Secondary minerals observed

The following example concerns a basaltic glass altered experimentally in seawater at temperatures between 25 and 90 °C for durations ranging from a few minutes to 30 days (Crovisier et al. 1982 Thomassin Touray 1982). Regardless of the temperature, the first secondary mineral observed was a hydroxycarbonate from... 

Elemental maps and p-XRF transects confirmed the high affinity of the secondary minerals to adsorb or incorporate many of the elements released by sulfides or gangue minerals (Fig. 2). In particular, we routinely observed significant concentrations of Ni, Cu, Zn, and As in the goethite-bernalite layers... 

Geochemical simulations (not shown) of water quality suggest that Ni is soluble in the test conditions, eliminating secondary mineral precipitation as an explanation for the absence of Ni in leachates. These observations could be explained by the metal retention potential of the Lac Tio waste rock being still active in the humidity cell tests. Consequently, the Ni produced in the humidity cell tests will continue to be retained by the fresh waste rock until saturation of the retention sites. 

Early work of Shields et al. (1965) has indicated a total variation of 12%o with the largest variations in low temperature secondary minerals. Somewhat smaller differences, but still in the range of 7 to 9%c, have been observed by Marechal et al. (1999), Marechal and Albarede (2002), Zhu et al. (2002), Ruiz et al. (2002), which are larger than for Fe. Nevertheless most samples so far analyzed vary between 8 Cu values from +1 to — l%c. 

The thermodynamic incompatibility of many of the solid phases present with each other as well as their local environment, results in formation of secondary minerals. Although the secondary materials may comprise only a small volume fraction of the waste, they (1) tend to increase in amount with time, as weathering processes proceed, (2) typically form at grain surfaces and are thus physically liable to react with percolating gas or liquids, and (3) may exhibit sites suitable for sorption or crystallo-chemical incorporation of trace elements (see Donahoe, 2004). Frequently observed secondary minerals include jarosite and ettringite the former is known to sorb ions such as Mn and As, whereas ettringite can form solid solutions, in which SO4 is replaced by Cr04 (Kumarathasan et al. 1990). 

The observed paragenesis contains a significant amount of feldspars. Although feldspars are not considered to crystallize in the numerical simulations (Jacquol 2000 Durst Vuataz 2001), our experimental results suggest that formation of clay minerals is controlled by previously crystallized feldspars. Therefore, the presence of feldspars is of importance for the crystallization of secondary minerals and the evolution of porosity in the stimulated reservoir of the HFR site. 

The tube-in-tube experiment is a very powerful method to determine the sequence of precipitation of secondary minerals as function of temperature for a chosen chemical system. Chemical reactions occur quickly (within 40 days) and the transport by diffusion of chemical elements is efficient. Similar crystallization sequences are observed in both experiments, suggesting that the transitions between the different mineral phases are not only controlled by the composition of the solution but also by temperature. The experimental design does not strictly correspond to the geometry encountered at the Soultz-sous-Forets site and therefore needs to... 

Predicted secondary minerals. As discussed above, direct evidence for the formation of secondary trace element phases in weathered ash is rare. Most evidence suggesting precipitation of trace element phases by weathering processes is therefore indirect. For example, geochemical modelling of pore fluids in CCB disposal facilities and ash leachate solutions indicates that aqueous trace element concentrations are controlled by a variety of secondary phases. Table 2 lists numerous secondary trace element phases predicted, but not yet observed, to form in weathering CCB systems. 

Bornite as a primary mineral has been observed in pegmatite veins and in igneous rocks and is also a common secondary mineral,... 

This chapter focuses upon some recent observations of mass-independent isotopic processes in nature. As discussed by Thiemens et al. (2001) and Thiemens (2002), there exist other mass-independent isotope effects in nature that derive from non-ozone reactions. For example, CO2 photolysis produces a large mass-independent isotope effect that, in part, may account for observations in the SNC (martian) meteorites and the synthesis of their secondary minerals. UV photolysis of SO2 produces new isotopic fractional effect. An accompanying mass-independent isotopic composition determines the evolution of oxygen in the Earth s earliest atmosphere. 

The mineralogy of ferricrete alteration profiles can be complex and varied because of the incorporation of mechanically derived materials and the retained importance of host rock composition after the formation of secondary minerals. In general, ferricrete profiles do not display the progression of alteration minerals observed in laterites. Where ferricretes are formed by mechanical accumulation, they can lie disconformably above unaltered bedrock (Bowden, 1987, 1997). In these instances, the ferricrete mineral assemblage will be inherited, in part, from the derived materials, and in part from later cementation processes that involve remobilised iron and alumina deposited as neo-formed oxyhydroxides. In such examples, determining the sequence of mineralogical transformations becomes exceptionally difficult. 

TABLE 12.7 Solubility products of some secondary aluminum oxyhydroxides and sulfate minerals observed resulting from the interaction of acid mine waters with geological materials... 

These trends, in conjunction with an observed decrease in organic content from 5% at the surface to 3% at depth, suggest that, as organic matter is degraded, some of the plutonium which it originally contained is released but is immediately taken up by other components of the sediment (i.e. Fe/Mn secondary minerals). This observation is compatible with... 

Recent, more detailed investigations of oxygen isotopic compositions of martian meteorite components have focussed on secondary minerals and water contained in the samples. Studies that report analyses of all three oxygen isotopes consistently show that secondary minerals and water in the martian meteorites do not lie on the MSFL. Karlsson et al. (1992) observed elevated A O values, up to +0.9 %o (or -0.6 %o above the MSFL) in water extracted by stepped heating from Nakhla, Lafayette and Chassigny, with the most pronounced effects observed in Nakhla. The water extracted from the shergottites generally records A O values between than the MSF and the TF line. Farquhar and... 

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