`Olmec Blue' and Formative Jade Sources: New Discoveries in Guatemala. (News & Notes)
Seitz, R., Harlow, G. E., Sisson, V. B., Taube, K. E., Antiquity
The discovery of jadeite rocks (jadeitites) in Guatemala in 1954 led to the recognition of the Motagua River Valley as a Maya jade source. While abundant and accessible, what is produced today for the tourist trade, mainly between Estancia de La Virgen and Teculutan (Harlow 1994), is mostly opaque and dull-coloured. It scarcely resembles the translucent and colorful `Olmec' blue-green jade found in Formative horizons in Mexico. This qualitative disparity has led to a search for Olmec jade sources elsewhere in Mesoamerica.
The Sierra de las Minas and the highlands south of the Motagua River have recently yielded some remarkably translucent, fine-grained jadeitites that closely resemble those worked in Formative times. Geological reconnaissance has expanded the known jade-bearing area at least six-fold.
The first deposits examined are at an elevation of ~1750 m, 13 km north of the limits of detailed geological mapping, on Cerro Bandera Perdida (see FIGURE 1). An ancient, and possibly trade-route related, dry-stone trackway parallels the 1700-m contour for at least 4 km and leads to the mine area at Los Cedros.
[FIGURE 1 OMITTED]
Alluvial jade was also found 8 km further northwest at Finca Santa Clara on the Rio Blanco near the intersection of Alta Verapaz and El Progreso. Another jade deposit was visited west of the town of Rio Hondo. These sources extend the described jade-bearing zone 10 km north and 18 km east.
Some 10 km south of the Motagua, alluvial jadeitite found in the Rio El Tambor is significant for its origin across a major fault, long considered the southern geological limit for jadeitite occurrence. In 1998 the floodwaters of Hurricane Mitch exposed much new jade which has been traced upriver into the department of Jalapa, at elevations from 600 to 1400 m. In 2001 more jadeitites and related rocks were found in the quebradas of the Rio Jalapa and at an outcrop near La Ceiba, all lying in east-west running bands of serpentinite. This southern band of the Guatemalan jade zone extends 18 km south of the northern zone and has the same east-west extent.
Matching jade artefacts with jadeitite sources has been a problematic endeavour. Chemical composition has been used for sourcing many lithic materials, but jadeitites are inherently inhomogeneous which precludes matching by whole-rock chemical analysis (see Lange 1993). Multivariate trace-element systematics shows promise but a statistically useful array of Olmec artefacts or potential source materials have yet to be measured.
Minor mineral constituents are better than whole-rock composition for sourcing, because they do not get lost in the noise of whole-rock analysis. …