The intriguing feature about this horizon is the epithermal vein system contains geyserite
(opaline silica), lattice-type veining, and fluorite in the historical Rubicon trenches.
The drusy and radial valentinite with yellow color and geyserite
usually coexist with stibnite and cinnabar (Figures 4(t)), the green massive malachite is intergrown with chalcopyrite, the brown-black massive ferrohydrite occurs in the surface overgrowing Mn-Fe carbonate and pyrite, and the white-grey sardinianite usually shows massive and nodular textures and coexist with galena.
They interpreted the deposits were formed on land, not in the ocean, by identifying the presence of geyserite
- a mineral deposit formed from near boiling temperature silica-rich fluids - that is only found in a terrestrial hot spring environment.