Lasail and Bayda, Semail Ophiolite. Oman

Lasail and Bayda formed in the short time interval between the eruption of footwall basalts (Geotimes Unit) formed along a marginal basin spreading axis and a hangingwall lava unit (Lasail Unit) associated with an off-axis seamount.

Major Minerals:

Pyrite, chalcopyrite, magnetite, haematite

Minor Minerals:

Sphalerite, marcasite

Trace Minerals:

Include sphene, bornite, pyrrhotite, carrollite, cubanite, molybdenite, mackinawite, native gold


Optical zoning of pyrite (related to the cobalt content) is common. Minor amounts of cobaltian pyrite are associated with carrollite in chalcopyrite. Inclusions of mixed pyrrhotite-chalcopyrite and pyrrhotite-chalcopyrite-cubanite occur within euhedral pyrite and are due to the breakdown of iss. Both pyrite and sphalerite are extensively replaced by chalcopyrite, pyrite along its cleavage, and sphalerite along twin planes and grain boundaries


Haymon et al., 1984; Ixer et al., 1984, 1986; Haymon and Koski, 1985