Oxidized sulfur-rich arc magmas formed porphyry Cu deposits by 1.88 Ga.

Most known porphyry Cu deposits formed in the Phanerozoic and are exclusively associated with moderately oxidized, sulfur-rich, hydrous arc-related magmas derived from partial melting of the asthenospheric mantle metasomatized by slab-derived fluids. Yet, whether similar metallogenic processes also operated in the Precambrian remains obscure. Here we address the issue by investigating the origin, fO2, and S contents of calc-alkaline plutonic rocks associated with the Haib porphyry Cu deposit in the Paleoproterozoic Richtersveld Magmatic Arc (southern Namibia), an interpreted mature island-arc setting. We show that the ca. 1886-1881 Ma ore-forming magmas, originated from a mantle-dominated source with minor crustal contributions, were relatively oxidized (1‒2 log units above the fayalite-magnetite-quartz redox buffer) and sulfur-rich. These results indicate that moderately oxidized, sulfur-rich arc magma associated with porphyry Cu mineralization already existed in the late Paleoproterozoic, probably as a result of recycling of sulfate-rich seawater or sediments from the subducted oceanic lithosphere at that time.

Synthesis, properties, and mechanistic insight into the self-assembly of a lamellar fibrous superstructure from a synthetically simple discotic molecule.

The discotic molecule 4-chloro-2,6-bis(octadecylamino)-pyrimidine-5-carbaldehyde, displays gelation behavior in dodecane, heptane, chloroform, and dichloromethane. The aggregation behavior of this material was studied by dynamic light scattering, differential scanning calorimetry, scanning electron microscopy, polarized optical microscopy, small-angle X-ray diffraction, and wide-angle X-ray diffraction techniques. Combined with molecular modeling calculations, Fourier transform infrared, and 1H NMR studies, we propose a mechanism for the self-assembly of this fibrous lamellar architecture. Notably, we have shown that the fibers grow via stacking interactions along their main axis, via hydrogen bonding along their short axis, and via van der Waals interactions (lamellae) along the third axis. This type of morphology is desirable since it provides an opportunity to synthetically control and optimize mechanical, electrical, optical, and transport properties along the length of the fiber.