Abstract: Geologic Controls Over Hot Water Migration at Selected Hot Springs, Southwestern Montana

Robert A. Chadwick, Michael J. Galloway, John D. Goering

Development of models for thermal water circulation in areas away from active volcanism is needed. In southwestern Montana, 27 hot springs (discharges above 35°C) are under geologic investigation for geothermal potential. Many springs are on or near faults or major fractured zones. Preliminary investigation suggests several models for thermal-water circulation; permeable joint-shear zone intersection, graben-block, and synclinal controls are exemplified by Potosi, Wolf Creek, and New Biltmore hot springs, respectively.

Potosi hot springs waters issue as numerous seeps from N85°W permeable joints where intersected by a N5°E shattered zone in quartz monzonite of the Tobacco Root batholith. Water evidently percolates to depth along the permeable joints and rises where they intersect the relatively impermeable shattered zone. This model, with modifications, may apply to Boulder and other hot springs in fractured crystalline rock.

Wolf Creek hot springs issues from a N5°W recently active fault which displaces bench gravels in the upper Madison Valley and may form the west edge of a deep sediment-filled graben in Precambrian metamorphic rocks. The Madison Range frontal fault bounds the graben on the east. Water may circulate to depth beneath the graben or within the valley-fill sediments and may rise along the bounding fault. Chico and Bozeman hot springs also may illustrate graben or hinged fault-block control.

New Biltmore, Renova, and LaDuke hot springs waters may have risen along Paleozoic carbonate aquifers from depths of synclines located beneath the Big Hole, Jefferson, and upper Yellowstone Valleys respectively.

AAPG Search and Discovery Article #90971©1976 AAPG-SEPM Rocky Mountain Sections 25th Annual Meeting, Billings, Montana