The Wallace miner. [volume] (Wallace, Idaho) 1907-current, 1913-10-16
ORIGIN OF LEAD, ZINC


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tain, in Eko county, Nevada, lead
occurs with copper in contact dcpos-
Its that appear to have been some
what modified by secondary vein
action At the Mount Hope zinc
mine, in Eureka county, Nevada, a
dark ziucblende. accompanied by
little galcna and chalcopyrte, Is mix
ed with contact metamorphic sill
Gates produced by the intrusion OF
rhyolite rock into the Nevada lime
stone. There may be many other
places in Nevada where lead and
zinc sulphides are apparent primary
constituents of contact metamorphic
deposits, but believe 1t Is true that
they are relatively limited In extent,
have some copper sulphlde and ao-
probable quantities Of gold and sill
ver
Occurrence of Load IN Arizona.
! In Arizona, lead is usually absent
| from the primary naturalization or
the contact metamprphic copper de-
posits. In q district visited by mo,
galena occurs with quartz or f.uor-
| tie in fractures in the primary cop
per ore and clearly represents lat
cr stage of naturalization. At Butte,
Montana Mr. Weed says galena
seems not to be present in the old
copper veins, but to be confined 20
| the later fault veins Lead certainly
and zinc possibly must be placed IN
different category from copper ana
iron. The fact that iron, copper, gold
and silver deposits may often with
fair reason, be attributed to a mag
matte source must not be held as
support to the magmatic hypothesis
as applied to the great lead and ENC
deposits Of western America. The
latter must be clearly established by
local field evidence. 1t Is not sutil-
cient to show that cruptive rocks oc-
cur in proximity to the ores ana that
some Of the deposits have contact
mctamorphlc characters IhuS, III
the Park City district while 1t has
been shown that there Is an apparent
genctic connection between the ore
deposits and certain diorltic intru-
sives, actual tracing of the lead MIN
eral into the diorite is needed ~
bring conviction. In the absence OF
that, one is justified in placing on
one side the known existence OF great
lead concentrations by the sedigen-
etc process in the Mississippi valley
and on the other the absence of any
equally strong evidence of the form
alton anywhere of a great lead de-
post. low in silver and gold, by the
igneogenetic process What Wouid
happen If the Missouri and Wiscon-
Gin lead zinc districts were buried
under 5000 feet of sediment and In
truded by a granite magma? There
would be RECOMMENDATION of the min
erals and the formation of typical
lead and zinc contact deposits.
Conclusion.
In conclusion, submit that so far
as the origin of the lead and zinc de-
posjts that are being mined IN the
Occur d'Alcne district Is concerned,
the modified sedigenetic hypothesis Is
rational one. that there Is much
field evidence tending TO establish !,
and that the chief objection thai can
be brought against 1t Is the fact that
the supposed. diffused deposits IN the
sediments have not been found. Tho
last is purely negative evidence that
may exist only because the proper
search for these deposits has not been
made. The magmatic hypothesis, on
the contrary, Is not supported by anT
field evidence that can not be otner
wise satisfactorily explained, and II >
negatived by study of other min
eral deposits in the Occur d'Alen
district, in the region of the great
Idaho quartz monzonite intrusion and
in the western United States In gen
eral