Rodingitization of mafic and ultramafic rocks in ophiolites from Northern Greece, seen by non-traditional stable isotopes, such as Cu, Fe and Zn.

<p>Rodingites are metasomatic rocks, frequently found in ophiolitic complexes. They offer important information about the interaction between ultramafic-mafic rocks and metasomatizing fluids, as well as about the post-magmatic evolution of ophiolitic suites (Tsikouras et al., 2009; Hu & Santosh, 2017; Surour, 2019; Laborda-Lopez et al., 2020). Metasomatism, such as rodingitization, is a very intricate process, which depends on the mineralogy of the initial rock, the nature of the metasomatic agent, the fluid/rock ratio, the duration of metasomatism and the chemical disequilibrium at the time of metasomatism between the host rock and the metasomatic medium (Poitrasson et al., 2013). Rodingites from the Veria-Naousa and Edessa ophiolites, in Northern Greece, were geochemically analyzed and characterized by substantial overprint of primary textures. Their field observation, their neoblastic mineral assemblages and metasomatic textures reveal that they derived from ultramafic and mafic protoliths. The mineral phases in the ultramafic derived rodingites (UDR) include mainly diopside, garnet, chlorite, epidote, tremolite and Fe-Ti oxides whereas mafic derived rodingites (MDR) consist of diopside, garnet, vesuvianite, chlorite, quartz, prehnite and actinolite. The studied rodingites present δ<sup>65</sup>Cu values varying from -0.17‰ to 0.62‰ and for ultramafic and mafic parent-rocks from -0.49‰ to +0.50‰. The UDR and MDR from both ophiolites display δ<sup>66</sup>Zn range from -0.06‰ to 0.74‰ and their photoliths present a narrower range from +0.04‰ to +0.41‰. Rodingitization affects in different way UDR and MDR samples. On one hand, Cu isotope ratios are systematically heavier in rodingites compared to their respective protoliths, except for one rodingite sample that requires confirmation due to large error bar. On the other hand, Zn isotopes show enrichment in light isotopes (group 1: comprising all UDR and some MDR samples), or in heavy isotopes (group 2, only MDR samples). Intriguingly, the same protolith can lead to both group 1 and 2 rodingites, as defined here.  No mineralogical or geochemical trend can be found to understand the dual behavior of Zn stable isotopes during rodingitization so far. Fe isotopes do not show any significant fractionation of δ<sup>56</sup>Fe, ranging from +0.07‰ to +0.19‰ for the rodingites and from +0.12‰ to +0.23‰ for their protoliths, indicating that Fe isotopes are highly resistant to rodingitization. Our study shows that rodingitization enriches metasomatized samples in heavy Cu isotopes and has no impact on Fe isotopes. It remains unclear why Zn isotopes can be affected both ways.</p>

GEOCHEMICAL CHARACTERISTICS OF NOVOKOSTIANTYNIVKA URANIUM DEPOSIT

Paper research aim is to identify characteristics of spacious distribution of radioactive- and associated elements in albitites according to depth and ore-level attribution: case study of 35th survey line of Novokostiantynivka deposit. Geochemical characteristics of Novokostiantynivka deposit are defined by presence of upper and lower ore-bearing levels. Geochemical anomalies related to upper ore-bearing level have complex character (uranium, thorium, lanthanum, yttrium, ytterbium, vanadium, and zirconium). At apical part of the deposit (Eastern fault) the albitites of blended type (chlorite, rybekite, aegerine) are dominant. La, Th, Y, and U define geochemical trend. These elements are likely to be related to rare-earth mineralization (monazite, apatite, xenotime), to a lesser extent to thorium and uranium mineralization with subordinate zircon. At deeper levels (Western fault) albitites’ mineral composition becomes more monotonous of rybekite-aegerine, and aegerine. The lead elements are Zr, Y, V, U, Th; Zr and Y noticeably dominate over other elements. Both elements and, maybe, part of U are related to zircon (malacon) which is predominant over rare-earth and thorium mineralization. Geochemical anomalies related to lower ore-bearing level are distinctive with monometallic (uranium) trend. The albitites of large column-like body have rybekite-aegerine, or aegerine mineral composition; phlogopite occurs often. Associated elements like Th, La, Y, Yb, V, Zr specific to albitites of upper ore level are not characteristic to deeper one. Based on seldom minor Th, La, and Y content spikes, rare-earth and thorium mineralization is immaterial. Regarding Zr and V, their contents are not over but most of the time less than background values. Apparently, zircon is not formed in albitites of lower ore-level; vanadium content in darkcolored minerals becomes insignificant, and single lead element is uranium. The most essential feature of Novokostiantynivka deposit is a succession of complex mineralization with monometallic one with depth.

Geochemical comparison of the Stillwater complex and alpine-type ultrabasic complexes, Beartooth Mountains, Montana and Wyoming

SUMMARYThe field of composition and the geochemical trend of the lower portion of the stratiform Stillwater igneous complex correlate well with the field and trend for alpine-type ultrabasic masses in the nearby gneissic basement of the Beartooth Mountains. This is consistent with a derivation of some alpine-type masses by the tectonic disruption and metamorphism of stratiform complexes.