Intensely-altered andesite, Mocho Toms River, Back Rio Grande Study Area.
The alteration, which is argillic and pyritic in nature, is widespread and
normally barren, but with at least one local occurrence of gold in a highly sheared and
silicified zone. Marks to the right of the cavity are numbers sprayed onto
rock to mark location of stream-sediment sample, six years previously.
Abstract & Diagrams