Conceptual models that describe the essential characteristics of groups of similar deposits have a  long and useful role in geology. The first models were undoubtedly empirical attempts to extend previous experiences into future success. An example might be the seeking of additional gold nuggets in a stream in which one nugget had already been found, and the extension of that model to include other streams as well. Emphasis within the U.S. Geological Survey on the synthesis of mineral deposit models (as contrasted with a long line of descriptive and genetic studies of specific ore deposits) began with the collation by R. L. Erickson (1982) of 48 models. The 85 descriptive deposit models and 60 grade-tonnage models presented here are the culmination of a process that began in 1983 as part of the USGS-INGEOMINAS Cooperative Mineral Resource Assessment of Colombia (Hodges and others, 1984). Effective cooperation on this project required that U.S. and Colombian geologists agree on a classification of mineral deposits, and effective resource assessment of such a broad region required that grade-tonnage models be created for a large

number of mineral deposit types. A concise one-page format for descriptive models was drawn up by Dennis CO X, Donald Singer, and Byron Berger, and Singer devised a graphical way of presenting grade and tonnage data. Sixty-five descriptive models (Cox, 1983a and b) and 37 grade-tonnage models (Singer and Mosier, 1983a and b) were applied to the Colombian project. Because interest in these models ranged far beyond the Colombian activity, it was decided to enlarge the number of models and to include other aspects of mineral deposit modeling. Our colleagues in

the Geological Survey of Canada have preceded this effort by publishing a superb compilation of models of deposits important in Canada (Eckstrand, 1984). Not urprisingly, our models converge quite well, and in several cases we have drawn freely from the Canadian publication.

Mineral deposits are usually classified and described by the metals or the substances which they contain; for instance, deposits of copper are described together, with little or no effort to separate them into genetic groups. Where a genetic treatment has been attempted it appears to me to have failed in not giving due weight to the physical conditions attending the genesis. Furthermore, it is the custom to divide the mineral deposits into two groups—the metallic and the non-metallic—a line of division which can hardly be defended except on the ground of long-established habit.

This five day field trip is a general overview of the geology and tectonic history of central Colorado and of the geology of seven famous mining districts. Some of these mining districts had their most productive years in the latter decades of the 19th century, whereas others reached their peak production more recently. At present mining activity in some of them has ceased. In others it is at low levels compared to earlier years. The regional geology and the road log are compiled from numerous sources. The principal ones are field trip guides by Tweto (1978), Reed and others (1988), Lipman (in press) and unpublished field guides of the Colorado Scientific Society and the Society of Economic Geologists. Figure 1 shows the principal geographic features along the route of the trip. <...>

Historically documented mining in Finland started in the 1530s when the area formed part of Sweden. The post of commissioner of mines was founded in 1638. The Swedish government activated mineral exploration in Finland in the seventeenth century and, during the Age of Utility, in the eighteenth century. Numerous small iron, copper, and lead occurrences were found, as well as the larger Orijдrvi copper deposit. During 1809-1917 when Finland was a Grand Duchy within the Russian Empire, exploration was reorganized and strengthened. New, generally small iron deposits were discovered to supply iron works.