Clay minerals provide indicators of the evolution of aqueous conditions and possible habitats for life on ancient Mars. Analyses by the Mars Science Laboratory rover Curiosity show that similar to 3.5-billion year (Ga) fluvio-lacustrine mudstones in Gale crater contain up to similar to 28 weight % (wt %) clay minerals. We demonstrate that the species of clay minerals deduced from x-ray diffraction and evolved gas analysis show a strong paleoenvironmental dependency. While perennial lake mudstones are characterized by Fe-saponite, we find that stratigraphic intervals associated with episodic lake drying contain Al-rich, Fe3+-bearing dioctahedral smectite, with minor (3 wt %) quantities of ferripyrophyllite, interpreted as wind-blown detritus, found in candidate aeolian deposits. Our results suggest that dioctahedral smectite formed via near-surface chemical weathering driven by fluctuations in lake level and atmospheric infiltration, a process leading to the redistribution of nutrients and potentially influencing the cycling of gases that help regulate climate.

Interaction of mantle melts with the continental crust can have significant effects on the composition of the resulting melts as well as on the crust itself, and tracing this interaction is key to our understanding of arc magmatism. Lava flows and pyroclastic deposits erupted from similar to 50 to 7.7 ka at Mt. Mazama (Crater Lake, Oregon) were analyzed for their Re/Os and U-Th isotopic compositions. Mafic lavas from monogenetic vents around Mt. Mazama that erupted during the buildup to its climactic eruption have lower Os-187/Os-188 ratios (0.1394 to 0.1956) and high Th-230 excess ((Th-230/U-238)(0) of 1.180 to 1.302), whereas dacites and rhyodacites tend to have higher Os-187/Os-188 ratios (0.2292 to 0.2788) and significant U-238 excess ((Th-230/U-238)(0) of 0.975 to 0.989). The less radiogenic Os isotope compositions of the mafic lavas can be modeled by assimilation of young (similar to 2.5 to 7 Ma), mafic lower crust that was modified during regional extension, whereas the more radiogenic Os isotope compositions of the dacites and rhyodacites can be attributed to assimilation of older (similar to 10 to 16 Ma), mid to upper crust that acquired its composition during an earlier period of Cascade magmatism. Production of Th excesses in the lower crust requires very young garnet formation accompanying dehydration melting in the lower crust at less than a few 100 ka by heat from recent basaltic magma injection. The results from this study suggest that the combination of Os and Th isotopes may be used to provide insights into the timescales of evolution of the continental crust in arc settings, as well as the influence of the crust on erupted magmas, and suggest a link between the age and composition of the lower and upper crust to regional tectonic extension and/or earlier Cascade magmatism. (C) 2015 Elsevier B.V. All rights reserved.

Crystal chemical algorithms were used to estimate the chemical composition of selected mineral phases observed with the CheMin X-ray diffractometer onboard the NASA Curiosity rover in Gale crater, Mars. The sampled materials include two wind-blown soils, Rocknest and Gobabeb, six mudstones in the Yellowknife Bay formation (John Klein and Cumberland) and the Murray formation (Confidence Hills, Mojave2, and Telegraph Peak), as well as five sandstones, Windjana and the samples of the unaltered Stimson formation (Big Sky and Okoruso) and the altered Stimson formation (Greenhorn and Lubango). The major mineral phases observed with the CheMin instrument in the Gale crater include plagioclase, sanidine,P2(1)/c and C2/c clinopyroxene, orthopyroxene, olivine, spine], and alunite-jarosite group minerals. The plagioclase analyzed with CheMin has an overall estimated average of An(40(11)) with a range of An(30(2)) to An(63(6)). The soil samples, Rocknest and Gobabeb, have an average of An(56(8)) while the Murray, Yellowknife Bay, unaltered Stimson, and altered Stimson formations have averages of An(38(2)), An(37(5)), An(45(7)), and An(35(6)), respectively. Alkali feldspar, specifically sanidine, average composition is Or(74(17)) with fully disordered Al/Si. Sanidine is most abundant in the Windjana sample (similar to 26 wt% of the crystalline material) and is fully disordered with a composition of Or(87(5)). The P2(1)/c clinopyroxene pigeonite observed in Gale crater has a broad compositional range {[Mg0.95(2)-1.54(17)Fe0.18(17)-1.03(9)Ca0.00-0.28(6)](Sigma 2)Si2O6} with an overall average of Mg1.18(19)Fe0.72(7)Ca0.10(9)Si2O6. The soils have the lowest Mg and highest Fe compositions [Mg0.95(5)Fe1.02(7)Ca0.03(4)Si2O6] of all of the Gale samples. Of the remaining samples, those of the Stimson formation exhibit the highest Mg and lowest Fe [average = Mg1.45(7)Fe0.35(13)Ca0.19(6)Si2O6]. Augite, C2/c clinopyroxene, is detected in just three samples, the soil samples [average = Mg0.92(5)Ca0.72(2)Fe0.36(5)Si2O6] and Windjana (Mg1.03(7)Ca0.75(4)Fe0.21(9)Si2O6).

Minerals containing cobalt as an essential element display systematic trends in their diversity and distribution. We employ data for 66 approved Co mineral species (as tabulated by the official mineral list of the International Mineralogical Association, http://rruff.info/ima, as of 1 March 2016), representing 3554 mineral species-locality pairs (www.mindat.org and other sources, as of 1 March 2016). We find that cobalt-containing mineral species, for which 20% are known at only one locality and more than half are known from five or fewer localities, conform to a Large Number of Rare Events (LNRE) distribution. Our model predicts that at least 81 Co minerals exist in Earth's crust today, indicating that at least 15 species have yet to be discovered a minimum estimate because it assumes that new minerals will be found only using the same methods as in the past. Numerous additional cobalt minerals likely await discovery using micro-analytical methods.

The Diavik mine, located in the Archean-age Slave geologic province in northern Canada, is one of the world's preeminent sources of gem diamonds. Since mining operations began in 2003, it has produced over 100 million carats of diamonds. This article will review the discovery, development, and operation of the mine, which is situated in a remote subarctic setting in the Northwest Territories. Four kimberlite pipes occur in close proximity-three are being exploited, while the fourth will be brought into production in 2018. Diavik is now expected to operate through 2024; upon closure, the equipment, buildings, and infrastructure will be removed and the land returned as closely as possible to its original condition.

Gravimetry, the precise measurement of gravitational fields, can be used to probe the internal structure of Earth and other planets. The Curiosity rover on Mars carries accelerometers normally used for navigation and attitude determination. We have recalibrated them to isolate the signature of the changing gravitational acceleration as the rover climbs through Gale crater. The subsurface rock density is inferred from the measured decrease in gravitational field strength with elevation. The density of the sedimentary rocks in Gale crater is 1680 +/- 180 kilograms per cubic meter. This value is lower than expected, indicating a high porosity and constraining maximum burial depths of the rocks over their history.

The Re-Os systematics in 13 peridotite xenoliths hosted in young (<0.39 myr) rejuvenated lavas from the Samoan island of Savai'i and 8 peridotite xenoliths from 6 to 10 myr old lavas from the Austral island of Tubuai have been examined to evaluate the history of the oceanic mantle in this region. Modal mineralogy, trace element compositions and Os-187/Os-188 ratios suggest that these peridotites are not cognate or residual to mantle plumes but rather samples of Pacific oceanic lithosphere created at the ridge. Savai'i and Tubuai islands lie along a flow line in the Pacific plate, and provide two snapshots (separated by over 40 Ma in time) of Pacific mantle that originated in the same region of the East Pacific rise. Tubuai xenoliths exhibit Os-187/Os-188 from 0.1163 to 0.1304, and Savai'i (Samoa) xenoliths span a smaller range from 0.1173 to 0.1284. The Os-187/Os-188 ratios measured in Tubuai xenoliths are lower than (and show no overlap with) basalts from Tubuai. The Os-187/Os-188 of the Savai'i xenoliths overlap the isotopic compositions of lavas from the island of Savai'i, but also extend to lower Os-187/Os-188 than the lavas. 3 He/4 He measurements of a subset of the xenoliths range from 2.5 to 6.4 Ra for Tubuai and 10.8 to 12.4 Ra for Savai'i.

Tuite, -Ca-3(PO4)(2), is a potential host for rare-earth elements in the deep mantle. Eu-bearing tuite single crystals with chemical formulas of Ca2.93Eu0.04(PO4)(2) and Ca2.88Eu0.07Na0.06(PO4)(2) were synthesized at 16 GPa and 1600 degrees C, and their structures were investigated at room temperature with single-crystal X-ray diffraction. The structure refinements of Eu-bearing tuite indicate the preference of Eu3+ for the smaller 6-coordinated Ca1 site with a coupled vacancy due to the substitution of 2Eu(3+)+3 Ca2+. In NaEu-bearing tuite, both Eu3+ and Na+ occupy the smaller 6-coordinated Ca1 site according to the coupled substitution of Eu3++Na(+)2 Ca2+. The presence of Na results in more Eu2O3 in NaEu-bearing tuite, because the coupled substitution is energetically more favorable. REE-bearing tuite could be found on the Moon and the deep Earth's mantle as a consequence of REE-bearing apatite or/and merrillite transformation under high-pressure and high-temperature conditions.

The redox state of Earth's convecting mantle, masked by the lithospheric plates and basaltic magmatism of plate tectonics, is a key unknown in the evolutionary history of our planet. Here we report that large, exceptional gem diamonds like the Cullinan, Constellation, and Koh-i-Noor carry direct evidence of crystallization from a redox-sensitive metallic liquid phase in the deep mantle. These sublithospheric diamonds contain inclusions of solidified iron-nickel-carbon-sulfur melt, accompanied by a thin fluid layer of methane +/- hydrogen, and sometimes majoritic garnet or former calcium silicate perovskite. The metal-dominated mineral assemblages and reduced volatiles in large gem diamonds indicate formation under metal-saturated conditions. We verify previous predictions that Earth has highly reducing deep mantle regions capable of precipitating a metallic iron phase that contains dissolved carbon and hydrogen.