Abstract Examination of igneous rocks and/or alteration products associated with geothermal systems, ore deposits, and volcamsm suggests that magmatic volatiles may be active agents of acid alteration, ore-metal transport, magma ascent, and volcanic eruption. Thus, an understanding of the magmatic volatile phase (MVP) is critical to pure and applied geology. However, because of its fugitive nature, the magmatic volatile phase is difficult to sample or study. Therefore, experimental and theoretical modeling plays an important role in our attempt to understand magmatic-hydrothermal processes such as those thought to be active in the generation of granite-related ore deposits. Geologic studies of past magmatic-hydrothermal activity include a combination of experimental and field-based methods of analysis. However, the relationship between static, microscale, equilibrium experiments (e.g., studies of element partitioning, phase equilibria, etc.), and the complex, time-integrated natural world is a tenuous one. Without models, the deductive consequences of experiments cannot be tested against field observations. Candela and Piccoli (1995) refined a model (now called MVPart) that can be used to predict the concentration of ore metals in successive aliquots of a (Rayleigh) fractionating aqueous phase during second boiling. Here the term “second boiling” indicates volatile exsolution from a melt due to crystallization of the melt at a constant pressure. This model is available in the form of a DOS/PC executable file (see Appendix 1). The model requires several different types of input, such as the estimation of intensive parameters (e.g., temperature, pressure, the initial ratio of chlorine to water in the melt)

The material for this field trip covers only one stop: the abandoned workings and associated dump of the Mineral Hill mine, which is located on state land surrounding the Liberty Reservoir, Carroll County, Maryland. The mine is located approximately 15 miles west-northwest of the city of Baltimore in the Eastern Piedmont province of the Central Appalachians. Mineral Hill contains notable clastic-sedimentary and exhalative components, as well as an association with mafic and ultramafic rocks. A road log from the Baltimore Convention Center to the primary mine dump is included.