• University of Arizona, PhD, Economic Geology, 2000
• The Colorado College, BA, Geology, 1988

My current research and interests focus on the interplay between magmatism and external- and magmatic-hydrothermal fluids with emphasis on mass-balance considerations, both chemical and energy, within various geologic environments. Current work is directed at determining the extents and amounts of chemical exchange within the earth's crust, associated with hydrothermal systems. This is best accomplished by stepping back from the typical mineral deposit study, which generally focuses on the ore body/or deposit to work on well exposed systems in the western US and elsewhere where the whole hydrothermal system is exposed by topographic relief and mid-Tertiary extension.

This system-scale approach, utilizing constraints provided through field work, provides a fundamental background to assess controls on alteration and mineralization which include deposit-, district-, and system-scale zoning of alteration mineralogy, metals, and other components. A further interest of mine is the application of these regional/district-scale patterns in alteration and mineralization combined with other aspects of the associated geologic environments to the successful targeting of mineralized versus barren hydrothermal systems and defining other potential, yet undiscovered, regions of economic interest. The above pursuits partially stem from my childhood and later interest in mineral collecting and prospecting the "hills" in Colorado.

Current projects are: 1) mineral deposit modeling (particularly IOCG and related deposit types), 2) REE abundance, mineralogy, and possible REE production as a by-product in existing operations in conjunction with others at the USGS, 3) magmatic and basin-related mineral deposits of Mexico, 4) origin and mass-balance relationships in igneous-related, Fe-oxide-rich hydrothermal systems (global approach with field work concentrated in the western US, Latin America, and the Andes), 5) arc-related magmatism and mineralization (focused on the relationship between magmatic and fluid fluxes and resulting mineralization; eg. Life Cycle Porphyry Cu project USGS, Jurassic and Laramide magmatism and mineralization in western US and Mexico USGS, and other work in the Pacific Rim).

Selected publications:

Johnson, D.A. and Barton, M.D., Scales of Mass-transfer in Igneous-related Hydrothermal Systems. Submitted to Geology.

Johnson, D.A., and Barton, M.D., 2000, Time-space development of an external-brine-dominated, igneous-driven hydrothermal system: Humboldt mafic complex, western Nevada, in Thompson, T.B., ed., Society of Economic Geologists Guidebook, v. 32, p. 127-143

Barton, M.D., and Johnson, D.A., 1996, An evaporitic-source model for igneous-related Fe-oxide(-REE-Cu-Au-U) mineralization: Geology, v. 24, p. 259-262.