Location:

Parys Mountain, Britain

Massive sulphide ores stratigraphically overlay a quartz-pyrite-chlorite stringer zone. The bedded sulphides are zoned with lead and zinc-rich ores overlying copper-rich and, in turn, pyrite-rich ores. They were mined out in the nineteenth century. The ores occur within an Ordovician-Silurian acid volcanic-sedimentary sequence but later were subjected to Caledonian metamorphism and remobilization.

Major Minerals:

Pyrite, chalcopyrite, sphalerite, galena, locally magnetite

Minor Minerals:

Marcasite, tetrahedrite-tennantite, covelline

Trace Minerals:

Include arsenopyrite, TiO2 minerals, pyrrhotite, native gold, native bismuth, bismuthinite, bournonite, kobellite

Textures:

Multiple generations of pyrite have different habits. Euhedral pyrite encloses relict titanomagnetite, TiO2 and haematite inclusions; pyrrhotite and mixed pyrrhotite-chalcopyrite which are probably the breakdown products of iss; chalcopyrite, galena and sphalerite inclusions, some of which are replacing pyrite. Collomorphic pyrite is intergrown with marcasite and both are inclusion-free. Pyrite is replaced by chalcopyrite, galena and sphalerite along its cleavage or along internal growth zones. Extensive alteration of pyrite, especially the core and internal zones, produces atoll-textures-a relict outer rim of pyrite about a replaced core. Sphalerite has suffered widespread chalcopyrite disease but is overgrown by inclusion-free sphalerite rims. Chalcopyrite and galena shows recrystallization textures, namely polygonal crystals of a uniform grain size with 120' angles between grains, due to metamorphism of the ores

Reference:

Pointon and Ixer, 1980