Porphyry copper ores

Chalcopyrite and rutile. El Salvador, Chile

Anhedral chalcopyrite (yellow, top right) is intergrown with quartz (light grey, right centre). Rounded to euhedral rutile (grey-white, centre left) is disseminated throughout the host rock. The poorly polished dark grey gangue is phyllosilicate.

Polished block. plane polarized light, x 80, air

Pyrite, chalcopyrite and covelline. El Salvador, Chile

Subhedral to anhedral pyrite (pale yellow-white, left) carries silicate inclusions (left centre) and is surrounded by chalcopyrite (yellow, centre), which is extensively altered to fine-grained covelline (blues, centre right). Covelline shows bireflectance and reflection pleochroism from dark to light blue (centre). Quartz is the main silicate (top centre).

Polished block, plane polarized light, x40, air

Pyrite, magnetite, chalcopyrite, pyrrhotite and covelline. El Salvador, Chile

Coarse crystals of pyrite (yellow-white) carry abundant inclusions. These are euhedral magnetite (grey-brown, low reflectance, centre right), rounded pyrrhotite (brown, left centre, centre) and chalcopyrite (yellow, centre right). Mixed chalcopyrite-pyrrhotite inclusions (centre) are rarer than monophase inclusions. Chalcopyrite, which has altered to covelline (deep blue, centre bottom), has overgrown pyrite. Silicates are black areas. The association of pyrite with magnetite, pyrrhotite and chalcopyrite inclusions is common in many types of ore. Pyrrhotite-chalcopyrite inclusions are due to the unmixing of iss (intermediate solid solution).

Polished block. plane polarized light, x 160, oil

Chalcopyrite and covelline. El Salvador, Chile

Anhedral chalcopyrite (yellow) has been replaced by covelline (dark blue) along crystal boundaries and cleavage. The gangue comprises coarse crystals of quartz (dark grey, bottom right) and euhedral basal sections and tabular crystals of tourmaline (higher reflectance, centre). Black areas are polishing pits.

Polished block, plane polarized light, x 80, air

Chalcopyrite, bornite, chalcocite, covelline and molybdenite. El Salvador, Chile

Chalcopyrite (yellow, centre left) is intergrown with bornite (brown-orange, left centre) and lath-shaped molybdenite (light grey, top right). Both copper-iron sulphides have altered to chalcocite (light blue, left and bottom right), which itself has a covelline rim (dark blue) associated with malachite (grey, poorly polished, left). Thin chalcopyrite spindles along (100) of the host bornite (left) have been preserved in chalcocite replacing bornite (left centre). Chalcopyrite (top right) has altered about its margin and along a fracture to covelline which shows strong bireflectance and reflection pleochroism (light and dark blue, centre right).

Polished block. plane polarized light, x80, air

Chalcocite, bornite. chalcopyrite and covelline. El Salvador, Chile

Bornite (red-brown, centre) contains abundant chalcopyrite (yellow) as spindles parallel to (100) and as rounded inclusions (centre right). Bornite has extensively altered to blue chalcocite (light blue), but chalcopyrite has been preserved. Chalcocite itself has altered to covelline (dark blue, centre bottom) along its margin. Quartz (dark grey, bottom centre) is the main gangue. A single crystal of malachite (medium grey, centre right) has grown into a void.The bornite-chalcopyrite intergrowth is a replacement or exsolution texture but can be seen to be earlier than the replacement of bornite by chalcocite.

Polished block, plane polarized light. x 160. oil 69