AFMS & RMFMS ANNUAL SHOW AND CONVENTION, BIG PINEY, WYOMING, JUNE 2021: PART FOUR: ACANTHITE, MIMETITE, WULFENITE, CALCITE

 Mexico is a mosaic of different realities and beauties.

Enrique Pena Nieto

My last post commented on several specimens of calcite crystals that came up from Mexico via a grandfather and granddaughters. Exact collecting information was very fuzzy; however, I expect they came from one of the mines at Santa Eulalia in Chihuahua.  My purchase plan was to give these specimens to some younger rockhounds.

I did come back from Big Piney with some nicer specimens containing collecting information.  The first is a really nice barite matrix covered with gemmy orange wulfenite crystals associated with green botryoidal mimetite.  I have written about these minerals before but here is a partial repeat.

Mimetite is a lead chloro-arsenate [Pb₅(AsO₄)₃Cl] often found with pyromorphite and/or vanadinite.  In the former mineral the phosphate radical, PO₄, replaces the arsenate radical (AsO₄) while in the latter the vanadate radical (VO₄) replaces the arsenate.  However, mimetite is also closely associated with wulfenite [(Pb(Mo₄)] since both form as secondary minerals in the oxidation zones of primary lead minerals.

Mimetite seems mostly yellow in color although other colors are common—green, red, colorless, brown, orange-yellow and shades in-between.  It usually appears as small barrel shaped prismatic crystals but may be tabular, mammillary, granular, rounded, botryoidal and others.

Wulfenite is a lead molybdate with colors ranging from orange (common) to yellow, yelow-orange or red.  Crystals typically are tabular and transparent, at times opaque, but may form pyramids or stubs.

The specimen I brought home came from the La Morita Mine, Ascención Municipality, Chihuahua, Mexico.  This former polymetallic mine is well known for its luscious silky wulfenite crystals and the unique mimetite.  MinDat noted that since 2018 the Mine has been operated for specimen production rather than metallic ores.  However, my specimen was collected/mounted on the 2^nd of January 1972, about 50 years ago.

Barite matrix with wulfenite tabular crystals and botryoidal mimetite.  Width FOV ~4.8 cm.

Wulfenite tabular crystals.  Width FOV ~1.4 cm.

Green botryoidal mimetite.  Width FOV ~1.5 cm.

The second specimen I brought home exhibits pointy scalenohedron crystals of calcite covered by a secondary calcite druse with all sitting on a base of small gemmy quartz crystals.  It almost appears that the quartz is/was slowly replacing the calcite forming quartz ps. calcite. The specimen was collected from a mine in Guanajuato, Guanajuato Municipality, Guanajuato, Mexico.  I am guessing either the La Sirena or Valenciana Mine.

Scalenohedron crystals of calcite covered with secondary calcite druse on a base of gemmy quartz crystals. Width FOV ~5.3 cm.

 

A stubby original calcite crystal covered with a secondary calcite druse with tertiary quartz crystal growing near the top.  Width FOV ~1.5 cm.

An original calcite crystal covered by a secondary shiny druse of calcite. Width FOV ~1.5 cm.

The Guanajuato mines are classified as “epithermal vein deposits” where a variety of minerals are located in veins that are probably the result of previous fractures and cracks in the host rock.  The hydrothermal brines, especially sodium-calcium-chloride brines, are effective solvents and are able to dissolve the primary sulfide ores and circulate through the host rocks.  As these brines begin to cool, usually at shallow depths, deposition of minerals take place and often these veins of minerals are quite rich.  In fact, epithermal gold deposits are some of the richest gold deposits in the world. At Guanajuato mineralization consists dominantly of silver sulfides and sulfosalts (a metal + semi-metal + sulfur), base metal sulfides (metal + sulfur) mostly chalcopyrite, galena, sphalerite, and pyrite, and electrum (alloy of silver and gold). Gangue minerals (the waste rock) are generally quartz and calcite; the host rocks (holding the minerals) are Mesozoic sedimentary and intrusive igneous rocks and Tertiary volcanic rocks (Morgan and others, 2014).

The Rayas Mine, one of the richest of the Guanajuato mines, was located atop the mother lode, or veta madre, set prominently in the hills above the city. In fact, the mine still partially operates and produces ore, as well as specimens. The Rayas has a long history of bringing to grass specimens of acanthite, a silver sulfide [Ag₂S] that crystallizes in the Monoclinic Crystal System. It is a low temperature sulfide and is the stable form below 177 °C. The high temperature silver sulfide is argentite, crystallizing in the Cubic Crystal System, and as it cools below 177 °C it transforms to acanthite. Rockhounds still may find old specimens labeled as argentite; however, the only form  stable in “normal” air temperature is acanthite.   

Acanthite is a common ore of silver, lead grey in color although it tarnishes black (as on Sterling Silver), has a metallic luster, and is soft (~2.0-2.5 Mohs). What make acanthite such a nifty display specimen is that it often appears as a “stack” of pseudo-octahedral and/or pseudo-cubic crystals (formed during transformation from cubic argentite).

A “stack” of pseudo-octahedral and/or pseudo-cubic crystals of acanthite.  length of "stack" ~2.0 cm.

AFMS & RMFMS ANNUAL SHOW AND CONVENTION, BIG PINEY, WYOMING, JUNE 2021: PART THREE

 

                Last year (2020) in the middle of the pandemic the Rocky Mountain Federation of Mineralogical Societies (RMFMS) was forced to scramble after their scheduled meeting location closed shop due to state regulations.  Other regional Federations faced the same big questions and decisions loomed—cancel the meetings, postpone the meetings, or find new locations (in a hurry).  In an amazingly short period of time the Sublette County Rockhounds (Wyoming), with Jim and Leane Grey at the rudder, invited RMFMS to Big Piney in the western part of the state for the convention and show.  I guess the local rockhounds figured that the wide-open spaces would not allow the COVID 19 critters to congregate.  By all accounts the events were well attended and participants came away “happy.”  Hosts of the 2020 American Federation of Mineralogical Societies (AFMS) also needed to back out so a ZOOM meeting was held although a quorum was not reached, and official business could not be conducted.

But back to Wyoming.  The first thing that most RMFMS members needed to ask themselves was “Where in the world is Big Piney, Wyoming?”  It turns out that, as a local cowboy told me in the café, in a fast pickup and no big animals on the road, we can make it to Jackson in an hour and a half, a little less time if you are ill.  Jackson is 92 miles northwest of Big Piney.

Move forward a year and decision time was again at the table and host cities were backing out, mostly due to state rules and regulations.  Guess what?  Along came the Sublette County Rockhounds (with Jim and Leane still at the helm) with an offer to host the 2021 RMFMS show and convention, and oh by the way, you might as well throw in the AFMS hoopla.  The more the merrier.  Well, the Federations could not turn down an offer like that so here we come.

Although I could not attend in 2020, I made early plans to haul my travel trailer over the mountains and across the plains to Big Piney (I knew Bill Smith from Kansas would do the same).  I actually had been to the area before—in the summer of 1969 I worked for Texaco out of Casper and another geologist and I drove over to “check out the rocks.”  I remember little else about the town.  In addition, I came close several other times since fieldwork on my doctoral dissertation extended to north of Kemmerer (the town is 70 miles south of Big Piney) almost to Big Piney.

So off we went from Colorado Springs traversing the interstate from Hades (construction on I-35 from the Springs to north of Fort Collins) jerking a 38-foot 5^th wheel.  Wow.  Overnight in a campground in Cheyenne, a second cup of coffee in Laramie, and we were off to the races on I-80 along with several thousand 18-wheelers that were heading to the west coast. Unfortunately, as the journey resumed west to Rock Springs another  construction project, 18 miles of rough single lane with the trucks, was far from enjoyable.  Crossing the Green River at Green River, Wyoming, reminded me of one of my heroes, John Wesley Powell, who disembarked at that point in 1869 on his epic journey to, and through, the Grand Canyon.

Stamp published in 1969 by the U.S. Postal Service to commemorate Powell’s first journey down the Green and Colorado Rivers.

Citadel Rock butte, Green River Wyoming, 1868. Albumen print by Andrew J. Russell showing construction of a railroad bridge across the Green River.  The area is the Type Locality of the famous (fossilized fish and oil shale reserves) Green River Formation (mostly Eocene in age) and all rocks in the print are of the Formation.  The Butte is still an impressive site along I-80.  The photo is Public Domain and from the Library of Congress's Prints and Photographs division under the digital ID ppmsca.03147.

Finally, near the town of Green River we left the I-80 and headed north through some country where you could actually enjoy the rocks and landscape without fearing for your life traveling with the trucks.  On the two-lane without traffic, I tried to imagine what it was like for fur trappers who were heading north in the early 1800s to the big rendezvous on the Green River.

Annual rendezvous of Rocky Mountain trappers.
Original sketch in Oregon Trail Museum. Public Domain photo courtesy of U.S National Park Service and Scott’s Bluff National Monument.

Finally, there it was---Big Piney, much like I remembered---without a single pine tree, big or small.  I had to stop and ask a local about the fairgrounds, home of the show and convention.  Little did I know that one had to proceed through both Marbleton and Big Piney to locate the mass of fairground buildings.  An amazing setup for what must be a large county fair.

The Sublette Country Fair: Join us July 28-31, 2021! Photo courtesy of Joan Mitchell at the “Hog Show.”

Unfortunately, Marbleton and Big Piney (within a half mile of each other) have suffered like many other small rural towns---businesses have pulled up stakes and moved on.  What they left behind was one small eating establishment.  Fortunately, this café served some of the best Mexican style food in Wyoming.  Another business that survived is Jim and Leane’s rock shop in Marbleton---what a pleasant surprise and enjoyment.  Be certain to stop in if  you are in the area.

The eatin’ place in Big Piney.  Photo courtesy of Frank Tank.

The number of campsites at the fairground is quite large as I suppose the cowpokes attending the fair events need hookups for their horse trailers/sleepers.  The RVs were simply backed up to a barbwire (bobwire in the vernacular) fence and were awakened by “mooing” cattle in the morning.

There may not be Pine Trees in Big Piney; however, the sunsets are spectacular over the sagebrush steppe.  The RV was backed up to the bobwire fence.

Although the fairgrounds did not have a permanent eating establishment, two or three food trucks served the show visitors.  And speaking of visitors, I was amazed at the number of people of all ages who trekked across the country to visit the rocks and minerals.  I talked to one family who made a 100-mile (one way) trip to see the show---"heck, not far atall for some entertainment.”  Reminds me of my early hometown in Kansas.

Since this was both a RMFMS and AFMS get together I attended a number (well, actually there were just a few) of Federation meetings.  I will leave explanations and results of these meetings to the officers.  I headed for Colorado after the Sunday morning breakfast and awards presentations for writing and newsletters. I must say that CSMS came out a big winner in both RMFMS and AFMS contests.  Our local Society has a fantastic Pick & Pack editor in John Emery.  The following awards were presented to CSMS members:

American Federation of Mineralogical Societies (AFMS)

New Newsletter Editors

John Emery; 2nd Place: CSMS Pick & Pack

Junior Poetry

Josilyn Teague; 1st Place: The Crystal

Karah Teague; 3rd Place: Oh Colorado Mountains

Adult Article-Advanced

Mike Nelson; 2nd Place: Playing with Minerals and Surviving the Pandemic

Rocky Mountain Federation of Mineralogical Societies (RMFMS)

Photo Collage

John Emery; 1st Place: CSMS FIELD TRIP | ROCKY MOUNTAIN HIGH CLAIMS 1 & 2

Junior Poetry

 Karah Teague; 1st Place: Oh Colorado Mountains

Josilyn Teague; 2nd Place: The Crystal

New Newsletter Editor

John Emery; 2nd Place; CSMS Pick & Pack

Junior Articles

Jonathan Hair; 4th Place: Impact Gold

Adult Articles Advanced

Mike Nelson; 4th Place: Chasin' the Blues with Elwood, Jake, Bob, Kevin, Jerry & Bill

Mike Nelson; 2nd Place: Playing with Minerals and Surviving the Pandemic

Steven Veatch; 5th Place: Windy Point: A Photographic Essay

Since Big Piney is close to the fossil fish digs near Kemmerer several dealers had many nice Eocene specimens for sale.

The Wyoming State Gemstone is jade of the variety nephrite, a calcium magnesium silicate varying in composition from actinolite to tremolite (an amphibole).  Most Wyoming jade is some sort of green but blue, brown, black and white specimens are rare.

Fossil Butte National Monument is not far from Big Piney and the Ranger staff offered a nice display and explanation.

The local club excelled in offering opportunities for the younger rockhounds.

Flintknappers always draw an audience.

The Silent Auction is always popular.

During the shows and meetings, I kept gazing east across the sagebrush and the valley of the Green River to the Wind River Mountains.  This section of Wyoming has fascinated me since kiddom as I read a voluminous number of books and articles on the early fur trappers and their rendezvous along this section of the Green.  As a geologist I was always interested in the large number of mountain glaciers still present on the flanks of the peaks.  The Winds have the largest number of glaciers still alive in the lower 48 and Gannett Peak has the largest of these remaining glaciers.  As a result, the glacial topography presents a textbook study that beginning students can easily understand—horns, arêtes, cirques, etc. carved into the Precambrian granite.  Although there are no 14ers in the Winds, Gannett Peak at 13,809 is the highest point in the state of Wyoming.  Coming in second at 13,775 is the much better-known Grand Teton.  After that the next highest 19 Wyoming peaks are all located in the Winds.  It is truly a magnificent mountain range; unfortunately, I have explored very little of the topography (spending my time always wandering around Utah and Colorado).

Although I came to Big Piney for the meetings, deep down in my heart I came to see the headwaters lakes of the Green River! This particular area in the Winds has been on my bucket list for over a half century!  I had been close before but no bingo.  This time I was going to check it out, and so I did.

From Big Piney one travels north to Cora and east towards Pinedale before turning north on WY 352 for about 50 miles.  Approximately half is paved, and half is washboard bumpy gravel, but all is scenic as one follows the Green River to its source, a lake backed up behind a glacial moraine with a magnificent mountain called Squaretop Mountains (11,695 feet) at the far end.  WOW, what a view.  So inspiring. There are several small lakes in the source valley that are fed by glacier meltwater; however, the lake “at the end of the road” is usually referred to as the source of the Green.  BTW, there is a nifty little sandwich shop in Daniel on the way to the lake—take advantage, your last, before starting the 50-mile stretch.

Squaretop and the lake.

 

 

The far upper reaches of the fast-moving Green River below the source lakes.

Thirty miles below the source lakes the Green River meanders along in a wide valley.

So, it finally happened and was made so much better by the company of two friends from Salt Lake City (the dinosaur ladies) and my spouse.  Another checkoff on the list.  How many more bucket list spots can I make that check mark?  Don’t know. 

A different route was selected for the trip back home—different rocks and landscapes for an ole geologist to peek at. I wanted to see again the sagebrush steppe of the vast Wyoming Basin (actually composed of a number of smaller basins).  I had camped before on the Big Sandy River near the southern end of the Winds while on a field trip looking for fossils in Eocene rocks.  In addition, the area along the Big Sandy has the largest herd of migrating pronghorns in the U.S. (I only observed small groups or individuals).

At Rock Springs it was back to truck infested I-80 until WY789/CO13 turned south towards Craig, Colorado, and our campground along the Yampa River.  Decades ago, in my oil finding days, I had been through Baggs, Wyoming, on the state line.  If anything, this small oil community has, shall I say, gone downhill.  It was not a pleasant experience when, on this traveling Sunday, I blew the sidewall out of one of the 5^th wheel tires.  No indeed, not a pleasant experience; however, I got it changed and limped down to Craig and I-80, camped, and steered her home to Colorado Springs.  Yes, I stopped at several locations, but no one wanted to sell me a tire with installation—too busy today.

A group of partial and full scalenohedron crystals of calcite.  Width FOV ~2.0 cm.

A gemmy scalenohedron calcite crystal. Length of crystal ~1.0 cm.

 

Calcite crystals that may be hematite included and some may have phantoms.  Width FOV ~1.0 cm.

Although I enjoyed the show and vendors associated with the convention, I purchased very few specimens—nothing I really needed.  I did mange to bring home a number of hand size specimens mostly coved with scalenohedron crystals of calcite---really nice well-formed crystals.  The collecting location is a little fuzzy!  They were advertised as coming from Mexico.  In asking a more definitive location the two young sellers stated specimens were collected by their grandfather; in Santa Eulalia they thought.  Now the Santa Eulalia Mining is a very large mining district in Chihuahua with many mines; therefore, I am to further pinpoint the collecting locality.  I plan on giving these specimens to my kiddie (and a few adults) rockhound friends.  

So, the 2021 RMFMS and AFMS events are now history—at least in my mind.  A big thanks to Jim & Leane, the Sublette rockhounds, Prez Judy and the Central Office (Cheryl) from AmFed,  and Prez Bob, VP Sheri, Sec. Wayne, and my good friend Tres. Gene, who makes it all run, from RMFMS.