OP3 Slate Example

Petrolab Limited www.petrolab.co.uktel +44 (0)1209 219541 email [email protected]

C Edwards Offices, Gweal Pawl, Redruth, Cornwall TR15 3AERegistered in England & Wales Company No. 4777735

Moorland Slates

A ClientPetrographic Report OPxxxx(a) xx/xx/xxxx

Petrographic Report A Client

Contents Sample details............................................................................................1 Methods of investigation.............................................................................1 Petrographic description.............................................................................2 Summary.....................................................................................................3 Images........................................................................................................3

Moorland SlatesOPxxxx(a) xx/xx/xxxx

Issued by Petrolab Ltdi


Report identification

Client A Client

Report title Moorland Slates

Analysis required Detailed petrographic report by optical microscopy.

Client order ref. xxxxxx Client contact A Contact

Report ID (issue date) OPxxxx(a) xx/xx/xxxx Issue note Initial issue

Prepared by J Strongman MSci ARSM Checked by J Fletcher BSc MSc

LimitationsThis report relates only to those samples submitted and specimens examined and to any materials properlyrepresented by those samples and specimens. This report is issued to the Client named above for thebenefit of the Client for the purposes for which it was prepared. It does not confer or purport to confer onany third party any benefit or right pursuant to the Contracts (Rights of Third Parties) Act 1999.


Issued by Petrolab Ltdii


Sample detailsTwo samples of unused/ unweathered roofing slate (Moorland standard & Moorland reject),of dimensions 500 mm x 250 mm x 6mm (nominal thickness), were provided. Both samplesare reported to be from the same source; one is reported to be a standard slate and theother is reported to be a reject due to high pyrite content.

Table 1 Samples received

Sample ref. Type Mass ConditionMoorland standard roofing 2194 unused

Moorland reject roofing 2056 unused

The investigation requested was a detailed petrographic description of both samples anddetermination of sulphide content of the Moorland reject slate.

Methods of investigation Preliminary investigation

Both samples were examined, as received, and after careful washing to removeloose debris, using a Nikon SMZ-U stereomicroscope. The microscope has acontinuous zoom range of 7.5x to 75x and it is equipped with a 150W continuousring, fibre optic illuminator. It is useful for the preliminary examination of samples andit is possible to discriminate and sometimes identify features as small as 100 m insize. The microscope has a trinocular head and can be used for low powerphotomicrography.

Sample preparation Two standard 50 mm x 25 mm polished thin sections were prepared from each

sample. One section was cut perpendicular to cleavage and the other one parallel tothe relict bedding.

The sections were examined by conventional transmitted and reflected lightpolarising microscopy using a Nikon Labophot 2A research polarising microscope.Digital photomicrographs were taken using a Nikon DXM1200F 12 megapixelcamera fitted to the trinocular head of the microscope

The abundance of sulphide minerals in the reject slate was calculated from chemicalassay of the total and acid soluble sulphur in the slate.


Issued by Petrolab LtdPage: 1 of 7


Petrographic descriptionHand specimensBoth slates are unweathered/ unused slates. The slate is a uniform medium-greenish greycolour. They show evidence of lithological banding intersecting the cleavage surfaces,individual bands are approximately 1 mm thick. Isolated, unweathered pyrite crystals (FeS2)are disseminated through both the slates and are visible with the stereomicroscope. Theyare extremely fine, typically < 100 m. The reject slate also contains discontinuous bands (< 10 cm) of coarse pyrite, these bandsfollow relict bedding planes in the slate. Individual pyrite crystals are approximately 300m.Chemical analyses of the total sulphide and acid soluble sulphur content of the reject slategives an equivalent pyrite content of 0.15wt% pyrite.In both samples sulphide content is composed almost entirely of pyrite with only traces ofchalcopyrite and pyrrhotite. There is no evidence of the more reactive iron sulphidemarcasite.Petrography

Texture and fabric,weathering & alteration

The slate is made up principally from sericite mica and pale green chlorite with a very strong preferred orientation that defines the cleavage. The slate also contains minor quartz and iron oxides, and traces of calcite and sulphides (pyrite, chalcopyrite, pyrrhotite). The chlorite porphyroblasts and lenses of quartz and calcite give the appearance of a coarser grained textured slate. The sections show no weathering or discolouration.

Phase, abbreviation Abundance Grain size ( min | max | typical )

Sericite Major+ < 2.5 m 40 m 10 m

Description Platy crystals of sericite mica with a strong preferred orientation defining cleavage, interbedded with chlorite.

Chlorite Minor < 2.5 m 200 m 20 m

Description Platy crystals with a strong orientation defining cleavage, interbedded with sericite micas. Also occurs as larger porphyroblasts orientated at high angles to the foliation.

Quartz Minor 10 m 150 m 50 m

Description

Anhedral crystals clustered in layers defining original bedding at ~30o to cleavage. Also present with calcite in lenses orientated parallel to cleavage, these have maximum length of circa 500 m and are up to 100 m in thickness. Around coarse euhedral pyrites in reject sample also develops in pressure fringes parallel to cleavage.

Haematite/Limonite Minor < 2.5 m 50 m 20 m

Description Platy crystals, generally orientated parallel with cleavage. A small population inchlorite porphyroblasts are orientated at a high angle to foliation.

Calcite Trace 5 m 80 m 20 m

Description Subhedral crystals clustered with quartz in lenses orientated parallel to cleavage.

Pyrite Pyrrhotite Trace < 5 m 300 m 70 m




Description

In both samples found as disseminated subhedral grains and clusters of grains (subparallel with cleavage) they have an average grain size of


Samples received

A Samples received

Photograph of samples as received (scale in cm). Standard slate on left, reject on right. Location of thin sections is marked.

Image AFuji S3 Pro digital cameraDaylight balanced oblique light




Photomicrographs

B Standard

Chlorite (chl) porphyroblasts and mica layers in slate

Image BNikon Labophot petrological microscopePlane polarised transmitted lightx100

C Standard

Relict bedding defined by quartz (qtz) rich bands

Image CNikon Labophot petrological microscopeCross polarised transmitted lightx25



1 mm

250 m

chl

qtz


D Standard

Clusters and individual grains of fine disseminated pyrite

Image DNikon Labophot petrological microscopePlane polarised reflected lightx200

E Reject

Well developed cleavage plus chlorite porphyroblasts and mica layers

Image ENikon Labophot petrological microscopePlane polarised transmitted lightx100



250 m

100 m

py

chl


F Reject

Pyrite lens cutting through slate

Image FNikon Labophot petrological microscopePlane polarised reflected lightx25

G Reject

Euhedral coarse pyrite showing quartz pressure fringes

Image GNikon Labophot petrological microscopeCross polarised transmitted lightx40



500 m

1 mm

py

py

qtz

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OP3 Slate Example