Discovery of Jadeite in Guatemala

摘要

In 2001 local prospectors discovered a new occurrence of green and greenish blue jadeite south of the Motagua River Valley (fig. 1) about 80 km northeast of Guatemala City. All of the jade deposits known in Guatemala are found within the Motagua fault zone, an east-trending, seismically active, structural boundary between the North American and Caribbean tectonic plates (fig. 2). Along and adjacent to this zone, numerous sheared serpentinite bodies are present in an area 10 to 40 km wide and 100 km long (fig. 3). Jadeite occurs within the serpentinites as veins, lenses, and pods a few meters wide and up to tens, or even hundreds, of meters long. These primary jadeite bodies are the sources of the large alluvial jadeite boulders (fig. 4) found throughout the region. The jadeite is thought to have crystallized directly from a hydrous fluid at pressures of 5-12 kbar and temperatures of 200°-450°C (Harlow, 1994; Johnson and Harlow, 1999). Jadeite forms as vein-like pods within larger bodies of blueschist and eclogite. Protoliths for the blueschist and eclogite are graywacke and basalt/gabbro respectively. Both of these rocks were once part of the oceanic crust.