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The Almadin mercury deposits represent one of the largest geochemical anomalies on Earth, but the mode and timing of their formation remains a matter of controversy. There are two main possibilities: hydrothermal solutions associated with alkali basalt volcanism in the Silurian and Devonian; or regional hydrothermal activity during later Hercynian metamorphism. Although these models can be distinguished by determining the age of ore deposition, no suitable isotopic method had been applied to the problem prior to this study. We report here on vacuum encapsulated and more traditional laser "Ar/ "Ar dating performed on illite concentrates and Cr-rich micas that are intimately associated with mercury mineraiization in both Devonian and Silurian host rocks. Illite is associated with a later stage of Hg mineralization (cinnabar + kaolinite + pyrophyllite + chlorite) which locally replaces an earlier episode associated with carbonates and Cr-mica. The dating results from illite separates suggest that the later stages of Hg mineralization or remobilization occurred about 360 Ma, which is about 20 Ma younger than any mercury-hosting rocks in the district and coincides with the onset of regional deformation during the Hercynian orogeny. Cr-mica ages are variable and range from 365 Ma to 427 Ma. This age range spans the period between the deposition of the Criadero quartzite (the oldest sedimentary unit hosting mercury), and the later episode of mineralization. This suggests that mineralization started at least by the mid to lower Silurian and the younger argon ages for Cr-mica could represent partial to nearly total argon loss, caused by the Hercynian metamorphic event. It appears that both postulated styles of mercury mineralization occurred, separated in time by up to 80 million years.

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BackgroundViperid snakebite envenoming is characterized by prominent local tissue damage, including muscle necrosis. A frequent outcome of such local pathology is deficient skeletal muscle regeneration, which causes muscle dysfunction, muscle loss and fibrosis, thus provoking permanent sequelae that greatly affect the quality of life of patients. The causes of such poor regenerative outcome of skeletal muscle after viperid snakebites are not fully understood.Methodology/Principal FindingsA murine model of muscle necrosis and regeneration was adapted to study the effects of the venom and isolated toxins of Bothrops asper, the medically most important snake in Central America. Gastrocnemius muscle was injected with either B. asper venom, a myotoxic phospholipase A2 (Mtx), a hemorrhagic metalloproteinase (SVMP), or saline solution. At various time intervals, during one month, tissue samples were collected and analyzed by histology, and by immunocytochemical and immunohistochemical techniques aimed at detecting muscle fibers, collagen, endothelial cells, myoblasts, myotubes, macrophages, TUNEL-positive nuclei, and axons. A successful regenerative response was observed in muscle injected with Mtx, which induces myonecrosis but does not affect the microvasculature. In contrast, poor regeneration, with fibrosis and atrophic fibers, occurred when muscle was injected with venom or SVMP, both of which provoke necrosis, microvascular damage leading to hemorrhage, and poor axonal regeneration.Conclusions/SignificanceThe deficient skeletal muscle regeneration after injection of B. asper venom is likely to depend on the widespread damage to the microvasculature, which affects the removal of necrotic debris by phagocytes, and the provision of nutrients and oxygen required for regeneration. In addition, deficient axonal regeneration is likely to contribute to the poor regenerative outcome in this model.

New U-Pb zircon ages from the Santa Olalla Igneous Complex have been obtained, which improve the knowledge of the precise timing of Variscan magmatism in the Ossa-Morena Zone, SW Iberia. This complex has a special relevance as it hosts the most important Ni-Cu-platinum group element (PGE) mineralization in Europe: the Aguablanca deposit. U-Pb zircon ages have been obtained for seven samples belonging to the Santa Olalla Igneous Complex and spatially related granites. With the exception of the Cala granite (352 AE 4 Ma), which represents an older intrusion, the bulk of samples yield ages that cluster around 340 AE 3 Ma: the Santa Olalla tonalite (341.5 AE 3 Ma), the Sultana hornblende tonalite (341 AE 3 Ma), a mingling area at the contact between the Aguablanca and Santa Olalla stocks (341 AE 1.5 Ma), the Garrote granite (339 AE 3 Ma), the Teuler granite (338 AE 2 Ma), and dioritic dykes from the Aguablanca stock (338.6 AE 0.8 Ma). The Bodonal-Cala porphyry, which has also been dated (530 AE 3 Ma), comprises a group of sub-volcanic rhyolitic intrusions belonging to the Bodonal-Cala volcano-sedimentary complex, which hosts the igneous rocks. The knowledge that emplacement of the Aguablanca deposit was related to episodic transtensional tectonic stages during the Variscan orogeny will be fundamental in future mineral exploration in the Ossa-Morena Zone.

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The Aguablanca Ni-Cu-PGE ore deposit, in southwestern Iberia, has a magmatic origin, and has been reworked by later skarn-related hydrothermal activity. Base-metal sulfides are associated with igneous cumulates displaying subvertical layering consisting of gabbro, norite and dolerite, with fragments of pyroxenite and peridotite. These rocks show a pervasive retrograde alteration with an early overprint of actinolite ± chlorite ± epidote ± albite ± serpentine, followed by later growth of talc ± chlorite ± carbonates. The base-metal sulfides are concentrated in two subvertical bodies and consist of pyrrhotite, pentlandite and chalcopyrite, overprinted by fluid-deposited pyrite. The following types of mineralization have been recognized: 1) disseminated ore (1 < Ni/Cu < 1.5), with sulfides occurring interstitially to the igneous silicates, 2) semimassive to massive ore (2 < Ni/Cu < 5), with net-textured to poikilitic sulfides, 3) breccia ore, consisting of fragments of unmineralized ultramafic rocks in a massive sulfide matrix, 4) nodules of sulfides, 5) pyrrhotite veinlets, and 6) chalcopyrite veinlets. The PGE content and (Pt + Pd):(Ru + Ir + Os) ratio have their highest values in the Cu-rich disseminated ore and associated veinlets of chalcopyrite. The platinum-group minerals (PGM) associated with the base-metal sulfides at Aguablanca include michenerite, merenskyite, moncheite, palladian melonite and sperrylite. These mostly occur enclosed within sulfide minerals or close to contacts between them. The PGE tellurides show an extensive substitution of Bi for Te, indicating temperatures of formation below 500°C. A PGE oxide assemblage has also been discovered in samples from the surface gossan developed above the sulfides. The composition of the PGM and their association with magmatic base-metal sulfides suggest that they exsolved from the sulfides during subsolidus recrystallization, although some remobilization may have occurred in areas of pervasive circulation of fluid.