In addition to a series of ultramafic to mafic and alkaline igneous rocks, a granite body also occurs in the Ditrău Alkaline Massif, Eastern Carpathians, Romania. We present and discuss mineral chemical data, and major and trace element compositions of the granites in order to define their nature and origin and to determine the depth of the magma emplacement. The granites consist of K-feldspar, albite to oligoclase and quartz accompanied by Ti-rich annite ± calcic amphiboles. Depending on the amphibole content they are classified as less fractionated amphibole-bearing and amphibole-free varieties. Accessories include zircon, apatite, magnetite, ilmenite, and allanite or monazite. High Zr, Nb, Ga, Ce and Y content and Ga/Al and Fe/Mg ratios, together with low CaO, Sr and Ba contents and Y/Nb ratios of 0.04-0.88 are consistent with A1-type granites and mantle differentiates correspond to an intra-plate environment. The Ditrău Alkaline Massif granites were emplaced at middle -upper crustal levels between 14 and 4 km depth as indicated by the calculated crystallization pressure of 370 ± 40 MPa and the stability limit of calcic amphiboles.
The Ditrău Complex of the Carpathian Mountains in Romania is a Mesozoic igneous complex (~ 200-230 Ma) generated in a continental rift environment. Felsic rocks of the Ditrău Complex consist of nepheline syenite, syenite, quartz syenite, quartz monzonite, monzonite and granite. The Ditrău rocks have mantle-like ɛNd values that range from + 0.8 to + 5.5 ‰. High-temperature equilibrium O-isotope fractionations between minerals are generally preserved, although some subsolidus O-isotope re-equilibration occurred. Magma δ 18 O values estimated from quartz, feldspar and amphibole (5.7-11.7‰) are higher than those estimated from zircon. We suggest that this difference results from continuous crustal contamination, with zircon recording the early, high-temperature δ 18 O values, and quartz and the other silicate δ 18 O values, reflecting a combination of subsequent crustal contamination and deuteric alteration. Negative correlations between calculated magma δ 18 O values and Na 2 O and Al 2 O 3 content and εNd are consistent with the spectrum of felsic rocks from nepheline syenite to granite resulting from an increase crustal input. Both O-and Nd-isotope compositions are consistent with a dominantly mantle origin of hornblendites, diorites and nepheline syenites. The Nd-and O-isotope composition of the silica-oversaturated rocks can be explained by the assimilation of 20-60% upper crustal melts into the re-injected mafic alkaline parent magma to generate the Ditrău syenites, quartz syenites, quartz monzonites and granites.
The characterization of acid rock drainage (ARD) is traditionally based on mineralogical and geochemical techniques (e.g., Acid Base Accounting tests). The complexity of ARD processes warrants contribution of methods from various disciplines. In the past decade, the increasing role of environmental isotopes in pollution monitoring has enabled the successful application of isotope methods in ARD investigations. While isotopic compositions of different pollutants can refer to their parent mineral, the degree of isotope fractionations are indicative of the mechanisms taking place during the release and transportation of ARD-related contaminants. In natural environments, however, the measured isotope fractionations are predominantly the result of several coexisting or sequential processes. Therefore, the identification and quantification of the distinct contributions of these processes to isotope variations is difficult and requires well-defined laboratory conditions, where the influence of ARD generation on different isotope systems can be assessed with greater certainty. This review provides readers with a single source of information regarding isotopic variations generated by laboratory pyrite leaching.
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