Minerals systems

FIG. 20-31 Marcy grate-type continuous hall mill. (Allis Mineral Systems, S-oedala Inc. )... 

It is widely accepted that boiling of ore fluids took place in the epithermal Au— Ag mineralization system from the fluid inclusion data (Nakayama and Enjoji, 1985 ... 

Moh, G.H. (1975) Tin-containing mineral systems. Part II. Phase relations and mineral assemblages in the Cu-Fe-Zn-Sn-S system. Chem. Erde, 34, 1-61. 

Aeration should be correct in order to disperse fine air bubbles throughout the pulp. The extent of aeration needed depends upon the particular mineral system and quantity being floated. 

At greater depths, the redox characteristics are mainly determined by another mineral system fayalite (Fe2Si04), magnetite and quartz (Si02) (theFMQ system). The buffer properties of the two systems can be expressed in terms of the following equations ... 

The two mineral systems in the ocean crust are compatible, as has been shown by calculations for the following reactions (Helgeson et al., 1978) ... 

E. L. Shock (1990) provides a different interpretation of these results he criticizes that the redox state of the reaction mixture was not checked in the Miller/Bada experiments. Shock also states that simple thermodynamic calculations show that the Miller/Bada theory does not stand up. To use terms like instability and decomposition is not correct when chemical compounds (here amino acids) are present in aqueous solution under extreme conditions and are aiming at a metastable equilibrium. Shock considers that oxidized and metastable carbon and nitrogen compounds are of greater importance in hydrothermal systems than are reduced compounds. In the interior of the Earth, CO2 and N2 are in stable redox equilibrium with substances such as amino acids and carboxylic acids, while reduced compounds such as CH4 and NH3 are not. The explanation lies in the oxidation state of the lithosphere. Shock considers the two mineral systems FMQ and PPM discussed above as particularly important for the system seawater/basalt rock. The FMQ system acts as a buffer in the oceanic crust. At depths of around 1.3 km, the PPM system probably becomes active, i.e., N2 and CO2 are the dominant species in stable equilibrium conditions at temperatures above 548 K. When the temperature of hydrothermal solutions falls (below about 548 K), they probably pass through a stability field in which CH4 and NII3 predominate. If kinetic factors block the achievement of equilibrium, metastable compounds such as alkanes, carboxylic acids, alkyl benzenes and amino acids are formed between 423 and 293 K. 

The biological mineralizing systems for iron that have been studied the most extensively are the ferrihydrite (and, in prokaryotic ferritins, the amorphous... 

Solid solutions occur widely in inorganic and mineral systems (Table 4.2). The Hume-Rothery rules apply well in these cases, but it is important to add ... 

TABLE 4.2 Some Mineral Systems Showing Broad Solid Solution Ranges... 

KEYWORDS exploration, mineral systems, embedded researchers... 

Getting More Science into Exploration The Mineral Systems Perspective... 

The Five Questions geological description of a mineral system adopted by the AGCRC and the pmd CRC (Price Stoker 2002 Walshe et al. 2005) explicitly... 

Walshe, J.L., Cooke, D.R., Neumayr, P. 2005. Five questions for fun and profit A mineral systems perspective on metallogenic epochs, provinces and magmatic hydrothermal Cu and Au deposits. In Mao, J. Bierlein, F. P. (eds.), Mineral Deposit Research Meeting the Global Challenge, 1, 477-480. 

Surface spectroscopy offers the best opportunity to elucidate the structures of chemical species at the mineral-water interface (see Sposito, Chapter 11). The application of spectroscopic methods to probe the molecular environment of the interface is still a relatively new field. Chapters 16-19 present reviews and some recent advances in investigations of molecular structure at the mineral-water interface. A recent review of spectroscopic methods applied to soil and clay mineral systems is given in Stucki and Banwart (72). 

In view of the problems associated with the expanding 2 1 clays, the smectites and vermiculites, it seemed desirable to use a different clay mineral system, one in which the interactions of surface adsorbed water are more easily studied. An obvious candidate is the hydrated form of halloysite, but studies of this mineral have shown that halloysites also suffer from an equally intractable set of difficulties (JO.). These are principally the poor crystallinity, the necessity to maintain the clay in liquid water in order to prevent loss of the surface adsorbed (intercalated) water, and the highly variable morphology of the crystallites. It seemed to us preferable to start with a chemically pure, well-crystallized, and well-known clay mineral (kaolinite) and to increase the normally small surface area by inserting water molecules between the layers through chemical treatment. Thus, the water would be in contact with both surfaces of every clay layer in the crystallites resulting in an effective surface area for water adsorption of approximately 1000 tor g. The synthetic kaolinite hydrates that resulted from this work are nearly ideal materials for studies of water adsorbed on silicate surfaces. 

An understanding of much of aqueous geochemistry requires an accurate description of the water-mineral interface. Water molecules in contact with> or close to, the silicate surface are in a different environment than molecules in bulk water, and it is generally agreed that these adsorbed water molecules have different properties than bulk water. Because this interfacial contact is so important, the adsorbed water has been extensively studied. Specifically, two major questions have been examined 1) how do the properties of surface adsorbed water differ from bulk water, and 2) to what distance is water perturbed by the silicate surface These are difficult questions to answer because the interfacial region normally is a very small portion of the water-mineral system. To increase the proportion of surface to bulk, the expanding clay minerals, with their large specific surface areas, have proved to be useful experimental materials. 

Dissolution of minerals, such as may occur during dissimilatory Fe(lll) reduction, or precipitation of new biominerals during reductive or oxidative processing of Fe, represent important steps in which Fe isotope fractionation may occur. We briefly review several experiments that have investigated the isotopic effects during mineral dissolution, as well as calculated and measured isotopic fractionations among aqueous Fe species and in fluid-mineral systems. In some studies, the speciation of aqueous Fe is unknown, and we will simply denote such cases as Fe(lll)jq or Fe(ll)aq. 

Electrochemical phase diagrams have been used to investigate the collector water mineral system in which the experimental potential for flotation is compared with thermodynamic equilibriums for reactions in mineral/oxygen/collector system to... 

When we derived the phase rule, we assumed that all phases are at the same pressure. In mineral systems, fluid phases can be at a pressure different from the solid phases if the rock column above them is permeable to the fluid. Under these circumstances, the system has an additional degree of freedom and the equilibrium at any depth depends on both the fluid pressure Pp and the pressure on the solid Ps at that level. Each pressure is determined by p, the density of the phase, and h, the height of the column between the surface and the level being studied. 

Green E. J. (1970). Predictive thermodynamic models for mineral systems, I Quasi-chemical analysis of the halite-sylvite subsolidus. Amer. Mineral, 55 1692-1713. 

Newton R. C. (1987). Thermodynamic analysis of phase equilibria in simple mineral system. In Reviews in Mineralogy, vol. 17, P. H. Ribbe (series ed.), Mineralogical Society of America. 

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