Silicate minerals

About: Silicate minerals is a research topic. Over the lifetime, 1794 publications have been published within this topic receiving 67064 citations.

Comparison of static and mineralogical ARD prediction methods in the Nordic environment

Abstract: Acid rock drainage (ARD) is a major problem related to the management of mining wastes, especially concerning deposits containing sulphide minerals. Commonly used tests for ARD prediction include acid–base accounting (ABA) tests and the net acid generation (NAG) test. Since drainage quality largely depends on the ratio and quality of acid-producing and neutralising minerals, mineralogical calculations could also be used for ARD prediction. In this study, several Finnish waste rock sites were investigated and the performance of different static ARD test methods was evaluated and compared. At the target mine sites, pyrrhotite was the main mineral contributing to acid production (AP). Silicate minerals were the main contributors to the neutralisation potential (NP) at 60% of the investigated mine sites. Since silicate minerals appear to have a significant role in ARD generation at Finnish mine waste sites, the behaviour of these minerals should be more thoroughly investigated, especially in relation to the acid produced by pyrrhotite oxidation. In general, the NP of silicate minerals appears to be underestimated by laboratory measurements. For example, in the NAG test, the slower-reacting NP-contributing minerals might require a longer time to react than is specified in the currently used method. The results suggest that ARD prediction based on SEM mineralogical calculations is at least as accurate as the commonly used static laboratory methods.

New carbonatite complexes in the Archaean In'Ouzzal nucleus (Ahaggar, Algeria): mineralogical and geochemical data

Abstract: Several massifs of very old carbonatites have been discovered in the Archaean granulitic block of In'Ouzzal (Western Ahaggar, Algeria). These carbonatites are original since they are associated with Silica — saturated syenitic magmatism and present, in the late stages of evolution, a very uncommon mineralogy, with silicate minerals, especially wollastonite, allanite, and quartz. The mineralogy, C and O isotopes and R.E.E. distributions indicate that the late stages of crystallization occurred under high SiO2 activities, and produced the uncommon mineralogy and extremely high R.E.E. concentrations in phosphate minerals apatite and britholite. Interaction with continental crust is a possible mechanism to explain the original features of these carbonatite complexes.

Pathways for nitrogen cycling in Earth’s crust and upper mantle: A review and new results for microporous beryl and cordierite

Abstract: ![Figure][1] Earth’s atmosphere contains 27–30% of the planet’s nitrogen and recent estimates are that about one-half that amount (11–16%) is located in the continental and oceanic crust combined. The percentage of N in the mantle is more difficult to estimate, but it is thought to be near 60%, at very low concentrations. Knowledge of the behavior of N in various fluid-melt-rock settings is key to understanding pathways for its transfer among the major solid Earth reservoirs. Nitrogen initially bound into various organic materials is transferred into silicate minerals during burial and metamorphism, often as NH4+ substituting for K+ in layer silicates (clays and micas) and feldspars. Low-grade metamorphic rocks appear to retain much of this initial organic N signature, in both concentrations and isotopic compositions, thus in some cases providing a relatively un- or little-modified record of ancient biogeochemical cycling. Devolatilization can release significant fractions of the N initially fixed in crustal rocks through organic diagenesis, during progressive metamorphism at temperatures of ~350–550 °C (depending on pressure). Loss of fractionated N during devolatilization can impart an appreciable isotopic signature on the residual rocks, producing shifts in δ15N values mostly in the range of +2 to +5‰. These rocks then retain large fractions of the remaining N largely as NH4+, despite further heating and ultimately partial melting, with little additional change in δ15N. This retention leads to the storage of relatively large amounts of N, largely as NH4+, in the continental crust. Nitrogen can serve as a tracer of the mobility of organic-sedimentary components into and within the upper mantle. This contribution focuses on our growing, but still fragmentary, knowledge of the N pathways into shallow to deep continental crustal settings and the upper mantle. We discuss the factors controlling the return of deeply subducted N to shallower reservoirs, including the atmosphere, via metamorphic devolatilization and arc magmatism. We discuss observations from natural rock suites providing tests of calculated mineral-fluid fractionation factors for N. Building on our discussion of N behavior in continental crust, we present new measurements on the N concentrations and isotopic compositions of microporous beryl and cordierite from medium- and high-grade metamorphic rocks and pegmatites, both phases containing molecular N2, and NH4+-bearing micas coexisting with them. We suggest some avenues of investigation that could be particularly fruitful toward obtaining a better understanding of the key N reservoirs and the more important pathways for N cycling in the solid Earth. [1]: pending:yes