Quartz-sulphide vein mineralization

Sphalerite, chalcopyrite, covelline, galena and stannite. Rishi, Nigeria

Click hereSphalerite (light grey, right) is intergrown with chalcopyrite (yellow, centre). Sphalerite contains abundant rounded chalcopyrite inclusions, whereas chalcopyrite has small stannite stars (light brown, centre left). The main sulphides are fractured, and these are infilled by covelline (deep blue, centre) and secondary galena (white, centre right). Quartz is very dark grey (centre left) beneath resin (dark grey) with an air bubble (black); other black areas are polishing pits.

Polished block, plane polarized light. x80, air

Sphalerite, chalcopyrite, galena and pyrite. Rishi, Nigeria

Click hereThe main phase is sphalerite. Areas adjacent to fractures and those that contain abundant submicroscopic chalcopyrite inclusions have an anomalous red-brown surface colour (top left), whereas sphalerite with larger chalcopyrite (yellow) inclusions and few fine-grained chalcopyrite inclusions has a more characteristic grey colour (bottom right). A rounded galena crystal (white, centre) and small pyrite crystals (pale yellow, high reflectance, right centre) are intergrown with coarse chalcopyrite inclusions. Pyrite has been plucked from chalcopyrite (left centre). Black areas are silicate gangue. The anomalous sphalerite areas show anisotropy effects in crossed polars and have suffered extensive chalcopyrite disease the replacement of sphalerite by chalcopyrite.

Sphalerite, chalcopyrite, pyrrhotite and cubanite. Rishi, Nigeria

Click hereSphalerite (blue-grey) contains abundant chalcopyrite (yellow) inclusions ranging from submicroscopic (bottom right) to large (centre). The central area of sphalerite has few small crystals but has large subrounded chalcopyrite crystals intergrown with pyrrhotite (light brown, top right), which shows faint reflection pleochroism, and with cubanite (light brown, reflectance very similar to chalcopyrite, centre). Cubanite is often difficult to distinguish from chalcopyrite in plane polarized light, as is shown here. Black areas are polishing pits.

Polished block, plane polarized light, x 80, air

Sphalerite, chalcopyrite, stannite and galena. Rishi, Nigeria

Click hereGrey sphalerite is the main sulphide; locally, it has a faint brown colour due to submicroscopic inclusions of chalcopyrite (top right). Chalcopyrite (yellow) is intergrown with sphalerite as discontinuous veins and inclusions. Stannite (green-brown grey, centre left) has slightly lower reflectance than chalcopyrite and also forms a discontinuous vein accompanied by chalcopyrite. Thin veinlets carry galena (white, bottom right) and covelline (deep blue, top centre). The central veinlet in chalcopyrite (top right, oriented northwest-southeast) is poorly polished galena. Black areas are polishing pits.

Polished block, plane polarized light, x80, air

Galena, sphalerite, chalcopyrite, aikinite and stannite. Dawa, Nigeria

Click hereGalena (white, bottom) shows characteristic triangular polishing pits (black, right centre) due to plucking along (100). It is intergrown with a harder cream copper-lead-bismuth sulphosalt with the optical properties of aikinite (left centre and top centre). Sphalerite (grey, top left) has few chalcopyrite (yellow) inclusions whereas the aikinite has rare small stannite (brown-grey, centre, cut by northwest-oriented scratch) inclusions.

Polished block, plane polarized light. x80, air

Chalcopyrite, sphalerite and stannite. Ririwai, Nigeria

Click hereChalcopyrite (yellow) is intergrown with sphalerite (grey). Sphalerite carries chalcopyrite inclusions, whereas chalcopyrite has sphalerite inclusions (dark grey) rimmed by stannite (light brown-grey, centre). Stannite also forms an incomplete rim between chalcopyrite and sphalerite (top centre).

Polished block, plane polarized light. x 160, oil