Life in the USA is not normal. It feels pointless and trivial to be talking about small looks at the fascinating natural world when the country is being dismantled. But these posts will continue, as a statement of resistance. I hope you continue to enjoy and learn from them. Stand Up For Science!
While sorting and organizing old books, I happily encountered one I thought was missing: USGS Bulletin 182 from 1901, The Economic Geology of the Silverton Quadrangle, Colorado, by F. L. Ransome. It contains several beautiful chromolithographs of minerals. These are images of cut and polished slabs of ore.
The upper specimen above is alternating dark bands of sphalerite and galena (zinc and lead sulfide, respectively) separated by two-millimeter-thick layers of quartz.
The lower specimen, gold ore from the Camp Bird Mine, shows quartz crystals in the lower portion sitting on a 1- to 2-centimeter seam of chalcedony, carbonates, and kaolin (a clay mineral). Those crystals partly filled a fissure and were then encrusted by the band of material in the central lower part – a spotty dark band of free gold plus galena and sphalerite and unknown telluride minerals. The quartz crystals continued to grow (the largest crystals in the middle of the specimen) and were further encrusted with prominent layers of quartz, gold, sericite (another clay), fluorite, calcite, chlorite, dark galena, and sphalerite. The conspicuous wavy dark band just above the middle was called “the worm” by local miners and was a sign of good ore in the Camp Bird Mine. The size of this lower specimen is about 10 cm vertically by 11 cm horizontally.
The Camp Bird Mine, which is in Ouray County but in the Silverton Quad, produced about 1.5 million troy ounces of gold by 1990, together with 4 million ounces of silver. (Compare the entire Butte district, which produced just under 3 million ounces of gold and about 750 million ounces of silver. Butte is the third largest cumulative producer of silver in the world.)
The second set of chromolithographs shows three additional ore structures, including (A) radial quartz growing on kernels of tetrahedrite, from the Dives Mine; (B) massive, interlocking textures of quartz, galena, sphalerite, chalcopyrite, and pyrite, from the Silver Lake Basin mines; and (C) shattered fibrous and concentric bands of pyrite cemented by quartz and other minerals, from the Red Cloud Mine.
It’s really challenging to me to envision the lithographic effort that went into making these images. They were produced by A. Hoen & Co. of Baltimore using their patented version of chromolithography, called lithocaustic. The method involved covering the etching with a mix of citric acid and gum arabic so that the lithographer could see the progress of shaded patterns as they were etched into the lithographic stone. Individual color combinations had to be applied separately; and the gold or silvery metallic sheen (visible in the printed originals, not so much in my photos here) was created by dusting copper or silver powder onto the adhesive, which had been applied precisely where the powder was intended to adhere. This was done individually for each copy of each print, for a typical press run of USGS Bulletins of around 3,000. The Hoen & Co. building in Baltimore, constructed in 1885, still stands.
This gold specimen, given to me by my friend Steve Henderson, was labeled just “Ouray, Colorado,” but I feel strongly that it is probably from the Idarado Mine (Red Mountain District) in the Silverton Quadrangle.
These two hübnerite specimens are also from the Silverton Quad, from the Yukon Tunnel north of Silverton town (left), and the Ruby Mine near Howardsville (right). Hübnerite is manganese tungstate, MnWO4.
Early reports attempted to portray the three-dimensional workings of underground mines with complex multi-colored maps like this one of the Guston and Robinson Mines in the Silverton Quad, based on work done in 1890 and 1895.
Frederick Leslie Ransome (1868-1935) was British-born, and educated at the University of California. In addition to this report on Silverton, his work with the USGS resulted in reports on many major mining districts, including Cripple Creek, Colorado; Bisbee, Arizona (see an article in the PDF here); Coeur d’Alene, Idaho; Globe, Arizona; Breckinridge, Colorado; and Goldfield, Nevada. He also helped start the journal Economic Geology in 1905.
Lovely
Very interesting! Thanks!