COAL USAGE INDICATED AT CHAN CHAN, NORTHERN PERU

Ancient people from the north coast of Peru are known to have used coal for decoration and mirrors. And, their settlements were near the Alto Chicama coalfield, which is along the western flank of the cordillera where copper and gold were mined. However, this is the first study of the use of coal as a fuel in the archaeological record of northern Peru.

Ash horizons 10-30 cm thick are present at 4 burned sites at Chan Chan, the adobe-walled center of the Chimu empire (700-1400 A.D.), near Trujillo. The burned area at Ciudadela Tschudi, for example, is within a 25 x 75 m walled structure. Stratigraphy at each burned site includes: 1) oxidized floor, 2) plant charcoal, 3) fully combusted ash, and 4) scoria. Initially, the scoria was interpreted to be related to Chimu metallurgy; however, Lechtman and Moseley (1975) indicate a non-metallurgical origin of the scoria and that temperatures >1300°C melted the adobe to scoria.

Tylecote (1980) used SiO2, alkalies, and P2O5 to differentiate coal from wood ash from metallurgical furnaces. Therefore, oxide and trace element content of 14 Alto Chicama coal samples; one sample of algorrobo charcoal, a commonly used fuel in the region; and three samples of fully combusted C. Tschudi ash were determined.

Analyses (ash basis) were averaged: SiO2 of coal was 51%, charcoal 5.8%, Tschudi ash 52.9%; CaO of coal was 1.8%, charcoal 41%, Tschudi ash 4.2%; P2O5 of coal was 0.5%, charcoal 2.3%, Tschudi ash 0.6%; and Zr content of coal was 416 ppm, charcoal 8.5 ppm, Tschudi ash 200 ppm.

The coal and charcoal were ashed under laboratory conditions, however, the unknown Tschudi ash burned for 16-40 hours at temperatures >1300°C in a setting that has been exposed for over 1500 years. Comparison of the known ash compositions to the Tschudi ash suggests that coal was the likely fuel used at C. Tschudi. The data also provide a geochemical basis with which to examine the archaeological use of coal as a fuel for metallurgical or other uses in northern Peru. The purpose of the burned areas, however, is unknown.