****** Author's note -- an expanded version of this article is slated to appear in the March/April 2013 issue of Rocks & Minerals magazine. ******

A couple years ago, a rancher in Cochise Co., AZ asked me to conduct a mineral assessment of his property. Previously, a mining company had pushed in a drill pad to explore a contact between a granitic stock and limestone. The driller's exploration was not successful, but their bulldozer work had exposed quartz and fluorite seams at the surface, about which the rancher and his son were curious.

My first visit to the property was after the 2011 Tucson show. The rancher's son had done some hand trenching to expose the fluorite seam, and reported offering material to several dealers during the show, with little response. The surface material was purple and hemimorphic; the material offered were cleavage fragments of the hemispheres. I was also unimpressed with the fragments, but the overall texture of the rock intrigued me.

I arranged a lease and returned in Sept 2011, accompanied by a couple friends, to open up some new ground. We drilled 11 holes with a Cobra rock drill, 7 of which fell into vugs! An auspicious start for a new locality. After re-aligning our drill holes for pocket safety, our first shot opened vugs that took us 3 days to collect. Vugs ranged from 15 cm. to over 1 meter. All were lined with octohedral and cube-octohedral fluorite, some as distinct crystals to 1 cm, others as composites of crystalline stalactites. The matrix for the fluorites are quartz casts: "epimorphs" after calcite. These original calcites occurred in rhombohedrons, acute rhombohedrons, and scalenohedrons, all of which are well-preserved by the quartz coating. A second generation of calcite, the last mineral to crystallize, formed stalactitic druzes over the other minerals.

Stalactitic calcite in 1 m. wide vug

Archer McGill in fluorite vug

Fluorite octos on quartz epis after calcite, as collected

Cleaned detail of photo at left, FOV 4cm.

The material as collected is heavily encrusted with caliche, so much so that it more resembles coral than mineral specimens. During that first dig, we built a rock retaining wall of the coralloid material, only to find on later cleaning that material produced good specimens: fluorites of ‘ochsenauge’ habit. Ochsenauge means “ox-eye” in German. Not being familiar with eyes of oxen, or any other part for that matter, I think they resemble oranges cut partially through, and then spread to resemble flowers ... the kind of thing you’d see at a breakfast buffet. Ochsenauge fluorites are quite uncommon, mostly known from a couple European localities.

Ochsenauge fluorite

That first dig produced half a dozen ochsenauge pieces, more plates of curved octohedra on drusy quartz, and a tantalizing promise of vuggier ground beyond. On our second and third digs, in spring and fall 2012, we encountered vugs large enough to crawl into. A couple of those vugs produced well-formed quartz epimorphs after calcite, both scalenohedral and rhombohedral. The inside and outside surfaces of the epimorphs are partly to fully covered in lilac to dark purple fluorite crystals.

The ranch is located about an hours drive from Benson, AZ; our base of operations. Like many residents near our southern border, the ranch owner is very sensitive to trespass. My lease stipulates that I not reveal the location, so my apologies for the vague description, but I am required to be vague. At this point, we are uncertain as to the continuing viability of the locality. The vein has thinned as we've trenched uphill; overburden has become considerable, and both the hanging and footwalls are bounded by extremely hard, non-vuggy, silicified limestone. It would take a lot of work to further explore the vein.

Author drilling, Oct. 2011

Specimens will debut at the Tucson Gem & Mineral show, Feb. 2013.

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