Chlorites from cobalt pyrite horizons, Upper Martello Valley (Alto Adige, Northern Italy)

Chlorites from volcanic-sedimentary sequences, hosting the Borromeo Co-pyrite ores in the Upper Martello Valley (Italy), occur in phyllites of upper greenschist facies. Chlorites in the ore-mineralized phyllites are chamosites with a Fe/(Fe + Mg) ratio of 0.59-0.71; 2 samples from host phyllites are clinochlore with a Fe/(Fe+Mg) ratio of ∼0.40. The IIb polytype prevails in most chlorites. The presence of the metastable Ib polytype correlate with higher Fe-content. Possible diagenetic relicts exhibited by the chlorite-Ib polytypes suggest a premetamorphic origin.