Northeastern rim, Markov Deep, Sierra Leone fracture zone, Mid-Atlantic Ridge complex, Atlantic Ocean

The walls of the basin are composed of serpentinized peridotites and gabbroids, locally transformed into mylonites and cataclasites, and affected by metasomatic alteration. Intensely altered basalts and dolerites are exposed at the valley bottom, on its flanks, and in the upper part of the slopes; fresh basalts with glassy crusts occur at the valley bottom. The main ore-bearing zone is situated at the foot of the eastern wall, where it is hosted in cataclastic hornblende gabbro and gabbronorite of the Fe–Ti-oxide series. Ores in metasomatically altered rocks consist of quartz–sulfide and prehnite–sulfide veinlets, disseminated sulfide, and veined copper sulfide ore. At the foot of the eastern wall, immediately below the ore-bearing zone, loose sediments contain grains of native Cu, Pb, Zn, and Sn and intermetallic compounds (isoferroplatinum, tetraferroplatinum, and brass) that were apparently derived from the ore.

References:
- Sharkov, E.V., Abramov, S.S., Simonov, V.A., Krinov, D.I., Skolotnev, S.G., Bel’tenev, V.E., and Bortnikov, N.S. (2007): Hydrothermal Alteration and Sulfide Mineralization in Gabbroids of the Markov Deep (Mid-Atlantic Ridge, 6°N). Geology of Ore Deposits 49(6), 467-486.