Kuroko-style ores

Chalcopyrite, pyrite and sphalerite. Çeyeli, Turkey

Pyrite (pale yellow-white, high reflectance) forms euhedral crystals with thin chalcopyrite rims (bottom right) and is extensively replaced by chalcopyrite (yellow, centre right) in a characteristic texture found in many volcanogenic deposits. Euhedral to subhedral sphalerite (light grey) overgrows chalcopyrite (right centre).

Polished block, plane polarized light, x80, air

Sphalerite, chalcopyrite, pyrite, bornite and galena. Çeyeli, Turkey

Concentrically banded bornite (brown, centre) and chalcopyrite (yellow, centre) are intergrown with poorly crystalline pyrite (pale yellow-white, centre top) which shows variations in reflectance and surface colour due to differences in crystallinity (top left) and degree of replacement by chalcopyrite (bottom left). Coarse-grained chalcopyrite (centre bottom) is intergrown with galena (blue-white, centre bottom) about sphalerite (light grey, centre), which is free of fine-grained inclusions. Silicates and sulphates (dark greys) constitute the gangue.

Polished block, plane polarized light, x80, air

Chalcopyrite and sphalerite. Çeyeli, Turkey

Very finely banded ore comprising fine-grained chalcopyrite (yellow) and sphalerite (grey). Thin veinlets parallel with the layering carry coarse-grained chalcopyrite and sphalerite (top right). The individual minerals can be resolved at higher magnifications.

Polished block, plane polarized light, x80, air

Sphalerite, galena, chalcopyrite and pyrite. Çeyeli, Turkey

Reniform sphalerite (light grey, centre) is interbanded with galena (white, centre bottom) and chalcopyrite (yellow) in successive growth rings. Chalcopyrite in the centre of the right sphalerite has replaced poorly crystalline pyrite (white, top right). Chatcopyrite can be seen to have higher relief than galena (bottom left). The gangue (dark grey) is sulphate. Black areas are polishing pits.

Polished block, plane polarized light, x80, air

Sphalerite, tetrahedrite group mineral, chalcopyrite and galena. Çeyeli, Turkey

Sphalerite (grey) shows a slight variation in reflectance and very faint reddish internal reflections (both very difficult to see) due to submicroscopic inclusions of tetrahedrite (right centre). Coarse-grained tetrahedrite (green-blue, centre left) is also present within sphalerite as is chalcopyrite (yellow, bottom left). A minor amount of galena (white) lies in the gangue between sphalerite crystals (bottom right).

Polished block, plane polarized light, x 160, oil

Pyrite, chalcopyrite, galena, marcasite and native gold. Çeyeli, Turkey

Marcasite (light blue-white, bottom right) rhombs form the cores to pyrite crystals (light yellow-white, right), which are replaced by chalcopyrite (top right). One marcasite crystal (bottom right) is twinned and shows faint bireflectance and reflection pleochroism (grey to blue-grey). Pyrite is rimmed and replaced by chalcopyrite (yellow), which itself has a galena rim (blue-grey, centre). Native gold (light yellow, high reflectance, centre) is intergrown with galena. The low reflectance and blue-grey colour of galena against native gold is characteristic. The black area is resin-

Polished block. plane polarized light. x 160, oil