Carlin-type deposits contain gold in association with main-stage quartz-pyrite-kaolinite mineralization and late-stage orpiment-realgar-calcite-barite mineralization. Fluid characteristics for main-stage mineralization are well documented by fluid inclusion and stable isotope studies on quartz. In contrast, fluid characteristics for late-stage mineralization are not well constrained because of large ranges in fluid inclusion microthermo-metric data. These ranges could represent real variations in fluids or be a result of the reequilibration of fluid inclusions.

Microthermometric analyses were conducted on fluid inclusions in samples of barite, calcite, realgar, and or-piment from the Betze and Carlin mines, Nevada. Petrographic studies of individual crystals and cleaved sections reveal that fluid inclusions in realgar and barite have negative crystal shapes, in contrast to elongate and rounded inclusions in orpiment and calcite. Point-count data document that one-phase liquid inclusions (type 1) are the dominant type in barite and realgar, relative to two-phase, vapor-poor inclusions (type 2) in calcite and orpiment. Type 2 inclusions in realgar and barite commonly reequilibrate (e.g., stretch) during analysis and exhibit ranges in homogenization temperatures (Th) of 100º to 250ºC and 110º to 300ºC, respectively. In contrast, type 2 inclusions in orpiment and calcite have Th of 108º to 182ºC, which could be repeated to within 1ºC. Based on these results, fluid inclusions in barite and realgar are most susceptible to reequilibration, with Th of ~100º to 110ºC most representative. Fluid salinities for orpiment and calcite are 1.7 to 5.4 wt percent NaCl equiv, relative to 1.1 to 2.9 wt percent NaCl equiv for barite and realgar. The lower Th and salinity for fluid inclusions in barite and realgar suggest fluid cooling and dilution, following the deposition of paragenetically earlier orpiment and calcite.

In the broadest sense, the science of geophysics is the application of physics to investigations of the Earth,Moon and planets.The subject is thus related to astronomy. Normally, however, the definition of ‘geophysics’ is used in a more restricted way, being applied solely to theEarth. Even then, the termincludes such subjects asmeteorology and ionospheric physics, and other aspects of atmospheric sciences.

Why is economic geology essential to our progress? It has been said that agriculture is the most basic of man's activities, but in this time of overpopulation and indeed in the preceding centuries it would have been impossible to feed the world's teeming millions without recourse to mining and the use of minerals and metals for ploughing, fertilization, harvesting, food preparation and so on. Indeed, of these two basic industries— agriculture and mining—mining is the older. It started some 500000 years ago when man commenced exploring for tool-making materials — flint, obsidian, quartzite were chipped and ground to sharp cutting edges. Early man found that some localities were richer than others and began to search for these richer deposits, to mine them, establish axe factories and to trade in the finished products. He soon developed an appreciation of their geological occurrence. For example, by 3 000 B.C. large underground flint mines were in operation at Grime's Graves in Norfolk, U.K. and it is clear that the miners had noted that particular horizons in the chalk host rock carried the best and most numerous flints.

The onset and rapid spread of canals across the face of Britain in the late eighteenth century, closely followed by the building of the railway network in the early nineteenth century, were largely responsible for making the study of the strata, or stratigraphy, a subject of both practical and economic value. It is not surprising, therefore, that it was a land surveyor and canal engineer, William Smith (1769–1839), working initially in southern and eastern England, who first worked out that rock strata were not randomly disposed around the country but arranged in a definite order.