Lyon Nevada, Cu, Au, Fe prospect is near Yerrington (?). and is a skarn
type deposit. Samples were collected from a drillhole CL301 at depths
359 to 409 feet. Note the degree of variation over this short
Zonation of magnetite is also common at Tennant Creek, NT.
Kingston Summit, Nv (on Ca border?) is a defunct Fe(?) mine in a skarn
magnetite. Samples from this mine show even more intense decrepitation
than the Lyon samples.
These samples collected from the roadside show intense decrepitation
in magnetite, with very variable patterns. Samples 1340 and 1345 are
same sample, with 1345 being washed in acid to remove potentially
carbonates. In this case the 2 results are the same and so carbonate
has not been a problem.
Iron ore samples - Norway, Sweeden, Quebec and
Assorted iron ore samples from Sweeden, Quebec and Minnesota often show
intense decrepitation. In this plot, sample 137 is from Rana Gruber,
147 is from Mt Wright mine, Quebec; 160 is from Kiruna, Sweeden ; 47 is
the old ore from Minnesota and 41 is minnesota taconite (current ore).
(No geological sample descriptions available - these are samples of
Humboldt area, Nv - Buena Vista pits
This was mined for iron ore, but is now defunct. The ore is dominantly
magnetite, with scapolite common. It has been suggested to be of
origin but may be a replacement deposit. The temperature of such
is disputed and there is no syngenetic quartz from which to derive
inclusion temperatures. The decrepitation response in magnetite
varies widely but does suggest the involvement of high temperature
The following plots have been divided up with high intensity and low
samples in seperate plots for scaling convenience.
Non-magnetic samples from this mine show very weak decrepitation only
magnetic samples have no decrepitation recognizable above
All samples were collected from the (extensive) old mine dumps as no
access was possible.
This old iron mine is now defunct and is hosted in rhyodacite. Most
from the mine itself had very low decrepitation. Samples were also
from loose float material on the road access near the mine. These may
of alluvial origin, but these showed the best decrepitation responses
the area. Note that 1324 (non-magnetic) and 1325 (magnetic) are splits
from the same hand specimen and show essentially identical
response despite the change from magnetite to haematite.
Samples from the mine benches show low intensity decrepitation at
background levels with barely recognizable peaks near 650-700 C.
It was difficult to find magnetic samples in hand specimen at this
mine. The magnetic samples collected show no significant difference in
decrepitation from the non-magnetic samples, with the exception of
1336. However, even this sample was of only low decrepitation activity
(<300 counts max.) compared to the magnetite float sample from the
road float sample from the access road
(1325, above) or from other deposits.
On Bench 4 of the mine, 2 non-magnetic samples were collected at the
same sample site and these show marked difference from no response to
intense despite their identical location.
Mountain Pass, Ca. feldspar-magnetite
Two feldspar magnetite samples were each separated into magnetic
and non-magnetic (feldspar) fractions for analysis. The magnetite gave
very intense decrepitation, with an unuaually narrow temperature range
of decrepitation. Note that a magnetite sample from a carbonatite pipe
near Kapuskasing Ont. also gave a narrow decrepitation temperature
The co-existing feldspar however, gave almost no decrepitation, and
decrep[itation was at much higher temperature than the magnetite. One
of baryte was also analysed and it gave intense decrepitation at a
lower temperature. The genetic relation between the baryte and
The old workings occur on a single ridge, and all the FeOx samples here
are non-magnetic. Only one sample (1356) was weakly magnetic. These
show lvery weak decrepitation only.
To the north, the next hill shows abundant brecciation
and although there are no old workings, the samples give reasonably
decrepitation over a wide temperature range. Samples 1357 and 1358 are
from the ridge to the north which shows abundant brecciation and
1359 and 1360 are from the ridge to the east, where brecciation was not
Tennant Creek, NT, Australia. Au, Cu in
The Tennant creek goldfield has been proposed to be of sedimentary
with haematite secondary after primary magnetite. However, the rich ore
bearing magnetites have intense decrepitation at high temperatures and
many haematite samples also decrepitate. Consequently it is suggested
these deposits have a hydrothermal origin.