Abstract: Porphyry Cu–Au–Pd±Pt deposits are significant Au resources, but their Pd and Pt potential is still unknown. Elevated Pd, Pt (hundreds of ppb) and Au contents are associated with typical stockwork magnetite-bornite-chalcopyrite assemblages, at the central parts of certain porphyry deposits. Unexpected high grade Cu–(Pd+Pt) (up to 6 ppm) mineralization with high Pd/Pt ratios at the Elatsite porphyry deposit, which is found in a spatial association with the Chelopech epithermal deposit (Bulgaria) and the Skouries porphyry deposit, may have formed during late stages of an evolved hydrothermal system. Estimated Pd, Pt and Au potential for porphyry deposits is consistent with literature model calculations demonstrating the capacity of aqueous vapor and brine to scavenge sufficient quantities of Pt and Pd, and could contribute to the global platinum-group element (PGE) production. Critical requirements controlling potential of porphyry deposits may be from the metals contained in magma (metasomatized asthenospheric mantle wedge as indicated by significant Cr, Co, Ni and Re contents). The Cr content may be an indicator for the mantle input.
Abstract: Sedimentary deposits in Stoddard County, southeastern Missouri, reveal a K-Pg transition sequence represented by the uppermost Maastrichtian Owl Creek Formation and the Paleocene Clayton Formation. The Clayton Formation is characterized by a basal fossiliferous coquinite that contains reworked late Maastrichtian macrofossils. Dinoflagellate biostratigraphy is used to determine the age of the coquinite layer and specifically whether or not it is an end-K tsunamite deposit resulting from the Chicxulub impact event. Results indicate a mixed assemblage of late Maastrichtian and early Danian dinocysts within the basal coquinite of the Clayton Formation. Maastrichtian dinocyst taxa identified are Riculacysta amplexa, Pierceites pentagonus, Phelodinium tricuspe and Dinogymnium sp. and dinocysts utilized as global indicators of the basal Danian, also present in the coquinite, consist of Senoniasphaera inornata, Carpatella cornuta, Damassadinium californicum, and Lanternosphaeridium reinhardtii. A gray mud occurring above the coquinite in the middle of the Clayton Formation contains the mid-Danian dinoflagellate Senegalinium iterlaaense. Collectively, these data suggest that the coquinite was deposited well after the K-Pg event but before the middle Danian. The mixed assemblage of Late Cretaceous and Paleocene dinocysts preserved in the coquinite weakens the hypothesis that it is an end-K tsunamite deposit and suggests instead that it may result from a long-term transgressive lag. We also extend the stratigraphic range of the Paleocene Senegalinium simplex downward into the uppermost Maastrichtian.
Abstract: To better understand the origin of across-strike K2O enrichments in silicic volcanic rocks from the Andean Central Volcanic Zone, we compare geochemical data for Quaternary volcanic rocks erupted from three well-characterized composite volcanoes situated along a southeast striking transect between 21° and 22° S latitude (Aucanquilcha, Ollagüe, and Uturuncu). At a given SiO2 content, lavas erupted with increasing distance from the arc front display systematically higher K2O, Rb, Th, Y, REE and HFSE contents; Rb/Sr ratios; and Sr isotopic ratios. In contrast, the lavas display systematically lower Al2O3, Na2O, Sr, and Ba contents; Ba/La, Ba/Zr, K/Rb, and Sr/Y ratios; Nd isotopic ratios; and more negative Eu anomalies toward the east. We suggest that silicic magmas along the arc front reflect melting of relatively young, mafic composition amphibolitic source rocks and that the mid- to deep-crust becomes increasingly older with a more felsic bulk composition in which residual mineralogies are progressively more feldspar-rich toward the east. Collectively, these data suggest the continental crust becomes strongly hybridized beneath frontal arc localities due to protracted intrusion of primary, mantle-derived basaltic magmas with a diminishing effect behind the arc front because of smaller degrees of mantle partial melting and primary melt generation.
Abstract: In her paper, A.C. Marra intends to review the current knowledge on Quaternary mammals of Sicily. As a review, the paper should have presented a clear, updated and rigorous picture of the chosen topic. Actually, most of the paper’s contents come from previous review papers (quoted with the numbers 1–6, 18, 19 and 50), most of which are dated. Above all, A.C. Marra overlooked recent important data concerning the species contained in the different faunal assemblages of Sicily, as well as previous data concerning the stratigraphy and datings of the faunal deposits.