UTAH AZURITE & LACCOLITHS

Make choices based not on fear, but what really gives you a sense of fulfillment.  P. R. Chance

A long time ago, in human years and not geologic time, I managed to graduate from a small, really small (48 total students in school) high school in central Kansas.  As a first generation college student I headed off to school without the slightest idea about any sort of a career choice.  My knowledge about higher education consisted of wanting to play basketball as that activity paid the way for classes.  I sort of failed at both aspects as the court was full of much better players and my grades were not the best.  So, I decided to declare a major, engineering, to better define my goals (and hopefully my grades).  I was soon out of that field since my skills with a slide rule were pretty meager (hopefully some of the readers might remember these mechanical analog computers).  Next came chemistry; however, my only skill in that major was setting records for broken glassware (it cost me a fortune).  One day as a second year student, I “had” passed the first year, I was sitting around reading the college catalog and trying to figure out the rest of my life—when I came across “the geology major”.  An epiphany was in progress since my mind wandered back to childhood days of collecting rocks and minerals and I marched over to the department and declared a new major!  Wow, just like that I had a new meaning in life and I have never looked back.

View, in 1953, of Mount Holmes in the Henry Mountains with a core of diorite and upturned Jurassic beds along the flanks.  Photo courtesy of USGS.

So, how does my childhood relate to azurite and blueberries?  Well, one of the joys of being a geologist is “going to the field”, a term I have used several times before in these writings. Many years ago I was working with a paleontologist, in the field, chasing phytosaurs (crocodile-like animals) out near Bedrock, Colorado (far western part of the state).  Part of the group decided to wander, on the way home, over to the La Sal Mountains where there was an old copper mine.  And, that is how I was introduced to azurite. 

Cartoon showing an idealized laccolith intruding into sedimentary rocks. 

The La Sal Mountains are just across the Utah—Colorado state line near Moab, Utah.  They are part of a group of scattered and isolated mountain chains known as the laccolithic centers of the Colorado Plateau.  Laccoliths are igneous intrusions that have been injected into layers of sedimentary rocks and have pushed up the overlying rocks into a dome. The name, laccolite, was first coined by one of the most famous geologists in the annals of the U. S. Geological Survey (USGS), Grove Karl Gilbert in his monograph (1877), Report on the Geology of the Henry Mountains.  At the time Gilbert was working for the “Powell Survey”, one of the early USGS surveys designed to study the geology of the “American West”, and Gilbert was assigned to map the Henry Mountains, the last major mountain range to be “discovered” in the lower 48 states.  Gilbert noted in the Monograph introduction that the Henry Mountains have been visited only by the explorer.  Previous to 1869 they were not placed upon any map, nor was any mention made of them…  Gilbert also believed these island mountains were different, not really a chain, and maybe just a group of five individual mountains (Mts. Ellen at 11,522 feet, Pennell, Holmes, Hillers, and Ellsworth).  Furthermore, he stated that instead of rising [the magma] through all the beds of the earth’s crust it stopped at a lower horizon, insinuating itself between two strata, and opened for itself a chamber by lifting all the superior (overlying) beds.  Gilbert called this type of igneous formation a laccolite, currently known as a laccolith. Today, erosion has stripped off the overlying sedimentary rocks and the core diorite (dark gray igneous rock with large amounts of plagioclase feldspar; emplaced ~20--29 Ma; Sullivan, 1997) core is exposed with the tilted sedimentary rocks cropping out on the mountain flanks.  As in Gilbert’s Day, the Henry Mountains are still one of the most isolated ranges in the lower 48 states.

Location map of mountain ranges associated with laccolithic centers in the Colorado Plateau.  The Four Corners is represented by the red dot.  L, la Sal Mountains; A, Abajo or Blue Mountains; S, Ute Mountains; C, Carrizo Mountains; H, Henry Mountains; N, Navajo Mountains.  Photo from National Aeronautics and Space Administration Visible Earth Project.

After Gilbert’s work geologists then begin to describe other laccolithic centers in the Colorado Plateau.—the La Sal, Abajo, Carrizo, Ute Mountains, Navajo Mountain, Ophir-San Miguel-Klondike Ridge (Mutschler and others, 1997).  All of these laccoliths have the igneous rocks exposed in the center with the exception of Navajo Mountain on the Utah-Arizona state line.  At that locality, which is a single domed peak (10,388feet), the overlying sedimentary rocks have not been eroded away to expose the underlying igneous rocks.

Navajo Mountain with part of Lake Powell in the foreground.  Public Domain photo courtesy of G. Thomas.

I might add, at this point, that not all laccoliths are large mountains and not all are located in the Colorado Plateau.  For example, Tomichi Dome west of Gunnison, Colorado, is a laccolithic dome with igneous magma intruded into the Dakota Sandstone and the Mancos Shale.  Although the elevation is substantial (11,471 feet), the hill is much smaller in size than the large centers in the Colorado Plateau.

Tomichi Dome, a Tertiary laccolith located in Gunnison County about 20 miles east of Gunnison, Colorado.  The dome is situated just south of Waunita Hot Springs and their water temperature may be related to the heat of this igneous intrusion. 

The grandest laccolithic center of the Colorado Plateau is the La Sal Mountains near Moab, Utah.  Mt. Peale at 12,721 feet is the highest of this large group of peaks although 11 other peaks have elevations in excess of 12,000 feet.  The mountains are impressive and can be seen from tens of miles distance. The magma, now the rocks diorite and rhyolite, was emplaced around ~28-29 Ma (Sullivan, 1997).  The peaks are especially scenic when viewed from Arches National Park to the north.

La Sal Mountains as seen from Arches National Park.

Immediately to the south of the La Sal Mountains is Lisbon Valley containing the Lisbon Valley Anticline, a large salt anticline where the dipping beds are due to movement/solution of salt in the subsurface.  Several of these salt structures are found in the greater Paradox Basin (an evaporate basin in Utah and Colorado near the Four Corners).  Although the Valley has several tens of producing gas wells, the most active mineral commodity has been the numerous uranium mines (earliest report in 1913) and the area is undergoing uranium resurgence today.  Target zones have been, and still are, the Cutler Formation/Group (Permian), the Moss Back Member of the Chinle Formation (Triassic), and the Salt Wash Member of the Morrison Formation (Jurassic) found along the flanks of the anticline. 

Copper also is present in varying quantities and qualities in Lisbon Valley and has been periodically mined for decades.  Most of the paying copper deposits seem to be in the Dakota Sandstone and Burro Canyon Formation, both Cretaceous in age---therefore younger and above the uranium beds.  Most of the copper ore is chalcocite (Cu₂S) deposited by solutions brought up along the Lisbon Valley Fault (found along the crest of the anticline with offset approaching 4000 feet).  With time chalcocite oxidizes to such secondary minerals as azurite [Cu₃(CO₃)₂(OH)₂] and malachite [Cu₂(CO₃)₂(OH)₂], both copper carbonates, (but note that azurite commonly pseudomorphs to malachite), and tenorite [CuO] and cuprite [Cu₂O], both copper oxides (SRK Consulting, 2006).

Satellite image, oblique view, of Lisbon Valley looking northwest down the strike of the Lisbon Valley Anticline.  Photo courtesy of Mesa Uranium Corporation.

One of the earliest mining areas in the Lisbon Valley/La Sal District was originally organized in 1892 and generally goes under the name of Big Indian Copper Mine with later mines and claims termed Blue Jay Claim, Blue Grotto Prospect, Nevada Claim, Blue Crystal Mine, and the Texas Claim.  A copper processing mill was constructed in 1918 and mining continued sporadically for several decades.  The ore body is comprised of oxidized copper minerals (see above) emplaced in the Cretaceous Dakota Sandstone along the downthrown side of the Lisbon Valley Fault; mining has been via open pit and tunnels.  In the late 1970’s prospectors begin to notice beautiful azurite crystals and specimen collecting went into operation.  For example, in 1988 a cut on the Nevada Claim produced one hundred thousand specimens of azurite rosettes (for collectors) and 6000 pounds of broken nodules for paint pigment.  Today the claims are generally referred to as the Blue Crystal Mines and the company offers mineral collecting on a fee basis through tours arranged by Rockpick Legend Company in Salt Lake City and Deep Desert Expeditions in Moab.  

Besides the abundance of azurite, other minerals collected from the claims and mines include: Wulfenite, Tyrolite, Tenorite, Tennantite, Sphalerite, Quartz, Pyrite, “psilomelane”, Olivenite, Malachite, Kaolinite, Goethite, Enargite, Djurleite, Diginite, Cuprite, Covellite, Cornwallite, Copper, Conichalcite, Clinoclase, Chrysocolla, Chalcopyrite, Chalcopyrite, Chalcophyllite, Chalcocite, and Calcite.  Information in this paragraph came from an article by Arnold G. Hampson (1993).

During my little expedition in the latest 1970’s (maybe earliest1980’s??) I was able to collect numerous representatives of copper minerals; however, after several house moves and “give-aways”—I have three remaining specimens.  Fortunately I was able to keep one cluster or rosette and one “blueberry” of azurite and one small mass of malachite. The most unique of the specimens collected at the Blue Crystal Mine, then and now, are the “blueberries”, small (up to 5mm) concretions, often hollow, of microsized azurite crystals; some contain tiny rounded quartz grains mixed with azurite.  I have not been able to locate information on their formation; however, it appears that tens of thousands of these “blueberries” have been collected over the decades.  Rockhounds in Utah tell me that the mine is the single world source for these unique specimens; however, I have seen similar/almost identical specimens from the El Chino Mine in New Mexico.

The “azure colored” rosettes and crystal clusters “commonly occur as 3-8 cm rosettes of subparallel crystals and as individual crystals to 2.5 cm in length” (Hampson, 1993).  The blueberries are much lighter in color, perhaps a sky blue.   

Azurite crystal cluster bottom (3 x 2.6 cm) from Blue Grotto Prospect, La Sal/Lisbon Valley District.  Photo courtesy of Kevin Conroy.  Azurite blueberries, top.  Photo courtesy of Blue Crystal Mine.

 Azurite has been used as a dye and/or paint pigment for centuries; hence, several thousand pounds from the Big Indian area being shipped to Japan (see above).   At a hardness of 3.5 -4.0 (Mohs) azurite is somewhat too soft for certain jewelry pieces such as rings.  However, I have seen nice stones in pendants but the wearer must use extreme caution against “banging it around”.  Some Native American cultures regard azurite as sacred.  In my opinion, since azurite is such a stunning mineral the best use is as a specimen in the collecting case!  However, I have noticed that some spiritualists believe azurite may be used to expand the mind, fortify the memory, and clear stress---now that is a real stone for the baby boomers and I may go into business stimulating memories. 

So, that is the story of how a bunch of broken chemistry glassware led a directionless and drifting young man to collect azurite blueberries in a Colorado Plateau laccolithic center.

It was my good fortune in 1935 to be assigned chief of a U.S. Geological Survey field party studying and mapping the geology of the Henry Mountains, Utah. Geologically the area is of great interest because of the classic work done there in 1876 by G.K. Gilbert for the Powell Survey. In the 1930’s the area still was frontier—a long distance from railroads, paved roads, telephones, stores, or medical services. It was the heart of an area the size of New York State without a railroad, and a third of that area was without any kind of a road. This was not Marlboro country; it was Bull Durham country. The geological work had to be done by pack train; it was about the last of the big packtrain surveys in the West—the end of an era.  Charles B. Hunt

REFERENCES CITED

SRK Consulting, 2006, Constellation Copper Corporation: Resource Estimate Centennial Deposit: private report. 

Hampson, A. G., 1993, Minerals of the Big Indian Copper Mine San Juan County, Utah: Rocks and Minerals, v. 68, No. 6.

Mutschler, F. E., E.E. Larson, and M. L. Ross, 1997, Potential for Alkaline Igneous Rock-Related Gold Deposits in the Colorado Plateau Laccolithic Centers in Friedman, J. D. and A. C. Huffman (Coordinators), Laccolith Complexes of Southeastern Utah: Time of Emplacement and Tectonic Setting—Workshop Proceedings: U. S. Geological Survey Bulletin 2158.

  

Sullivan, K. R. 1997, Isotopic Ages of Igneous Intrusions in Southeastern Utah in Friedman, J. D. and A. C. Huffman (Coordinators), Laccolith Complexes of Southeastern Utah: Time of Emplacement and Tectonic Setting—Workshop Proceedings: U. S. Geological Survey Bulletin 2158.