The Colorado Springs Mineralogical Society lost a long-time member, Laurann Briding, in June 2020. Laurann was an active rockhound and had a large collection of both purchased and personally dug specimen. Recently the family had the rock/mineral estate appraised by local dealer Leonard Himes and material was then turned over to Rebecca Nohe Estate Sales for disbursement on August 7-9. Most of the material was sold by flats ranging in price from $5 to $1000 and hundreds of micromounts were available for a buck per piece. There were also several individual cabinet specimens highlighted by a $5000 rhodochrosite from the famous Sweet Home Mine near Alma, Colorado. Perhaps the most interesting item in the sale was a brass microscope owned by the CSMS founder and Honorary President for Life, Lazard Cahn. That was a real find and I was hoping that a benefactor would purchase the scope and turn it over to a museum.
A brass microscope once owned by Lazard Cahn, the Honorary President for Life of the Colorado Springs Mineralogical Society.
Due to Covid-19, I was hesitant to head out into a public area since I have pretty much self-quarantined at home since late March. But, access to the show room was limited and by appointment only (30 minutes only) and masks were required. So off I went to check out the goodies. As noted in my last posting, my best purchase was a nice specimen of the hydrated zinc arsenate legrandite [Zn2(AsO4)(OH)-(H2O)], a very collectable mineral due to its color and rarity. But I did purchase a few other minerals with good specimens scattered in the flats.
When rockhounds think of collectable amethyst the concretions from Brazil pop into their mind. Ask them about amethyst from Mexico and the gemmy quartz crystals from Vera Cruz are probably in their collection. However, amethyst from the Guanajuato silver mines are probably not familiar to most rockhounds. And speaking of silver, the Guanajuato mining district is one of the most prolific and best-known silver districts in the world. Silver was discovered in 1548 and estimates of historic production range from 700 million to 1.5 billion oz of silver, as well as 4.0 million to 7.0 million oz of gold. Guanajuato was a major center of a Spanish colonial mining boom; in-fact at one point, the La Valenciana mine to the north of the city accounted for up to two third of the worlds silver production. Within 20 miles of Guanajuato’s downtown there are at least eight major metal mines either in production, in development or recently closed, as well as a flurry of exploration activity. To the non rockhounds, Guanajuato may be best known as the home of painter Diego Rivera, the husband of painter and political activist Frida Kahlo.
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).
I did not come home with a piece of silver or gold but did acquire a showy purple and white specimen with a base of gemmy terminated crystals of amethyst covered with rosettes of tiny snow-white crystals of calcite. I could not locate information on the collector although the label appears to have some age and originally sold for $6.
Another specimen in the acquired mixed flat is a really nifty piece that has a core and base of white, well formed, dolomite crystals with a partial crust of surficial brownish-black to reddish-brown, botryoidal (individual botryoids ~4 mm) goethite. In cross-sectional view the botryoids are composed of radiating (from the center) long prismatic crystals that have a metallic luster and a steel-gray color. There are also tuffs or sprays of steel-gray or orange acicular goethite “sticking up” between some of the botryoids. A second round of goethite consists of tiny (less than 1 mm) black “balls” scattered randomly across exposed dolomite crystals. There are also: 1) numerous well-formed pyrite crystals mixed in with the micro balls; 2) a single large calcite crystal; 3) a few splotches of chalcopyrite; and 4) a hunk of massive, red hematite. All-in-all, it is an attractive specimen.
Cross sectional view of the large goethite botryoids showing acicular crystals. Width FOV ~1cm.
The specimen came from Wawa, Ontario, Canada, a town/township/area located near Lake Superior north of Sault Ste Maria and situated in a rugged sparsely populated area. Gold and iron mines and prospects dot the area and today there seems to be a mini gold rush in progress. The kimberlites in the area have produced diamonds and they also attract prospectors. As best I can determine the bedrock is Archean (old Precambrian.
The specimen has an old typed label from Wallings Collector, Westbury, L.I., NY. The address seems to indicate pre-Zip Code days, so it evidently was collected before 1963.
In order to keep the file size reasonable, I have split information about minerals of the estate sale into several manageable sections. There is more coming and the previous post highlighted the zinc arsenate legrandite.
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