PRECAMBRIAN WYOMING: SNOWY, MEDICINE BOW, LARAMIE & HARTVILLE RANGES

The southeastern part of Wyoming contains a number of interesting geological features, including several mountain ranges that extend north from Colorado.  One particular part of the country is the Medicine Bow Range of both states whose high peaks in Wyoming are known as the Snowy Range.  Another is the Wyoming extension (Laramie Range) of the Front Range of Colorado.  I have camped, hiked, collected and fished along a good part of these ranges and have tried to pay some attention to the great exposures of Precambrian rocks.

In all of my other articles I have used the term Precambrian in a very lose sense to indicate very old rocks of the earth’s crust.  What I have failed to indicate is that the Precambrian represents a very, very long time span, perhaps the first four billion years of geologic time—the vast amount of mind-boggling time before the appearance of hard-bodied animals (animals with shells or bones). In contrast to the Precambrian, these hard-bodied animals have only been around for less than .5 billion years.  So, the time period of life, as we generally know it, is only about 12% of geologic time.

The Precambrian, and it is formally called a Supereon, is divided into three Eons (remember the Paleozoic, Mesozoic, and Cenozoic are Eons):  the Hadean (4.5-3.95 Ga), Archean (3.95-2.5 Ga) and Proterozoic (2.5-.542 Ga) with the abbreviation Ga referring to billions. The .542 Ga or 542 Ma (542 million) is the base of the Cambrian and the time when geologists begin to find hard-bodied animals such as trilobites and brachiopods.  Since these shelled fossils are often used to date rocks, the time since the Precambrian has been subdivided into quite small units of time.  Another mitigating factor is that many/most Precambrian rocks have been subject to episodes of metamorphism and igneous activity, both in the Precambrian and the later Eons.  It is easy to go out and locate a post-Precambrian sandstone or limestone.  However, very few of these sedimentary rocks are preserved as such in the Precambrian record (except some very young ones).  Most have been metamorphosed to quartzite or schist or gneiss or marble or actually re-melted and turned into igneous granite.

For additional information on geologic time see the Geological Society of America time scale at: www.geosociety.org/science/timescale/timescl.pdf

Sims and Finn ( 2001) have described the Precambrian rocks (aka “the basement”) of Colorado in great detail and the following description is from their paper.  In most of our state, the basement consists of crystalline igneous and metamorphic rocks lying stratigraphically below the layered sedimentary rocks of the post-Precambrian (aka Phanerozoic).  In some places, however, sequences of younger Precambrian sedimentary rocks overlie the crystalline rocks; these sequences are included as basement.

The oldest rocks in Colorado are found in a very small area (less than 50 acres) in far northwestern Colorado in the Uinta Mountains (Matthews, 2009).  These rocks are termed the Owiyukuts Complex and were metamorphosed about 2.7 Ga—in the Archean.  This means that the original rocks were older than this date; something had to be there to metamorphose!  The Owiyukuts Complex is actually part of Wyoming –more on this later.  

Owiyukuts Complex (Archean) exposed in northwestern Colorado overlain by the Proterozoic Uinta Mountain Group.  Photo cropped from Matthews, 2009.

 Most of the Precambrian rocks of Colorado, the ones that core the north-south trending mountain ranges and are composed largely of Proterozoic metamorphosed volcanic-sedimentary gneisses and schist, and some igneous intrusive rocks.  The radiometric dates cluster around 1.75 Ga but again there needed to be earlier rocks to metamorphose—geologists just don’t know where they came from but suspect oceanic volcanic island rocks.  Then around 1.4 Ga a second major intrusive event emplaced several granitic types of rocks such as the Sherman Granite in northern Colorado.  And finally, a single large batholith (large intrusive event) left us the Pikes Peak granite at ~1.05 Ga.  In summary, readers can think of Precambrian rocks in Colorado as being ~1.75 Ga metamorphic rocks, ~1.4 Ga granite, and ~1.05 Ga Pikes Peak granite. 

The Precambrian rocks of Wyoming consist mainly of three major geologic terranes: the Archean Wyoming Province, the Proterozoic Trans-Hudson Orogen , and the Proterozoic Colorado Orogen (part of the Yavapai Terrane).  In this usage orogen refers to a belt of deformed rocks commonly metamorphosed and intruded by igneous bodies—the rocks associated with a tectonic or mountain building event.

The oldest rocks in Wyoming include intrusive igneous and granite-like rocks as well as some metamorphic rocks. The Wyoming Province is often called the Wyoming craton since it represents a very stable part of the Precambrian “continent”.  Most of the state’s mountain ranges where the Precambrian crops out have rocks of this age.  Rocks of the Trans-Hudson Orogeny, ~1.9 Ga, are found only in the subsurface in the eastern part of the state, but are exposed in the nearby Black hills.  The Colorado Orogen, or Colorado Province, includes the metamorphic rocks with dates around 1.75 Ga as well as the 1.4 Ga intruded granites in the southern Laramie and Medicine Bow ranges such as the Sherman Granite.

Landsat satellite image Medicine Bow Mountains, Wyoming.  Cheyenne Belt trending NE-Sw below high peaks of the Snowy Range (compare with map below).  Image from www.geology.com

 One of the amazing features associated with the Precambrian rocks of Wyoming is a narrow belt of highly deformed and tectonically disturbed rocks termed the Cheyenne Belt.  This zone is the tectonic suture between two Precambrian provinces, a place where the older Archean rocks collided (plate tectonics) with the younger Colorado Province and were welded together.  This is an amazing site, at least for a geologist! 

Sketch map showing location of Cheyenne Belt in southeastern Wyoming.  From Ward, 2010: www.colorado.edu/GeolSci/Resources/WUSTectonics/CheyenneBelt/index.html

 One of the best places to see the suture zone up close is to travel WY 130 west from Laramie through Centennial over the Medicine Bow Mountains to Saratoga.  Popularly known as the Snowy Range Scenic Byway, the highway travels through some of the most fantastic scenery in Wyoming.  At the Nash Fork Campground the road crosses the suture line and travelers may observe slate and phyllite that that is complexly folded and crinkled (Hausel, 1993).  Rocks north of the Cheyenne Zone in the Medicine Bow Mountains  contain the very old Archean crystalline rocks overlain by several tens of thousands of feet of late Archean and early Proterozoic metavolcanics, metasediments (last two terms refer to lightly metamorphosed sediments and volcanics), quartzite, conglomerate and various other rocks that were deposited in rivers, braided streams and shallow marine waters in this ancient Precambrian environment—perhaps an environment similar to the Atlantic coast of North America.  The best known geologic unit is the Snowy Pass Supergroup that includes the Medicine Peak Quartzite, the almost white sugar sand quartzite that forms the high peaks of the Snowy Range.  Also in the Snowy Pass Supergroup are other sedimentary rocks containing some of the most beautiful stromatolites in the U.S.   These features are composed of calcium carbonate, cabbage-like domes deposited in shallow marine waters by cynobacteria (aka blue-green algae).  They may be seen near the Sugarloaf Recreation area.  

For a very good description of the Snowy Range, complete with road log stops, see the Wyoming Geological Survey Information Circular No. 32 (author: Dan Hausel) at: www.wsgs.uwyo.edu/Publications/OnlinePubs/docs/PIC/PIC-32.pdf. 

Rocks south of the Cheyenne Belt are metamorphic rocks (~1.75 Ga) intruded by granitic plutons (~1.4 Ga).

The Cheyenne Belt extends southwest and barely clips northwestern Colorado where the Owiyukuts Complex is part of the old Archean Wyoming Craton; hence the earlier statement that these rocks are part of Wyoming!  To the east the Belt is buried under the Great Plains.  Chamberlain (1998) believes the Cheyenne Belt may extend as far as northeastern Nevada. 

All of this discussion on the Precambrian leads the traveler back to WY 34 heading northeast from Bosler (north of Laramie).  The highway traverses through numerous outcrops called the Laramie anorthosite and they are worth a stop to examine the road cuts.  Anorthosite is a rather strange igneous rock that is composed almost entirely (at least 90%) of the feldspar mineral plagioclase, but especially common is the variety termed laboradorite.  Geologists have determined that the igneous process forming the rock could not have been 90% enriched with plagioclase.  Therefore, the mineral must have somehow segregated from the main magma mass (Lindsley and others, 2010).  At any rate, the anorthosite was intruded into the Laramie Mountains during the ~1.4 Ga igneous event.  North of these outcrops the mountains cross the shear zone and the rocks become older. Many rocks display the laboradorensence of the mineral, and specimens are really nice when slabbed and polished.

Outcrop of anorthosite east of Bosler, Wyoming, Laramie Range.

Hand specimen of anorthosite showing laboradorensence.

  The final tour of the Wyoming is to examine exposures along WY 270 from Guernesy north to Manville.  This road bisects a geologic structure called the Hartville Uplift, a north-south trending Laramide (Rocky Mountain) uplift exposing Precambrian rocks in the center surrounded by outward dipping Paleozoic rocks (Sims and Day, 1999).   The uplift is part of the Wyoming Craton and ties in the Laramie Range to the Black Hills and also separates the Denver Basin (east) from the Powder River Basin (west); the rocks are mostly Archean in age but there are some Proterozoic igneous intrusions.

The Precambrian exposures are of interest to Coloradans since the rocks contain large deposits of iron, both banded iron formations and specular hematite.  Iron was first produced from the Sunrise mine, and later the Chicago, Central, and Good Fortune mines, near the towns of Hartville and Sunrise in the late 1800’s.  These mines then shipped this hematite ore to the Colorado Fuel and Iron Corporation open-hearth furnaces

in Pueblo, Colorado. (Sims and Day, 1999). At the time when mining ceased at the Sunrise mine in 1980, the Hartville district had produced about 45 million tons of iron ore (Hausel, 1989).

Sunrise Mine ca. 1907.  Photo courtesy of Wyoming Tales and Trails.

  The September 13, 1907 edition of the Mines and Mining reported: Sunrise is a company town in the fullest sense. Everything, and may it be said everybody, is owned by the Colorado Fuel and Iron Company. No special brand is necessary, for the fact impresses itself indelibly on all who come here. Visitors are not especially welcomed, which a glance at the passenger accommodations on the train that meets the Colorado & Southern at Hartville Junction forces itself on all comers.

From Hartville Junction the spur to Sunrise via Guernsey, a distance of about fifteen miles, belongs and is operated by the Colorado Fuel and Iron Company. It is a fine piece of railroad engineering with its high grades and frequent curves and one would not mind paying two prices for transportation, as he must. If only the accommodations were adequate, but, as has been said, the company seems not to care for that sort of traffic. Having constructed the line for its own convience, no doubt it considers itself an accommodator of the public by attaching a caboose to its trains of ore cars, which caboose has poor seating capacity for about eight people, through several times that number travel over the route as a rule.

The employees were forced not only to depend on the favor of the Company for the opportunity to earn a living, but to live in such houses as the Company furnished, to buy such food, clothing and supplies as the Company sold them, to accept for their children such instruction as the companies wished to provide, and to conform even in their religious worship to the Company's wishes.

In summary, southeastern Wyoming has a number of interesting geological features and rocks associated with the Precambrian.  The southern Medicine Bow and Laramie ranges have rocks that belong to the Colorado Orogen and date to the younger part of the Precambrian termed the Proterozoic.  Metamorphic rocks have dates ~1.75 Ga and are intruded by granites, such as the Sherman, with dates clustering around ~1.4 Ga.  The northern boundary of these rocks is a shear zone termed the Cheyenne Belt and represents the suturing of the Colorado Orogen to the much older Wyoming Craton (rocks of the older Precambrian termed the Archean).  These Archean rocks are exposed in the northern part of these ranges as well as in the Hartville Uplift.  In addition, in areas around the suture zone in the Laramie Range (northeast of Bosler) large plutons of anorthosite crop out.

Travelers should make every effort to travel these secondary as they offer many more chances to examine the geology than say, I-25!  We also need to remember that the total environment back in the Precambrian was so much different than what we see at the present.  Physical environments were similar in that the land contained streams and the oceans had different marine zones; however, plants and animals as we know them did not exist.  In addition, the atmosphere contained much less oxygen and the ozone layer did not exist.

Enjoy the travel and remember the words of J. W. Schopf: For four-fifths of our history, our planet was populated by pond scum!    

REFERENCES CITED

 Chamberlain, K. R., 1998, Timing of Deformation and Model of Crustal Structure Produced During Continent-arc Collision, ca. 1.78 Ga, Southeastern Wyoming:  Rocky Mountain Geology, v. 33; no. 2.

Hausel, W.D., 1989, The Geology of Wyoming’s Precious Metal Lode and Placer Deposits: Geological Survey of Wyoming Bulletin 68.

Karlstrom, K. E. and E. D. Humphreys, 1998, Persistent Influence of Proterozoic Accretionary Boundaries in the Tectonic Evolution of Southwestern North America: Interaction of Cratonic Grain and Mantle Modification Events: Rocky Mountain Geology v. 33, no. 2.

Lindsley, D. H., B. R. Frost, C.. R. Frost, and J. S. Scoats, 2010, Petrology, Geochemistry, and Structure of the Chugwater Anorthosite, Laramie Anorthosite Complex, Southeastern Wyoming: The Canadian Mineralogist, v. 48.

Matthews, V., 2009, Messages in Stone: Colorado Geological Survey, Denver.

Sims, P. K. and W. C. Day (compliers), 1999, Geologic Map of Precambrian Rocks of the Hartville Uplift, Southeastern Wyoming with a section on Mineral Deposits in the Hartville Uplift by Terry Klein: U. S. Geological Survey  Map I-2661.

Sims, P.K., and Finn, C.A., 2001, Precambrian Basement Map of Colorado—A Geologic Interpretation of the Aeromagnetic Anomaly Map: U.S. Geological Survey Open-file Report 01-364.

DIOPSIDE-ACTINOLITE AT CALUMET MINE

THE "CUT" AT THE CALUMET IRON MINE.  THE LARGE BLOCKS COMING DOWN THE HILL ARE PIECES OF THE LATE PALEOZOIC LIMESTONE.  MANY DISPLAY SURFACE AREAS COVERED WITH CRYSTALLINE EPIDOTE AND DIOPSIDE--ACTINOLITE.  NOTE PERSON FOR SCALE (DIGGING FOR QUARTZ CRYSTALS)

 Colorado is fortunate to have a large number of collecting areas available for visiting by rock and mineral clubs.  One of the standard collecting localities for club members is the Calumet Iron Mine down in Chaffee County about 7 miles north-northeast of the city of Salida.  There seems to be a gazillion articles written about field and collecting trips to the Calumet, so I will just add another one!

Fall weather in Colorado 2012 has been spectacular for collecting trips but less so for the skiers.  At this writing in early December the highs are in the low 60’s and several ski resorts remain closed---no snow.  So, when Yam of the West called me about a trip on Saturday, I eagerly accepted.  Where to---a creek walk for petrified wood?  To northeast Colorado for barite crystals?  Or over to Salida for actinolite, epidote and other crystals?  I chose the latter since I had never actually visited the old mine, and I am a sucker for green minerals.  So, off we (Yam of the West, SharonRocks, and Phil the Digger) went the next day and with a couple of coffee stops arrived mid-morning.

The Mine was discovered/located shortly after 1880 and seemed to be a major producer until the end of the century, generating somewhat less than 250k tons of iron ore.  The ore was taken from the large veins of high grade magnetite shot through the area.  Today there is a large open cut (actually “cuts”) on the hillside plus a number of shafts leading underground (to where I don’t have the slightest idea since the tunnels seem quite decrepit and my momma didn’t raise no fools).  According to Modreski (2005) late Paleozoic carbonate rocks were baked and altered by igneous rocks associated with emplacement of the Whitehorn Granodiorite; remnants of the limestone are clearly visible. Wrucke (1974) described the Whitehorn as including a pluton and a couple of small satellite bodies that intrudes the Paleozoic rocks (and also some of Precambrian age) along the east flank of the Arkansas River Valley east and northeast of Salida.  The rocks generally range in composition from quartz monzonite (less quartz than granite and equal amounts of plagioclase and orthoclase feldspars) to granodiorite (similar to granite but with more plagioclase feldspar than orthoclase feldspar) along an outcrop area of ~16 miles by ~5 miles.  The small satellite body at Calumet is a sill where the igneous rocks are tabular or sheet-like in shape. Wrucke (1974) reported radiometric dates of ~70 Ma or Late Cretaceous and associated with the Laramide Orogeny (the mountain building event associated with the Colorado Rocky Mountains).  The Turret Mining District (includes the Calumet) also has produced small amounts of copper, gold, silver, vermiculite, marble, and feldspar. In 2011 Real Aspen (www.realaspen.com) noted that, “earlier this month, Canada-based Rare Earth Industries announced it is exploring tantalum, beryllium and manganese at the formerly abandoned Turret Mines it acquired northeast of Salida in Chaffee County, Colo”.

One of the more interesting aspects of the Calument mine era was the construction of the Calumet Branch of the Denver & Rio Grande Western narrow gauge railroad in 1881.  The Calumet was a spur line off the main line (Tennessee Pass) and ran from Hecla Junction in Browns Canyon about 8 miles to the mine.  The short line brought the ore down from the mine and transferred it to a line that ultimately moved it to the big steel mill, Colorado Fuel & iron (C&FI), in Pueblo.  The short line was especially steep, about 7% grade, and the curves were tight.  The empty ore cars returning to the mine were “pushed” up the canyon with a locomotive in the rear.  The cars coming down the canyon were “pulled” but the train had a brakeman stationed on each car (shoes wore out quickly).  The mine closed in 1899 and the line was wiped out by a flood in 1901 (above from Rio Grande Info, www.DRGW.net).  Today, concrete remnants of the loading docks and rail line are still in place, having survived weathering for over 100 years.

THE DYNAMITE SHACK AT CALUMET.

I suppose the Calumet Mine is best known for a couple of minerals: diopside--actinolite pseudomorphs, and epidote.  The most interesting might be the former.  Diopside is a magnesium-calcium pyroxene, MgCaSi₂O₆, (see blog posting November 25, 2012) and forms a solid solution with end member hedenbergite (iron-calcium silicate) while augite is situated somewhere in the middle with differing amounts of added titanium, aluminum and sodium.  I remember in my intro geology class that somehow I was always confusing augite with hornblende (a complex amphibole) since both minerals are black in color and both are common constituents in igneous rocks.  After letting me suffer for several labs the instructor finally explained about cleavage, ~56^o and 124^o in hornblende while cleavage in augite is nearly “square” at 90^o.  That tidbit of information really helped! 

DIOPSIDE--ACTINOLITE PSEUDOMORPH.

LONG BLOCKY CRYSTALS OF DIOPSIDE-ACTINOLITE.  WIDTH OF SPECIMEN ~3.5 CM.

Diopside is commonly found in mafic igneous rocks (containing high amounts of magnesium and iron such as gabbro) but also in metamorphic rocks, especially where contact metamorphism has heated some carbonates.  Diopside crystals commonly are columnar to prismatic and are close to augite in cleavage angles: ~87^o and 93^o—sort of like elongated rectangles!

DIOPSIDE-ACTINOLITE.  NOTE LARGE BLOCKY CRYSTAL TO RIGHT.  WIDTH OF SPECIMEN ~4.5 CM.

At the Calumet Mine, results of the contact metamorphism included the formation of many crystals of diopside.  However, post-metamorphism the crystals have pseudomorphed, or altered, into actinolite while keeping the same crystal shape of diopside.  Now, most readers realize that I often just fumble around with the complexities of mineralogy and petrology.  And, this is a case of “how did it happen and why”?  I don’t have the slightest idea about the intricacies of this alteration and certainly could use some help from a competent mineralogist.  At one time the diopside-actinolite was given the mineral name, uralite (now discredited).

Actinolite is a complex amphibole silicate, Ca₂(MgFe)₅Si₈O₂₂(OH)₂, and is the  middle member of a solid solution series between tremolite (magnesium-rich end member) and ferro-actinolite (iron-rich end member).  From my observtions I probably cannot tell the difference between actinolite and tremolite and I believe there is much gradation between the two (and also most likely with the ferro-actinolite).  Actinolite often occurs in long prismatic crystals with two planes of cleavage so that a cross section of a single crystal would resemble a diamond (it is an amphibole and resembles the cleavage of hornblende); fracture is often “splintery”. 

PHOTOMICROGRAPH SHOWING "SPLINTERY" SMALL CRYSTALS OF DIOPSIDE--ACTINOLITE.

Some actinolite, the non-pseudomorph type, may have an interesting crystal appearance.  The mineral occurs as blades radiating out from a central point.  I picked up my specimen from an old mine dump on the trail back to the vehicle.

There are a couple of other very interesting types of actinolite out in rock land.  Very fibrous actinolite is classified as a form of asbestos.  I don’t believe that the mineral is mined for such at the present.  Second, a variety called nephrite is one of the two forms of jade (and that mineral is confusing enough), the other being jadeite, a pyroxene.  No wonder I get the amphiboles and pyroxenes confused!  The famous ‘apple-green” jade from Wyoming is nephrite. 

RADIATING CRYSTALS OF ACTINOLITE.  WIDTH OF SPECIMEN ~6 CM.

We also returned to the Springs with a variety of other minerals including garnet, epidote, and quartz.  However, that will be another story.

REFERENCES CITED

Modreski, P. J., 2005, Colorado Mineral Collecting Localities: Rocks and Minerals, Sept.-Oct.

Wrucke, C.T., 1974, The Whitehorn Granodiorite of the Arkansas Valley in Central Colorado.  U. S. Geological Survey Bulletin 1394-H.

CINNABAR and MERCURY

TWINNED CINNABAR CRYSTALS IN GROUND MASS OF CALCITE AND QUARTZ.  WIDTH OF SPECIMEN IS ~ 6.5 CM.  THE CINNABAR CRYSTAL ON THE RIGHT IS ~ .7 CM AND DISPLAYS A SCARLET END SECTION FACING CAMERA.

Mercury (quicksilver) is one of those interesting minerals that I vividly remember from my college days in mineralogy and chemistry.  However, one must remember that those days were long ago and generally before anyone thought too much about mercury’s toxicity.  But in those “olden” days mercury was “fun” to play with since it is the only mineral metal that is liquid at room temperature.  I distinctly remember “defacing” (in those days a federal crime I believe) copper pennies by subjecting them to a bath in nitric acid.  We then smeared these reduced-size pennies with mercury and tried to pass them off as dimes (when dimes were worth “more”).  We also played games on the black lab tables with moving liquid globs of mercury!  In mineralogy class, we loved to heat up ore and watch the mercury bubble up on the surface.  Have a time machine take us back to the late 1990’s when a mercury thermometer broke on the floor in the hallway of the science building.  In a few minutes the building was evacuated and the fire team arrived in space-like hazmat suits (we soon replaced all of those mercury thermometers).  In addition, when living in Wisconsin I watched my dietary intake of fish caught in lakes contaminated by mercury. My teeth have numerous amalgam fillings from 50 years ago.  However, they are slowly breaking apart and being replaced by quite expensive ceramic caps.  As Bob Dylan crooned, The times they are a-changin’!

The other day, after an appointment with a dentist to replace an amalgam filling, I was “thinking” about mercury.  Did any of that metal really leach into my system from over 50 years of having that mixture in my teeth?  Did I eat too many walleye in past years?  What about the chemistry labs, did I absorb the liquid?  I don’t seem to have any symptoms of mercury poisoning so maybe I am “OK”.  I am hoping that the odds for contracting mercury-related problems are sort of like the odds in the recent Power Ball lottery ($550 million) where a person was approximately 100 times more likely to be killed by a swarm of killer bees than win the grand prize. I figure my chances are about the same with the mercury.

After pondering these deep thoughts I decided to check my collection since I knew that at least one specimen had some nice crystals of cinnabar, the major ore of mercury.  I don’t know an awfully lot about cinnabar except that it is a scarlet color, quite soft, and mines in Nevada had produced some nice crystals.  I picked up this specimen at an auction and it was unlabeled but I assumed Nevada (I learned that from Brian P).    After some detective work on the internet and in the library, I now am certain the specimen is from Nevada, most likely from the Antelope Springs District in Pershing County, and quite possibly the Red Bird Mine.

As far as I can tell, there are no operating mines in the U.S where mercury is the primary objective; however, there may be mercury produced as a byproduct of mining other metals.  In past years Nevada was a (?the) major state for the production of mercury and as a result parts of the state, especially in western and central regions, are littered with abandoned mines.  In the 1990’s the USGS begin a long-term study examining the effects of the abandoned mines on the surrounding ecosystems (Gray and others, 1999).  They noted: “Mercury is a heavy metal of environmental concern because highly elevated concentrations are toxic to living organisms, and thus, the presence of these abandoned mercury mines is a potential hazard to residents and wildlife when drainage from the mines enters streams and rivers that are part of local ecosystems…At the abandoned mercury mines in Nevada, the presence of cinnabar remaining in ore and calcine piles (roasted ore), and any elemental mercury around the mill and retort areas are environmental concerns. For example, in all the districts studied, there is cinnabar visible in the area of the open pit cuts and trenches, ore piles and tailings, as well as in the calcine piles…Detrital cinnabar and cobbles containing cinnabar visible in streams drainages below the mines indicate that mercury present at these sites is eroding down gradient from the mines.”  That sounds like pretty messy stuff to me and I remain uncertain about cleanup efforts, if any.

Mercury was mined in Nevada from about 1907 (discovered by then at Antelope Springs and with mining beginning in 1914) until the early 1990’s. The District mines produced from veins in Triassic limestone, dolomite, conglomerate, and shale (Gray and others, 1969). Evidently these veins were emplaced during the Miocene as a result of extensional magmatism (Noble and others, 1988).  That is, Miocene extensional tectonics involved the stretching of the earth’s crust producing what we know today as the Basin and Range physiographic province.

Cinnabar, the major source of mercury, often is “massive”, with poorly-formed crystals; however, there are exceptions and one of those crystal localities is found in Nevada.  Here the individual crystals are large (for cinnabar), very soft (easily scratched by a fingernail, 2-2.5 Mohs), and their scarlet color is often somewhat masked on the surface and they seem to display a submetallic luster.  However, underneath the surface the beautiful scarlet color stands out with an adamantine luster.  The Antelope Springs crystals are well known among collectors as individuals are often twinned (penetration twins) with six-sided crystals surrounding a top pyramid.  The twins are two “penetrated” individual crystals with a common C-axis rotated 180 degrees from each other.  At Antelope Springs the ground mass is composed of calcite and quartz, some with nice crystals.  

PHOTOMICROGRAPH OF BROKEN CRYSTAL OF CINNABAR SHOWING FACE VISIBLE IN MACROPHOTO.

PHOTMICTOGRAPH OF CRYSTAL OF CINNABAR WITH A NICE GEMMY CRYSTAL OF  QUARTZ.

As a point of interest (to me anyway) is that Meriwether Lewis took along, as a medicine, substantial amount of mercury and mercurial compounds to fight rampant outbreaks of venereal disease (and others) among the boatmen.  Some brought it along as a pre-existing condition while other crew members picked it up along the way from Native Americans who in turn had contracted  it from British traders.  The most famous of the mercury pills were the Bilious Pills of Dr. Benjamin Rush.  These powerful pills, termed Rush’s Thunderbolts or Thunder Clappers acted as a laxative and a body purger; they really cleaned out the digestive system!  The major ingredient of the pills was mercury chloride.  So, if the syphilis didn’t get you, the gums bled and your teeth loosened and fell out.  And if things were really bad the expedition leaders had packed several urethral or penis syringes in order to inject mercury solutions directly into the urethra.  Ouch! Those men were one tough breed. Today modern historians are able to accurately locate many campsites of Lewis and Clark since the ground still retains mercury---in elevated amounts! 

In today’s hectic and uncertain world (the Fiscal Cliff) I  continue to remember Dylan’s words:

Come senators, congressmen
Please heed the call
Don't stand in the doorway
Don't block up the hall

REFERENCES CITED

Gray, J.E., M.G Adams, J.C. Crock, and P.M. Theodorakos, 1999, Geochemical Data for Environmental Studies of Mercury Mines in Nevada: U. S. Geological Survey Open-File Report 99-576.  

Noble, D.C., J.K. McCormack, E.H McKee, M.L. Silberman, and A.B. Wallace, A.B., 1988, Time of Mineralization in the Evolution of the McDermitt Caldera Complex, Nevada-Oregon, and the Relation of Middle Miocene Mineralization in the Northern Great Basin to Coeval Regional Basaltic Magmatic Activity: Economic Geology, v. 83