but
25. 600 feet. hence the relation OF these
camps TO each other is very marked.
geographically considered, the most