Petrographic Report: Polished Thin Section ME-01P
Rock Type: quartz-sulphide vein in clay-altered host rock.
The thin section is of a milky white quartz vein bearing abundant sulphides. In hand sample, light grey
silicified and clay-altered host rock with rounded fragments is preserved and cut by thin grey quartz-sulphide
veins (up to 2 mm wide). The host rock is preserved in the thin section as a few rounded fragments up to 1 cm
wide. These fragments are of clay-altered (illite, with minor smectite and sericite) crystal tuff with quartz (and
possibly heavily illitized K-feldspar) and minor iron oxides. One clast has preserved relict layering. Sericite is
coarser grained of the clays. The fragments contain minor amounts of stringy galena that is locally parallel to
layering (Fig. 1). The fragments also contain trace chalcopyrite, zircon, rutile, and sphene.
The main vein mainly comprises white, bladed to euhedral coarse quartz with abundant sulphides,
including coarse, rounded, irregular to euhedral pyrite, irregularly shaped sphalerite, and subhedral galena.
Pyrite is typically fractured, rounded, and contains rounded droplet-shaped inclusions of native gold, galena,
chalcopyrite, and rarely sphalerite. A single grain of pyrrhotite occurs as an inclusion in pyrite associated with
gold/chalcopyrite. Sphalerite in the vein is generally coarse-grained, irregular, and colourless to pale brown-grey
in colour, rarely deep red. Sphalerite grains always exhibit abundant chalcopyrite disease, commonly with
relatively coarse chalcopyrite (up to 0.1 mm). Galena within the main vein is subhedral and commonly
overprinted around rims and fractures by anglesite (Fig. 2), an oxidation product of galena. This replacement is
generally accompanied by limonite staining and trace biotite in radiating fans and masses. Covellite is also
Modal Percent Abundance
Size Range (mm)
Quartz-sulphide vein
Quartz
Sphalerite
Pyrite
Galena
Muscovite
Anglesite
Limonite
Chalcopyrite
Covellite
Biotite
Native gold
Pyrrhotite
Mineral
35
14
16
10
7
5
2
2
1
Trace
Trace
trace
Up to 5 cm
Up to 8 mm
Up to 5 mm
Up to 4 mm
Up to 0.5 cm
Up to 1 mm
Up to 0.2 mm
Up to 0.1 mm
Up to 0.1 mm
Up to 0.15 mm
Up to 50 microns
Up to 50 microns
Fragments
Quartz
Illite (± smectite)
Sericite
Iron oxides (limonite?)
K-feldspar
Galena
Chalcopyrite
Zircon
Rutile
Sphene
3
3
2
trace
trace
trace
trace
Trace
Trace
Trace
Up to 0.2 mm
Up to 30 microns
Up to 50 microns
Up to 50 microns
Up to 0.3 mm
Up to 0.4 mm
Up to 50 microns
Up to 50 microns
Up to 50 microns
Up to 40 microns
Cliffmont
Sample ME-01P
Page 1
associated with anglesite and sphalerite as very fine disseminations throughout, but mostly along fractures and
cleavages. Covellite rarely replaces sphalerite along its rims. Sulphide mineralization is cogenetic with quartz
veining.
py
ang
cpy
gn
po
gn
Figure 1: Photomicrograph of stringy galena (gn) in a
preserved fragment of host rock parallel to layering.
Photo taken in plane polarized reflected light.
Figure 2: Photomicrograph of galena (gn) being
replaced by anglesite (ang) around its rims. Pyrite (py)
often contains inclusions of chalcopyrite (cpy), and
this grain also includes pyrrhotite (po) associated with
the chalcopyrite. Photo taken in plane polarized
reflected light.
Figure 3: Photomicrograph of inclusions of
chalcopyrite (cpy) and native gold (au) hosted in pyrite
(py). The two inclusions are optically identical and
were distinguished by SEM-EDS. Photo taken in plane
polarized reflected light.
au
py
cpy
Cliffmont
Sample ME-01P
Page 2