Clastic-hosted copper ores

Djurleite, bornite and TiO₂ minerals. Mount Gabriel, County Cork, Ireland

Djurleite (white, centre bottom) is intergrown with bornite (pink-brown, centre). An aggregate of TiO₂ mineral grains (light grey, centre right) has djurleite overgrowing it. Some of the djurleite crystals are tarnished to pale blue (centre and centre left). Calcite (dark grey) is the matrix and shows faint bireflectance (bottom right). Black areas are polishing pits.

Polished block. plane polarized light, x 80, air

Djurleite and bornite. Mount Gabriel, County Cork, Ireland

Djurleite (white) is intergrown with bornite (orange-brown), both in random orientation (left of central grain) and as a crystallographically controlled texture (centre of grain). The latter texture is due to the replacement of bornite by djurleite. The sulphides infill pore spaces between elastic quartz and feldspar grains (dark grey), which have euhedral metamorphic overgrowths (centre top and bottom centre), proving the mineralization to be post-metamorphism. Poorly polished areas are phyllosilicates.

Polished block, plane polarized light, x 80, air

Covelline, blaubleibender covelline, djurleite and chalcopyrite. Mount Gabriel. County Cork, Ireland

Djurleite (white, centre) is replaced by bladed covelline (purple-blue). Other grains (bottom left) are replaced by a mixture of blaubleibender covelline (light blue) and covelline (red-purple). Minor amounts of chalcopyrite (yellow, bottom centre) are replaced by covelline. Djurleite in this ore is light sensitive (not-shown), suggesting that silver minerals are associated with it. Malachite (light and dark grey) forms radiating crystal aggregates (bottom left), and shows clear bireflectance between adjacent crystals and faint green internal reflections (top right). Black areas are polishing pits.

Polished block. plane polarized light. x 180, oil

Digenite, bornite and covelline. Mount Gabriel, County Cork, Ireland

Digenite (light blue, centre left) has cleavage and is intergrown with bornite (pink-brown, centre). Covelline (dark blue) as radiating crystals is replacing digenite along grain boundaries and fractures (centre right). Quartz (dark grey, bottom) is euhedral. East-west oriented malachite (medium grey, bottom right) veinlets cross-cut digenite.

Polished block, plane polarized light, x SO, air

Blaubleibender covelline, covelline, digenite and bornite. Mount Gabriel, County Cork, Ireland

Digenite (light blue, little cleavage, bottom left of main sulphide) is extensively replaced about its margins by covelline (dark blue, centre left) and by coarse crystals of blaubleibender covelline. Blaubleibender covelline shows strong reflection pleochroism from blue-white (centre right of sulphide with good cleavage, oriented north-south) to medium blue (top left of sulphide with central polishing pits, oriented cast-west). Bornite (pink-brown, centre) also is being replaced by covelline. Minor amounts of malachite (light grey, centre) form veinlets cutting the sulphides. Euhedral feldspars (grey, top centre, bottom centre left) and quartz (grey, centre left) are associated with phyllosilicates (grey, poorly polished). Black areas are polishing pits.

Polished block, plane polarized light, x80, air

Digenite and covelline. Mount Gabriel, County Cork, Ireland

The main sulphide (blue-green) is banded on a very fine scale but has the optical properties of digenite. However, X-ray diffraction suggests that it is an intimate mixture of digenite and covelline. It is replaced along its edges by radiating sheaves of covelline which show extreme anisotropy from deep red (centre left) to golden-yellow (bottom centre). Dark grey phases with internal reflections are silicate gangue minerals, mainly quartz, which show euhedral crystal forms (left centre).

Polished block, partially crossed polars, x 180, oil