Solubility of quartz in crustal fluids: experiments and general equations for salt solutions and H2O–CO2 mixtures at 400–800°C and 0.1–0.9 GPa

The solubility of quartz has been measured in a wide range of salt solutions at 800°C and 0.5 GPa, and in NaCl, CaCl₂ and CsCl solutions and H₂O–CO₂ fluids at six additional P–T conditions ranging from 400°C at 0.1 GPa to 800°C at 0.9 GPa. The experiments cover a wide range of compositions along each binary. At P–T conditions where the density of pure water is low (0.43 g cm^?3), addition of most salts produces an enhancement of quartz solubility at low to moderate salt concentrations (salt‐in effect), although quartz solubility falls with further decrease in X_H2O. At higher fluid densities (0.7 g cm^?3 and greater), the salt‐in effect is generally absent, although this depends on both the cation present and the actual P–T conditions. The salt‐in effect is most readily produced by chloride salts of large monovalent cations, while CaCl₂ only produced a salt‐in effect at the most extreme conditions of high‐T and low‐P investigated (800°C at 0.2 GPa). Under most crustal conditions, the addition of common salts to aqueous fluids results in a lowering of quartz solubility relative to that in pure water (salt‐out effect). Comparing quartz solubility in different fluids by calculating X_H2O on the basis that all salts are fully associated under all conditions yields higher quartz solubility in solutions of monovalent salts than in solutions of divalent salts, absolute values are also influenced by cation radius. Quartz solubility measurements have been fitted to a Setchenow‐type equation, modified to take account of the separate effects of both the lowering of X_H2O and the specific effects of different salts, which are treated as arising through distinct patterns of non‐ideal behaviour, rather than the explicit formation of additional silica complexes with salt components. Quartz solubility in H₂O–CO₂ fluids can be treated as ideal, if the solvation number of aqueous silica is taken as 3.5. For this system the solubility (molality) of quartz in the binary fluid, S is related to its solubility in pure water at the same P–T conditions, S^o, by: Quartz solubility in binary salt systems (H₂O–RCl_n) can be fitted to the relationship: where salt concentration mRCl_n is expressed as molality and the exponent b has a value of 1 except under conditions where salting‐in is observed at low salt concentrations, in which case it is <1. Under most crustal conditions, the solubility of quartz in NaCl solutions is given to a good approximation by: We propose that quartz solubility in multicomponent fluids can be estimated from an extended expression, calculating X_H2O based on the total fluid composition (including dissolved gasses), and adding terms for each major salt present. Our experimental results on H₂O–NaCl–CO₂ fluids are satisfactorily predicted on this basis. An important implication of the results presented here is that there are circumstances where the migration of a fluid from one quartz‐bearing host into another, if it is accompanied by re‐equilibration through cation exchange, may lead to dissolution or precipitation of quartz even at constant P and T, with concomitant modification of the permeability structure of the deep crust.     

The role of the state in resource use decision-making: the case of the Moomba-Sydney gas pipeline

The development of a 1300 km natural gas pipeline in Australia in late 1976 is used to unravel some of the more important determinants of state action. The analysis highlights the contradictory position of the state in democratic capitalist societies. The separate actions taken by the state in support of the developer, the environmentalists, or to put into effect political ideals reflect a complex set of determinants of the state's behaviour. It is this fact which makes it difficult always to predict the state's response to individual incidents of conflict over resource use. The analysis also illustrates how time and place influenced the action and reaction of the participants in the debate over the location of the pipeline.     

LONGBRIDGE DEVERILL COW DOWN, WILTSHIRE, HOUSE 3: A MAJOR ROUND HOUSE OF THE EARLY IRON AGE

Summary. The settlement complex on Longbridge Deverill Cow Down in west Wiltshire comprises two major farmsteads, with their associated trackways and field systems, which were in use from the 8th to the 2nd century BC. The excavations, between 1956 and 1960, could only sample Enclosures II and III, whose ditches turned out to be relatively late features belonging to the larger and longer lived of the two farms. However, by good fortune, the interior areas excavated contained the very well-preserved post-holes of no less than four successive great round houses, the largest up to 60 feet (18.30 m.) in diameter, with masses of surviving structural evidence, pottery and other finds. This article describes and discusses the latest and best preserved of the great houses, House 3 of the end of the 6th century, and it attempts to throw new light not just on the construction and internal lay-out of these huge structures, but also the manner in which they may have been used, domestically and ceremonially, by their inhabitants at the end of the Late Bronze and beginning of the Iron Age in Wessex.     

FOURTH MILLENNIUM BC SILVER FROM TELL ESH-SHUNA, JORDAN: ARCHAEOMETALLURGICAL INVESTIGATION AND SOME THOUGHTS ON CERAMIC SKEUOMORPHS

Summary. Analytical and contextual details are given for a piece of silver sheet recovered by dry-sieving from a fourth millennium B.C. deposit at Tell esh-Shuna in the north Jordan Valley. Analysis proved that the fragment was composed of a silver-gold-copper alloy. The possible origin of such aurian silver artefacts is considered in the light of current geological evidence, and alternative mechanisms for their appearance reviewed, taking into consideration recent data pertaining to the use of 'non-utilitarian' metals in the southern Levant during the fifth and fourth millennia B.C. Reasons are given for believing that silver artefacts are under-represented in the archaeological record, and the imitation of silver vessels is suggested as a possible explanation for the appearance in Palestine of the distinctive Grey Burnished ceramics at the beginning of the Early Bronze Age.