The Wallace miner. [volume] (Wallace, Idaho) 1907-current, 1917-02-08
CAUSE OF ENRICHMENT
ABOVE PLANE OF FAULT
DISCUSSION or INTERESTING
SUBJECT BY IDAHO MINING
SCHOOL PROFESSOR.

Professor E. K. Soper, of the mining
engineering department of the Uni
Yersity of Idaho. gives some interest
ing observations on the effects of
faults on enrichment of ore In the cur
rent issue of the Mining and Scientific
Press, which are here reproduced.
Elm the discussion columns of your
issue OF December 23, 1915 under the
heading. Effects of Faults on Richness
of Ore, Enquirer observes that in most
instances under his notice where a
vein or ore body is intersected by a
fault, the continuation of the ore be-
meath the plane of dislocation is of
lower value than that above the fault.
This Is condition which / have
often observed, especially in veins
carrying copper, gold or silver. While
II is dangerous to generalize too broad
~ in mining geology, I am convinced
that in most of the deposits of this
nature which l have studied the ex-
PLANTATION lies in the fact that above
the fault intersection the ore in the
veins has undergone secondary en-
riehment by cold descending solutions
The mineral bearing solutions upon
verted from the vein to the fault zone
which is often more permeable than
the vein itself. Thus the process of
secondary enrichment is confined to
that portion of the vein above its in
tersection with the fault. This con-
elnson Is supported by the frequent
existence of sulphides and oxidized
minerals above the fault, below which
the ore changes abruptly In character,
and consists of the primary minerals.
| have observed this most commonly
in copper deposits, but secondary en-
richment also plays an important part
in gold silver, and zinc deposits. Ga
lena veins are seldom enriched to any
marked degree most of the galena
being primary.
THE decided enrichment in the vein
or ore body just above the fault plane,
noted by your correspondent, is
which, / think, many of
us have observed. and it may be ex-
planned by the fact that such an in
tersection of two assures is an espe-
cially favorable place for ore DISPOSE
ton. The descending solutions from
the upper part of the vein may be
'ponded' there temporarily, and in
copper, gold and silver deposits ex-
such places. Moreover these de-
scending solutions may encounter 9TH
er solutions ascending along the fault
zone and precipitation of rich ore
minerals may result.
"Often secondary minerals are
found in the portion of the vein be-
low the fault intersection, but gener-
ally in smaller amount than above. In
such cases they have usually been in
troduced before faulting occurred, and
enrichment would be con-
fined to the upper portion of the vein
above the fault, On the other hand,
the existence of a fault across the
vein does not necessarily imply a de-
crease in the value of the ore below
the fault intersection, for it is not I'M
usual for the value of the ore to con-
-inue unchanged, especially if condi-
ions are unfavorable to secondary
Every mine has it's own peculiar
problems, and I would not |
nfer that the above explanation will
over every case, but l believe 1t will |
Lpply in many instances under the
stated"