Integration Of Geochemical And Geophysical Data For The Montana Mineral-Environmental Study

Aeromagnetic, Landsat multispectral scanner (MSS), radiometric, and geochemical data covering the state<br>of Montana were digitally integrated to identify areas that may be negatively affected from surface-water<br>contamination by metals and acid run-off due to mining activity and natural processes. Two mineralenvironmental<br>models were constructed using a variety of statistical, image processing, and frequency<br>filtering techniques. The first model is a combination of relative magnetizations (calculated from the<br>aeromagnetic data) and two suites of geochemical elements. The geochemical distributions include one<br>based on a lanthanide association, which characterizes intermediate and alkalic intrusives; another<br>association characterizes sulfide mineralization. The second model is a mathematical combination of<br>relative magnetizations, iron oxide data (calculated from MSS data), and apparent potassium<br>concentrations (derived from airborne gamma-ray data). This model is useful for locating areas of possible<br>potassic alteration and leaching or weathering of exposed and shallowly buried iron-rich igneous rocks.<br>Magnetization domains associated with iron oxide and relatively high potassium concentrations can be<br>indicative of hydrothermal alteration environments that host metal sulfides. Despite sedimentary cover in<br>eastern Montana, both models reveal areas where magnetization sources are at depths shallow enough to<br>permit leaching, possible alteration, and the presence of heavy metals at the surface. Follow-up studies<br>and integration of these results with geologic and hydrologic information will provide a clearer<br>understanding of the possible environmental effects within the identified areas.