This study aims at better constraining the link between magmatism and metallogeny in the south-easternmost sector of the Bor Metallogenetic Zone (BMZ), where the world-class copper and gold deposit of Čukaru Peki was recently discovered. The obtained U/Pb zircon ages confirm the earlier knowledge that the major Cu–Au porphyry and epithermal mineralization in the BMZ is genetically related to the first volcanic phase (‘Timok andesite’; 85–90 Ma). However, the data also suggest that during this phase, two subgroups of andesite porphyry were formed; they are named volcanic phase 1A (V1A) and volcanic phase 1B (V1B). The V1A andesite (89–90 Ma) is plagioclase-hornblende phyric, holocrystalline and ubiquitously hydrothermally altered and/or mineralized, whereas the V1B (85–86 Ma) is hornblende-plagioclase phyric, holo- to hypocrystalline, fresh, and non-mineralized. According to our simplified model, the contrasting productivity of the V1A and V1B is explained by fluctuations during AFC (assimilation-fractional crystallization) processes of water-rich parental magma, which have controlled the order of crystallization of hornblende and plagioclase in the V1A and V1B andesite.

The present study provides data on the high-grade metamorphic basement of the Serbo-Macedonian Massif (SMM) that is exposed in Ograzhden and Belasitsa Mountains, SW Bulgaria. We combined the conventional ID-TIMS with the in-situ LA-ICP-MS U-Pb zircon dating and compiled them with petrological and geochemical studies to better constrain the age and origin of the protoliths and the grade of metamorphic overprint. The orthogneisses are dated in the range of 450–455 Ma, except for the Kolarovo metagranites, which define two clusters of age data at 554.8 ± 3.3 Ma and 510.2 ± 3.5 Ma. We assume sedimentary origin for the plagiogneisses that show zircon population and age distribution similar to the gneiss-schists: main peak at ~600 Ma and minor populations at 700–800 Ma, 1000–1100 Ma and 2400 Ma. The amphibolites yield the youngest precursor ages of 435–440 Ma. The whole succession of rocks is metamorphosed to upper amphibolite facies conditions, with peak temperatures (Tmax) between 675–710 °C in Ograzhden Mountain and at ~650 °C in Belasitsa Mountain. Pressure estimates (Pmin) range from 6–8 kbar to 12–13 kbar, based on 3T phengite relics and application of different calibrations of phengite barometer. However, higher pressures cannot be excluded due to evidence from the eclogitic metabasites. The metamorphism has been dated in zircon rims of metasediments, vein rocks and amphibolites, as well as in xenotime of newly formed leucosome, at ~330 Ma. The wide range of primary rocks, their major- and trace-element chemistry and Sr-Nd isotope signature, combined with the age data of zircon populations, give evidence for an old crustal fragment with Gondwana affinity that was rejuvenated in the Ordovician–Silurian, before the collision and metamorphic overprint during the Variscan orogeny.

U-Pb-zircon and monazite ID-TIMS and in-situ LA-ICP-MS and EPMA analyses are combined to define the magmatic age of the Igralishte granite, which is exposed over 32 km2 in the high-metamorphic rocks of the Serbo-Macedonian Massif (Ograzhden Mountain, SW Bulgaria). The granite is dated at 243.28 ± 0.84 Ma by concordant zircons (ID-TIMS data) and this intrusion age is confirmed also by in-situ LA-ICP-MS and EPMA monazite analyses. The intrusion of the Igralishte granite at middle Triassic time defines the age of the high-grade metamorphism in Ograzhden Mountain as Pre-Triassic. A tectonic and hydrothermal overprint is dated at 36.36 ± 0.56 Ma by the Rb-Sr whole-rock-biotite reference line. This age is considered as the youngest thermal event in the region of the Igralishte pluton that reached the 300 ± 50 °C closing temperature of the Rb-Sr isotope system in the biotite, but could not fully reset the Rb-Sr isotope system of the muscovite. The initial strontium ratio of 87Sr/86Sri = 0.7078 and the inheritance of old lead components in the zircons suppose crustal-dominated source of the magma. Preferred tectonic scenario suggests dehydration melting and granite formation in the middle/upper crust at the Permian-Triassic boundary and the Lower-Middle Triassic caused by mafic intrusions at the base of the crust.

Our study is focused on REE and yttrium (REY) geochemistry of pore waters from core-box sediments. The samples were collected from the 0–5 cm, 10–15 cm, 25–30 cm, and 35–40 cm depth intervals of four stations of the eastern part of block H_22 of IOM license area of the Clarion-Clipperton Fracture Zone, NE Pacific. The REE studies in marine pore fluids were limited by analytical challenges. The pore water analysis we applied is based on a modern, improved analytical technique (ICP-MS, Perkin-Elmer SCIEX Elan DRC-e) with a cross-flow nebulizer and a spectrometer optimized (RF, gas flow, lens voltage) using a quadrupole cell in a DRC (Dynamic Reaction Cell) mode that allowed us to define the whole suite of REE. The ƩREY values of the samples vary from 4.05 μg/l to 106.34 μg/l. The REE content is at least one order of magnitude higher than the oceanic water. We followed the natural variations of La, Lu, Ce, and Y in absolute concentrations for station 3607. Cerium and Y are slightly enriched around the water-sediment interface, while La and Lu are enriched in the deeper layers. PAAS normalized REY patterns show a pronounced negative Ce/Ce* ratio together with a little MREE and HREY enrichment. The relatively “flat” REE patterns are typical for the shallow open ocean and characterize REE released from the organic matter degradation. We assume that the decomposition of and adsorption on organic matter and oxidation conditions are the main factors for REE fractionation in the pore water. The reason for some scatter in our REY data might be linked to bioturbation that has affected the sediment profiles.

The Skrut granitoids crop out in the western part of Belasitsa Mountain in SW Bulgaria. They are intruded in biotite gneisses and mica schists, building up together a complex nappe structure in the frame of the Serbo-Macedonian Massif (SMM). Main rock forming minerals in the Skrut granitoids are plagioclase, potassium feldspar, quartz, and biotite and accessories are apatite, allanite, epidote, zircon, titanite and garnet. These granitoids have undergone processes of dynamic metamorphism and non-uniform hydrothermal alteration. In respect to K2O content they belong to the high potassium calc-alkaline magmatic series while according to the ASI coefficient they are related to the weakly per-aluminium granitoids. The magma is enriched in water and REE. Probably, its crystallization has proceeded at pressure of 11 to 11.5 kbar (presence of magmatic epidote) and temperature of 800 to 600°C. The positive ε-Hf values of zircon crystals (from +0.4 to +3.5) propose mixed crust-mantle magma source whereas calc-alkaline characteristics and discrimination diagrams propose a volcanic-arc/continental margin or postcollisional environment of the magma generation. The age of the granitoids is determined by conventional U-Pb method on zircons as 248.85±0.70 Ma. The regression line obtained by the Rb–Sr isotope analyses on whole rock samples yield an age of 167.3±8.1 Ma, which is interpreted as a mixing line, probably influenced also by overprinted events. The new data suggest formation of the Skrut granitoids during the Early Triassic as a result of Late Variscan event in extensional conditions and block dismembering (rifting?). The post-metamorphic intrusion of the granitoids defines the high grade metamorphism in Belasitsa Mountain as pre-Triassic in age.