TY  - JOUR
A1  - Förster, Hans-Jürgen
A1  - Tischendorf, Gerhard
A1  - Rhede, Dieter
T1  - Mineralogy of the Niederschlema-Alberoda U-Se-polymetallic deposit, Erzgebirge, Germany. v. watkinsonite, nevskite, bohdanowiczite and other bismuth minerals
N2  - The uranium deposit at Niederschlema-Alberoda, Germany, contains a rich variety of Bi minerals deposited between the Permian and the Cretaceous; these have been studied for paragenetic relations, composition, and conditions of formation. Particular attention is given to the rare Bi selenides watkinsonite, nevskite, and cuproan bohdanowiczite. Whereas watkinsonite and nevskite only occur intergrown with clausthalite, bohdanowiczite is more widespread and also is associated with Cu selenides. Watkinsonite from this second confirmed locality worldwide has an average composition (Cu1.47Ag0.49)(Sigma 1.96)(Pb1.01Hg0.01 Fe-0.01)(Sigma 1.03)Bi-3.98(Se7.98S0.05)(Sigma 8.03), ideally (Cu,Ag)(2)PbBi4Se8. These findings suggest that the empirical formula of watkinsonite originally proposed for the type specimen from the Otish Mountains uranium deposit in Quebec [CU2+xPb1+xBi4-xSe,S,Te)(8), x approximate to 0.3] requires revision. The composition of nevskite is (Pb0.06Bi0.95)(Sigma 1.01)Se-0.99, on average. Bohdanowiczite from the Cu- selenide assemblage shows extensive substitution of Cu+ for Ag+, expressed by the crystallochemical formula (Ag1.80- 0.94CU0.16-1.05Pb0.00-0.05)(Sigma 1.97-2.07)BiSigma 1.97-2.03SeSigma 3.96-4.04. This observation seems to argue for the natural existence of CU2Bi2Se4, the Se-dominant analogue of emplectite. The Bi selenides were deposited at temperatures of about 100 degrees C, in the Jurassic. The lack of thermodynamic data for all the Bi selenides limits reliable inferences on the fugacities of selenium and sulfur that prevailed during their formation. Other Bi minerals from this locality comprise members of the bismuthinite-aikinite solid-solution series of Permian age and, more importantly, native Bi and Bi sulfides (matildite, bismuthinite, wittichinite), deposited in the Cretaceous
Y1  - 2005
ER  - 
TY  - JOUR
A1  - Förster, Hans-Jürgen
A1  - Tischendorf, Gerhard
A1  - Rhede, Dieter
A1  - Naumann, R.
A1  - Gottesmann, Bärbel
A1  - Lange, W
T1  - Cs-rich lithium micas and Mn-rich lithian siderophyllite in miarolitic NYF pegmatites of the Konigshain granite, Lausitz, Germany
N2  - Annite and Fe-rich siderophyllite constitute the rock-forming micas in the late-Variscan composite granite pluton of Konigshain, Lausitz, Germany. This multiphase pluton is composed of three fractionated, but not chemically specialized monzogranite types, which contain lithophile elements such as Li, Rb, Cs, Sn, and F in average quantities. Abundant miarolitic pegmatites of the NYF family with a broad diversity of rare minerals occur in the apical part of the pluton. These pegmatitic cavities locally contain di- and trioctabedral micas as well as cation-deficient micas. Trioctahedral micas comprise F-rich manganoan lithian siderophyllite to manganoan zinnwaldite, zinnwaldite, and minor lepidolite. The formula [calculated on the basis of 22 anion valencies and 2 (F + OH + Cl)] of the most Mn-rich siderophyllite is (K0.85Rb0.08Na0.04)(0.97)(Al0.99Li0.91Fe0.51Mn0.42Ti0.01Zn0.01)(2.85) (Si3.21Al0.79)(4)O- 10(F1.80OH0.19Cl0.01)(2). This mica constitutes one of the most Mn-rich siderophyllite compositions reported to date. The lithium micas poorer in Mn are distinguished by elevated concentrations of Rb (up to 2.5 wt % Rb2O), CS (UP to 1.2 wt % Cs2O), and F (up to 9.6 wt %). This fluorine content is probably consistent with the maximum possible F occupation of 2 of the (F,OH,Cl)-site. The structural formula of the most Li-rich lepidolite is (K0.83Rb0.07Cs0.03)(0.93) (Li1.62Al1.00Fe0.38)(3.00)(Si3.62Al0.38)(4) O-10(F1.91OH0.09)(2). During hydrothermal alteration, lepidolite and zinnwaldite became partially depleted in K, Li, Rb, Cs, and F and gradually transformed into cation-deficient micas (lithian phengite to illite of phengitic affinity)
Y1  - 2005
ER  -