Saturday, March 15, 2014

Prospecting for Gem-Quality Garnet in the Cowboy State

Aren't these pretty? Garnets in schist from the Wrangell mine, Petersburg district, Alaska. Yes,
I know these are not from Wyoming, but they are very attractive and give you a general idea of
the common crystal habit of many garnets.
Almandine garnet (about 1 inch in diameter) from the Teton
Range
Garnets occur in many Precambrian rocks in Wyoming and most are associated with mica schists in the state. The garnets range from microscopic minerals to a few that are fist-sized.

Yes, I found many garnets in mica schists of Archean (more than 2.5 billion years in age) and Proterozoic age (600 million years to 2.5 billion years in age) in the cores of many of Wyoming's mountain ranges. But I also found them in a few 1.4 billion year old pegmatites (coarse-grained granites) in the Sherman Granite in the Laramie Mountains, and also found them in every kimberlite I investigated. And many of the kimberlite pipes also contained diamond. These rare breccia pipes erupted in the Cambrian and Early Devonian in Wyoming and in neighboring Colorado. 

Wyoming traffic jam (sketches by the GemHunter).
Many gem-quality garnets I collected in Wyoming, were associated with diamond-bearing kimberlite pipes in the State Line district and Iron Mountain district in the Laramie Mountains. Other places we found gem garnets included detrital gems associated with stream sediments in the Miracle Mile area along the edge of the Seminoe Mountains district, and in sediments and anthills in the Green River Basin. These latter garnets are found in diamond-bearing lamprophres along the southern margin of Cedar Mountain, in the Bishop Conglomerate in the same region, and in anthills in the Butchknife Draw area near Cedar Mountain. I also recovered gem-quality garnets along with ruby and diamonds from the northern margin of Diamond Peak in Colorado - the site of the 1872 diamond hoax. This latter group of gemstones were actually 'salted' by scam artists - no I don't mean congress or the president, a couple of enterprising prospectors from the 19th century.

And there are many other places to look for gem garnet in Wyoming - some of the better sites I published in my recent book on gemstones.


Don't horse around - get out there and look for gemstones.

When I began mapping the Colorado-State Line district, I found several rounded and sheared pyrope-almandine
 megacrysts (giant crystals like this one sitting next to a .45 caliber cartridge. These ranged from several inches to about 2
 inches across.


This is what the gem-quality pyrope garnets and their angry ants look like in the field.
Wow! All of these pyrope and chromian diopside gems were collected by Dick Kuchera from the group of lamprophyre diamond pipes on Cedar Mountain
Amazing how these ants in the basin pick up the gemstones - and my gosh, they
even cut them for you for a price.

Diamond indicator minerals associated with the Sloan kimberlite in Colorado. These two Sloan pipes have a considerable
 diamond resource associated with them, as well as all of these beautiful gemstones. Likely hundreds of millions of carats of colored gemstones that companies always ignore.
One of my favorite rocks - a kyanite eclogite I collected from the Aultman kimberlite in Wyoming. The nodule consists of
chromian diopside, kyanite and garnet. I later found another of these that was about 5 times larger.
Mining Districts and Mineralized areas of Wyoming (after Hausel)


A few books by the GemHunter. See more at Amazon