Determination of equilibrium conditions of carbonate percipitation in Postojna cave with possible application to paleoclimatology

Sadržaj stabilnih izotopa ugljika i kisika, 13C i 18O, u sekundarno taloženim karbonatima (sigama) u špiljama krškog područja može dati važne informacije o paleoklimatskim uvjetima na tom području ako su sige nastale u uvjetima izotopne ravnoteže, tj, ako je izotopni sastav siga ovisan samo o temperaturi taloženja. Cilj ovog istraživanja bio je odrediti područja unutar Jame s ravnotežnim izotopnim uvjetima stvaranja siga na kojima bi se mogla provoditi buduća paleoklimatska istraživanja primjenom izotopnih tehnika. Pratili su se okolišni uvjeti (temperatura, koncentracija CO2), kemijski sastav prokapne vode, te izotopni sastav vode, CO2 i taloženih karbonata na devet lokacija tijekom jedne godine. Razlika između δ13C u suvremenom karbonatu i u DIC-u usporedila se s ravnotežnim faktorom ε. Fraktionacijski faktor α određen je iz izmjerenih vrijednosti δ18O prokapne vode i karbonata te je uspoređen s ravnotežnom vrijednošću αeq. Iako okolišni i kemijski parametri upućuju na postojanje preduvjeta za taloženje karbonata u izotopnoj ravnoteži, pogotovo na unutarnjim lokacijama, izotpni sastav karbonata, δ13C i δ18O, ukazuje na odstupanja od izotopne ravnoteže na većini lokacija. Jedino lokacije 06 - Stebrišče i 09 - Zgornji Tartar i pokazuju potencijal za buduća paleoklimatska istraživanja. Istraživanja su također pokazala da recentni karbonat istaložen na satnim staklima ne odražava izotopni sastav karbonata. Utvrđen je proces prethodnog taloženja karbonata u šupljinama nadsloja na lokaciji 05 - Podrti kapnik.The contents of stable carbon and oxygen isotopes, 13C and 18O, in secondary precipitated carbonates (speleothems) of caves in karst areas can provide important information about paleoclimatic conditions of the area if the speleothems are formed at equilibrium conditions, i.e., if the isotopic composition of speleothems depends only on the deposition temperature. The purpose of this study was to determine areas within Postojna Cave with isotopic equilibrium conditions of carbonate precipitation where future paleoclimate research may be conducted. Environmental factors (temperature, concentration of atmospheric CO2), chemical composition of drip water, isotopic composition of water, CO2 and deposited carbonates were monitored during one year at nine locations. Difference between δ13C in modern carbonates and in DIC was compared with the equilibrium fractionation factor ε. Fractionation factor α was determined from measured δ18O values of drip water and carbonates and compared to its equilibrium value αeq. Although environmetal and chemical parameters pointed to the fulfillment of preconditions for isotopic equilibrium precipitation of carbonates, specially at inner locations, isotopic composition of carbonates, both δ13C and δ18O, did not show equilibrium precipitation at most of the studied locations. Only locations 06 - Stebrišče and 09 - Zgornji Tartar have the potential for future paleoclimatic studies. It was also shown that recent carbonate precipitated on watch glasses did not reflect the isotopic composition of speleothems at the same location. Process of prior calcite precipitation was identified at location Podrti kapnik

Origin and K-Ar age of the phreatomagmatic breccia at the Trepča Pb-Zn-Ag skarn deposit, Kosovo: Implications for ore-forming processes

The Trepča Pb-Zn-Ag skarn deposit in Kosovo is spatially and temporarily related to the phreatomagmatic breccia of Oligocene age (~23 Ma). The deposit shows features typical for skarn deposits worldwide, including a stage of isochemical metamorphism, a prograde stage of an anhydrous, low oxygen and low sulfur fugacity character and a retrograde stage characterized by an increase in the water activity as well as by an increase in oxygen and sulfur fugacities. The mineralization is hosted by the recrystallized Upper Triassic limestone. The prograde mineralization consists mainly of Ca-Fe-Mn±Mg pyroxenes. The host recrystallized limestone at the contact with the prograde (skarn) mineralization have the increased content of Fe, Mn, Mo, As, Au, Cs, Ga, REE and Y suggesting their transport by infiltrating magmatic fluids. The decreased  d13C and  d18O values reflect a contribution of magmatic CO2. The retrograde mineral assemblage comprises ilvaite, magnetite, arsenopyrite, pyrrhotite, marcasite, pyrite, Ca-Fe-Mn±Mg carbonates and quartz. Hydrothermal ore minerals, mostly galena, sphalerite and pyrite, were deposited contemporaneously with the retrograde stage of the skarn development. Syn-ore and post-ore carbonates reflect a diminishing influence of magmatic CO2. Syn-ore carbonates are enriched in Fe, Mg, Mn, many chalcophile elements, including Ag, As, Bi, Cd, Cu, Pb, Sb and Zn, as well as in Au, Y and REE. The post-ore stage accompanied the precipitation of significant amount of Ca-rich carbonates including the travertine deposits at the deposit surface. The phreatomagmatic breccia was developed along a NW dipping contact between the ore bearing recrystallized limestone and the overlying schist. It has an inverted cone shape with the vertical extension up to 800 m and diameter up to 150-m. The upper part of the diatreme (an underground segment of the phreatomagmatic breccia) is characterized by the presence of a hydrothermally altered rootless quartz-latite dike surrounded by an unsorted polymict breccia mantle. Despite the alteration processes, the dike has a preserved porphyritic texture. Partly preserved sanidine, accompanied with the mixture of muscovite and quartz, reflects a near-neutral to weakly acidic environment. The clasts of country rocks and skarn mineralization underwent intense milling and mixing due to repeated magmatic penetrations. Sericitization of the breccia matrix, locally accompanied with minor kaolinitization, point to an increased water activity under near-neutral to weakly acidic conditions. Large fragments originally composed of anhydrous skarn minerals (pyroxenes) are usually completely altered to a mixture of fibroradial magnetite, quartz and various amount of carbonates suggesting an increase in oxygen fugacity. Their pyrite rims reflect that the increase in oxygen fugacity was followed by an increase in sulfur fugacity. The clast predominantly composed of Fe-sulfides and minor Bi-sulfides point that the increase in sulfur fugacity was locally sufficient to complete sulfidation of hedenbergite to pyrrhotite and/or pyrite. Although the phreatomagmatic breccia at the Trepča Pb-Zn-Ag skarn deposit does not carry significant amounts of the ore mineralization, its formation was crucial for the ore deposition. Phreatomagmatic explosions and formation of the breccia turned the system from the lithostatic to hydrostatic regime and triggered the retrograde stage increasing the water activity and oxygen fugacity in the system. In addition, cooling and decompression of the system contributed to more effective degassing of magmatic sulfur increased the sulfur fugacity. </p

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements