As a side note, when panning for gold, often there is much magnetite rich
"black sands" left with the gold. One way of sorting through it all is to
use a magnet to remove the magnetite. This increases the concentration of
any gold in what all is left.
Bart
-----Original Message-----
From: Arch-Metals Group [mailto:[log in to unmask]] On Behalf Of
Dave Killick
Sent: Monday, December 14, 2009 4:37 PM
To: [log in to unmask]
Subject: Re: Black sand
Ed -
There is plenty of evidence for the use of black sands as ore for
smelting in historic times, but not all black sands can be considered
ores. Black sands are placer deposits produced by erosion and by sorting
of minerals according to density. The black minerals are generally
accessory minerals in rocks and are liberated by erosion. Magnetite is a
common accessory minerals in many rocks, and magnetite placers make
excellent iron ores. They were (and are) the ores used for the Japanese
tatara process, and were used in many parts of Africa, where impure
black sands were washed or winnowed in the winds to upgrade them. I have
watched the smelting of black sands in Cameroon (see N. David et al.,
African Archaeological Review, 1989) and there was a paper in the
Journal of Archaeological Science this year by Louise Iles et al on the
smelting of black sands in Kenya. Effie Photos had a paper in World
Archaeology a long time ago (1995?) on ancient smelting of black sands
in ancient Greece, and I'm sure that there are lots of other examples.
There is no great difficulty in reducing magnetite when it is in such
small particles, though some of the particles may trickle down to the
base of the furnace before they can be reduced. Making pellets by adding
very small amount of a binder, such as clay, can counteract this.
Most black beaches are however mixed iron and titanium oxides, and these
beach placers are mined for titanium in Australia, South Africa and the
USA (see Eric Force, Geology of titanium-mineral deposits, Geological
Society of America Special Paper 259, 1991). The main mineral in these
is ilmenite, FeTiO3, but usually there is magnetite also present, and
often other heavy minerals too, like rutile, zircon and monazite. There
may well have been attempts to smelt these, but the usual product will
just have been a Ti-rich slag, with little or no iron metal.
Black sand beaches adjacent to ultramafic rocks, as for example the
peridotites on New Caledonia, are usually dominated by chromite
(Fe2CrO4) and are not ores either.
David Killick
Ed wrote:
> Dear All,
>
> I keep coming across comments that black sand was used as an ore for
> producing iron in ancient times. While clearly black sand would be
> recognized by the ancients and would be easily recovered, is
> their actual archaeometallugical evidence that the ancients actually
> used black sand as an ore for iron? Without some technology for
> agglomeration of the black sand, I would think that using black sand
> would have been quite difficult? Any guidance to specific evidence for
> or studies of the use of black sand as an ore of iron would be much
> appreciated.
>
> Sincerely,
> Ed Sharp
>
>
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