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Petrographic Report: Polished Thin Section SLD-05-01P
Rock Type: clay-altered and silicified feldspar-phyric crystal-lithic tuff
The thin section displays a fragment-bearing feldspar-phyric lithic-crystal tuff that is moderately to
strongly clay-altered and cut by randomly oriented sulphide-bearing quartz-muscovite veins. The fragments are
rounded and on the order of 0.2 to 4 mm wide. Euhedral feldspar phenocrysts and fragments are completely
replaced by sericite and illite-smectite (and trace kaolinite), and are difficult to differentiate from the
groundmass due to the degree of clay alteration. Thin carbonate veinlets overprint the quartz-muscovite veins.
The sample is moderately to strongly altered with approximately three-quarters of the primary mineral
assemblage overprinted. The primary mineral assemblage was dominantly very fine- to fine-grained K-feldspar
and quartz with approximately 10% phenocrysts of euhedral lath-shaped feldspar (difficult to identify which
feldspar though) ranging in size up to 2 cm wide. This composition would classify the original rock as a clayfeldspar-phyric crystal-lithic tuff. The hand sample exhibits quartz veins over 2 cm wide and a groundmass that is
white to pale grey in colour. The offcut has been stained to check for the presence of K-feldspar, and a weak,
pale yellow colour was taken on in the groundmass, indicating some K-feldspar is present. There are at least
three generations of alteration. The early alteration event is characterized by an initial sericitization and clay
alteration (illite-smectite) of the host rock. Quartz-muscovite veins ranging from 0.1 mm to greater than 2 cm
associated with contemporaneous patches of secondary quartz, muscovite,
Mineral
Primary rock
Quartz-1
K-feldspar
Unknown, blue, pleochroic
Early clay alteration
Illite-smectite
Sericite
Limonite
Kaolinite
Hematite
Epidote-clinozoisite
Quartz veining and silicification
Quartz-2
Muscovite/Sericite
Rutile
Pyrite
Illite
Sphene
Pyrrhotite
Chalcopyrite
Galena
Late carbonate veining
Calcite
Modal Percent Abundance
Size Range (mm)
10
8
trace
Up to 0.3 mm
Up to 1.5 mm
Up to 0.1 mm
11
7
2
1
Trace
Trace
Up to 30 microns
Up to 0.5 mm
Up to 5 microns
Up to 50 microns
Up to 0.1 mm
Up to 0.1 mm
38
12
4
4
1
Trace
Trace
Trace
Trace
Up to 5 mm
Up to 50 microns
Up to 2.2 mm
Up to 0.4 mm
Up to 50 microns
Up to 50 microns
Up to 40 microns
Up to 50 microns
Up to 0.1 mm
2
Up to 0.3 mm
rutile, and sulphides are randomly oriented and cut the host rock. This was followed by the development of thin
(up to 0.2 mm wide), discontinuous carbonate veinlets that cut the quartz veins (Fig. 1).
Cliffmont
Sample SLD-05-01P
Page 1
The first alteration event was a pervasive sericitization and clay alteration event represented by finegrained, felty and knot-textured sericite, illite, smectite, and minor kaolinite completely replacing feldspar
phenocrysts, and finer grained, felty-textured illite-smectite and trace kaolinite overprinting fragments and finegrained K-feldspar in the groundmass. A minor amount of cryptocrystalline limonite and trace hematite are
associated with the clay alteration and commonly outline or rim altered feldspars and fragments. The hematite
is locally acicular or bladed. Trace, fine-grained, euhedral prismatic epidote-clinozoisite is disseminated
throughout the host rock. The alteration mineral assemblage here is consistent with the sericitic or argillic
alteration assemblage.
The second alteration consists of randomly oriented quartz-muscovite veins with varying widths and
minor patches of secondary quartz and muscovite overprinting the wall rock. Quartz is generally anhedral with
hexagonal zonation, and zonation is defined by trails of fluid inclusions. Muscovite occurs as fans and clumps up
to 1 mm wide and is especially abundant along veins edges. A minor amount of rutile occurs as inclusions within
quartz crystals (Fig. 2), as well as a minor amount of fine-grained rutile in clusters up to 0.3 mm wide in the wall
rock. Minor subhedral to euhedral cubic zoned pyrite also occurs within the quartz veins. Zonation is defined by
mineral inclusions. Sphene, chalcopyrite, pyrrhotite, and galena occur as very fine (up to 0.1 mm wide) anhedral
and irregular inclusions in pyrite (Fig. 3). These inclusions are more abundant in pyrite hosted in the quartz veins
than in pyrite hosted in secondary quartz patches within the wall rock. A single irregular grain of galena also
occurs within the quartz. The alteration mineral assemblage here is consistent with a silicic alteration
assemblage.
Calcite occurs in short, discontinuous veinlets up to 0.2 mm wide and 2 mm long that are randomly
oriented and cut across quartz-muscovite veins. Calcite veins typically occur along fractures and also as wormy,
poorly developed veinlets in the wall rock.
qtz-2
qtz
frag
cal
rt
qtz-ms
frag
fsp
hem
Figure 1: Photomicrograph of the relationships seen in
this thin section. Pervasive clay alteration of host rock,
fragments (frag), and feldspar phenocrysts (fsp) is cut
by randomly oriented quartz-muscovite (qtz-ms) veins.
The quartz-muscovite veins are cut by thin carbonate
(cal) veins which mostly follow fractures. Photo taken
in cross polarized transmitted light.
Cliffmont
Sample SLD-05-01P
hem
Figure 2: Photomicrograph of anhedral fractured rutile
and bladed (hem) in a quartz (qtz) vein. Photo taken
in plane polarized reflected light.
Page 2
py
spn
po
Figure 3: Photomicrograph of a euhedral zoned pyrite
(py) grain hosting inclusions of pyrrhotite (po), sphene
(spn), and chalcopyrite (cp). Photo taken in plane
polarized reflected light.
cp
Cliffmont
Sample SLD-05-01P
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