Type Locality Schirmerite
Last Updated: 17th Feb 2012
The specimen, photo 423520, is 2 cm x 2 cm x 3 cm mass of slightly vuggy Quartz with 1-2 mm blue grey non-cleavage masses of Schirmerite and/or Treasurite. There are also thicker lighter grey laths that may be Heyrovskyite and the thinner acicular laths that may be Lillianite/Gustavite, both of which are reported from here. White possible Bi secondary minerals occur with the laths in surface cavities. Several of the larger, 1-5mm, laths on this sample are compound crystals with a 1 mm tin-white striated central core surrounded by a 1 mm black, fine-grained overgrowth. The overgrowth appears to be composed of random grains and is not oriented. Most of the smaller laths are composed of aggregates of the black phase. The sample matches the description of the Schirmerite bearing early stage Ag-Bi veins from this district in the 1887 edition of Minerals of Colorado so it is from the correct paragenesis. The Mindat.org sample is identical to this one, down to the white Bi minerals. Schirmerite from this paragenesis is unique as occurring in separate grains and not as inclusions in Galena, as all of the other localities are. It does not have euhedral crystals in the vugs. Schirmerite is difficult to distinguish optically from the other lead-silver-bismuth sulphosalts so the grain size difference might pass unnoticed in a polished section.
The 2006 report on the Classification of Sulphosalts by the IMA says: Reexamination of Schirmerite from the type deposit (1997references) proved it to be a disordered intergrowth of different proportions of slabs 4L and 7L with a composition between those of Gustavite and (AgBi)-rich Heyrovskyite. The paper recommends that Schirmerite from this locality be discredited as a mixture. The IMA report says that Treasureite is a recognized Lillianite homologue species with a structure close to Gustavite. The 2008 final Sulphosalt Committee Report validates the 2006 report for the Treasury Mine that Treasurite is a valid species and Schirmerite is an intergrowth of phases at the unit cell level. Treasurite was only identified in 1979, as a separate species, on a sample in the AMNH’s Roebling collection labeled as Schirmerite.
Karup-Moller’s (1973) re-determination of Schirmerite was done on several samples from the “Geneva District” and the “Treasury Lode, Geneva District”. The study redefines Schirmerite and lists the characteristic accessory minerals. He says: The schirmerite in specimens R9714 and 257I is identical. The mineral occurs, as described by Ramdohr (1960), as randomly-oriented crystals up to several mm in size in an aggregate of sugary quartz. Schirmerite is the only primary sulphide present. The individual crystals are sometimes slightly bent and always fractured. Secondary bismuth, silver and lead minerals were reported along cracks and along Schirmerite-Quartz boundaries. This article was written before the characterization of Treasurite in 1979 so it is impossible to know if his Schirmerite is Treasurite. The later Galena-bearing veins from this district were also investigated but did not contain Schirmerite, it is confined to the early Quartz-Bi-Ag veins.
The Karup-Moeller study used two samples from the Treasury Mine, Colorado, one of Schirmerite and the other of Treasurite. The article did not mention the other Lillianite homologues that occur at the Treasure Mine. Karup-Moeller did 20 analyses of Schirmerite grains in one polished section and found large variations in the Pb: Bi ratio, enough to establish each grain as separate mineral species, but within each Schirmerite grain the composition was very restricted. No Sb or As was detected in the analyzed Treasury Mine Schirmerite.
A PhD thesis by Botinelly (1979) on the mineralogy of the Geneva district has a completely different suite of sulphosalt minerals from Mindat.org. He may have analyzed the non-Schirmerite bearing Galena veins.
A 1979 article (Makovicky; Geo Survey of Denmark) characterized Treasurite as a separate species. It had several samples from the Treasury Mine (Treasury Lodge in one instance, a spelling error for Lode), one, from the Smithsonian was Treasurite and the remainder, from a different museum, was Schirmerite. The samples were not described in enough detail to indicate whether Schirmerite and Treasurite exist in equilibrium on the same sample. The Treasurite forms 1 x 1.5 mm aggregates in sample R9714, labeled “schirmerite” from the Treasury Mine. The aggregates consist of only a few Treasurite grains. Partial, presumably hypogene, alteration of Treasurite has resulted in an intergrowth of a very fine grained mineral with the same optical properties as Treasurite. Microprobe analyses of the Treasurite aggregate gave the published formula of Ag7Pb6Bi15S32. This is higher in bismuth than the corresponding Schirmerite grains and plots well away from the Schirmerite composition field. The article also said Schirmerite occurs as lamellar crystals up to 2 mm in length interstitial to Quartz. It is the most complex phase studied and is locally replaced by a very fine grained hypogene phase; a chemical analysis showed this has less bismuth and more lead than the co-existing Schirmerite grain. It plots on an extension of the Schirmerite composition field. The larger Schirmerite grains are chemically homogeneous within each grain but the total microprobe analyses give an elongate spread of values with relatively constant Ag/Pb+Bi ratios. This indicates that the grains are disordered intergrowths of two Ag-Pb-Bi phases with constant Ag and different Pb-Bi ratios. This is the reason that the IMM does not have a certain formula or physical characteristics for Schirmerite nor is even certain whether it is a mineral.
An article on Colorado Ore Mineralogy in the Min. Record Colorado Issue v. 7 no. 6 indicated that at Schirmerite sample from the Geneva District gave an XRD pattern similar to Pavonite but not quite matching. The author did not go any further except to say the sample was not Schirmerite, though he did not describe the sample in detail.
The separation of the Bi-Ag and PbS in the Geneva District veins is very unusual. Normally the Lillianite homologues occur as inclusions in Galena, where they carry the silver values. This made their identification critical in the 1800’s for milling and smelting purposes. The Colorado silver mines are very complex in their mineralogy and this partially defeated the early miners who often could not process what was rich ore because it would not smelt.
The Treasury Vault is a small rich silver mine high in the mountains southwest of the city of Denver. The area was opened up in the Colorado Gold Rush of the 1860’s and almost all mining was halted by the 1890’s silver panic. The 1887 edition of Minerals of Colorado, in its entry on Schirmerite, says: First noticed in the Treasure Vault mine, Geneva district, Clear Creek county, from whence the mineral came which was analyzed by Mr. Genth. It occurs in all the older veins in the district, finely disseminated through quartz. It has never been noticed in the newer or subsequently-formed veins which carry a large amount of galena, very little of which is found in the bismuth-bearing veins. This was written long before the complexity of the bismuth bearing veins was investigated. However the Karup-Muller (1973) article indicates that samples of these later-stage veins have gone to museums with the Schirmerite label, even though it is not present with Galena.
This sample came with two previous labels, without county designations, written prior to the label of Donald Olson who sold it to me at the Detroit Show in 1985 as: Schirmerite, Geneva District, Co.. The first label is hand-written and contains the designation 125/1-1552 in the lower right corner and 125 in the upper left. The second label is typed and has the designation 125 in the upper right. Neither has a source notation or an autograph nor had a county designation for the Geneva District. These numeric designations were not carried to the Olson label nor are there any markings or labels on the specimen itself. The sawn Schirmerite sample in Mindat.org has an old type-written Wards label with “Schirmerite, Geneva District, Clear Creek County, Colorado”. The entry does not match the internet mineral list for Clear Creek County, but it does for Summit County.
Genth (1886) says of his original description: Under the name schirmerite I described, in 1874, a mineral from the Treasury Mine, Geneva District, Park county, Col., of the formula PbS. 2Ag 2 S. 2Bi 2 S , which I had received about twelve years ago from Mr. Schirmer. Later, he sent me as schirmerite several specimens from the Treasury Vault Mine, Summit county, Colorado, and has furnished the latter mineral to numerous friends. He has not been able to give me another specimen of the original schirmerite, and I do not know that it has been preserved in any collection. When I took up the investigation of the sulphobismutites above described, I observed that the original schirmerite, which was bright and fresh when received, had tarnished, was quite dull, and some portions almost black, while the mineral from the Treasury Vault Mine was quite fresh in appearance. As this indicated a difference in the composition, its true nature was endeavored to be established by an analysis. That from the Treasury Vault Mine occurs in small particles and patches, the largest about 10 mm in size, disseminated through quartz, associated with cubical crystals of pyrite, very little chalcopyrite, and, in some of the cavities, a yellowish earthy coating, probably of bismite.
A note in Mindat.org, April 25, 2008 says: The Geneva district is actually in the alpine country 2 miles SE of Montezuma where Summit, Clear Creek, and Park counties meet. Depending upon when the specimen was collected, there could be just a Queen mine. The data in mindat is from "Mineralogy of Colorado" and the MRDS data from the USGS. The USGS data would appear to be limited to mines that were still active in the 1900's. The district probably also includes the Lamartine district in Clear Creek county as well as the Montezuma area in Summit Co. and Geneva district in Park Co. Mindat.org has the Treasury Mine in Park County Colorado as the only locality for Schirmerite in Colorado and the Treasurite locality in the Treasure Vault Mine, Park County Colorado. The 2004 Glossary of Mineral Species has Treasure Vault (misnamed Treasure Mine) Geneva District, Park and Summit Counties. New Dana says that Schirmerite occurs in “several mines along the Treasure Vault and parallel lodes” and indicates this is its type locality, as it is for Treasurite.
Article has been viewed at least 7604 times.
|Fade toolbar when not in focus||Fix toolbar to bottom of page|
|Hide Social Media Links|
|Slideshow frame delay||seconds|
Locality Updated: Cala d'Oliva, Asinara Island, Porto Torres, Sassari Province, Sardinia, ItalyFrom Alessandro Marini, 20th Jun 2013 12:20:09