The circulation of hydrothermal fluids through young oceanic crust causes serpentinization, alteration of the peridotites and alteration of minerals in the gabbros and basalts to lower temperature assemblages. For example, plagioclase, pyroxenes, and olivine in the sheeted dikes and lavas will alter to albite, chlorite, and serpentine, respectively. Often, ore bodies such as iron-rich sulfide deposits are found above highly altered epidosites (epidote-quartz rocks) that are evidence of (the now-relict) black smokers, which continue to operate within the seafloor spreading centers of ocean ridges today.