September 17, 2012

Monday Geology Picture(s): Garnet Sands in Nome, Alaska

Posted by Evelyn Mervine

Gold-bearing garnet sands on Western Beach in Nome, Alaska, Summer 2012.

Gold-bearing garnet sands on Western Beach in Nome, Alaska, Summer 2012.

Above is a gorgeous beach sand picture for this week’s Monday Geology Picture. I took this picture a few weeks ago in Nome, Alaska after a summer storm. The beaches of Nome are rich in red garnet grains. The beaches of Nome are also very rich in grains of gold, and you can bet that if you pan some of the red garnet sand along the Nome beaches, you will find dozens of small flakes of gold. If you pan some of the more gravely beach material, you may even find yourself a gold nugget!

The beaches of Nome are always a rich red color, but after a storm the beaches look particularly red. This is because the storm waves remove some of the lighter beach sand grains (quartz and such) while leaving behind a lag of beautiful bright red garnet… and dark heavy minerals… and gold!

Here’s two more pictures of the red garnet beach sands in Nome:

More red garnet sands along Western Beach in Nome, Alaska, Summer 2012.

More red garnet sands-- and beach cobbles-- along Western Beach in Nome, Alaska, Summer 2012.

And here’s proof that if you pan some garnet sand from Nome, you will find gold:

Panned garnet sands from Western Beach in Nome, Alaska, Summer 2012. Note all the little gold glakes on the left side of the pan. Click to enlarge picture.

Gold panning is a gravity concentration process in which a large plastic pan and water are used to separate minerals according to their density. Gold is a very dense material (pure gold has a density of ~19.3 g / cm3), so gold will be sink to the bottom of the pan while much lighter sand grains are washed off during the panning process. Panning first removes the lightest sand grains such as quartz (density of ~2.7 g / cm3) and muscovite (density  of ~2.8 g / cm3) and leaves behind heavier grains such as garnet (density of ~3 to 4 g / cm3), magnetite (density of ~5.2 g / cm3), and ilmenite (density of ~4.7 g / cm3). Eventually, the panning process leaves behind a dark-colored, heavy mineral concentrate that is rich in gold!

Here I am with just such a concentrate from Western Beach in Nome:

Me, with a gold pan and a bag of gold-bearing heavy mineral concentrate in Nome, Alaska, Summer 2012.

That’s an old gold dredge in the background of the above photo; I’ll write about the some of Nome’s old dredges in another post.


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