THE PYRITE ENIGMA AT WEBSTER PASS, COLORADO

Geologic and geochemical studies, together with core drilling, confirm the presence of a large igneous-hydrothermal system in the vicinity of the Continental Divide at Webster Pass, Colorado. Clues to the importance of the system exist as extensive ferricrete deposits in Handcart Gulch and the upper Snake River valley, on either side of the Divide. These deposits probably date to around 10,000 years b.p., but continue to form as groundwater percolates through the mineralized rocks. It is estimated that as much as 10 million tons of pyrite were oxidized to produce the iron in the ferricretes. A large quantity of pyrite must be present in the area, but core drilling during the summer of 2001 did not identify such deposits.

Pyrite is disseminated in the core and occurs in veins and veinlets throughout the 2000 foot depth of core, and it has been oxidized and leached from the surface to a depth of 200 feet. Sulfur contents in the core have been converted to "pyrite equivalents" that average 5.89% from 200 to 2000 feet (range 2.56 - 9.20%) -- in the leached zone the average is 0.22%. Iron averages 2.41% in the leached zone and 4.41% below 200 feet. If 2% iron was leached from a mass of rock 3700 feet square and 200 feet deep, it could produce the ferricrete deposits in Handcart Gulch and the Snake River valley. There is not enough rock, however, in the vicinity of the Continental Divide to produce that much iron by this process alone.

It is concluded, either that there exist major deeply circulating groundwater cells that are destroying pyrite in the mineralized country rock, cells that were not penetrated by the drilling, or that groundwater is attacking one or more large masses of pyrite that were not intersected by the drilling. Both scenarios may exist, and we hope to solve the enigma as we continue to evaluate the igneous-hydrothermal system.