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Origin of serpentinite-related nephrites from Gogołów-Jordanów Massif, Poland

Gil G., Barnes J. D., Boschi Ch., Gunia P., Szakmány G., Bendő Z., Raczyński P., Péterdi B.

Geological Quarterly

2015

Vol. 59, No. 3

457--472

The Gogołów-Jordanów Massif (GJM) in the Fore-Sudetic Block, SW Poland, hosts nephrites traditionally interpreted as serpentinite-related (ortho-nephrite). This contribution confirms the serpentinite-related origin of the nephrites on the basis of mineralogy, bulk-rock chemistry, and O and H isotopes. Rock-forming amphiboles from nephrites of the GJM have 7.73–7.99 Si apfu, comparable to 7.76–8.03 Si apfu of serpentinite-related Crooks Mountain nephrite amphibole (Granite Mountains, Wyoming, USA). The GJM amphiboles also have Mg/(Mg + Fe2+) values ranging from 0.82 to 0.94, similar to serpentinite-related Crooks Mountain and New Zealand nephrites amphiboles with Mg/(Mg + Fe2+) values of 0.86–0.90 and 0.91 to 0.92, respectively. The GJM nephrite amphiboles differ from the Val Malenco dolomite-related nephrite (Italy) amphibole, e.g., Val Malenco has a higher Si content (~8.0 Si apfu), although it overlaps with some of the GJM nephrite samples, and ~1.0 Mg/(Mg + Fe2+), also higher than the GJM samples. Also, apatite in the nephrite studied from the GJM has a slightly higher Ca content than apatite from dolomite-related nephrite. Chlorites found in the Jordanów nephrite have similar compositions to that of chlorites in the serpentinite-related nephrites and also to chlorites associated with serpentinisation/rodingitisation. The bulk-rock FeO vs. Fe/(Fe + Mg), Cr, Ni, and Co are also typical of the serpentinite-related nephrites. The d18O values range from +6.1 to +6.7‰ (±0.1‰), and the average dD values = –61‰, corresponding with the serpentinite-related nephrites range. Based on petrographic observations, we suggest four crystallisation stages (including rodingitisation prior to nephrite formation): 1 – leucogranite rodingitisation and black-wall formation; 2 – tremolite formation at the expense of rodingite diopside and black-wall chlorite (nephritisation) and garnet break-down, with spinel and chlorite formation (chlorite can be a product of garnet break-down or spinel with serpentine reaction); 3 – prehnite vein formation; 4 – tremolite formation at the expense of prehnite veins and actinolite veins formation. Spinels composed of 0.29–1.96 wt.% MgO, 24.87–29.67 wt.% FeO, 8.72–22.82 wt.% Fe2O3, 3.11–4.36 wt.% Al2O3, and 39.07–54.46 wt.% Cr2O3 suggest nephritisation in the greenschist to lower-amphibolite-facies conditions.

Petrographic and geochemical investigation of a stone adze made of nephrite from the site Balatonőszöd – Temetői dűlő (Hungary)

Péterdi B., Szakmány G., Judik K., Dobosi G., Kasztovszky Z., Szilágyi V., Maróti B., Bendő Z., Gil G.

Geological Quarterly

2014

Vol. 58, No. 1

181--192

The present study reports on results of petrographic and geochemical analyses on a stone adze from the archaeological site Balatonőszöd – Temetői dűlő (Hungary). This is the largest excavated site of the Baden Culture in Hungary (more than 200.000 m2) and has the longest continuous settlement history. In the site, features of the Balaton-Lasinja Culture (Middle Copper Age) and the Boleraz Culture were also found. Altogether 500 stone artefacts were found and registered. The present study reports on the results of the investigation of a unique stone adze made of nephrite, found on the site. The nephrite adze found in Balatonőszöd – Temetői dűlő has proved to be the first find made of nephrite having an established archaeological context in Hungarian prehistory. By applying detailed petrographic, geochemical and petrophysical methods as well as comparing data from technical literature we located the origin of the raw material of the nephrite adze. Its most probable source is the Northern part of the Bohemian Massif, Lower Silesia, a geological site near Jordanów (Poland).