Tag Archives: kyanite

Geology of Gemstone Deposits

Large chlorite pseudomorph after garnet found in the Sierra Madre Mountains, Wyoming. The chlorite slowly replaced
the garnet and accepted the garnet’s crystal form. 
Much of Wyoming is underlain by Archean cratonic basement rocks and cratonized Proterozoic rocks that provide favorable geological environments for a variety of gemstones – notably diamond, iolite, ruby, sapphire, garnet, kyanite, andalusite, sillimanite, labradorite, jewelry grade gold, platinum and palladium nuggets, emerald, aquamarine, helidor, tourmaline, spinel, clinozoisite, zoisite, apatite, jasper, specularite, etc. Thick Phanerozoic sedimentary rock successions with lesser Tertiary volcanic rock cover large portions of the basement terrain. Some of these Phanerozoic rocks provide favorable hosts for other gemstones including opal, placer diamond, placer gold, placer platinum, placer ruby, jasper, agate, emerald, varisite, etc.
Using traditional exploration and prospecting methods, dozens of gem and precious metal deposits were discovered over the past 3 decades, including major discoveries and geological and mineralogical evidence for significant undiscovered deposits. Major swarms of mantle-derived kimberlite, lamproite and lamprophyre, many of which have proven to be diamondiferous, also host colored gemstones including pyrope garnet (Cape Ruby), spessartine garnet, almandine garnet, chromian diopside (Cape Emerald) and chromian enstatite. One lamproite also yielded peridot.
Favorable conditions for crystallization of metamorphogenic gemstones during regional amphibolite-grade metamorphism occurred during the Precambrian. In this terrain, metapelite in the central Laramie Range hosts kyanite, sillimanite and andalusite. These three minerals provide evidence of favorable pressures and temperatures needed for crystallization of aluminous gemstones including ruby, sapphire and kyanite. Cordierite (iolite) another aluminum-rich gemstone, formed during a later thermal event. This later event was responsible for deposition of world-class iolite (Water Sapphire) gemstone deposits.

While searching for gold, I came along
this giant jasper deposit.
Evidence for undiscovered gemstone deposits is predicted based on mineralogical anomalies detected during various research projects from 1977 until 2005. These include ruby, sapphire, gold and aquamarine found in stream sediment samples as well as favorable geological terrains that remain unexplored. Other anomalies include pyrope garnet (several with G10 geochemistry), picroilmenite, and some chromian diopside that provide evidence for hundreds of undiscovered diamond deposits. Elsewhere, detrital diamonds reported by various prospectors provide direct evidence for undiscovered diamond deposits. Other geological and mineralogical evidence suggest the presence of additional undiscovered opal, cordierite (iolite) and kyanite deposits. Wyoming could potentially become a major source for gemstones including diamond, gold, platinum, palladium, Cape ruby, Cape emerald, iolite and opal.

Giant chrome diopside gem in kimberlite from Colorado.

OPAL

A rockhound from Riverton mentioned opal south of town. The Cedar Ridge deposit lies along the highway & is cut by numerous oil field roads, no one had recognized that this place had one of the largest opal deposits on earth! A few old geological reports from 50 years ago briefly mentioned opal, so I was surprised to find opal scattered over 14 mi2, opal masses >79,000 cts along the edge of the road & common, fire & precious opal with scattered Sweetwater agate & some of the nicest decorative stone on earth. All within Tertiary age volcaniclastic sedimentary rocks that had a notable contribution of volcanic ash erupted from Yellowstone in the geological past.

This gave me a clue – nearly all of Wyoming was blanketed by volcanic ash (as was Nebraska and South Dakota). Guess what? There are other opal fields waiting to be discovered. So I found millions of carats of common & fire opal & traces of precious opal (including black opal) that suggest as soon as someone digs, valuable veins of precious opal will be found as depth!
Photos show precious opal, Sweetwater agate, cobbles of opal in oil field adjacent to road. Below are fire and common opal

IOLITE (WATER SAPPHIRE)

A 16-carat iolite from Palmer Canyon, Wyoming.

I discovered iolite (water sapphire) at Palmer Canyon in 1995. The iolite occurred with gem-quality kyanite in mica schist & gneiss adjacent to vermiculite that had enough silica to form these gems. I couldn’t believe the amount, size & beauty of the stones. The single, largest, iolite gemstone on earth was found at this time -the baseball sized Palmer Canyon Blue Star- a 1,720 ct flawless gem.

First group of iolites gems cut from
Palmer Canyon rough. The bed of
material that the iolites sit in has tiny
white fibers that unfortunately sit
in front of the iolites at the top. But
these iolites were flawless.

So I went looking in similar terrains & predicted in a book I would find iolite at Grizzly Creek to the south. In 2005, I discovered iolite at Grizzly Creek & recovered the largest iolite gem (24,150 carats) on earth (the football sized Grizzly Creek Blue Giant), but this was dwarfed by giant, VW bug-sized masses in the outcrop I left behind because I didn’t have tools necessary to recover such large gems of 1 to 5 million + carats. Based on geology, I predicted several other iolite deposits would be found in central Laramie Range & Copper Mountain, but most remain unexplored. Over the years I tried to get some investors interested in forming a company to take advantage of these giant deposits – explore for more, mine them, cut the gems, design jewelry and market them, but no one wanted to take on this task, so they all essentially sit there collecting dust and eroding away.

But nothing could match the potential discovery further to the south. Some geologists had explored this region for aluminum & magnesium & during the mid 20th century and they reported one deposit that had been trenched and mapped contained 500,000 tons of cordierite (when gem-quality, cordierite is known as iolite). I began looking at this deposit & found flawless gem-quality ioilte along the edge of the deposit. All of the material reported by theses earlier geologists likely was part of the largest gemstone deposit found in history. But they were so focused on the use of the material for magnesium and aluminum, they overlooked the gem potential. Besides, in the mid-20th century, there was not much of a market for iolite gemstones.

Iolite in outcrop at Grizzly Creek, Wyoming. Note the rusty matrix to the
right of the iolite. This is limonite replacing the iolite. Iolite has considerable
iron and will ‘rust’ under the right conditions.

But let’s look at this deposit as a potential gem deposit. It is unexplored for gems except along the one margin where everything I examined was of the highest quality gem material. The rest of this deposit needs to be examined. Why?  One ton of material contains 4.5 million carats! Multiply that by 500,000 tons and this could potentially have more than 2 trillion carats just on the surface and no one knows how deep it goes. If it is just 100 feet deep (it likely is a few thousand or more feet deep), it would dramatically increase the amount of recoverable gemstones. Iolite sells for only about $15 to $150 per carat, but if marketed like Tanzanite was marketed, one could increase the value of this (and other deposits in this region) to the most valuable mineral deposits on earth! But to develop this will take a lot of money and support.

The Palmer Canyon blue Giant sits on cover of
ICMJ Prospecting & Mining Journal. At 1,750
carats, this was the largest iolite gem reported
in the literature until I found much larger
stones at Grizzly Creek, Wyoming.

So what did I get for finding two of the largest colored gemstone deposits on earth? Well, like the song goes, the director got the mine and I got the shaft. But am I bitter? Yes!

Largest iolite in world at 24,150 carats from Grizzly Creek, Wyoming. Much larger stones were left in outcrop.

RUBY & SAPPHIRE

Ruby & Sapphire are beautiful stones. In 1995, I discovered my first ruby-sapphire-corundum deposit mixed with iolite & kyanite at Palmer Canyon west of Wheatland. After I recognized this association of gems with a rock type known as vermiculite, I started searching other vermiculites. It turns out that vermiculite is a alteration product known as glimmerite formed by retaining aluminum in the original rock & removing all silica (under pressure). Thus, one ends up with a rock that is essentially nothing but aluminum-rich mica. Ruby and sapphire are aluminum oxides are require high pressures and temperatures to form (as well as a good source of silicate poor aluminum). (photos above show one of the largest rubies found on earth at the Red Dwarf deposit. Sample is partially replaced by green zoisite; and a pink sapphire with excellent cleavage from vermiculite. Middle photo is a 1.1 carat ruby cut from material at Palmer Canyon and lower photo is a ruby from the Red Dwarf).

Earlier work in the Elmers Rock greenstone belt had shown rocks in the central Laramie Mountains formed at great pressures & temperatures that were high enough one might expect to find ruby & sapphire. So I was not surprised when I found these gems. Luckily, two geologists had put together a report on vermiculite in the 1940s, so I took their publication & began searching all vermiculite deposits for ruby – about 30% contained ruby! In addition to these, other rubies were found in the southern Wind River Mountains & the source remains to be found, even though some rubies found by prospectors weighted as much as 80 carats. At another deposit in the Granite Mountains, I mapped 3000 ft of ruby schist at what is known as the Red Dwarf deposit & recovered some of the largest rubies ever found.