Chemical composition and formation of a massive sulfide deposit, Middle Valley, northern Juan de Fuca Ridge (Site 856)

Abstract

Enrichment of Zn and minor elements in the upper part of the deposit, which is typical of ancient massive sulfide deposits, is attributed to the zone-refining process of progressive upward replacement of lower temperature minerals by higher temperature minerals during growth of the sulfide body, with the concomitant hydrothermal leaching of trace metals. Later, the deposit was hydrothermally altered, probably due to lateral flow of evolved seawater along turbidite layers. The secondary convection system that caused alteration of the massive sulfides could have been driven by one of the sills emplaced into Middle Valley sediments subsequent to sulfide formation. -from Authors