SAPPHIRE DEPOSITS AT BACK PLAIN
NEAR GLEN INNES NSW AUSTRALIA
Before you
read this blog, I recommend that you read my blog entry “The Red Rock Sapphire Deposit” (here). It deals with gemstone deposits in the same general
area as I am covering here.
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A good
starting point in understanding the sapphire deposits at Back Plain (not Back
Plains, by the way) is the map at the back of “Records of the Geological Survey of NSW, 14 Part 1 (1971)”, DIGS
reference R00050764. If you haven’t downloaded this document yet, you should do
so. The map shows only that Wellingrove
Creek (left) and the Wellingrove
Fossicking Area (on the letters Pgw)) are sources of sapphire. Both are
marked in green. The reddish area near the centre of the map (marked Ts) is apparently
an area of Tertiary sediments associated with the basalt.
The next map
is extracted from the “Quarterly Notes of
the Geological Survey of NSW 103, April 1997” (page 13). The DIGS Reference
is R00040935. My extract from the map shows the following sapphire bearing
areas of interest to us here: Back Plain
Creek in the centre, with a tributary
to the west of it and the creek
flowing down from the Wellingrove Fossicking Area into Wellingrove Creek.
The third
map has been extracted from the Grafton-Maclean
Metallogenic Map (DIGS reference R00056102). To help you align it with the other maps, the Wellingrove Fossicking Area is
approximately in the centre, shown as 1835. 1836 is identified in the accompanying
notes as Pablos Mine and 1837 as the
Back Plain Creek deposit, elsewhere
called the Truro Mine. We can
distinguish two types of sapphire deposits on this map. Firstly, the close
cross hatched areas (Wellingrove Creek, the stream draining the Wellingrove
Fossicking Area and Back Plain Creek, not named on the map) which are regular
alluvial deposits, and secondly, the broad hatched areas (one around Pablos
Mine and the other near the top of the map adjoining an area of Tertiary basalt
labelled Tb. These are locations where spinel, sapphire and zircon are to be found
in the soil, possibly derived from tuffaceous sediments intercalated with the
earliest basalt flows. The Red Rock deposit (see above) is like that and the
Wellingrove Fossicking Area deposit could be a contemporaneous alluvial
concentration derived from such sediments.
There isn’t
much information available about these deposits, except for one (Truro) and
even that isn’t clear
 |
| Ruwenzorie Road turnoff (on right) |
cut. Starting from the north, we have a site which has at
least the potential to produce some gems. This is the area shown in broad
hatching along Ruwenzorie Road,
which branches off to the right (north) from the Strathbogie Road. This is
before you come to the back road from Wellingrove (Polhill Road). This road crosses
Back Plain Creek after 2.5km at a place where there are some rocky outcrops. I only went
there once and found some colour easily enough (without getting wet
or covered with leaches). It’s certainly worth a try, if it’s still accessible.
Then there is the possibility of gems in the soil on the road side. You could
try dry sieving and then take the concentrate to Back Plain Creek to see what’s
in it.
%2BPablos.jpg) |
| Pablos Mine location (from Mindat) |
Pablos Mine appears to be on a tributary of Back
Plain Creek south of the Wellingrove Fossicking Area. All I can find from the
metallogenic notes is that it was worked by Pablos Mining (1970-73) by shallow
pits or scrapings. It’s described as a “modern placer (fluvial)”.
The problem starts with the Back Plain Mine. The metallogenic notes contain quite a bit of
information – worked by SC Burgis (1971), Pablos Mining (1970-73) and Nunan Pty
Ltd circa 1990. “This deposit comprises high grade sapphires and
abundant zircon. The headwaters of the creek drain from a red soil
%2BTruro.jpg) |
| Back Plain Mine location (from Mindat) |
plateau
where the deposits were quite rich. The abundant zircon contrasts strongly with
Reddestone Creek immediately to the east where zircon is relatively minor.
Alluvial placer”.
The difficulty arises when you look at the Mindat information for the Back
Plain Mine (here). It is clearly identified as the Back Plain Mine
(Truro). This would be fine, except that we have a lot of information about the
Truro Mine from the NSW Department
of Minerals and Energy publication Minfo 27 (1990) which deals with the opening
of the mine belonging to TJ and PV Nunan Pty Ltd. You can download the document
from DIGS, reference number R00040997. The included map shows that the mine was
on the right hand
.jpg) |
| Truro Mine location (from Minfo 27) |
side of the Strathbogie Road, past the Wellingrove turnoff.
This is several kilometres from the indicated site of the Back Plain Mine.
Perhaps the wash from the Back Plain Mine was trucked to Truro Mine for
treatment. That there was a mine near Truro homestead is beyond doubt. You
could see the activity from the Strathbogie Road, but when it closed down I
can’t say.
My thanks go to the NSW Geological Survey, Mindat and Google Maps for information and illustrations used in this blog. Without these it would be difficult to make sense of this interesting area.
To explore the satellite images better, I suggest a Google search for "Mindat Pablos Mine NSW" and "Mindat Back Plain Mine NSW". You can then follow the "Maps" link, "Maps Pages" and select "satellite"to get to the images shown above.
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