Abstract
Synopsis The information presently available — in particular, that derived from the use of the isotopes ( 87 Sr/ 86 Sr, δ 18 O and δ 34 S) as geochemical tracers — indicates that a model for mineralization and metamorphism of the Upper Cretaceous ophiolitic rocks of the Troodos Massif, Cyprus, which involves hydrothermal convection of sea water, is reasonable. During water-rock interaction in the recharge part of the cycle of convective heat and mass transfer, the pillow lavas, Sheeted Dyke Complex and uppermost gabbros were hydrothermally metamorphosed at zeolite facies to amphibolite facies conditions, and base metals (e.g. Fe, Mn, Cu, Zn, Pb, Ni, Co, Ag and Au) were leached by the fluid from the rocks. At the positions of discharge of hot fluid at the sea water-rock interface sulphide ore deposits or ferromanganoan hydroxyoxide sediments (umbers) were precipitated. By calculation of a Rayleigh number for the conditions of hydrothermal activity it is shown that the fluid dynamic requirements for vigorous free convection were satisfied. It is deduced that the ore deposits developed within the active zone of a spreading oceanic ridge, and took ∼ 10 5 yr to form. Available geochemical evidence is discussed to demonstrate that the hydrothermal convection model is chemically, as well as fluid-dynamically, reasonable.
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