Topic
Dyscrasite
About: Dyscrasite is a research topic. Over the lifetime, 6 publications have been published within this topic receiving 101 citations.
Papers
TL;DR: In this paper, the post-Variscan Wenzel vein-type deposit near Wolfach, in the Black Forest, Germany, the type locality of the Ag-Sb alloy dyscrasite, was investigated by ore microscopy, electron-microprobe analysis, stable isotope and fluid-inclusion analysis.
Abstract: The post-Variscan Wenzel vein-type deposit near Wolfach, in the Black Forest, Germany, the type locality of the Ag–Sb alloy dyscrasite, was investigated by ore microscopy, electron-microprobe analysis, stable isotope and fluid-inclusion analysis. Three stages of mineralization could be distinguished. Whereas the first stage is a typical sulfide mineralization including galena and tetrahedrite, the second and third stage show a sulfide-poor association of Ag–Sb alloys, as well as Fe, Co and Ni arsenides and sulfarsenides, in a calcite matrix. The main ore minerals of this stage are allargentum and dyscrasite. The microprobe data for the diarsenides show extensive, and partly hitherto undocumented, solid solution in Fe–Co–Ni space. Seven distinct generations of calcite were distinguished. The δ13C (V–PDB) and δ18O (V–SMOW) values of these generations show a positively correlated trend that evolves from −13.0 to −4.0‰ and from 12.3 to 23.6‰, respectively. Fluid-inclusion data of stage I show homogenization temperatures of 100–180°C at salinities of 17–26 wt.% NaCl eq. Fluid inclusions in stage-II calcite display similar, but more restricted values, 110–150°C and 25–28 wt.% NaCl eq., respectively. The stage-III fluid inclusions show similar temperatures of homogenization, but different salinities. Earlier calcite of this stage contains inclusions with salinities of 27–30 wt.% NaCl eq., whereas later calcite has lower salinities, 3–10 wt.% NaCl eq. The initial temperatures of ice melting of most fluid inclusions range between −45 and −60°C and are typical of an H2O–NaCl–CaCl2 fluid. On the basis of all available geochemical data and phase-equilibrium constraints, we favor a model in which basement-derived near-neutral-pH hydrothermal fluids remobilized older products of mineralization. Mixing of these fluids with more alkaline formation-waters from the Mesozoic cover rocks resulted in the precipitation of the silver alloys in an enrichment zone at P–T conditions of 120–150°C and approximately 200 bars. A significant shift in pH from near-neutral to alkaline can explain the abundant association of silver alloys with calcite gangue and the general absence of quartz in the enriched ore zone. This conceptual model can be applied to similar ore deposits worldwide, where rich silver ores are hosted by calcite-rich and quartz-poor assemblages of gangue minerals.
58 citations
TL;DR: The structure of allargentum is known to deviate from the face-centered cubic motif of the distribution of atoms, and it is possible to assume that antimony is a stabilizer of the hexagonal structure characteristic of native silver.
Abstract: an antimonian variety of native silver, crystallizing in the hexagonal system - allargentum of Ramdohr ( 1962). The structure of allargentum, containing 8-15% Sb and observed together with dyscrasite as a product of the decomposition of a solid solution of silver and antimony, can be determined, according to Ramdohr, as a solid solution of silver in hexagonal closest packing with statistical distribution of antimony, Allargentum is generally accepted as a separate phase of the system AgSb. This is not certain, however, and it is possible to assume that antimony is a stabilizer of the hexagonal structure characteristic of native silver. It thus becomes evident that careful studies are required of the structure of native silver, starting with the assumption that it can deviate from the face -centered cubic motif of the distribution of atoms.
44 citations
TL;DR: In this article, the first two generations of native silver were separated in time by the formation of Ni-Co-Fe sulfarsenides and the monoarsenide niccolite along rims of silver crystals.
Abstract: The Kongsberg silver district has been investigated by microscopy and electron microprobe analysis, focusing primarily on the Ag-Hg-Sb mineralization within the context of the updated mineral paragenesis. The earliest mineralization stage is represented by sulfides, including acanthite, and sulfosalts. Native silver formed initially through breakdown of early Ag-bearing phases and later through influx of additional Ag-bearing fluids and silver remobilization. The first two generations of native silver were separated in time by the formation of Ni-Co-Fe sulfarsenides and the monoarsenide niccolite along rims of silver crystals. The presence of As-free sulfosalts and the absence of di- and tri-arsenides suggest a lower arsenic/sulfur activity ratio for the Kongsberg deposits compared to other five-element deposits. Native silver shows binary Ag-Hg and Ag-Sb solid solutions, in contrast to the ternary Ag-Hg-Sb compositions typical for other deposits of similar type. Antimonial silver together with allargentum, dyscrasite, and pyrargyrite was documented exclusively from the northern area of the district. Elsewhere, the only Sb-bearing minerals are polybasite and tetrahedrite/freibergite. Hg-rich silver (up to 21 wt% Hg) has been documented only in the central-western area. Myrmekite of freibergite and chalcopyrite reflects exsolution from an original Ag-poor tetrahedrite upon cooling, while myrmekite of pyrite and silver, forming through breakdown of low-temperature phases (argentopyrite or lenaite) upon heating, characterizes the Kongsberg silver district. Based on the stabilities of minerals and mineral assemblages, the formation of the silver mineralization can be constrained to temperatures between 180 and 250 °C.
18 citations
Journal Article•
TL;DR: In this article, the ternary system Ag-Hg-Sb is studied in the Proterozoic Pb-Zn ores of Sala, central Sweden, with pyrrhotite, sphalerite, galena and magnetite as main constituents.
Abstract: Minerals in the ternary system Ag-Hg-Sb are important carriers of Ag in the Proterozoic Pb-Zn ores of Sala, central Sweden. The ores with pyrrhotite, sphalerite, galena and magnetite as main constituents are hosted by a skarnbearing dolomite. Sphalerite may contain up to 1 wt.9o Hg. The Ag-Hg-Sb minerals plot in five compositional fields: a) native silver and antimonial silver, forming a continuous series with cr-Ag-Hg-amalgam with up to 51-52 wt.9o Hg; b) schachnerite with approximately 60 wt.9o Hg and probable paraschachnerite; c) allargentum with up to 5 wt.qo Hg; d) Hg-bearing dyscrasite forming a continuous solid-solution series along the join Ag3Sb-Ag3Hg, with up to 23 wt.olo Hg; in the samples richest in Hg the structural position of Sb is occupied mainly by Hg; e) native Sb, only present in very minor amounts. Important miscibility gaps exist in this system. The coexistence of two phases is widespread, and the coexistence of three phases occurs only occasionally. Lamellar intergrowths between allargentum and antimonial silver or o-amalgam indicate unmixing due to low-temperature re-equilibration; presence suggests that the stability fields, especially those of allargentum and Sb-bearing o-amalgam, were larger at the original temperature of crystallization, which did not exceed 280'C, the upper stability limit of gudmundite, a trace constituent of most samples.
10 citations
1 Jan 1982
TL;DR: The discovery of a complex paragenesis of silver minerals in the primary ores of the Kamariza deposit, Greece, resulted in the discovery of new minerals including acanthite, andorite, argentopyrite, diaphonie, dyscrasite, miargyrite and pyrostilpnite as discussed by the authors.
Abstract: Ore-microscopic and X-ray investigations of hand specimens from the Kamariza deposit, Greece, resulted in the discovery of a complex paragenesis of silver minerals in the primary ores. This includes acanthite, andorite, argentopyrite, diaphonie, dyscrasite, miargyrite, “owyheeite”, pyrargy-rite, (?) pyrostilpnite, silver-bearing tetrahedrite and at least two phases which probably represent new minerals. The silver minerals are associated with native arsenic, stibarsenic and a variety of other components.
1 citations
Related Topics (5)
Performance Metrics
| Year | Papers |
|---|---|
| 2021 | 1 |
| 2018 | 1 |
| 2007 | 1 |
| 1987 | 1 |
| 1982 | 1 |
| 1981 | 1 |