Petrographic Report: Polished Thin Section ME-02P
Rock Type: quartz-sulphide vein
In hand specimen the quartz hosts large, rounded and fractured pyrite grains (up to 2 cm wide). No fragments of host rock are preserved in the hand specimen. The thin section comprises only a milky white quartz sulphide vein. The vein consists ofis comprised mainly of white, bladed to euhedral coarse quartz with abundant sulphides, minor bladed to fan-shaped muscovite, trace amorphous limonite and iron oxide staining in places, and trace secondary quartz. Muscovite occurs throughout the thin section, but is more prevalent in fractures and between quartz grains. Secondary quartz is characterized as short (less than 2 mm), randomly oriented veins (up to 0.25 mm wide) of finer -grained quartz which is locally associated with fine-grained, anhedral pyrite (Fig. 1). These secondary veins cut the main vein with the thin section. They display similar texture and suphide mineralogy and thus both veins observed in this thin section are interpreted as one sustained quartz veining event. Sulphide mineralogy in the main vein includes coarse, rounded, irregular to euhedral pyrite which contains inclusions of sphalerite, galena, chalcopyrite, pyrrhotite, and native gold. Pyrite is often typically rounded to euhedral and fractured or brecciated by quartz veining (Fig 2). Pyrite is locally embayed and partly replaced by quartz locally. Sphalerite occurs as inclusions along fractures in pyrite and also as intergrowths in pyrite. Sphalerite along fractures post-dates pyrite. Sphalerite is colourless to very pale grey-brown and rarely exhibits chalcopyrite disease typically displayed in other samples from this suite. Galena occurs as larger inclusions in pyrite (Fig. 3) and as infill along fractures, indicating it post-dates pyrite. Chalcopyrite is observed as isolated rounded inclusions within unfractured portions of pyrite (Fig. 3). Pyrrhotite is always associated with chalcopyrite in pyrite (Fig. 3). The chalcopyrite and pyrrhotite are locally syngenetic with pyrite. Two grains of native gold (Fig. 3) are associated with a sphalerite inclusion in pyrite.
Mineral / Modal Percent Abundance / Size Range (mm)Quartz-sulphide vein
Quartz / 65 / Up to 1 cm
Pyrite / 32 / Up to 2 cm
Muscovite / 1 / Up to 0.15 mm
Galena / 1 / Up to 0.8 mm
Chalcopyrite / 1 / Up to 0.15 mm
Pyrrhotite / Trace / Up to 0.25 mm
Sphalerite / Trace / Up to 0.1 mm
Native gold / Trace / Up to 40 microns
Limonite / Trace / Up to 10 microns
The quartz in this sample hosts abundant fluid inclusions ranging in size up to 20 microns. The fluid inclusions are two-phase (liquid and vapour) fluid inclusions at room temperature, probably comprised of a brine and water vapour bubble. This is a typical fluid inclusion assemblage observed in epithermal deposits. Likewise the observed ore mineral and alteration assemblages are typical of an epithermal ore deposit.
There are minor amounts of deformation visible in the sample: these are brecciated pyrite and parallel sets of microkinks in quartz.
Figure 1: Photomicrograph of secondary quartz (qtz2) veinlets associated with minor pyrite cutting primary, main vein quartz (qtz1). Photo taken in plane polarized transmitted light. / Figure 2: Photomicrograph of brecciated pyrite (py) cut by fine-grained quartz (qtz) vein. Photo taken in plane polarized reflected light./ Figure 3: Photomicrograph of inclusions of pyrrhotite (po) associated with chalcopyrite (cpy), native gold (au) associated with sphalerite (sph), and coarse, irregular galena (gn) hosted in fractured, anhedral pyrite (py). Photo taken in plane polarized reflected light.
Cliffmont Sample ME-02P Page 2