WENDOVER WILL AND ADAMITE

WENDOVER WILL, ALL ~65 FEET WITH A MECHANIZED WAVING HAND, BECKONED VISITORS TO THE STATE LINE CASINO IN WENDOVER, NEVADA. AFTER 120 MILES OF BONNEVILLE SALT FLATS UTAHANS WERE READY FOR A LITTLE ACTION AND AN ADULT BEVERAGE.  PHOTO COURTESY OF WENDOVER HISTORY

Gold Hill is one of those classic collecting areas for Utah rock hounds, and those others pilgrims willing to travel to the far western reaches of that fine state.  Of course, the bi-state town (Nevada-Utah) of Wendover is on the route if one is interested in mining recent gold or needing a motel room and an adult beverage.

In the “old days” I had a research area down west of the Deep Creek Mountains to the south of Wendover and my crew always wanted to stop at the casino for a “good meal”.  They seemed not to really like my cooking campfire meals down in the desert!  So, it was off to the Stateline Hotel and Casino (currently operating as the Wendover Nugget Hotel and Casino), home of Wendover Will.  Seems like a entrepreneur by the name of Bill Smith operated a gasoline station in Utah (right east of the state line).  Never one to miss an opportunity,  when gambling was legalized in Nevada in 1931 Bill added a casino across the state line!  During the years that I was stopping in for a refreshment before heading to the desert, the vehicle was parked in Utah, we crossed a white painted line, and voila---we we in a different world with Wendover Will  welcoming all.

Leaving the world of bright lights and tinkling slot machines behind we heading south but often could not resist a side trip to the old mining town of Gold Hill, Utah.  I previously wrote about the mines and collecting conichalcite, a bright green copper calcium arsenate hydroxide, [CaCu(AsO₄)(OH)]---see that blog on December 8, 2011. The information sign at Gold Hill notes that the usual gold, silver, copper and lead were initially mined but when those minerals became depleted, the boom was over and the town became a ghost.  During World War I, arsenic was in demand as insect control for creatures devastating the cotton fields of the southern U. S.  So, Gold Hill opened up again and mined arsenates. 

COLORLESS AND VITREOUS ADAMITE CRYSTALS ON LIMONITE. SPECIMEN IS 4.3 CM WIDE.

Another mineral that Gold Hill is “famous for” is adamite, a zinc arsenate hydroxide [Zn₂ (AsO₄)(OH)]. Adamite is one of those minerals that usually occurs in the oxidized or secondary mineralized zone where zinc is present, and arsenic was in the hydrothermal solution. 

MODIFIED ORTHORHOMBIC AND COLORLESS CRYSTALS OF ADAMITE.  INDIVIDUALS ARE .5MM OR LESS IN LENGTH.

 Most of the Gold Hill adamite that I have seen is composed of very tiny crystal druses or ball-like clusters that are either yellow or various shades of green in color.  It appears that either iron or copper make some element substitutions.  However, pure adamite is colorless, transparent and quite vitreous. In fact, I paid little attention to my specimen of ademite from Gold Hill since I thought it was just “sort of a pretty” rock with numerous tiny quartz crystals.  But, much to my amazement, under high power of a binocular microscope those tiny crystals (mostly modified orthorhombic) turned out to be colorless adamite.  Some may have hints of very pale green but with my color blindness, it is hard to tell!

A VUG IN THE SPECIMEN CONTAINING AN UNKNOWN SPRAY OF MINERALS.  THE LONGEST INDIVIDUAL ROD IS ABOUT .5 MM.

CLOSE-UP PHOTOMICROGRAPH OF UNKNOWN MINERAL.  ANY IDEAS?

I tried to find other associated minerals in my small specimen,such as austinite, but no luck.  However, there are tiny mammillary structures that are either goethite or limonite, perhaps ?pseudomorphs after smithsonite.  And, there are a few sprays of an unknown mineral present!

PHOTOMICROGRAPH OF TINY MAMMILLARY STRUCTURES OF GOETHITE OR PERHAPS LIMONITE.  ARE THESE PSEUDOMORPHS AFTER SMITHSONITE?

I just need to revisit Gold Hill and do some dump digging; however, it is a fair trip from the Springs and with the price of diesel….!  But wait, all I would need is a couple of lucky pulls on the machine :)
mike

CARTOON OF MODIFIED ORTHORHOMBIC CRYSTALS COMMON TO ADAMITE.

STRANGE MARKINGS IN THE THE MOENKOPI FORMATION

Since my initial geological contact with the Colorado Plateau in 1967, I have been impressed and “excited” with the Moenkopi Formation.  It may not be as colorful or fossiliferous as other red rocks of the Plateau (i.e. Chinle Formation with the magnificent fossilized wood), nor as cliff forming as the Wingate Sandstone, nor as majestic as the Navajo Sandstone.  However, it has a certain undescribed cachet to which I have bonded!

The Lower and Middle Triassic Moenkopi, and its stratigraphic equivalents, crop out over much of the Colorado Plateau but are especially colorful and well exposed in many of the National Parks and Monuments in Utah.  Most of the unit is red or red-orange in color and the original sediments were deposited in a wide variety of depositional environments including floodplains, tidal flats, stream channels, dunes, beaches, near-shore marine, sabkhas.  The streams, both large and small, generally flowed west or northwest from highlands such as the Ancestral Rockies and perhaps even those associated with the Ouachita Front (southern supercontinent slamming into U.S.)  To the west these streams met marine waters and in places near-shore marine rocks are interbedded with terrestrial rocks of the Moenkopi.  The dominant red colors most likely are the result of oxidation of iron rich minerals found in Precambrian rocks of the exposed highlands.

Tilted and brightly colored beds of the Moenkopi Formation resting on flatirons (darker beds with vegetation) along Green River at the mouth of Split Mountain Canyon, Dinosaur National Monument, Utah.  The Park City overlies massive sandstone beds of the Weber Formation.

The Moenkopi seems to be bounded by unconformities; however, the amount of missing geological time is difficult to determine.  Most likely the entire Middle Triassic is missing between the Moenkopi and Chinle while “some” of the Early Triassic and “most” of the Middle and Late Permian is missing in the lower unconformity (the “Permo-Triassic Unconformity”).  At Dinosaur National Monument (northeast Utah) the Moenkopi rests on the Lower Permian Park City Formation (phosphatic and marine) and is overlain by the conglomeritic Gartra Grit Member of the Chinle (Shinarump equivalent).  At Zion National Park (southwest Utah) the unit rests on the Permian Kaibab Formation (marine) and is overlain by the Shinarump Member of the Chinle.  At Canyonlands National Park the Moenkopi overlies the Permian Cutler Group/Formation (wind, stream, marine) and is overlain by the Chinle.

Most of the Moenkopi is rather unfossiliferous; however, I rather enjoy looking at ichnofossils and trace fossils, and they are quite common and somewhat spectacular. Various sorts of ripple marks are spectacular and the burrows and crawling marks seem enough to get anyone excited.  There are vertebrate footprints in some areas; however, I have not experienced these in the field.

So my advice for what it is worth.  If you are in the Colorado Plateau where the Moenkopi is exposed, take a hike along the outcrop and keep your eye on the rocks!  

mike 

Dessication cracks in a mudstone, San Rafael Swell.

Mudcracks, and "perhaps" raindrop impressions.

Current ripple marks.

Dessication cracks near Moab.

Bioturbation: burrows, large and small, and crawling trails.