The Cotter Copper project is located in Lewis and Clark County, Montana, approximately 7.5 road miles north of Lincoln.

The project targets copper-bearing shear zones and fissure veins within thin-bedded dolomitic limestone of the Helena Formation. The principal shear zone strikes N. 75° W. and dips 25° SW. Including the adjacent sheared wallrock, total mineralized widths average 16.1 feet.
Metals contained include copper and silver, with minor gold, lead, and zinc; the gangue is predominantly calcite and quartz. Identifiable ore minerals are bornite, chalcocite, azurite, malachite, chalcopyrite, galena, and sphalerite.
The geologists who examined the project concluded “additional copper-silver resources probably occur farther down the projected dip of the shear zone southwest of the inferred block”.
A faulted extension near the Decker adit exposes a copper-bearing zone up to 7 feet thick with higher grades. A small surface exposure of quartz monzonite and an associated positive magnetic anomaly suggest a buried intrusive stock at depth, which should expand the resource potential significantly.

Initially developed through early underground workings, the Cotter Basin property focused on the principal calcite-bearing shear zone. Early development included the lower Decker adit, which intersected a 7-foot-thick copper zone at a major fault intersection.
In 1973 and 1974, K & W Mines and Gemco International initiated an extensive exploration and development program, shipping minor amounts of copper-silver ore. The companies drove a new upper adit and developed an open pit that exposed the shear zone for 600 feet eastward. Extensive sampling across the zone and adjacent wallrock confirmed a 16.1-foot average mineralized thickness.
This exploration delineated an identified resource of 1 million tons (490,000 tons indicated, 530,000 tons inferred) extending 570 feet downdip. Surface exploration, including trenches and roadcuts, tracked the zone for 1,100 feet along strike. These efforts significantly advanced the understanding of the property's mineral potential and set the stage for future development.

The Cotter Copper project is available for sale for $85,000 on an installment sale of $5000 paid quarterly.