Super-deep diamonds from kimberlites in the Juina area, Mato Grosso State, Brazil

One thousand three hundred sixty-five diamonds from seven newly discovered kimberlitic pipes in the Juina area were comprehensively studied. These diamonds, like the ones from previously studied Juina placer deposits, are very homogeneous in their morphology and optical properties. Two diamond populations exist in the Pandrea pipes: the major population with a highly aggregated nitrogen impurity (% NB = 75-100%), and a secondary population with a moderately aggregated nitrogen impurity (% NB = 20-65%), while only one major population is present in the diamonds from placers. The diamonds from the pipes have a permanent, relatively high hydrogen impurity concentration. Among the mineral inclusions in diamonds from the Juina pipes, ferropericlase is predominant; chrome spinel, picroilmenite, Mn-ilmenite, MgCaSi-'perovskite' phase, rutile, sulphide, native iron, and iron-oxides were also identified. Most of the inclusions belong to the lower-mantle paragenesis; some (rutile and sulphide) are of eclogitic paragenesis. Mineral inclusions in diamonds from kimberlitic pipes are different in composition from the same minerals in placer diamonds. Both kimberlitic and placer diamonds belong to the same carbon isotopic population, but have differences in the δ13C distribution and were probably formed from different local carbon sources. These data indicate that diamonds from both groups, kimberlites and placer deposits, in the Juina area, belong to the same genetic population with most of the stones originating within the super-deep conditions. However, there are differences between these two groups, which indicate that besides the known Pandrea pipes which may have partly supplied diamonds to the placer deposits, there may be other, still unknown primary sources of diamonds in the Juina area.10 page(s

Diamond from the Los Coquitos area, Bolivar State, Venezuela

A set of 77 diamond crystals from the Los Coquitos placer on the Guaniamo River in Bolivar State, Venezuela, has been comprehensively studied and compared to previously studied diamond from the Quebrada Grande kimberlite sills and placer deposits, both located 50 km to the southeast. The diamond crystals in the Los Coquitos placer are generally similar to those of the Quebrada Grande area, but with significant morphological differences. Diamond from the Los Coquitos placer has a higher total nitrogen content (Ntot = 719 at.ppm versus 614–706 at.ppm in diamond from Quebrada Grande) and a lower level of nitrogen aggregation (% NB = 65 versus 68 in diamond from Quebrada Grande). Carbon isotope values, δ¹³C, of the Los Coquitos diamond vary from +0.4 to –20.5‰, compared with –3.2 to –28.7‰ in the Quebrada Grande diamond. In the Los Coquitos suite, mineral inclusions in diamond are characterized by a lower Ca content in garnet, wider compositional variations in pyroxene (mg in the range 0.683–0.849), and lower Fo component in olivine (mg in the range 0.926–0.932), compared to inclusions in diamond in the Quebrada Grande suite. Los Coquitos diamond shows greater depletion in LREE compared to Quebrada Grande diamond. Diamond crystals at Los Coquitos were derived, at least in part, from a new, undiscovered kimberlite source in the Guaniamo River basin. These rocks are similar in type to the Quebrada Grande kimberlites, but were sampled from a different section of the subcontinental lithospheric mantle. The existence of two separate populations of diamond, each with its own primary source, suggests that other localities of placer diamond in Venezuela may have their own local sources.18 page(s

Measurement of pseudorapidity distributions of charged particles in proton-proton collisions at sqrt(s) = 8 TeV by the CMS and TOTEM experiments

Pseudorapidity ( $\eta$ ) distributions of charged particles produced in proton–proton collisions at a centre-of-mass energy of 8 $~\text {TeV}$ are measured in the ranges $|\eta | < 2.2$ and $5.3 < |\eta | < 6.4$ covered by the CMS and TOTEM detectors, respectively. The data correspond to an integrated luminosity of $\mathcal {L} = 45 \mu {\mathrm {b}}^{-1}$ . Measurements are presented for three event categories. The most inclusive category is sensitive to 91–96 % of the total inelastic proton–proton cross section. The other two categories are disjoint subsets of the inclusive sample that are either enhanced or depleted in single diffractive dissociation events. The data are compared to models used to describe high-energy hadronic interactions. None of the models considered provide a consistent description of the measured distributions