An interesting article on the mineralogy and microbiology near hot springs and geysers:

Microbial Composition of Near-Boiling Silica-Depositing Thermal Springs throughout Yellowstone National Park.
Applied and Environmental Microbiology, October 2002, p. 5123-5135, Vol. 68, No. 10
http://aem.asm.org/cgi/content/full/68/10/5123

In the full-size version of Fig.1, there appear to be nodules that may be analogous to the nodules seen in Pot-of-Gold. Look near the hammer in the image.

Bob Clark

FIG. 1. Edge of the source pool of Queen's Laundry. Spicular geyserite is shown in the splash zone at the air-water interface. Stratiform geyserite is formed beneath the water in the subaqueous environment.