[ RadSafe ] Red Sand

[Dan McCarn]

Dear Michael:

I think it is highly unlikely to be garnet.

The described material is far more likely to be a red zircon sand, hard and
abrasive, and can be concentrated in beach and stream placers in & around
igneous and metamorphic terrains because it does not tend to weather. From
memory, it can contain up to about 1% uranium. Zircon is a zirconium
silicate for which the zircon can be replaced with a significant amount of
rare-earth elements including thorium as well as uranium.

For a zircon containing 0.25% U-nat, that would amount to an activity of
about 30 Bq/g for each member of the decay chain.  I have seen and
mapped Cretaceous beach placers in the Trinidad sandstone of Colorado / New
Mexico for many kilometers.  Undoubtedly, the beach sand was derived from
the ancestral Rockies, full of granite with abundant zircon.
 Long-shore drift concentrated the beach placers giving them
a significantly higher gamma "kick" with borehole-logging tools than would
be expected, and were occasionally mistaken for "roll-front" type sandstone
uranium deposits, but are of no economic interest (for uranium) due to the
chemically inert nature of zircon. Neither uranium nor thorium would leach
from zircon sands.

See http://en.wikipedia.org/wiki/Zircon

"Zircon occurs in many colors, including red, pink, brown, yellow, hazel,
or black. It can also be colorless. The color of zircons can sometimes be
changed by heat treatment. Depending on the amount of heat applied,
colorless, blue, or golden-yellow zircons can be made. In geological
settings, the development of pink, red, and purple zircon occurs after
hundreds of millions of years, if the crystal has sufficient trace elements
to produce color centers. Color in this red or pink series is annealed in
geological conditions above the temperature about 350 °C."

"Zircon is a common accessory to trace mineral constituent of most
granite<http://en.wikipedia.org/wiki/Granite>
 and felsic <http://en.wikipedia.org/wiki/Felsic> igneous rocks. Due to its
hardness, durability and chemical inertness, zircon persists in sedimentary
deposits and is a common constituent of most sands. Zircon is rare within mafic
rocks <http://en.wikipedia.org/wiki/Mafic_rock> and very rare within
ultramafic <http://en.wikipedia.org/wiki/Ultramafic> rocks aside from a
group of ultrapotassic intrusive
rocks<http://en.wikipedia.org/wiki/Ultrapotassic_igneous_rocks> such
as kimberlites <http://en.wikipedia.org/wiki/Kimberlite>, carbonatites, and
lamprophyre, where zircon can occasionally be found as a trace mineral
owing to the unusual magma genesis of these rocks."

"Zircon forms economic concentrations within heavy mineral sands ore
deposits <http://en.wikipedia.org/wiki/Heavy_mineral_sands_ore_deposits>,
within certain pegmatites <http://en.wikipedia.org/wiki/Pegmatite>, and
within some rare alkaline volcanic rocks, for example the Toongi Trachyte,
Dubbo, New South Wales
Australia[9]<http://en.wikipedia.org/wiki/Zircon#cite_note-9> in
association with the zirconium-hafnium minerals
eudialyte<http://en.wikipedia.org/wiki/Eudialyte> and
armstrongite."

Dan ii

Dan W McCarn, Geologist
108 Sherwood Blvd
Los Alamos, NM 87544-3425
+1-505-672-2014 (Home – New Mexico)
+1-505-670-8123 (Mobile - New Mexico)
HotGreenChile at gmail.com (Private email) HotGreenChile at gmail dot com


On Sat, Mar 23, 2013 at 10:51 PM, Cowie, Michael I <michael.cowie at aramco.com
> wrote:

> Abrasive Sand/grit
>
> Also recently encountered some red coloured fine sand, it has been
> suggested the material is "Garnet". Activity concentration is in the order
> of 30Bq/g (Total activity), and have measured gamma dose rates of in excess
> of 3microSiverts/hr from the material. A few years ago we ceased using
> abrasive sands/silica for blasting/preparation ops due to health related
> issues (silicosis) and the replacement material is a type of black grit (a
> trade name I have seen is EuroGrit, but there are others). This also has
> slightly enhanced activity levels but only around 1Bq/g. So it came as a
> bit of a shock to find this material, particularly with such enhanced
> activity levels and associated gamma dose-rate.
>
> Again a couple of questions:
>
> Are the activity concentrations in the "granet" or Rad Sand typical?
> Are there standards to which suppliers should adhere?
>
> I am pretty certain that this material if shipped now would trigger alarms
> at ports of entry if exported.
>
> Mike
>
>
>
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