don findlay wrote:




It seems to me the easiest explanation is fine volcanic ash (maybe
cemented
with some water from snows when the orbital eccentricity changes)is
the bed
rock and the spherules are hematite rich condensed globules. So any
geologist know of a plausable process by which a volanic eruption
would make
both ash and hematite rich spherules?

If it is explosive, and high in Fe, the iron spherules could be formed
easily by spatter and air resistance. Ever notice what shape welding rod
spatter takes? Little balls.


The rocks look for all the world like Archaean rhyolitic ignimbrites
(colour, platy parting and all). Spherules are characteristic;
coalesced pairs common.
http://users.indigo.net.au/don/pr/dogsballs.html (sometimes in
threes)
(The haematite would be unusual though. )

The spherules are a puzzle (to me). The spherule texture is little
different from that of the matrix.

df.

Not necessarily strange. 1.4Ga rhyolite ignimbrites and tuffs around
here here (Earth) are fairly high in Fe and Mg, AND amazingly enough
some of the crumbly stuff contains iron amygdules. I think I have piece
in the basement somewhere. Iron is a mix of magnetite and hematite.
Some seems to be primary, and some secondary deposits. Saw a paper at
GSA North Central last spring where people were debating biogenic or
abiogenic origins of iron spheres in this ore and possible bacterial
involvement in forming the spheres. Much of the SE Mo iron industry was
founded on rhyolitic Fe rich deposits. Even the granite around here is
magnetic.

On the other hand, maybe I have been teleported to Mars, and no one told me.