Tectonic settings of porphyry-type mineralization and hydrothermal alteration in Paleozoic island arcs and active continental margins, Kyrghyz Range, (Tien Shan) Kyrghyzstan

Ore deposits in the fold belts of the northern Tien Shan have been formed in two stages and occur in two types of tectonic settings. The first type is represented by Early Ordovician island arcs hosting the Karakol ore district. These east–west trending island arcs are interpreted to have evolved above the south dipping subduction of oceanic crust of the Central Asian paleo-ocean. The second type of tectonic setting hosting the Octorkoy Ore District, has evolved on a Devonian-Carboniferous active continental margin of the Central Asian paleo-ocean above north dipping subduction of the oceanic crust. The second type is superposed on the first tectonic setting. The Oktorkoy ore district is characterized by thrusting and similar circular structures as in the first stage and its polygenic mineralization is associated with multiphase granitoid complexes. Zonality of porphyry copper deposits of the Kyrghyz Range is associated with the following hydrothermal alteration sequence: potassium alteration - phyllization (beresitization) - prophyllitization (epidote-chlorite-albite) - tourmalinization - argillization - prophyllitization (epidote-actinolite-albite). Received: 3 June 1996 / Accepted: 10 January 1997