THE FIRST REPORT OF COBALT PENTLANDITE FROM A MID-ATLANTIC RIDGE HYDROTHERMAL DEPOSIT

NADEZHDA N. MOZGOVA
IGEM RAS, Staromonetny 35, Moscow, 109017, Russia

SERGEY G. KRASNOV
VNIIOkeangeologiya, Angliysky Prospect 1, St. Petersburg, 109121, Russia

BORIS N. BATUYEV
PMGRE, Sevmorgeologiya Association, Pobedy, 24, Lomonosov, 189510, Russia

YURY S. BORODAEV
Department of Geology, Moscow State University, Moscow, 119899, Russia

ANDREY V. EFIMOV
IGEM RAS, Staromonetny 35, Moscow, 109017, Russia

VLADIMIR F. MARKOV
PMGRE, Sevmorgeologiya Association, Pobedy, 24, Lomonosov, 189510, Russia

TAMARA V. STEPANOVA
VNIIOkeangeologiya, Angliysky Prospect 1, St. Petersburg, 109121, Russia

Abstract

We report the first occurrence of cobalt pentlandite in oceanic deposits at 14 45'N, Mid-Atlantic Ridge (MAR). The mineral occurs as small (less than 20 痠), round to irregular grains and aggregates associated with chalcopyrite, bornite, isocubanite, chalcocite, digenite, with minor pyrite and marcasite, and with rare covellite and Au-bearing zincian copper. On the basis of twenty-two analyses, the compositional range (in wt.%) is: Co 42.9-53.9, Ni 7.2-12.4, Fe 3.4-5.5, Cu 0.7- 9.4 and S 31.6-32.9. Seventeen of the twenty-two compositions plot between Me9S8 and Me13S15. The narrow range of sulfur contents corresponds closely with those of synthetic pentlandite (44.2-47.9 at.%). The cobalt content of a pentlandite-group mineral depends on the mineral assemblage with which it is associated.