The Mineralogical Characteristics of Pyrite at 26°S Hydrothermal Field, South Mid‐Atlantic Ridge

The pyrite in 26°S can be classified into four distinct types: Type-I occurs as colloform texture and show banded and circled characteristics. It has the lowest reflectivity, and always co-existing with Type-II. Type-II occurs as anhedral texture with poor crystallization degree and porous. They all show aggregate structure and assemble with Type-I. Type-III occurs as subhedral-euhedral cubic crystals, always occupy in the margin of the aggregation of Type-I and Type-II. Its’ optic character was similar to Type-II. Type-IV occurs as euhedral cubic crystals with larger grain than Type-III and co-existed with chalcopyrite. These pyrites always occupy in the fissures and pores of the aggregation of Type-I and Type-II. Type-I → Type-II → Type-III represent the different crystallinity of the same hydrothermal mineralization stage. Abundant pores and fissures can be found in the aggregate of first stage pyrite. Type-IV, occupying in these fissures and pores and co-existing with chalcopyrite, represents the later hydrothermal mineralization stage.