[meteorite-list] Meteorites delivered Earth's gold - Then plate tectonics concnetrated it

[Paul H.]

In "[meteorite-list] Meteorites delivered Earth's gold" at:
http://six.pairlist.net/pipermail/meteorite-list/2011-September/079706.html
Carl Asked,

"It seems to me that much of the Gold found on Earth 
is accompanied by Quartz. In fact most of the finest 
Non-nugget specimens are usually found in quartz. 
That said; If this gold came from space then where 
did the quartz come from and for that matter why is 
gold not found buried in chonditic rock instead of 
quartz. Quartz does not seem to be terribly abundant 
in meteorites. Just curious why we don't find gold / 
quartz meteorites. What changed meteorites? 
Do we have any witnessed falls of Gold meteorites?
Do these researchers consider the Quartz issue 
here?"

Nothing has changed in the composition of meteorites.

The quartz came from a combination of primary 
differentiation, by the crystallization and preferential 
settling of mafic minerals, of the magma that intruded 
into the Earth's crust and by melting and recycling of 
older sedimentary rock to form silica-rich magmas. This 
happened long after the gold was theoretically was 
delivered to the Earth by meteorites and asteroids. There 
was no quartz in the meteorites and asteroids, which 
were proposed to have brought the gold to Earth. 

During the last 3 or more billion years, the meteorites, 
asteroids, impactites, and gold in them were completely 
consumed by either erosion or plate tectonics and 
recycled by plate tectonics along with large parts of the 
Earth's crust. The crust included sediments in which quartz 
has been concentrated by weathering. In a subduction 
zone, some of these recycled materials were melted and 
turned into magma, of which some intruded back into 
the overlying crust. As these magma intrusions cooled,
some of it differentiated to enrich the magma in silica. As
these magmas cooled to form large bodies of plutonic rocks, 
i.e. granitic batholiths, various processes concentrated the 
gold and quartz from the magma together into gold-bearing 
veins. Thus, the gold and quartz came together only in the 
process of the gold-bearing deposits being created. Before 
that time, they were separate from each other. For a more 
detailed explanation, go see:

Macdonald, E. H., 2007, Handbook of gold 
exploration and evaluation. Woodhead Publishing,
Cambridge, England. 647 pp. ISBN 1845692543

http://www.worldcat.org/title/handbook-of-gold-exploration-and-evaluation/oclc/77257822?referer=di&ht=edition

Yours,

Paul H.