Latin American Antiquity: Volume 5 -

Ecuadorian Obsidian Sources Used for Artifact Production and Methods for Provenience Assignments
Frank Asaro, Ernesto Salazar, Helen V. Michel, Richard L. Burger, Fred H. Stross
Published online by Cambridge University Press:

20 January 2017, pp. 257-277
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A study by neutron activation analysis and X-ray fluorescence measurements of 116 Ecuadorian obsidian artifacts as well as primary and secondary source samples has shown that the material originated from two Andean sources in north-central Ecuador, a flow in the valley of Mullumica, and deposits found on Yanaurco Chico and the nearby Quiscatola crest. The Yanaurco-Quiscatola deposit complex, homogeneous within our ability to measure, is represented by 18 percent of the artifacts. The Mullumica source has variable, apparently linearly related element abundances that may have resulted from the incomplete mixing of two magmas within a magma chamber. Seventy-eight percent of the samples studied are deduced to have originated from that source. Five artifacts from La Chimba cannot be assigned an origin, but four of them have the same provenience. To test the validity of the mixed-magma theory, we present equations to calculate the abundance of any measured element from that of iron. On the average, agreement within about 3 percent is obtained for artifacts.