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Collecting Wind Mountain (in the Cornudas Mountains, NM, USA): Part I

Last Updated: 4th Jul 2017

By Michael C. Michayluk

Collecting Wind Mountain (in the Cornudas Mountains of Otero Co., New Mexico, USA); Part I
by: Michael C. Michayluk and Jerry Cone
Introduction
This article is the result of 5 collecting trips to Wind Mountain by the authors between February and April of 2016.


Brief description of local geology


The Wind Mountain laccolith is one of several intrusive igneous bodies found in the Cornudas Mountains. The Cornudas are a small mountain range on the border of New Mexico and Texas which rises above the Diablo Plateau in Otero Co., New Mexico and Hudspeth Co., Texas. Several laccoliths and stocks, along with dikes, sills, and smaller plugs of varying textures have intruded Permian limestone and other sedimentary rocks in the Cornudas Mountains area (McLemore et al 1996). Nepheline syenite predominates, although phonolite, trachyte, and syenite are common (McLemore et al 1996). Wind Mountain consists of two textural varieties of nepheline syenite porphyry and four textural varieties of syenite porphyry (McLemore et al 1996). The zonation is attributed to crystal fractionation,volatile separation and cooling history, not to different pulses of magma (McLemore et al 1996). Phonolite dikes crosscut the syenite bodies in multiple places. Also, syenite dike-like bodies outcrop in the limestone near the base of the mountain (Boggs 1986). These dikes have metamorphosed the adjacent limestone to a hornfels facies. The emplacement of the main intrusion between sedimentary units altered the country rock to hornfels as well, and one can find large boulders of it on the talus slopes. The Cornudas Mountains have been examined for potential economic deposits of gold, silver, beryllium, rare-earth elements, niobium, and uranium, but no production has occurred (McLemore et al 1996).The nepheline syenite porphyry at Wind Mountain is being considered as raw material for use in dark-colored glass and ceramics. As a result of this prospect, an adit greater than 100 feet in length has been driven into the base of the mountain at the southern end. Wind Mountain is the type locality for the zirconium silicate georgechaoite (Boggs 1985).


Here is a link to the mindat locality page for Wind Mountain, Cornudas Mts, Otero Co., New Mexico, USA



Summary of field-trips

We did some research on how to get to the location and although we were warned that there were locked gates near the mountain, we didn’t quite realize the severity of the situation. Most anywhere we tried to get through from Texas, we ran into gates that were locked. Eventually we made it to the mountain by going through Dell City, Texas, then back-tracking north-west. While this route puts a lot of extra miles on the truck, it’s actually not that much longer because you are on paved, 75 mph highway for a lot of the time. Another bonus of taking the long way is it brings you past the very small town of Cornudas, Texas on Highway 180/ US-62, home of the Cornudas Cafe. Here one can get a great home cooked meal, and while the staff was a little brisk at first, they warmed up to us quickly!

Wind Mountain is an impressive mountain, absorbing your entire view as you drive by. Depending on where you park it could be up to a mile to the base of the mountain. Our first trip we collected only from a few talus boulders on the eastern slopes. We brought back enough rock to get us excited, although we could identify little of it besides analcime, aegirine and feldspar!

Our second trip was about as productive. By this time we had learned to identify natrolite and suspected we were into catapleiite. Much of the catapleiite can look like well-formed mica to the untrained eye, but so far, everything we thought might be mica turned out to be catapleiite when analyzed. Radial sprays of thomsonite-(Ca) were identified for the first time on this trip. Again, we collected mainly from various talus boulders.

We decided to stay overnight on our third trip and quickly learned why it’s called Wind Mountain. It nearly blew the tent away and and the truck rocked all night long. Any hardship experienced was well worth it. It was on this trip that we located a phonolite dike outcropping on the northeast slopes of the mountain. We spent the day working about a 100m section of the dike which was relatively rich in a mineral later identified as yofortierite, a Mn-silicate. This is the first recorded occurrence of yofortierite in the state of New Mexico. EDS and XRD analyses were performed, and while WDS analysis has not been performed yet, the ID remains fairly confident. The yofortierite occurs as acicular sprays ranging in color from yellow to brown to golden and bronze (never the more purple/pink tones) Interestingly, one specimen was recovered with more of a greenish hue. The yofortierite is associated with aegirine, analcime, natrolite, and chabazite. It is found both embedded in the phonolite as well as in open cavities.

We tried for the west side of the mountain on our fourth trip and almost made it, one locked gate blocking the way. This trip we collected the phonolite dike for a second time as well as a few talus boulders. 



On our fifth trip, we finally found a route to the west side of the mountain, including the old adit. This adit was much larger than previously described extending more than one hundred feet into the mountain. Unfortunately the rock we collected from inside the adit was barren of rare minerals, although it did produce some nice zeolites. Perhaps there are better places to collect than we did, as we were stopped by a foot of water about 100 feet into the adit. It should also be noted that some float cobbles near a dike outcropping in the mine road on the southwest side of the mountain provided our best specimens of pink eudialyte. This route allows one to get much closer to the mountain, making for a much less strenuous day trip.



Georgechaoite remains elusive for us! We may have collected some, but have not identified it yet. 


Descriptions of minerals collected by the authors


Aegirine: NaFe3+Si2O6 - Ubiquitous. Occurs as prismatic crystals of varying thickness, as well as acicular and blocky habits; green to black in color; both transparent and opaque. Largest crystal collected intact by the authors is only about 5 mm tall, but larger, embedded crystals have been observed larger than 6 cm. Boggs et al (1986) also describe aegirine embedded in a dike up to 6 cm long.







Albite: Na(AlSi3O8) - Found as colorless and white, platy and tabular crystals; often twinned.



Analcime: Na(AlSi2O6)·H2O - Ubiquitous. Found coating miarolitic cavities, replacing nepheline, and as individual crystals. Largest in-tact crystal found to date is only about 7mm in diameter.








'Biotite' - Embedded in phonolite and hornfels, in cavities in syenite



Calcite: CaCO3 - Fairly common in all units. Colorless to white, as micro-crystalline coatings and larger euhedral crystals. Often etched.





Catapleiite: Na2Zr(Si3O9) · 2H2O - Platy to thin tabular, brown to tan and orange, translucent and opaque (or coated). Found in miarolitic cavities and interstitial spaces in syenite and phonolite









'Chabazite' - Pseudorhombohedral crystals, colorless to very light tan as well as golden yellow; in miarolitic cavities in phonolite and syenite, often twinned.






Eudialyte: Na15Ca6(Fe2+,Mn2+)3Zr3[Si25O73](O,OH,H2O)3(OH,Cl)2 - Embedded and in interstitial spaces in vein/dike like bodies of syenite/phonolite, pink, pink/brown, peach, orange/brown, and yellow. None yet analyzed, basing ID's off of work done by Boggs, Horvath, and Stoll.





Låvenite: (Na,Ca)2(Mn2+,Fe2+)(Zr,Ti)(Si2O7)(O,OH,F)2 - Golden yellow/brown prismatic crystals in miarolitic cavities and interstitial spaces in syenite. EDS confirmed





Microcline: K(AlSi3O8) - Blocky white/beige crystals.


Molybenite: MoS2 - Platy, metallic luster, silver/grey/bluish . EDS confirmed



Monazite: Ce(PO4) - Colorless to tan, orange and brown, tabular as well as more equant crystals; usually less than 1 mm; found in miarolitic cavities in syenite; rarely occurs pseudomorphing catapleiite and perhaps other minerals. EDS confirmed`










Natrolite: Na2Al2Si3O10 · 2H2O - Prismatic crystals, colorless to tan and pink, shallow pyramidal terminations help identify natrolite compared to some of the other similar looking zeolites. In the phonolite dike outcropping on the east side of the mountain, natrolite commonly occurs as shorter, blocky crystals.









Nepheline: (Na,K)AlSiO4 - Prismatic to tabular hexagonal crystals, white, often altered to or coated by analcime and clay
. None yet confirmed by analysis.

Nordstrandite: Al(OH)3 - Spherical aggregate of white crystals, analyzed by EDS only, could be gibbsite or another aluminum hydroxide.



Opal: SiO2 · nH2O - colorless spherules, often coating crystals



Siderite: FeCO3 - Orange, distorted rhombohedrons. Only one confirmed sample. The authors have collected much unanalyzed material that may be siderite exhibiting more brown and yellow colors.



Smectite Group - Ubiquitous. Often as spheres or coating or pseudomorphing minerals. In all rock types

Thomsonite-(Ca): NaCa2[Al5Si5O20] · 6H2O - Radiating prismatic crystals as well as isolated clusters of short prismatic crystals. Also thin, flaky crystals. EDS confirmed







'Wad'- Black spherical aggregates



Yofortierite: Mn5Si8O20(OH)2 · 8-9H2O - Yellow/brown/gold/bronze and green acicular crystals, often in spherical or radiating aggregates. EDS and XRD confirmed.







Stay tuned for Part II!




Works Cited

Boggs, R.L., and Ghose, S. (1985) Georgechaoite NaKZrSi3O9•2H2O, a new mineral species from Wind Mountain, New Mexico. Canadian Mineralogist: 23: 1-4.

Boggs, R.L. (1986) Mineralogy and textures of a eudialyte-bearing dike, Wind Mountain, Otero County, New Mexico. New Mexico Mineral Symposium abstract
https://geoinfo.nmt.edu/museum/minsymp/abstracts/view.cfml?aid=78

McLemore, V.T., Lueth, V.W., & Pease, T.C. (1996): Petrology and mineral resources of the Wind Mountain laccolith, New Mexico and Texas. Canadian Mineralogist: 34: 335-347.




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Discuss this Article

6th May 2016 12:39 BSTLarry Maltby Expert

Well Done, Michael, great information about a neat locality.

You may like to try this procedure. If you go to your edit page for your article, there is a box at the top that says “location”. If you type or paste the exact location into this box and then click on “find” the software will recognize the locality. Then when you save this, a link to your article will automatically be added to the location page.

8th May 2016 21:50 BSTMichael C. Michayluk

Thanks for the comment Larry! There is now a link on the locality page!

9th May 2016 14:12 BSTLarry Maltby Expert

The link looks great, Michael. Your article contains a lot of important information about collecting at this locality and the link is a nice finishing touch.

6th Aug 2019 18:26 BSTDerek Leung

Hi there, great pictures and great info, and I hope I get to visit Wind Mountain someday. Just wanted to say that the "yofortierite" is probably not yofortierite, but a new mineral species. More data will come out in the next few months!
 
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