MCI Project Summaries 2008 - Smithsonian Institution

Smithsonian Tropical Research Institute
MCI 6021 Rock samples from La Pintada Site, Panama
MCI Staff: Harriet (Rae) F. Beaubien, Lynn B. Brostoff
Four rock samples, analyzed at MCI, were collected from the site of La Pintada, near
Penonomé, Panamá, which shows evidence of having been a pre-Columbian mining site of some
kind. Among its features are a large gallery carved into the vertical face of a rocky outcrop,
identified as basalt and tuff by archaeological project members, and a flat platform area in front
of the entrance. Tool marks are evident on various surfaces, and various tools that could be used
for mining, including hammer stones, have been found there. Pronounced green coloration in the
roof area of the chamber has led the researchers to hypothesize that copper was being mined,
with some processing taking place on the cleared spaces nearby. If this interpretation is correct, it
would be a significant contribution to research that has recently focused on the origins and
development of metalworking in pre-Columbian Panamá.
Because mineral products exploited for metal production are often highly colored, these
components of the rock samples were of particular interest, especially the green covered
fragments flaked from the chamber roof. Unfortunately, they proved not to be copper-bearing as
hoped. The green material was identified as green algae, both by the morphological
characteristics of the granules, as seen under a microscope, and by the cellular structure apparent
at high-magnification. This biological identification was further supported by the absence of a
crystalline pattern with X-ray diffraction analysis, the absence of a copper signature by portable
X-ray fluorescence spectroscopy, as well as indications of a proteinaceous material by Fourier
transform infrared spectroscopy.
That said, there is clearly some ancient mining activity at the site and further
investigation is warranted to determine the material for which mining tools, such as hammer
stones found at the site, were being used.
The La Pintada site, showing gallery entrance and possible working surface in front and a view of the gallery
ceiling’s green coloration
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