Ornamental Jadeites from the Levoketchpel Deposit in the Polar Urals of Russia
Although most jadeites on the market are from Myanmar, other sources include Guatemala, Japan, Kazakhstan, and Russia. Russian jadeites have been studied using geological and petrological approaches (e.g., A.M. Fishman, Gems in the North Ural and Timan, Geoprint, Syktyvkar, 2006, pp. 1–88; F. Meng et al., “Jadeitite in the Syum-Keu ultramafic complex from Polar Urals, Russia: insights into fluid activity in subduction zones,” European Journal of Mineralogy, Vol. 28, No. 6, 2016, pp. 1079–1097), but their gemological characteristics are still unclear. To date, several jadeite deposits have been found within some ultramafic complexes at the Polar Urals (Fishman, 2006). In August 2013, the authors visited a closed jadeite mine at the Levoketchpel deposit in the Voykar-Syninsky ultramafic complex of the Polar Urals to collect samples (figure 1). Here we describe the gemological and trace element chemistry of these jadeites.
The jadeites were found as dikes within serpentinized peridotite (figure 2A). The Levoketchpel deposit was reportedly discovered in 1959 (V.F. Morkovkina, “Jadeites in the hyperbasites of the Polar Urals,” Izvestiya Akademii Nauk SSSR (Seriya Geologicheskaya), 1960, Vol. 4, pp. 103–108). Mining at this area was done on a small scale, and the quality was low. In the outcrop, the jadeite dike is surrounded by phlogopite-rich rock (figure 2B) and peridotite. The Levoketchpel jadeites are translucent to opaque, and whitish to pale green and vivid green with a mottled color distribution. The samples showed a mosaic to fibrous aggregate structure. We collected 10 samples from the jadeite dike (five of these are shown in figure 1) and rubbles produced during mining. For the gemological observation, advanced testing, and quantitative laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) analysis of trace elements, we prepared wafers and thin sections (figure 3). Standard gemological testing revealed RI values of 1.66 to 1.67 and hydrostatic SG values of 3.2 to 3.4. In a handheld spectroscope, the whitish and pale green zones in the samples showed fine chrome lines at 630, 655, and 691 nm, and the diagnostic 437 nm line. These results strongly suggested that the samples were all jadeite.
EDXRF testing also indicated that the samples were composed mainly of jadeites. The pale green jadeites were characterized by a low CaO/Na2O ratio of 0.20 to 0.26, and a relatively high Al2O3/Fe2O3 ratio of 11.03 to 20.14. The vivid green parts tended to be slightly rich in Ca (CaO/Na2O ratio, 0.32 to 0.34), and the compositional ranges are suited for jadeite (Al2O3/Fe2O3 ratio of 10.73 to 20.14). Vivid green zones were slightly higher in Cr2O3, 0.06 to 0.16 wt.%, than the whitish and pale green samples (Cr2O3 up to 0.01 wt.%).
Careful observation and Raman spectroscopic analysis suggested that the samples were mainly composed of fine jadeite grains with minor amounts of omphacite, natrolite, feldspar, phlogopite, zircon, and chromite. Natrolite was found as the interstitial phase between jadeite grains. Jadeite crystals surrounding chromite crystals tended to be rich in green color. This green color concentration around chromite crystals is probably due to chromium diffusion from chromite during the jadeite’s formation. The coexisting mineral assemblage observed is consistent with previous petrological studies (e.g., G.E. Harlow and S.S. Sorensen, “Jade (nephrite and jadeite) and serpentinite: metasomatic connections,” International Geological Review, Vol. 12, 2005, pp. 49–68). In UV-Vis spectra, vivid green regions of the jadeites from Levoketchpel show an Fe3+ band and strong chromium bands in the 550–700 nm range. Similar results were also reported from jadeites from the Polar Urals (A. Abduriyim et al., “Japanese jadeite: History, characteristics, and comparison with other sources,” Spring 2017 G&G, pp. 48–67).
Trace element compositions (Rb, Sr, Y, Zr, Nb, Ba, and the rare earth elements Hf, Ta, W, and U) were analyzed by LA-ICP-MS for 10 samples (70 spots total). Four of the samples had both whitish to pale green and vivid green zones. Chemical analyses were conducted on five spots for each of these zones. The whitish to pale green jadeites were depleted in REEs, while the vivid green zones tended to be richer in REEs. We calculated the primitive mantle–normalized trace element patterns and the chondrite-normalized REE patterns (figure 4) of the vivid green Levoketchpel jadeites (W.F. McDonough and S.-S. Sun, “The composition of the earth,” Chemical Geology, Vol. 120, 1995, pp. 223–253) and compared them to jadeites with similar color ranges from another jadeite locality in the Polar Urals (the Pusyerka deposit in the Syum-Keu ultramafic complex; Meng et al., 2016), Myanmar, Guatemala, and Japan (Abduriyim et al., 2017; Abduriyim et al., unpublished data). The primitive mantle–normalized trace element patterns of the Lavoketchpel jadeites reveal strong positive anomalies of Sr, Zr, and Nb (figure 4A). Such enrichment of the large-ion lithophile elements (LILE) and the high field strength elements (HFSE) in jadeites have been reported previously in jadeites from other localities (e.g., G.E. Harlow et al., “Jadeites and plate tectonics,” Annual Review of Earth and Planetary Sciences, Vol. 43, 2015, pp. 105–138). In these patterns, green jadeites from each locality show a very close overlap. In the chondrite-normalized patterns, the Levoketchpel jadeites show a right-downward slope: the light rare earth element (LREE) La, Ce, Nd, and Sm concentrations tended to be higher than the heavy rare earth element (HREE) Eu, Gd, Dy, Y, Er, Yb, and Lu contents (figure 4B). The Levoketchpel jadeites are depleted in HREE relative to the Pusyerka jadeites. Jadeites from Myanmar and Guatemala have higher total REE concentrations than the Polar Ural and Japanese jadeites (figure 4B). Burmese jadeite patterns show a gentle right-downward slope from La to Lu, and Guatemalan jadeites tend to be enriched in HREE. The Levoketchpel jadeites and some Japanese jadeites display a similar slope in REE concentration, although the former tend to be relatively depleted in HREE.