MSCC3 3rd MINERAL SCIENCES IN THE CARPATHIANS ...

Acta Mineralogica-Petrographica, Abstract Series 5, Szeged, 2006MÖSSBAUER (NGR), XRD, TEM/SAED AND ESR INVESTIGATIONS ON SOME SULPHIDESFROM COSTEŞTI, VALEA LUI STAN AND JIDOŞTIŢA GOLD ORES (SOUTHERNCARPATHIANS, ROMANIA)UDUBAŞA, S. S. 1 , CONSTANTINESCU, S. 2 , POPESCU-POGRION, N. 2 , GRECU, N. M. 2 & UDUBAŞA, G. 31 Department of Mineralogy, University of Bucharest, 1 Nicolae Bălcescu Blvd., RO-010041 Bucharest, RomaniaE-mail: udubasa@geo.edu.ro2 National Institute of Material Physics, Atomiştilor 105bis,RO- 76900 Bucharest-Măgurele, PO Box: MG-7, Romania3 Geological Survey of Romania – IGR, 1 Caransebeş Str., RO-012271 Bucharest, RomaniaIn the metamorphic rocks of the Getic Realm in theSouthern Carpathians (Romania) there are several shear-zonerelated gold ores/mineralizations, i.e. Valea lui Stan, nearBrezoi and Costeşti, near Horezu, both in Vâlcea county, andJidoştiţa, near Drobeta-Turnu Severin, in Mehedinţi county.Although quite similar, these occurrences show somepeculiarities as concerns the main elements and the relatedprotores, as summarized by UDUBAŞA (2004). Gold iscommonly associated with, or included in, arsenopyrite,pyrite, chalcopyrite and sometimes quartz. “Invisible” goldhas been identified in arsenopyrite by using EPMA, showinggradual decrease of concentration around optically visiblegold inclusions.In the frame of a research project (CERES C4-209/2004)the investigations have been continued by using extensiveXRD, Mössbauer and TEM/SAED techniques, in cooperationwith physicists. Powdered samples have beeninvestigated at room temperature by using all the techniques.57 Fe Mössbauer spectra of arsenopyrite have beenregistered and analyzed. Spectral parameters revealed that thedominant FeAsS phase represent 74%, 70% and 47% for thesample from Costeşti, Valea lui Stan and Jidoştiţa,respectively. The accompanying phases were identified in allthe investigated samples. (Co, Fe)AsS and traces of FeAs 2(~4%) have been found in the sample from Valea lui Stan.Pyrite and a larger quantity of loellingite (~28%) have beenfound in the sample of Jidoştiţa. In all the phases theMössbauer spectra show an octahedral oxygen arrangementand a fractional ionic valence (~+2) low spin. The Mössbauerspectra of chalcopyrite and pyrrhotite exhibit the magneticordering and coexistence of the main phase with pyrite and/ormarcasite.Preliminary XRD analysis of arsenopyrite evidencedquartz as accompanying phase for all the investigatedsamples and cupride of gold (Cu 3 Au) for the Valea lui Stanand Jidoştiţa ores. Cupride of gold was also recognized in theXRD spectra of chalcopyrite at Costeşti.Hyperfine interactions of isolated Mn 2+ were observed byESR technique. Spectral parameters suggest Ca carbonate ashost matrix. A more significant signal of manganese ion incalcite (axial symmetry) is observed in chalcopyrite. Alsotwo distinct signals of Fe 3+ probe (g ef = 2.0 corresponding tothe orthorhombic symmetry and g ef = 3.78, only for the Valealui Stan sample) were evidenced in the spectra).SAED analyses carried out on powdery samples haveshown nanometric “precipitates” of Au or an (Au, Ag) alloyon arsenopyrite grain surfaces, showing a great diversity ofmorphologies, i.e. from isolated gold nanoparticles, sometens of nanometers in size, up to “coral-like” aggregates.Such nanograins or aggregates have also been identified(although more rarely) on pyrrhotite and chalcopyrite. This isthe third mode of occurrence of gold in/on sulphides, called“nano-minerals” by UDUBAŞA G. et al. (2006).Moreover, in addition to metallic gold, further goldbearingminerals have been identified, i.e. uytenbogaardtite,Ag 3 AuS 2 , closely associated with pyrrhotite at Costeşti, andauricupride, Cu 3 Au, associated with arsenopyrite at Valea luiStan and Jidoştiţa. During the investigations, some other newminerals for these ores have also been identified: cobaltite,CoAsS, in arsenopyrite samples from Valea lui Stan andJidoştiţa and in sphalerite samples from Jidoştiţa, as well asloellingite, FeAs 2 , in sphalerite samples from Jidoştiţa,maghemite in sphalerite samples from Jidoştiţa, moganite(monoclinic SiO 2 ) in arsenopyrite samples from Costeşti andJidoştiţa, and CuO in chalcopyrite samples from Valea luiStan.AcknowledgementsThe financial support of the Ministry of Education andResearch of Romania through the research grant CERES C4-209/2004-2006 is gratefully acknowledged.ReferencesUDUBAŞA, S. S. (2004): Metalogeneza auriferă asociatăzonelor de forfecare din Munţii Căpăţânii. (Goldmetallogenesis associated with the shear zones in theCăpăţânii Mts. In Romanian.). PhD thesis, Manuscript,Archives of the University of Bucharest, Romania, 182 p.UDUBAŞA, G., CONSTANTINESCU, S., POPESCU-POGRION, N. & UDUBAŞA, S. S. (2006): ActaMineralogica–Petrographica, Abstract Ser. 5 (thisvolume): 122.www.sci.u-szeged.hu/asvanytan/acta.htm 123