DAYDREAMING ABOUT NATURE: MIXITE, FROM TINTIC, UTAH

Joys come from simple and natural things; mist over meadows, sunlight on leaves, the path of the moon over water. Even rain and wind and stormy clouds bring joy.

I often “daydream” as I write since remembrances of my past help me to contemplate the present, and brings joy to my life.  I may not remember where my truck keys are stored but have very sharp recollections of my time spent in the wilderness waters of northern Minnesota: As long as there are young men with the light of adventure in their eyes or a touch of wildness in their souls, rapids will be run.

A “long time ago” I satisfied two great personal “loves” by combining both teaching geology and canoeing in an outdoor classroom.  My first classes were held on the Current River in southern Missouri, a newly designated National Scenic Riverway (the first in the nation).  While interesting, it was not the wilderness area that I craved.   So, the next few years I moved to the Boundary Waters Canoe Area Wilderness (BWCA) in northern Minnesota headquartered in Ely.  At that time the great author, environmentalist and strong advocate for the protection of wilderness was still alive and living in Ely---Sigurd Olson (1899-1982).  I had devoured, several times, all of his books and still bring out The Singing Wilderness (a signed copy) for a yearly reading.  I figured that a man who took his wife canoeing on their honeymoon was my kind of hero, and Mrs. Olson was my picture of a strong spouse and partner. I did not take my wife canoeing on our honeymoon (the two days that it was—no money) but not long after I had her carrying packs over the portage trails in the BWCA.  Again, a strong spouse and partner.

I bring this up since the writings of Olson often just flow across my mind and present vivid pictures: The mist was all gone from the river now and the rapids sparkled and sang. Sometimes today the words associated with geology just sort off spin off my tongue and flow across my mind with vivid pictures: Ajax, Black Dragon, Black Jack Empire, Boss Tweed, Bullion Beck, Carissa, Eureka Hill, War Eagle, Scotta, Uncle Sam, Opoltonga, Humbug, May Day, Godiva, Sunbeam.  All of these locations, plus many others, are mines in the greater Tintic District in Juab and Utah counties in the central part of the state. I have not seen most Tintic mines but never-the-less can picture them in my mind and wonder about the names.  Was the “boss” of Tammany Hall, William Tweed, investing in Utah Mines?  Or was the mine owner or foreman an admiring Democrat? Did some miner hit a rich vein and yell Eureka?  Did a mine tunnel collapse and someone yelled Mayday?  Those are some of life’s persistent questions.  

Satellite image of Utah showing location of Tintic Mining District and Salt Lake City.  Image courtesy of Ray Sterner, Johns Hopkins University.

The Tintic District is located about 50 miles south-southeast of Salt Lake City on the west central slope of the East Tintic Mountains.  The mountains are part of the Basin and Range Physiographic Province and connect the Oquirrh Mountains to the north (also Basin and Range mountains and the range visible directly to the west of Salt Lake City) and the Canyon Range to the south.  

Google Earth image© of Tintic Mining District including Mammoth Mine.  Utah Lake is the large body of water in the northeast.

The Tintic Mining District was discovered in ~1869 and its geology/mineralogy was summarized by Wilson (1995) who noted the presence of ~175 species of minerals…”Much of the production of siliceous ore in the district [was] utilized by smelters in Tooele and Salt Lake City to mix with more iron-rich ores of Bingham.  Tintic has produced gold, silver, lead, copper, iron and zinc as its major commodities.”  Morris (1968) noted the primary ores consisted of “sulfides and sulfosalts of silver, lead, copper, iron, zinc and bismuth in association with jasperoid (silicified carbonate rock), barite, aggregates of quartz crystals, calcite, dolomite, and ankerite…gold is locally common…”

The geology of the Mining District is related to several large volcanoes that erupted in the Tintic area (and much of western Utah) during the early Oligocene (Hintze and Kowallis, 2009) and covered Paleozoic rocks that were folded and faulted by an earlier mountain building event termed the Sevier Orogeny (Cretaceous).  During the later Oligocene, these volcanoes begin collapsing and large calderas formed.  The hydrothermal solutions associated with the volcanics followed the cracks and faults in the Paleozoic rocks and helped dissolve portions of the limestones.  As these solutions cooled the minerals begin to crystallize forming the ore bodies in the limestone.

Although the Tintic mines currently are closed (although many are under claim), their total mineral production, about 20 million tons, would translate into about three billion dollars (2006 dollars).  The most valuable metals were silver (~42%), gold (29%), lead (17%), copper (~6%) and zinc (~6%).  Production peaked in the first half of the 2oth Century and finally ceased with the 2002 closing of the Trixie Mine (Krahulec and Briggs, 2006).   For a great history of the mine transportation network check out Railroads and Mining at Tintic at www.utahrails.net.

One of the smaller mines in the District is the Carissa, a mine found on the slope of Mammoth Peak, home of the well-known Mammoth Mine.  It was connected by a tunnel to its more productive neighbor the Northern Spy Mine. Carissa may not have been a large gold-silver producer; however, it was later (years?) a specimen producer of very nice crystals of the arsenates adamite [(Zn,Cu)₂AsO₄OH], conichalcite  [(CaCuAsO4(OH)], mimetite [Pb₅(AsO₄)₃Cl], olivenite [CuAsO4(OH)], mixite [Cu₆Bi(AsO₄)₃(OH)₆-3H2O)] and the copper carbonates rosasite and azurite.  All of these minerals are secondary and found in the oxidation zone where primary lead (argentiferous galena), zinc (hemimorphite?), bismuth (bismuth) and copper (copper, cuprite, enargite) were present.  The enargite could also have provided the arsenic for the arsenate (AsO₄) ion with a charge of Minus 3.

In an arsenate ion, individual arsenic atoms are surrounded by four oxygen atoms that form a strongly-bonded group that are linked together by weaker bonds involving the metal cations plus the hydroxyl ion (OH) and the water molecule (H₂O).  For example, in mixite the metal cations are bismuth and copper. In the agardite series (five minerals of the Mixite Group), there are numerous Rare Earth Elements (REE) serving as cations.

Goethite matrix with various minerals as listed below (except azurite).  Width of specimen ~5 cm.

A second specimen from the Cariss with visible azurite.  Width ~1.7 cm.  Matrix includes much baryte.

The most interesting specimen mineral collected from the Carissa, as least to me, is the rare copper bismuth arsenate named mixite.  Essentially a micromineral, mixite occurs as very tiny, slender acicular needles that often congregate together in tuffs or radial sprays. Although the crystals are usually some shade of green to blue-green, occasionally they are white to light blue.  Individuals appear to have an adamantine luster although this is a difficult call. The tuffs are more silky in nature. Crystals belong to the Hexagonal System and appear to be translucent to transparent.  Hardness is listed as 3.5-4 although that is tough for me to determine. 

The above eight photomicrographs are from specimens collected at the Carissa Mine.  M=mixite, B=baryte, C=single green "ball" of conichalcite, A=azurite, R=rosasite, G=goethite.  Each photomicrograph has a width 1 cm.

Mixite is the namesake of the Mixite Group, as assemblage of about a dozen arsenates or phosphates containing hydroxyl ions and water molecules but with different cations--all look similar and are difficult to distinguish between. I know my specimens from the Carissa Mine are mixite since they have been identified by X-Ray Diffraction (XRD) methods. 

Unknown mineral.  Note penetrating twin.  Crystal ~ 6 mm.

Flat-bladed green mixite crystals collected from Gold Hill Mine, western Utah.

How often we speak of the great silences of the wilderness and of the importance of preserving them and the wonder and peace to be found there. When I think of them, I see the lakes and rivers of the North, the muskegs and expenses of tundra, the barren lands beyond all roads. I see the mountain ranges of the West and the high, rolling ridges of the Appalacians. I picture the deserts of the Southwest and their brilliant panoramas of color, the impenetrable swamp lands of the South. They will always be there and their beauty may not change, but should their silences be broken, they will never be the same.

All quotes above are from the writings of Sigurd Olson.

REFERENCES CITED

Hintze, L.F. and B.J. Kowallis, 2009, Geologic History of Utah: Brigham Young University Geology Studies, Special Publication 9.

Krahulec, K. and D. F. Briggs, 2006, History, geology, and production of the Tintic Mining District, Juab, Utah, and Tooele Counties in R.L. Bon, Editor, Mining Districts of Utah: Utah Geological Association Publication 32.

Morris, H.T., 1968, the Main Tintic Mining District, Utah in Ore Deposits of the United States, 1933-1967: American Institute of Mining Engineers, Graton-Sales Volume, New York, v. 2. 

Wilson, J.R., 1995, A Collector’s Guide to Rock, Mineral & fossil Localities of Utah: Utah Geological Survey, Misc. Publication 95-4.

AUGELITE: AN UNCOMMON GREEN PHOSPHATE

The trouble with doing nothing is that you never know when you are finished.

Ah, another fairly rare phosphate mineral has popped up on my radar screen.  The other day, in a fit of doing nothing of importance, I spotted a photo of a sparkling faceted gemstone called augelite.  Somewhere from the back recesses of my mind a bell started ringing and forced my memory to “get in gear.”  Yep, now I remember that at a Tucson show I picked up a specimen of augelite from a Peruvian dealer: 1) it was a “pretty” specimen; 2) it was a phosphate mineral; 3) it was not in my mineral vocabulary; 4) it was reasonably priced; and 5) the dealer was a pleasant person.  Upon returning home I stuck the specimen in the drawer labeled South America #1 and promptly moved on to other “things.”  OK, my mind works in mysterious ways so I recently hauled out the specimen and again thought it was nice and decided to widen my mineral vocabulary!

 

A pale green crystal of augelite (A) attached to several gemmy quartz crystals (Q).  The C-axis runs the length of the crystal.  See below. Maximum length of crystal is ~1 cm.

A computer-generated crystal of augelite.  Compare with photo above.  Note C axis runs length of crystal.  Image courtesy of  www.smorf.nl.  Original drawing in V.M. Goldschmidt, Atlas der Krystallformen, 1913-1923.

Augelite is an uncommon hydroxyl aluminum phosphate [Al₂PO₄(OH)₃] that has been reported from several localities around the world but specimens on the market seem to come from just a few localities in in Bolivia, Peru, Canada (Dawson Mining District), and California (the now depleted Champion Mine).  In fact, most market specimens are from the "world’s best occurrence" at Mundo Nuevo Mina, Huamachuco, Sanchez Carrion Province, La Libertad Department, Peru (Moore, 1915).  The crystals from Mundo Neuvo are usually apple-green to colorless, transparent to semi-transparent, have vitreous to pearly luster, and are well developed. Crystals are commonly striated, have a white streak and are ~4.5 hardness (Mohs). Other localities have yielded colorless to white to pale yellow and even pale blue crystals. Most of the Peruvian specimens are intimately associated with quartz crystals and “needle quartz” is especially attractive.  Crystals are Monoclinic and commonly appear as thick tabs.

Augelite crystal shown above.  Note tiny terminated quartz crystal extruding from crystal face at end of arrow.  Length of quartz crystal is less than 1 mm.

“Augelite forms in a variety of situations including high-temperature Al-rich hydrothermal deposits, tin- and/or lithium-bearing pegmatites, hydrothermally altered andesites, Al-rich metaquartzites” (Visser and others (1997), “hydrogen metamorphism of phosphate-bearing rocks in peraluminous sediments” (AZO Mining, 2017) and by “metasomatic replacement of aluminosilicates minerals” (Wise, 1975).  I remain (after several hours of searching) uncertain about the geology of the Mundo Neuvo Mine.  At one time it produced hubnerite and scheelite so perhaps the initial target was tungsten?  According to Moore (2015), Mundo Neuvo was last used as a specimen mine (especially for augelite).

I noticed that augelite has been found in the Black Hills of South Dakota from the Rough and Ready Mine (Tinton District), and the Bob Ingersoll, Etta and Hugo mines in the Keystone District.  All localities are lithium-rich pegmatites so perhaps augelite formed from the alteration of primary lithium minerals?  At the famous Palermo #2 Pegmatite in New Hampshire, augelite forms as a high temperature (~500-300C), oxidizing to non-oxidizing, alteration product of montebrasite [LiAlPO₄(OH)], and in oxidizing to non-oxidizing, low temperature (~300-100 C) conditions (Nizamoff, 2006).  See previous posting on alteration of lithium-rich minerals.

So, augelite is another of those uncommon phosphate minerals that has entered my specimen vocabulary.  I look forward to a continued learning experience about rather exotic, at least in my collection, minerals.   

REFERENCES CITED

AZO Mining, 2017, Augelite-occurrence, properties and distribution: www.azomining.com.

Moore, T.P., 2015, What’s new in the Mineral World: The Mineralogical Record, Report #40.

Nizamoff, James, 2006, The Mineralogy, geochemistry and phosphate paragenesis of the Palermo #2 Pegmatite, North Groton, New Hampshire: University of New Orleans Theses and Dissertations, Paper 398.

Visser, D., R.O. Felius, and M. Moree, 1997, Augelite and cerian crandallite in dumortierite quartzites, Vaca Morta quarry, Vereda Range, Macaubas, Bahia, Brazil: Mineralogical Magazine, vol. 61, issue 4.

Wise, W.S., 1975, Solid solution between the alunite, woodhouseite, and crandallite mineral series: Neues Jahrbuch fiir Mineralogie Monatshefte.

PURPURITE (PHOSPHATE) FROM SOUTH DAKOTA AND COLORADO

For my part, I travel not to go anywhere, but to go. I travel for travel’s sake. The great affair is to move.

          Robert Louis Stevenson

This past summer I had an opportunity to revisit the Helen Beryl Mine in Custer County, South Dakota in the Black Hills.  I had first explored the area in the spring of 1966 as a geology graduate student enrolled in the University of South Dakota.  I, and a few of my geology friends, initiated a road trip to prospect for minerals in the Hills.  Our intention was to collect specimens for our introductory geology labs with the “leftovers” made into kits for sale to other interested students. 

If I remember correctly, we really did not sell any specimen kits back on campus.  But I do remember locating places and “things” in the Hills that I had never seen before.  We explored caves and mines and roadcuts and roadhouses with beer and country music and even had time to pound and collect minerals.  Growing up in Kansas I had never seen beryl before let alone spodumene.  The trip opened my eyes to the wonders of the Hills and was the highlight of the semester!

In revisiting the Helen Beryl Mine, I only had an opportunity to sort through part of the dump piles since I was hobbling around on my cane awaiting another knee surgery upon returning to Colorado Springs.  I did not find much of real interest but did bring home small specimens of purpurite and alluaudite, both phosphate minerals.

Purpurite [Mn⁺⁺⁺PO₄] is an interesting mineral that is the oxidation product of a lithium-rich mineral called lithiophilite [LiMn⁺⁺PO₄] and/or triphylite [LiFe⁺⁺PO₄].  There is a little confusion here and some of these minerals are difficult to distinguish between.  For example, purpurite is the manganese-dominant phosphate and is in solid solution with the iron-dominant phosphate called heterosite [Fe⁺⁺⁺PO4]; both are similar appearing to each other.  The parent of heterosite is triphylite with the latter in solid solution with lithiophylite.  So, nature has provided us with lithium-iron-manganese phosphates that weather to purple- to reddish purple- to rose- colored purpurite or heterosite.  During the weathering process, the lithium leaches away.  Can I tell the difference between purpurite and heterosite?  Maybe, but probably not.  My identification is based up two things: 1) the more purple to purple- red colored specimens are probably manganese-dominant purpurite since an increase in iron darkens the color; and 2) the locality mineral list published by MinDat!  

Purpurite (P) from the Helen Beryl Mine. A? may be alluaudite.  Specimen maximum width ~2.6 cm.

Purpurite seems never to form crystals but is always massive to granular.  Mineralogists with much more knowledge than me have placed the mineral in the Orthorhombic Crystal System.  I have described the color, and the hardness is about 4.5 (Mohs).  It has a dull or earthy luster and I obtained a red streak.  Once observed, purpurite/heterosite is easy to spot as it appears as a purple or purple-red “stain” on the matrix.

For purpurite/heterosite to form, a lithium(s) mineral must be present in the parent rock (precursor), usually igneous in nature.  As I understand the situation, lithium-rich minerals are not all that common in the rock record with the most abundant being “the lithium aluminosilicates spodumene,  petalite, and eucryptite , the phosphates amblygonite-montebrasite and lithiophilite-triphylite, several species of mica (mostly known as lepidolite), and the tourmalines (elbaite, rossmanite, liddicoatite)” (London, 2017).   It also seems these lithium-rich minerals are most abundant in pegmatites. My next question then was—what was the original source of the lithium? 

London (2017), in a fantastic article in Rocks and Minerals, explained the situation quite clearly: sediments containing fine-grained micas and clays that are lithium-rich collect in ocean basins and form a mud drape over the oceanic basaltic crust.  This mud lithifies into shale that later, during mountain building events, becomes a metamorphic mica schist.  During even later events the lithium in the mica was incorporated into molten granitic magma that upon slow cooling becomes pegmatites with lithium-rich minerals.   The formation of lithium-rich pegmatites is much more complex than this skeletal summary and I would suggest interested readers examine Professor London’s article.  

   

The Black Hills of South Dakota have numerous pegmatites containing many lithium-rich minerals.  For example, some of the largest spodumene crystals in the world have been identified in pegmatites of the Etta Mine near Keystone. 

The Helen Beryl Mine, southwest of Custer, is an oval mass of pegmatite about 250 feet long and 130 feet wide (Lufkin and others, 2009).  MinDat.org indicates the presence of lithium precursors spodumene, lithiophylite-triphylite and montebrasite-amblygonite (need chemical analysis to distinguish). London (2017), noted that “an abundance of amblygonite-montebrasite or lithiophilite-triphylite is indicative of the high phosphorus content of the marine shales from which most Li-rich pegmatites are derived.”  As the name implies, the Helen Beryl location was mined primarily for beryl.

The phosphate mineral alluaudite 

[(Na,Ca)(Mn,Mg,Fe⁺⁺)(Fe⁺⁺⁺,Mn⁺⁺)₂(PO₄)₃] also occurs at the Helen Beryl Mine.  This uncommon phosphate has a range of colors from green to yellow to tan to brownish yellow but is usually observed as a dirty yellow, opaque, earthy mass of tiny fibers and/or nodules---pretty nondescript; however, I have seem samples that are a dark greenish-black.  MinDat.org noted alluaudite is an alteration product of the complex phosphates varulite and arrojadite (see Blog posting April 2, 2013).

Photomicrograph of tan alluaudite from a second small specimen from the Helen Beryl Mine.  Length of tan spot ~2 mm.  The black matrix could also be alluaudite or some sort of phosphate.

My next question revolved around the “cause” for oxidation of divalent (++ charge) iron and manganese to the trivalent (+++ charge) forms.  At least in some cases the oxidation is due to bacteria.  However, I doubt that is the case in South Dakota pegmatites.  One of life’s persistent questions waiting for an answer!  

But, hold on, and paraphrasing the NPR show Wait, Wait Don’t Tell Me, London (2017) again provided an answer.  It seems as lithium-rich minerals in pegmatites decompose rather rapidly!  Toward the end of pegmatite formation, and in the presence of hot aqueous solutions, the early formed lithium-rich minerals undergo alteration: “spodumene and petalite alter to eucryptite + albite and to mica + albite. Montebrasite is commonly replaced by intergrowths of apatite + mica… Lithiophilite-triphylite alter to a large array of hydrous and more oxidized species of phosphates.”  In addition, the oxidation of lithium-rich minerals continues with surface weathering. At the Helen Beryl Mine the minerals include the oxidized (and lithium leached) heterosite, purpurite and sicklerite (intermediate solid solution mineral between unoxidized and oxidized end members). Ain’t learning fun?

I recently attended the Denver Gem and Mineral Guild spring show and picked up a nice specimen of purpurite collected from the Rainbow’s End Claim, Storm Mountain Pegmatite, Crystal Mountain District, Larimer County, Colorado: ~13 miles west of Fort Collins and Loveland.  The pegmatites seem related to the Silver Plume granites (Precambrian: ~1.4 Ga) and were intruded into schists of the Idaho Springs Formation (Precambrian: ~1.7 Ga   ) (Martin, 1993).  Jacobson (1986) was one of the last authors (I think) to report on the Crystal Mountain District and noted “blue apatite crystals, purpurite, spodumene, chrysoberyl and beryl are some of the choice mineral specimens available for collecting…This is one of the few pegmatite districts in Colorado where neither all the pegmatites have been found and studied or mapped nor all the minerals described.”  He listed 41 minerals of record.  Thirty years later MinDat.org has listed 55 valid minerals from ~ 60 claims, mines, prospects.  Most of the mining activity in the District, starting in 1884, centered around production of “mica” and beryl although most mines were rather unsuccessful (Thurston, 1952).  Jacobson (1986) stated that the pegmatites are beryl-rich and the rare lithium-rich minerals are in the most distal part away from the “parental granite.”

Purpurite (P) and alluaudite (A) on a "mica" schist (M) collected from the Rainbow's End Claim.  Width of specimen ~10.5 cm.

Purpurite is the most common phosphate mineral in the District and occurs in several of the prospects, mines, etc. (Eckel and others, 1997).    In addition, the purpurite specimens are a bright purple-lavender mass and are quite spectacular. Many/most purpurite specimens from the District are accompanied by the uncommon, tan phosphate, alluaudite 

[(Na,Ca)(Mn,Mg,Fe⁺⁺)(Fe⁺⁺⁺,Mn⁺⁺)₂(PO₄)₃].  Chemical analysis (EDS) by Modreski (Eckel, 1997) noted that some mines, prospects, etc. in the District produce purpurite while others offer heterosite.  At any rate, the Crystal Mountain District seems the only locality in Colorado that contains the phosphates purpurite/heterosite and alluaudite.

REFERENCES CITED

Eckel, E.B. and others, 1997, Minerals of Colorado: Fulcrum Publishing, Golden, Colorado. 

Jacobson, M.I., 1996, Pegmatites of the Crystal Mountain District, Larimer County, Colorado: in Modreski, P.J., ed., Colorado pegmatites---Abstracts, Short Papers, and Field Guides of the Colorado Pegmatite Symposium, May 30-June 2, 1986: Denver, Colorado Chapter, Friends of Mineralogy.

London, D., 2017, Reading pegmatites: part 3---what lithium minerals say:  Rocks and Minerals, vol. 92, issue 2.

Lufkin, J.L., J.A. Redden, A. Lisenbee and T. Loomis, 2009, Guidebook to the geology of the Black Hills, South Dakota: Golden Publishers, Golden, Colorado.

Martin, C. M., 1993, Reconnaissance investigations of selected columbium and tantalum occurrences in Colorado: U.S. Bureau of Mines Open File Report 17-93.

Thurston, W. R., 1952, Pegmatites of the Crystal Mountain District, Larimer County, Colorado: U.S. Geological Survey Trace Elements Investigations 139.