Full article available in PDF version.

Full article available in PDF version.

Full article available in PDF version.

Full article available in PDF version.

Full article available in PDF version.

Full article available in PDF version.

Full article available in PDF version.

Full article available in PDF version.

Full article available in PDF version.

Full article available in PDF version.

Full article available in PDF version.

Full article available in PDF version.

Full article available in PDF version.

Full article available in PDF version.

Abstract In Chapter 1, R. W. Henley summarized our understanding of the chemical and hydrodynamic structure and the transport properties of active hydrothermal systems, with particular emphasis on terrestrial magmatic-hydrothermal systems. Such an overview is especially valuable because active geothermal systems are modern “archetypes” of the ancient systems which concentrated metals in their upper portions to form epithermal ore deposits. More than any other factor, the study of active systems has provided the framework on which the observations on epithermal deposits have been arranged in the relatively recent development of comprehensive models of epithermal ore formation. The Principle of Uniformitarianism has served us well in this instance. In this chapter, we focus on observations on epithermal ore deposits in continental silicic to andesitic volcanic terranes. Volcanic-hosted deposits offer the most direct comparison with many of the well-studied modern geothermal systems. We first compare the attributes from a number of epithermal ore deposits and show how they may be used to identify two important, and distinct volcanic-related hydrothermal environments. We then examine the best-studied deposit of each type: Creede and Summitville, both of which are located in the San Juan Mountains in southwest Colorado. In so doing, we are able to examine epithermal deposits for evidences of processes that are now occurring in geothermal systems. Finally, we use the observational base and interpretations derived from each deposit type to develop generalized “geothermal” models of mineralization. The models have been taken, in large part, from the excellent synthesis by Henley and Ellis

X-ray crystallographic data are of particular importance to the mineralogist. Beyond the considerations of structural chemistry, they provide one of the most accurate methods for phase and/or compositional determination and for obtaining the molar volumes and densities of minerals (Table 5-2). Selected data for approximately 300 minerals are tabulated in Table 5-1. These are taken from the recent literature or from unpublished sources. With minor exceptions, we have restricted ourselves to data for chemically and physically well-defined phases for which the unit cell parameters are known with an accuracy of the order of .2 per cent or better. The data are presented by mineral groups following Dana's System. Within a group, however, the order may be alphabetical, structural, or for the sulfides, approximately by increasing sulfur-metal ratio. Temperatures at which the measurements were made are given in the second column from the right. The letter r indicates the data were obtained at an unspecified room temperature and may be taken as 25° ± 5° C. The number of gram formula weights per unit cell is given in the column labeled Z. Compounds denoted by an asterisk indicate the measurements were made on natural specimens which may have deviated slightly from the listed formula. Substances of rhombohedral symmetry are denoted by the symbol hex-R to distinguish them from materials of true hexagonal symmetry. The space group is given along with its number in the 1952 International Tables for X-ray Crystallography (Henry and Lonsdale, 1952). All cell dimensions are given in Angstrom