Motagua Valley, Guatemalai

Regional Level Types
Motagua Valley	Valley
Guatemala	Country

After the discovery in 1952 of some river pebbles of jadeite on the north side of the Motagua River Valley, various jadeite outcrops have been identified along both sides of the Motagua River.

The Guatemala jadeite jade deposit occurs in the North America–Caribbean plate collision zone in southern North America. The Guatemala Suture zone, also called the Guatemala Central fault zone, separates the Maya Plate from the Caribbean Plate. High pressure and low temperature (HPLT) metamorphism exists on both the north and south sides of the Motagua fault zone. However, the compositions of orebodies on both sides show distinct characteristics. In the southern orebodies, there is a large amount of jadeitite, eclogite, glaucophane-eclogite, glaucophane schist, and other HPLT rock minerals, which act as crystalline and metasomatism-type jadeite jade deposits, formed during the late Jurassic period at 154 Ma. Meanwhile, the northern orebodies contain a large amount of jadeitite, albite, garnet-clinozoisite amphibolite, or clinozoisite eclogite, which is a crystalline jadeite deposit, formed during the late Cretaceous period at 98–95 Ma. HPLT-eclogite, garnet amphibolite, and jadeite in the central Motagwa River Valley rock masses can be found, while the commercial exploitation value of Guatemalan jadeite jade is mostly discovered in the Mesozoic tectonic serpentinite rock mass along the Motagwa fault zone.
The Guatemala jadeite jade is usually generated in serpentinite bodies in lenticular or veined shapes, and some exist as single structural inclusions. Jadeitite is commonly associated with albite. Albitites are formed at a lower pressure at the expense of jadeitite, and some albite-mica rocks could have formed at pressures comparable to jadeite and yet others formed at lower pressure conditions. In addition, the enrichment layers of jade also exist in the alluvium and riverbed terraces of the Motagua River, with gravels up to 1 m in diameter. The jadeite jade formation temperature is <400 °C, while the pressure is between 0.5 and 1.1 GPa.

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References