Cataclastite Phyllonite


An Interactive Poster


Red amygdaloidal andesite

massive block fracture, lack of parallel fracture or cleavage indicates sample is outside the fault/shear zone


Black slatey cleaved argillite

The very platy fracture of the sample is typical of a cleavage or fracture cleavage formed by deformation, and within phyllonite/shear zones, its texture is suggestive of proximity being within to a fault structure.


Laminated siltstone

thin reddish silt interlayered with grey siltstone/fine sandstone. Note: the bedding is cut at high angles to the bedding laminations.   Strong cleavage fracture, suggestive of within the fault/shear domain.


Tuffaceous mudstone

red hematitic feldspathic volcanic mudstone tuff: fine, crudely developed parallel fracture indicates the early development of a slatey cleavage—incipient fracture ‘distal’  from a possible structure.

N.B....Note that the understanding or recognition of any structure(or other features) is made from a collection of observations, seldomly from one rock, as most/many textures found in a rock may have a variety of explanations


Sericite phyllite/phyllonite

white, fine grained, platy fractures.  Development of recognizable, pervasive, fine white mica (sericite/illite) along the platy surfaces marks the growth of new, secondary minerals.  This platey to schistose texture with the sericite/illite indicates that the rock reached a temperature favourable for potential mineralization- strong guide to potential shear zone mineralization. Sample from hanging wall of shear hosted veins at Dome Mountain, Smithers.


Quartz-sulphide ore vein

sulphides are pyrite and galena, vein selvage whitish and greenish sericite, brown carbonate (ankerite, siderite?)


Sericite shear with minor fold

altered fine grained, pale green sericite (fine white mica), quartz, carbonate (ankerite), and minor chlorite; minor pyrite and sphalerite along thin quartz bands.   Rock within mineralized zone of shear   (N.B.  the sericite/phyllonite sample represents a more distal style of alteration, peripheral to mineralization.


Sericite, chlorite, quartz, phyllite, quartz-carbonate veinlets (ankeritic?)

Strong development of alteration, proximal to potential mineralization.


Chlorite, sericite, phyllite

well developed foliation/cleavage,  quartz-carbonate (ankerite?) gash veinlets.   The presence of chlorite dominant over or lack of sericite suggests the composition of the rock

N.B.….the rock in the picture is very light coloured suggesting that chlorite is accompanied by other minerals, perhaps sericite\illite.  If sericite, then the alteration, with the presence of chlorite suggests the rock to be distal from the mineral zone.  Texture is a good guide within potential shear zone mineralization.

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