Cover. Part of a color shaded-relief aeromagnetic map of north-central Minnesota. Color changes represent broad changes in magnetic field strength. The warm colors (red, orange, and yellow) represent areas of magnetic field highs; the cool colors (green, blue, and purple) represent magnetic field lows.[From Horton, R.J., Day, W.C., and Bracken, R.E., Aeromagnetic survey of north-central Minnesota, chap. T of Scott, R.W., Jr., Detra, P.S., and Berger, B.R., eds., Advances Related Geographic landscapes change only slowly, but political and economic landscapes can change abruptly and unexpectedly The geological sciences are contributors to changes in these landscapes, but they also serve as a source of information on which an informed polity may base decisions on behalf of a society. The U.S. Geological Survey (USGS) is dedicated to providing information for the public good in all aspects of the geological sciences, including mineral resources.Mineral resources are a part of the geosciences that impact all aspects of a society from national economic security to national defense to land-use decisions to health and welfare these impacts affect not just humans but all other animals as well as all flora. Minerals are an essential part of the well-being of both a society and the Earth. They serve as the basis for infrastructure, technological innovation and development, economic policies, national defense, and national economic security; they are also essential to informed decisions on environmental risk and environmental tradeoffs in any decision-making process.The USGS provides mineral resource information, knowledge, and technical analyses from highly trained scientists with broad-ranging technical skills to Federal, State, and local governments; industries; schools and universities; and the general public of the United States. It also engages in cooperative studies with other countries and their institutions to provide training, exchange information and understanding, and attack important scientific problems. This Bulletin, Advances in research on mineral resources, 1994, reports progress on some of the current domestic and international research activities of the Office of Mineral Resources, Geologic Division of the USGS.
ESTABLISHING A GEOLOGIC FRAMEWORK FOR MINERAL DEPOSITSSince the emergence of economic geology as a recognized subdiscipline within the earth-science research community within the last century, there has been heated debate about the role of igneous processes in the genesis of deposits that are spatially associated with intrusions and volcanic rocks. Do the metals in most deposits come from magmas, or is the magma merely a partial contributor or simply a heat engine? Even the use of sophisticated new technologies in the post-World War II era has not caused the issue to wither. Although there are stable-isotope methodologies to fingerprint probable water sources and radiogenic methodologies that reveal the source of some metals (and most deposits and rocks can now be dated with high precision), the...