Ancient oxide- and sulphide-mineralization in the islands of Tenerife and La Gomera (Canary Archipelago, Spain)

The alkaline intrusive complexes of Tenerife and La Gomera (Canary Archipelago, Spain) are formed by nepheline syenites and alkali gabbroids, and represent part of the oldest magmatic episodes in both islands. This work presents new studies of the petrographic and geochemical features of these rocks, and offers the first data about their respective ore minerals (iron oxides and sulphides). Mineralization is represented in both complexes by iron-rich patches and veins displaying a simple paragenesis of magnetite, ilmenite, pyrite and pyrrhotite, in association with widespread chloritic alteration of the intrusive host rocks. The comparative study of the mineralogical, textural and chemical characteristics of the ore minerals allows a metallogenetic model to be proposed which comprises two stages (magmatic and hydrothermal) in La Gomera and only one (magmatic) in Tenerife. The migration of the sulphide-bearing hydrothermal fluids far from the intrusive complex in Tenerife, and/or possible re-melting process could explain the apparent absence of the later hydrothermal stage in Tenerife. Received: 29 January 1998 / Accepted: 1 April 1998