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Primary Minerals of the Jáchymov Ore District

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Primary Minerals of the Jáchymov Ore District Journal of the Czech Geological Society 48/34(2003) 19 Primary minerals of the Jáchymov ore district Primární minerály jáchymovského rudního revíru (237 figs, 160 tabs) PETR ONDRU1 FRANTIEK VESELOVSKÝ1 ANANDA GABAOVÁ1 JAN HLOUEK2 VLADIMÍR REIN3 IVAN VAVØÍN1 ROMAN SKÁLA1 JIØÍ SEJKORA4 MILAN DRÁBEK1 1 Czech Geological Survey, Klárov 3, CZ-118 21 Prague 1 2 U Roháèových kasáren 24, CZ-100 00 Prague 10 3 Institute of Rock Structure and Mechanics, V Holeovièkách 41, CZ-182 09, Prague 8 4 National Museum, Václavské námìstí 68, CZ-115 79, Prague 1 One hundred and seventeen primary mineral species are described and/or referenced. Approximately seventy primary minerals were known from the district before the present study. All known reliable data on the individual minerals from Jáchymov are presented. New and more complete X-ray powder diffraction data for argentopyrite, sternbergite, and an unusual (Co,Fe)-rammelsbergite are presented. The follow- ing chapters describe some unknown minerals, erroneously quoted minerals and imperfectly identified minerals. The present work increases the number of all identified, described and/or referenced minerals in the Jáchymov ore district to 384. Key words: primary minerals, XRD, microprobe, unit-cell parameters, Jáchymov. History of mineralogical research of the Jáchymov Chemical analyses ore district Polished sections were first studied under the micro- A systematic study of Jáchymov minerals commenced scope for the identification of minerals and definition early after World War II, during the period of 19471950. of their relations. Suitable sections were selected for This work was aimed at supporting uranium exploitation. electron microprobe (EMP) study and analyses, and in- However, due to the general political situation and the teresting domains were marked. With EMP, marked existence of the Iron curtain, the deposit became a Ter- places were first examined, and where necessary, the ra prohibita. Only shortly before the closure of uranium remaining parts of section were examined, too. Chemi- mining, in the period of 19561960, a research of non- cal composition was examined in a qualitative mode, uranium ores was conducted in the mines, including a and quantitative analyses were made on selected objects. wider mineralogical study [351]. Following this period, Both types of analyses were performed with ED system, only several isolated studies were undertaken, including but in cases of line coincidence of the analysed elements some students diploma works. Studies of Jáchymov min- (PbBiS, HgS), WD system was used, or a special erals realized that specimens accompanied by a detailed software, allowing separation of coinciding lines. Cor- location are of particular value for genetic and interpre- rection programs ZAF4, Phi(rhoZ) and Quadrilateral tative work. The non-accessibility of such samples at were used for conversion of the measured values to present was significantly offset by the opportunity to weight percentages. The following natural minerals and study samples collected during the late fifties and depos- synthetic phases were used as standards for analysis of ited in the permanent documentation of the Czech Geo- individual elements: pyrite, galena, stibnite, arsenopy- logical Survey, Prague. A valuable listing of samples with rite, bismuthinite, löllingite, sphalerite, cinnabar, cas- details of location was secured from records of the late siterite, scheelite, quartz, wollastonite, hyalophane, al- F. Mròa. Significant quantities of material were obtained bite, orthoclase, PbTe, Cu Se, PbSe, SnS , TiO, Al O , 2 2 2 3 from several museums, from private collectors, and FeSiO , MnSiO , metallic Cu, Ni, Co, Ag. 4 4 through new collecting. Analytical conditions: CamScan 4 with ISIS eLink Approximately seventy primary minerals were known energy dispersion analyser, 15 kV, 3 nA for silicate anal- from the district before the present study. This research yses, 25 kV, 2.5 nA for other analyses, WD Microspec added another forty-four primary minerals, thus the num- analyser. ber of described and/or referenced minerals from the Já- Results of quantitative analyses are presented, with the chymov deposit has increased to 384. A list of primary descriptions of the individual minerals, in tables consist- minerals is included in the Appendix. ing of two parts. The first part gives analyses in wt.%, and analyses are arranged in the sequence of sample num- Analytical part methods bers. In the second part, calculated numbers of atoms per formula unit (apfu) are given, data are ascendently sort- All mentioned minerals in the following encyclopaedia ed according to values in the highlighted column. Refer- are identified unambiguously by X-ray diffraction and/ ence to data from literature is by citation number in or chemical analysis. square brackets. 20 Journal of the Czech Geological Society 48/34(2003) Analysis of proustite-pyrargyrite phases A routine spot analysis resulted in the destruction of min- eral phases accompanied by a considerable increase in a relative proportion of Ag. To eliminate phase destruction due to thermal instability, the minerals were not analy- sed in spots but by scanning mode from small areas, ap- proximately 80×50 ìm in size, with homogeneity con- trolled with BSE image. This situation set limits to the size of the analysed objects, excluding thin lamellae and minute inclusions. Electron microscopy TESLA BS 340 scanning electron microscope with 75 to 3000 magnification was used. Samples were coated by Fig. 1. J114P/C. Grow zone in sphalerite contains fine grains of acanthite. 1 acanthite + sphalerite, 2 sphalerite, 3 rammelsbegite. Svornost AuPd, C or Al. shaft, 8th level, Geschieber vein. BSE image. Magnification 160×. Crystal structure analysis a thorn or an arrow, reminiscent of the shape of its X-ray powder diffraction analysis was done with Philips crystals. Individual, seemingly orthorhombic acanthite Xpert System diffractometer using the following condi- crystals are deposited on drusy gangue. The crystals are tions: Cu K radiation, 40 kV/40 mA, secondary graphite up to 5 mm long, terminated by a steep pyramid. They á monochromator, step 0.02° 2θ, time 410 s, samples placed are black in colour, with metallic lustre, and the mineral on Si wafer. The recorded data were processed using the is malleable. ZDS-WX Search/Match X-ray diffraction software [478]. Polished sections show some isotropic domains besides Qualitative phase analysis was made with the same soft- dominant anisotropic parts. Microhardness values and op- ware with the support of the ZDS-WX Search/Match tical properties are similar to those of argentite. This ma- X-ray diffraction database [478]. Data were calibrated with terial corresponds to acanthite sections orientated at ran- an internal standard (quartz, Si), or using a calibration pro- dom, since argentite is unstable below 176 °C. cedure, correcting for sample eccentricity (correction fac- The study of polished sections of acanthite pseudomor- tor cos(θ).cotg(θ)/λ2). Refined unit-cell parameters were phs after argentite shows obvious photosensitivity in a light calculated with the FullProf program [462]. beam of microscope. In the course of observation of freshly polished samples, the surface is coated by minute silver PRIMARY MINERALS ENCYCLOPAEDIC PART particles, which diffuse light in a similar manner as dust on the surface of a polished section. The phenomenon is Acanthite Ag S best observed under crossed polarizers. The effect appears 2 in several seconds and the number of particles increases Acanthite was described by Kenngott [221] in two with time. Subsequent checking with lower magnification samples collected at Jáchymov in the 18th century and shows the limits of affected area. Similar effects were not deposited in the Emperors mineral collection in Vienna. observed in proustite or pyrargyrite. No reference to the The mineral name is derived from the Greek acanthi for above effect was found in ore microscopy textbooks. Table 1. Chem ical analyses of acanthite. Aikinite PbCuBiS 3 sample pt. Ag Cu Fe Co Ni S As Sb Total It forms anhedral grains up to 50 µm weight % in size, enclosed in chalcopyrite, J-702 9 86.15 0.12 0.05 0.07 0.19 12.61 0.55 0.61 100.35 along fractures in chalcopyrite and J-702 10 87.92 0.08 0.08 0.07 0.07 12.44 0.05 100.71 along arsenopyrite-chalcopyrite in- J-702 11 85.16 0.06 0.05 0.04 0.06 12.72 0.07 98.16 terface. It is often accompanied by J-702 12 87.16 0.09 0.05 0.09 0.08 12.82 0.40 100.69 stannite, in part in mutual inter- growth. Aikinite crystallized probably Table 2. Calculated unit-cell parameters of acanthite from in a similar interval as stannite. The studied sample Jáchymov for the space group P2 /c. 1 comes from the Giftkies adit. sample a b c β Aikinite and matildite, usually in a mixture, replace several grains of bismuth enclosed in uraninite, which is (Å) (°) surrounded by rammelsbergite. The sample comes from J-824 4.2399(6) 6.9224(9) 9.549(1) 125.607(8) the Eliá mine. Journal of the Czech Geological Society 48/34(2003) 21 Albite NaAlSi O 3 8 Albite is a widespread mineral in albite-muscovite mica schists occurring in the eastern part of the Jáchymov ore district. Common are albite porphyroblasts with a zon- ing structure indicated by inclusions of quartz, mica and rutile. Chemical composition varies to An with rims 10 containing more than 10 mol. % anorthite. Albite is ac- companied by numerous minerals including pyrite, graphite and rare arsenopyrite. Albite forms minor grains in quartz
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