HYDROTHERMAL GARNIERITE - AN OCCURRENCE A T BOU-AZZER, MOROCCO

In the mining district of Bou Azzer, garnierites containing variable p roportions of Ni-kerolite and Ni-lizardite occur within a serpentinize d ultramafic body of Precambrian-II age. These garnierites have high N i-contents partially substituted by Co. Their oxygen isotope compositi on (delta(18)O = +16.5 (p)arts per thousand) and the random distributi on of Ni and Mg cations in the octahedral sheet of kerolites indicate a formation temperature higher than 25 degrees C. These data and the o ccurrence of garnierites within veins, located along faults and associ ated with Ni-arsenate ores, show that these garnierites were formed du ring an early low-temperature hydrothermal event. This is the first re cord of such a garnierite occurrence since all the other ones, recent or ancient, are considered as lateritic weathering products of ultrama fic rocks.