WAVELLITE & FUELLITE ON THE ROAD TO WINNEMUCCA

 I was totin' my pack along the dusty Winnemucca road

When along came a semi with a high and canvas covered load

"If you're going to Winnemucca, Mack with me, you can ride"

So I climbed into the cab, and then I settled down inside

He asked me if I'd seen a road with so much dust and sand

And I said, "Listen, Bud, I've traveled every road in this here land"

I've been everywhere, man

I've been everywhere, man

Hank Snow version

An army of caterpillars crawling northward.     Clarence Dutton

Google Earth© image of Basin and Range Province around Lovelock, Nevada, and the West Humboldt Range. home of the Willard Mine. The Basin and Range is defined by narrow faulted mountain ranges with adjacent rather flat basins—a horst and graben topography. The topography is due to extensional tectonics (pull-apart) of the later Tertiary (Miocene, ~17 Ma and probably continuing).

The name Willard conjures up a vivid picture of Ben and his rat friends devouring their former human friend Willard! I am not a big fan of Sci Fi or horror films, but Willard is not one to watch before hitting the rack. But 1971 was many decades ago and now the name is much more exciting---a mining district, and mine, located in a desolate part of Pershing County, Nevada, in the north end of the West Humboldt Range not too far from the County Seat of Lovelock. In fact, Lovelock is the only town in this large county. What is the landscape like? Ask Center Divide a group who recorded the album From Lovelock to Winnemucca:

If you make that drive
And you like tunes you better have a tape deck
Airwaves are empty
Ain't a lot on the radio
Better yet you can sit and ride
And listen to the dry wind
Flappin' through the window
Breathe in the scent of sage
Breathe it in real slow
And you breathe deeper
I swear you will

That description of driving across Nevada is one for the ages. Try the drive with a couple of youngsters sometime---been there, done that.

If you ever drive
From Lovelock to Winnemucca
I suggest you stop at every Dairy Queen
Towns are few and they're far between
And you'll have to fill up anyway
And there's something 'bout a frosty
Makes the pain go away

Somewhere near Lovelock is the Willard Mine, or the Willard Mines, all clustered together in the Willard Mining District. The area has a long history of exploration dating back to the early 1900s with most tunnels and shafts producing minor amounts of silver, gold, and antimony until mid-century. Drilling exploration found mineable gold in the 1980s and production lasted for about two to three years from 1990-1993. The initial gold was from near surface free-milling gold and later recouped by heap leaching. The mineralization was in the Late Triassic to Early Jurassic Auld Lang Syne Group (slightly metamorphosed siltstones and limestones). Fractures and brecciation zones in these sedimentary rocks allowed for gold- and silver-bearing hydrothermal solutions, associated with Tertiary intrusive rocks, to spread throughout. I could not locate production figures; however, exploratory drilling continued into the early 21^st century but today mandatory remediation has covered much of the area.

So, other than there's a whole lotta room to lose a broken heart (Center Divide) what else is neat about the area? Well, for starters a 1905  paleontological expedition led by John C. Merriam of UC Berkeley found a substantial number of Ichthyosaurs (Mesozoic marine reptiles), Cymbospondylus petrinus, and transported most back to the UC Museum. Twenty fives years later even larger and better preserved Ichthyosaurs, Shonisaurus popularus were located in nearby Nye County that later became Berlin-Ichthyosaur State Park.  More importantly for this Post, there are 41 mineral species known known from the Willard (MinDat) and the mine “is the site of the world's largest crystals of fluellite and perhaps also minyulite; and it has furnished what are by far the finest quality specimens of wavellite, fluellite and minyulite ever discovered in the state [Nevada]… along with other minerals including… crandallite, dufrenite, gypsum, jarosite, native selenium and strengite/variscite” (Jensen and others, 2001). It is a treasure trove of spectacular supergene phosphate minerals in a sediment-hosted, epithermal, Carlin-type gold deposit. (See Blog Post on Carlin Deposits August 19, 2020).

Over the years I have picked up Willard specimens of fluellite (mineral was unknown to me) formerly in the collection of Robert Pederson, and wavellite (it was not green like Arkansas) formerly in the collection of Jim Thow--- or Jim Thon---?

                  

-

Transparent fluellite crystals on top of quartz crystals. Largest crystal, top microphotograph is ~1 mm in width. Most are submillimeter. 

Fuellite crystals at Willard (at least in my specimen) are colorless, transparent, sharp, mirror-lustrous, euhedral, orthorhombic crystals. A few other localities may produce lavender or yellow crystals. Fluellite is a  rather rare fluoro-hydroxyl, secondary, phosphate [Al₂(PO₄)F₂(OH)-7H₂O] that is usually associated with pegmatites and phosphorite deposits. At Willard, fluellite is found in a supergene phosphate zone and is paragenetically late and often occurs directly upon lustrous quartz crystals. “These are very likely the best and largest examples of the species found in the world” (Jensen and others, 2001). 

Microphotographs below show numerous radiating clusters of clear to white  fibrous crystals.  Most are 1-2 mm in size although some are submillimeter.

 

Submillimeter pyrite.

Chalcedony-like mass of what I presume is wavellite--note striations. The dark flakes might be native selenium?

Hexagonal molds left by quartz crystals (epimorph?)

Although I usually associate wavellite as a green mass (colored by vanadium) of radial crystals found in Arkansas, the wavellite specimens in these phosphate rocks of Nevada are completely different. The Willard wavellites are radiating clusters of clear to white (no vanadium) fibrous crystals in a delicate  “jackstraw” type of arrangement. Almost hidden away among the fibers are scattered, quite tiny, pale gray to white wavellite spheres. Wavellite [Al₃(PO₄)₂(OH,F)₃·5H₂O] is also found in the phosphate supergene. “Paragenetically, wavellite occurs either on quartz or the phosphates crandallite, and/or variscite” and are easily ranked as the finest examples of wavellite ever found in Nevada” (Jensen and others, 2001).

But really confusing to me is that recently (Kampf and others, 2017) described fluorwavellite [Al₃(PO₄)₂(OH)₂F·5H₂O] as the F analogue of wavellite. It is visually indistinguishable from wavellite, since it is essentially identical to wavellite in appearance and physical properties. It has the same structure as wavellite, differing only in having one of the two independent hydroxyl sites replaced by F. Therefore, MinDat at about the same time, noted that the Willard wavellite is actually fluorwavellite distinguishable only with the use of electronic gizmos. Way above my pay grade!

REFERENCES CITED

Jensen, M., J. Leising, 2001, Wavellite, fluellite and minyulite from the Willard Mine, Pershing County, Nevada: Mineralogical Record vol.32, no.4.

Kampf, A.R., P.M. Adams, H. Barwood, B.P. Nash, 2017,  Fluorwavellite, Al₃(PO₄)₂(OH)₂F·5H₂O, the fluorine analogue of wavellite: American Mineralogist 102.

ALSO see:

Conelea, R. and W.C. Howard, 2010, The geology and gold-silver mineralization of the Wilco Project—Willard Mining District, Pershing County, Nevada in Great Basin Evolution and Metallogeny: 2010 Symposium Proceedings of the Geological Society of Nevada.

AND REMEMBER:

If you ever drive
From Lovelock to Winnemucca,
It's a good idea to pack your cares along
The desert's big and wide
Those mountains stand far apart.