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A PETROGRAPHIC STUDY OF ROCKS FROM WINDY LAKE, SIC

AND PARKIN TOWNSHIP, ONTARIO

Prepared For: John Smolen M.Sc.

Geological Assistant

Watts, Giffis and McOuat CONSULTING GEOLOGISTS AND ENGINEERS

December 4, 2004

tltECE\\IEO JUl ,3 20 ~

SESSMENl GEOSC\EN~~~S E

2 plagioclase grains, annealed. Width of field: 0.45mm

Prepared by: Eva S. Schandl Ph.D.

www.consultgeo.com

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TABLE OF CONTENTS

INTRODUCTION AND OBJECTIVES

DISCUSSION AND CONCLUSIONS

REFERENCES

PETROGRAPHY

1

Page

1

2

4

5-48

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INTRODUCTION AND OBJECTIVES

The present petrographic study includes a suite of 10 samples from Windy Lake, and.a suite of 3 samples from Parkin Township, NE of the SIC. One thin section was prepared from each rock sample for microscopic investigation.

The objectives of the study were:

1. To determine the mineralogy of the 13 samples, and visually estimate the % , minerals in the individual thin sections

2. To identify the rock types, and

3. To determine if samples 1 & 2 from the Parkin Township represent offset dikes, and if samples 4, 5, 9, 10 & 11 within the IRM suite represent the Footwall Breccia or Sudbury Breccia

DISCUSSION AND CONCLUSIONS

Objective 1 The suite of 13 covered thin sections were studied under transmitted light of a

polarizing microscope. As the thin sections were covered and not polished, the opaque minerals could not be identified. The mineralogy of individual thin sections is described in detailed in the section on Petrography, and salient features are demonstrated with photomicrographs.

Saline fluid inclusions: Recrystallized quartz grain in a brecciated granite (sample 4883) contains small fluid inclusions with halite daughter minerals. This suggests the circulation of saline fluids during brecciation and recrystallization of the granite. Saline fluids associated with the ores at the SIC have been well documented by cf. Farrow et al. (1994) and Molnar et al. (2001). The photomicrograph of such fluid inclusion in the recrystallized quartz is shown on page 4.

Objective 2 Due to extensive alteration, brecciation fragmentation, and the possible mixing of

different lithological units (i.e. sediments and granitic rocks), the identification of the various rock types was not always straightforward. The effect of alteration is apparent on the mafic intrusive rocks. For example, distinction between gabbro and diorite is difficult when the mafic minerals have all been replaced by amphibole, and the plagioclase are epidotized, reducing their An content from i.e. labradorite to andesine. Thus, although the rock types were identified on the basis of their primary mineralogy and texture, where the primary minerals were destroyed, assumptions had to be made from the type of replacement assemblages.

2

Sample #

22304 (1) 22305 (2) 22306 (3) 22313 (4) 22314 (5) 22315 (6) 22316 (7) 22317 (8) 22320 (9) 22323 (10) 4883 (11) 22324 (12) 22325 (13)

Objective 3

Rock Type

Quartz-diorite (offset dike?) Quartz-diorite (offset dike?) Gabbro Footwall Breccia? Footwall Breccia? ? Epidotized fragmental or sediment Amphibolite Metasediment Footwall Breccia (+dacite?) Brecciated granite Quartz diorite or highly fractionated gabbro? Gabbro- diabase?

'II The mineralogy and texture of samples 22304 & 22305 (1&2) are comparable to .,; fine-grained altered quartz diorites (off-set dikes), but also to some footwall breccias.

They contain variable proportions of granophyre and chlorite, some quartz oikocrysts <tI with plagioclase inclusions and small, tabular to lath-shaped plagioclase phenocrysts. r~

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Samples 22313 & 22314 (4 & 5) consist of brecciated granite fragments (some of which are annealed), and fragments of Huronian sediments (arkosic quartzite). Annealing, brecciation and the intercalation with sediments may be consistent with a type of footwall breccia. One thin section however, is insufficient to come to conclusions with respect to the origin.

Sample 22320 (9) is a metasediment.

Sample 22323 (10) is probably footwall breccia intercalated with dacite (?). This conclusion is based on (a) the presence of a small lithic fragment with igneous texture within the thin section (2x5mm), having mineralogy and texture comparable to footwall breccias as described by McCormick et al. (2002), and (b) some of the broken plagioclase clasts in the fine-grained quartz-rich host have unusual morphology (annealed plagioclase: 22323-8), and some are extensively brecciated (22323-A). The lithic fragment is in sinuous contact with the fine-grained quartz-rich host.

Sample 4883 (11) is a brecciated granite fragment. Recrystallized quartz in the granite contains fluid inclusions with halite daughter minerals, suggesting the circulation of hyper-saline fluids during its recrystallization. Such fluids have been documented in the orebodies of the SIC by cf. Farrowet al. (1994) and Molnar et al. (2002).

3

•

•

4883. Cubic halite daughter minerals in aqueous fluid inclusion in recrystallized quartz.

Note: Poor quality of several of the thin sections (holes, inadequate thickness, air, oil or water bubbles?) significantly reduced the usable surface of the sections for petrography.

REFERENCES

McCormick K.A., Fedorovich J.S., McDonald A.M, and James R.S. 200:2. A textural, Mineralogical and Structural Study of the Footwall Breccia within the Strathcona Embayment of the Sudbury Structure: Econ. Geo!. v. 97, p. 125-144.

Molnar F., Watkinson D.H. and Jones P.C. 2001. Multiple hydrothermal processes in footwall units of the North Range, Sudbury Igneous Complex, Canada, and implications for the genesis of vein-type Cu-Ni-PGE deposits. Econ. Geo!. v. 96, p.1645-1670.

Farrow E.G., Watkinson D.H. and Jones P.C. (1994): Fluid inclusions in sulfides from North and South Range Cu-Ni-PGE deposits, Sudbury structure, Ontario. Ec:on. Geo!. v. 89, p. 647-655.

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PETROGRAPHY

Ppl = Plane polarized light XN = crossed nicols

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Sample Number: 22304 (1) Rock Type: Quartz-diorite (offset dike)?

Location: Parkin: 510363 5186613

Petrographic Description:

Fine-grained igneous rock with granophyric texture. It consists predominantly of lath-shaped plagioclase, interstitial graphic quartz, anhedral quartz, and large chlorite patches that contain skeletal ilmenite. Some of the ilmenite was partly replaced by titanite. Graphic quartz is relatively abundant and it is interstitial to the feldspars. Some of the larger, anhedral quartz grains resemble oikocrysts and contain inclusions of lath­shaped plagioclase. Fine-grained biotite, carbonate and sericite partly replaced the feldspars, and late chlorite veins contain inclusion of biotite, carbonate, sericitized plagioclase and perthite. The mineralogy and texture of the rock is comparable to some quartz diorite offset dikes, but also to some of the footwall breccia as described by McCormick et al. (2002).

Mineral %

Plagioclase 35

Quartz 20

Chlorite 40

Carbonate 3

Detailed mineralogy

Grain size(mm) Comments

<0.3-1.0 Sericite and carbonate altered plagioclase are mostly lath-shaped, and less commonly, they occur as stubby, equant grains. Some plagioclase are included in anhedral quartz, whereas some of the longer laths are bent, and have displaced twin lamellae.

variable, up to 1.3 Graphic quartz is interstitial to the feldspars, and they also occur as oikocryst-like grains that contain plagioclase inclusions. All quartz are strained and have undulose extinction.

minute-0.3

6

Chlorite occurs as replacement after earlier mafic minerals, as suggested by the amphibole shape of some chlorite patches. Late veins contain inclusions of fine­grained biotite, carbonate and sericitized feldspars. Chlorite after mafic minerals contain skeletal ilmenite and aggregates of fine-grained rutile.

Fine-grained carbonate occurs as

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Sericite I 1 muscovite

Ilmenite I 1 magnetite

Biotite <0.5

<0.2-0.4

av.O.2

replacement after plagioclase, and as anhedral grains interstitial to the feldspars and quartz.

The feldspars are sericitized and a few small «0.3mm) muscovite grains are interstitial to the quartz and feldspars.

Skeletal ilmenite and anhedral magnetite grains occur mostly in chlorite. Several of the grains are partly or completely replaced by fine-grained titanite.

Fine-grained biotite are included in some of the chlorite-rich domains, and some are interstitial to plagioclase and quartz.

Accessory minerals: titanite, allanite or monazite (?), apatite (acicular)

7

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22304-8 . Skeletal ilmenite chlorite (after i Width of photo: 2.3mm. Ppl.

22304-A. Quartz "oikocryst" with inclusions of small plagioclase. Width of photo: 2.3mm. XN .

Sample Number: 22305 (2) Rock Type: Quartz-diorite (offset dike)?

Location: Parkin: 510340 5186593

Petrographic Description:

The rock is almost identical to sample 22304, although it is slightly more coarse­grained and contains somewhat more chlorite. Pseudomorphic replacement of amphibole phenocrysts by chlorite and lesser biotite is apparent and chlorite-rich domains contain several opaque minerals, most of which are skeletal ilmenite. Chlorite is abundant and forms large domains in the rock. Fine-grained carbonate is interstitial to chlorite, and it also occurs as replacement after some of the plagioclase. Plagioclase occur as sericitized laths and as nearly equant grains. Small grains of perthite occur as inclusions in quartz and they are interstitial to the quartz and plagioclase. Most quartz have graphic-granophyric texture, and are interstitial to plagioclase. Some of the quartz rec'rystallized to semi-granoblastic aggregates. Some quartz contain inclusions of small grains of plagioclase and perthite ("oikocrysts"). Sericite alteration of the feldspars is pervasive. Fine-grained carbonate occurs with sericite and as inclusions within chlorite­rich domains.

Mineral %

Plagioclase 30

Quartz 23

Chlorite 40

Detailed mineralogy

Grain size(mm)

<0.3-1.3

<0.2-1.4

9

Comments

Most plagioclase occur as small laths. They are extensively sericitized, and their composition cannot be estimated due to the destruction of the twin lamellae by sericite. A couple of large areas (up to 2mm) consist of sericitE! aggregates, suggesting the replacement of a large plagioclase phenocrysts.

Anhedral quartz are interstitial to the plagioclase. They often have graphic texture, some are intergrown with the plagioclase, and some occur as small "oikocrysts" that contain inclusions of plagioclase.

The shape of some chlorite-rich domains suggests that chlorite crystallized after coarse-grained, prismatic amphibole. Other chlorite-rich domains are interstitial to the feldspars and quartz.

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Sericite

Ilmenite I magnetite

Carbonate

5

1

1

Up to 0.4

up to 0.5

Fine-grained sericite is a replacement after plagioclase. It also occurs in aggregates with interstitial, graphic quartz, suggesting the replacement of alkali feldspars (granophyre).

Skeletal ilmenite and blocky magnetite occur within chlorite-rich domains. Some ilmenite are partly replaced by fine-grained titanite.

Carbonate occurs as replacement after plagioclase, and it often occurs within chlorite-rich domains.

Accessory minerals: biotite, titanite, allanite or monazite (7), apatite

10

Width of photo: 2.3mm. Ppl.

phorlo: L .~mrn . XN.

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Sample Number: 22306 (3) Rock Type: Gabbro

Location: Parkin: L32S + 0 + 75W + 15N

Petrographic Description:

Medium-grained, altered gabbro. It consists of relict colorless and weakly pleochroic green amphibole, subhedral plagioclase (mostly andesine). secondary amphibole (actinolite), clinozoisite that partly replaced some of the plagioclase, interstitial quartz, and anhedral opaque minerals - probably magnetite. The presence of plagioclase inclusions in the "relict" amphibole suggest that the amphibole crystallized after pyroxene. Apatite is a common accessory mineral. The major minerals, plagioclase and amphibole, are variably altered. Clinozoisite is a common replacement after plagioclase, and the "relict" amphibole are replaced by fine-grained, acicular actinolite. Graphic quartz and alkali feldspars are interstitial to the plagioclase and the amphibole. Alteration in the rock is extenSive, but mostly pseudomorphic, thus, the igneous texture is well preserved.

Mineral %

Plagioclase 45

Amphibole 52

Opaque <1 minerals

Detailed mineralogy

Grain size(mm) Comments \

0.3-2.0 Plagioclase phenocrysts are lath-shaped,

<0.3-2.5

0.2-0.8

12

some are equant and some are narrow, prismatic grains. Their composition has a narrow range of An45-5o, although the altered grains are generally more sodic. The major replacement mineral after plagioclase is, clinozoisit1e, and minor sericite.

Anhedral first-generation amphibole are generally stubby, equant grains, whereas replacement actinolite after the primary amphibole occur as narrow, prismatic and acicular grains that form aggregates, or they pseudomorph the original amphibole. Secondary amphibole is weakly pleochroic green. At least 50% of the primary amphibole were replaced by actinolite.

Anhedral opaque minerals are probably magnetite. They occur with the altered amphiboles.

Clinozoisite 2 Av.O.2

Graphic qtz. + 1 Variable alkali feldspars

Accessory minerals: Sericite, apatite, titanite

13

Anomalous blue clinozoisite occur as inclusions in plagioclase, as well as granular aggregates in the altered domains of the rock.

Anhedral quartz, and graphic quartz+alkali feldspars are interstitial to the amphiboles and the plagioclase.

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Sample Number: 22313 (4) Rock Type: Footwall breccia?

Location: IRM: 451313 5170344

Petrographic Description:

The rock consists of brecciated granite fragments intercalated with Huronian sediment fragments. The sediment is a matrix-supported arkosic quartzite.

The granite fragment(s) consist of quartz + plagioclase + perthite. These fragments show evidence of brecciation, granulation and annealing. The grain boundaries of the above minerals are sutured and embayed, suggesting disequilibrium.

The sediment matrix consists of interlocking grains of microcrystalline quartz and feldspars, minor chlorite and biotite, and the clasts are predominantly subrounded to sub-angular quartz, lesser plagioclase and perthite.

~ Some of the (angular) perthite and plagioclase clasts that are intercalated with the sediment fragments were evidently derived from the granite. Their morphology is

,J different from the subrounded quartz clasts that are part of the sediments. Minor chlorite and biotite are interstitial to the fine-grained quartz-rich matrix and form rims on the granite fragments. Fine-grained titanite occur in stringers and in aggregates within the

~ sediment matrix. Several grains of dark and partly altered zircons were identified in the fine-grained matrix. The rock shows evidence of granulation and partial recrystallization, and some plagioclase contains exsolved quartz (?) stringers perpendicular to the twin

~ lamellae (partial melting?). A few grains of opaque minerals and banded red Fe-oxide after magnetite (goethite?) occur in the sediment fragment.

Mineral %

Quartz 65

, I

Plagioclase 20

Detailed mineralogy

Grain size(mm)

Minute to 3.5

Minute to 3.0

15

Comments

In the sediment, the matrix quartz is sub­microscopic and forms interlocking aggregates. The quartz clasts are ca. 0.5mm in diameter, they are subrounded, strained, have undulose extinction, and smooth grain boundaries. Some of the clasts are fractured. In the granite fragments, the grain size of anhedral quartz is up to 3.5mm, they have sutured and embayed grain boundaries, some are brecciated. and are generally intergrown with the feldspars.

In the granite fragment, anhedral plagioclase (albite-oligoclase) are

Perthite 10

Chlorite 4

Biotite 1

<0.5-3.0

<0.2- 0.5

intergrown with quartz and perthite. Their grain size is up to 3mm. In the sediment, plagioclase (albite­oligoclase) occurs as angular to sub­angular "fragments, some of which were probably derived "from the fragmented granite. Fine-grained detrital plagioclase are also interstitial to the matrix quartz.

Anhedral perthite is intergrown with quartz and plagioclase in the granite fragment, whereas small, angular grains of perthite (derived from the granite) are intercalated with the sediment.

Weakly pleochroic chlorite is interstitial to the sediment matrix and to the fragmented granite. Some contain inclusions of fine­grained titanite.

Anhedral biotite occurs with late chlorite, it is interstitial to the matrix sediments and to quartz and feldspars in the granite.

Accessory minerals: titanite, opaque minerals, goethite{?), zircon, apatitE~

16

2231

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F"'grne"ted plagioclase and annealed quartz photo: 2.3mm. XN.

2231 i are alfrlost oriihoclonaj twin lamellae in plagioclase. Width of photo: XN.

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Sample Number: 22314 (5) Rock Type: Footwall breccia?

Location: IRM: 451313 5170344

Petrographic Description:

A granulated and biotite-altered rock that consists of biotite and chlorite-altered sediment and coarse-grained granite fragments.

The granite fragments consist predominantly of quartz and feldspars. The feldspars are predominantly albite-oligoclase and minor perthite. They are all fractured, fragmented, granulated and brecciated, and several of the plagioclase have deformed or off-set twin lamellae. All of the feldspars and quartz in the granite fragments have sutured and embayed grain. boundaries, and several domains are partly recrystallized. Corroded and fractured zircon is included in one of the granite fragments.

The sediment fragment consists of fine-grained quartz, chlorite, and biotite-rich matrix, and subrounded to sub-angular and angular clasts of quartz and plagioclase. Some of the plagioclase and quartz fragments were evidently derived from the granite (the grains have similar morphology), but the subrounded quartz and sub-angular clasts with smooth grain boundaries were part of the sediment. Other minerals in the rock include fine-grained, lath-shaped, stubby muscovite, needle-shaped sericite inclusions in plagioclase, a few grains of small, blocky opaque minerals.

Mineral %

Plagioclase 25

Quartz 35

Detailed mineralogy

Grain size(mm) Comments

<0.5-4.0 In the granite fragment, plagioclase are coarse-grained, fractured and fragmented. Deformation of some grains is apparent from their bent twin lamellae. They are intergrown with quartz, and all have sutured and embayed grain boundaries. The plagioclase fragments broken off from the granite have comparable morphology. In the sediment fragment, plagioclase is rare within the altered matrix, and most plagioclase clasts appear to have been derived from the granite.

<0.2-3.0 Anhedral, fractured and fragmented quartz with sutured and embayed grain boundaries occur in the granite fragments, and subrounded quartz with smooth grain boundaries are clasts in the sediment fragment. Fine-grained matrix quartz is

19

Chlorite 20

Biotite 20 up to 0.3

interstitial to biotite and chlorite.

Fine-grained chlorite is intergrown with biotite in the sediment matrix, and it occurs in aggregates within fractures of the granite fragments.

Fine-grained biotite (brown pleochroism) occurs with chlorite in the sediment matrix and in the fractured granite fragments. In the latter they form aggregates with chlorite.

Accessory minerals: muscovite/sericite, opaque minerals, zircon, titanite, apatite, carbonate

20

•

22314-A. Sediment fragment. Width

Width of photo: 2.3mm. XN .

\

i I Width of photo: 2.3mm. XN .

-

Sample Number: 22315 (6) Rock Type: ?

Location: IRM: 451699 517034, L3S + 8 + 50E + 75N

Petrographic Description:

An extensively granulated, very fine-grained, featureless rock. It consists predominantly of microcrystalline granoblastic quartz and parallel bands of almost isotropic chlorite with fine-grained interstitial biotite. Chlorite-rich domains make up ca. 1/3rd of the rock, and contain inclusions of metamict, fine-grained titanite after titanomagnetite or ilmenite, and radiating aggregates of biotite. Chlorite and biotite-rich bands define the rock fabric. Late vein lets of quartz and albite are interstitial to chlorite and biotite-rich domains. The microcrystalline quartz-rich domains contain several euhedral, blocky opaque minerals that are rimmed by quartz pressure shadows. Biotite and chlorite form rims on the pressure shadows, suggesting that the opaques and the quartz pressure shadows pre-dated biotite and chlorite. A few grains of anhedral carbonates occur within quartz aggregates and in the chlorite-rich domains.

Note: the major and trace element geochemistry of the rock (low 8i02, high Fe203, MgO, Ti02, P205, Cr, Ni, Co and Sc) suggest a mafic protolith.

Mineral %

Quartz 35

Chlorite 30

Detailed mineralogy

Grain size(mm)

minute to 0.5

Comments

Microcrystalline quartz (granoblastic aggregates) makes up a significant part of the matrix. Quartz also occurs in discontinuous vein lets with albite, as well as larger (O.3mm) grains in granoblastic aggregates within the chlorite-rich domains. Most granoblastic quartz are unstrained or weakly strainE~d, suggesting recrystallization. Some opaque minerals are rimmed by quartz pressure shadows.

Weakly pleochroic green, almost isotropic chlorite defines the rock fabric. It is interstitial to the quartz-rich domains and contains stringers of fine-grained biotite.

Biotite 25 minute to 0.6 Most biotite occur within the chlorite-rich domains and also define the rock fabric. Radiating biotite occurs with some of the quartz-albite veins.

Accessory minerals: albite, carbonate, opaque minerals, titanite, apatite

23

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22315-C. Fine-grained titanite (with remnants of ilmenite) in chlorite-biotite-rich domain. Width of photo: 0.45mm. Ppl..

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2231 i Width of photo: 2.3mm.

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Sample Number: 22316 (7) Rock Type: Epidotized fragmental or sediment

Location: IRM: L 1 OS + 4 + 25E + 30N

Petrographic Description:

An extensively epidotized rock with interstitial chlorite and biotite. The fine­grained matrix consists of angular and granulated quartz, broken plagioclase clasts, interstitial clinozoisite, biotite aggregates, and a few grains of titanite. Fragments of anhedral, angular quartz and feldspars, some of which resemble phenocrysts, suggest that the rock may be an extensively epidotized fragmental. Pervasive epidote alteration is apparent, as epidote occurs as large porphyroblasts and poikiloblasts, as fine-grained aggregates interstitial to the matrix, as well as cross-cutting veins that consist of quartz + epidote. The shape of some of the epidote porphyroblasts and fine-grained aggregates resemble phenocrysts (plagioclase and pyroxene), but as alteration is pervasive, this observation is tentative. Biotite occurs locally as fine-grained aggregates, ~ and they are also disseminated through the rock. Chlorite aggregates occur in small pods and as cross-cutting veinlets. Both, biotite and chlorite post-dated epidote, as they form rims on epidote aggregates. The presence of biotite inclusions in chlorite suggests that chlorite post-dated biotite (retrograde metamorphism). Opaque minerals are rare, and the few anhedral grains occur with epidote aggregates.

Mineral %

Quartz 45

Epidote 35

Detailed mineralogy

Grain size(mm) Comments

<0.2-2.5 Most quartz are angular, broken clasts of variable size. Some quartz that are rimmed by epidote, have resorbed grain boundaries, suggesting their partial replacement by epidote. With the exception of a small, cross-cutting composite vein, there is no evidence to suggest that the crystallization of epidote and the quartz in the rock were contemporaneous.

<0.2-1.5 Epidote occurs as porphyroblasts, poikiloblasts, as fine-grained aggregates interstitial to matrix quartz, and as cross­cutting veins. Most of the interstitial fine­grained aggregates are clinozoisite, as suggested by their low birefringence and the anomalous blue color. Textural evidence suggests that replacement by

26

Plagioclase 10

Biotite 5

Chlorite 5

<0.-1.5

<0.3

epidote pre-dated all other alteration in the rock.

Plagioclase occurs as broken clasts, and as part of the fine-grained matrix. Most grains are angular, but some have resorbed grain boundaries. Their composition cannot be determined.

Fine-grained biotite occurs in aggregates and as single grains disseminated through the matrix. Some form rims on epidote, suggesting that they post-dated epidote replacement.

Chlorite occurs in small patches within the fine-grained matrix, and as small cross­cutting veinlets. They form selvages on epidote veins, suggesting that they post~ dated epidote alteration.

Accessory minerals: titanite, rutile, opaque minerals, sericite, apatite, zircon

27

22316-A. Epidote porphyroblast (green) in quartz-rich matrix. Width of photo: 2.3mm. XN.

22:31Ei-B Epiclote aggregates (yeilic lw-orang',) Width of photo: 2.3mm. XN .

Sample Number: 22317 (8) Rock Type: Amphibolite

:J Location: IRM: L 10 + 4 + 80E + 40N

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Petrographic Description:

Note: The thin section is ground too thin and it is full of holes!

An almost monomineralic rock, consisting of prismatic actinolite, minor chlorite and fine-grained titanite and rutile. Two amphibole generations were identified. The earlier amphibole was pleochroic brown and fragments of the relict grains are included in the present coarse-grained actinolite. Actinolite predominates, and occurs as randomly oriented, large, prismatic and fibrous grains. Fine-grained actinolite aggregates are interstitial to the large grains. Titanite and rutile are disseminated through the rock. Some probably crystallized from the break-down of more calcic and Ti-rich amphibole, and from the breakdown of ilmenite.

Mineral % Grain size(mm)

Actinolite 96 <0.2-4.0

Relict hornblende? 2 <0.5

Chlorite 2 3(") 4·6 2. 1 ; . ." ~.

Titanite+ rutile trace

29

22317-A. Relict amphibole rimmed by fibrous actinolite. Width of photo: 2.3mm. XN .

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2231 7-8. Fibrous actinolite weakly chloritized. Width of photo: 2.3mm.

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22317-C. Titanite (dk. brown) after ilmenite. Width of photo: 2.3mm. XN .

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Sample Number: 22320 (9) Rock Type: Metasediment

Location: IRM: L8S + 4 + 60E + 8N

Petrographic Description:

Note: A poorly prepared thin section. The surface of the cut rock is partly covered by epoxy and/or air bubbles, which compromised the optical properties of some minerals.

A medium-grained clast-supported sediment, similar in texture to the sediment fragment in sample 22314. It consists of subrounded to sub-angular quartz, plagioclase and microcline clasts and interstitial matrix (cement) consisting of microcrystalline quartz, carbonate, green and brown pleochroic biotite and muscovite. The rock texture and mineralogy are comparable to some of the arkosic quartzites of the Huronian sediments. However, the presence of few large quartz and feldspar clasts suggest that the rock may be either a poorly sorted sediment or the sediment is intercalated with quartz and feldspar fragments derived from the footwall breccia. Observations based on one thin section are inadequate to come to reasonable conclusions.

Mineral %

Quartz 65

Plagioclase 10

Microcline 15 and perthite

Detailed mineralogy

Grain size(mm)

<0.2-3.0

<0.3-2.0

<0.5-4.0

32

Comments

Quartz occur as subrounded, sub-angular and angular clasts, and as fine-grained matrix interstitial to the clasts. The subrounded clasts (pebble-shaped) have smooth grain boundaries, and the sub­angular and angular clasts have slightly resorbed, sutured grain boundaries. Some of the triangle-shaped angular clasts have sharp terminations, as if derived from brecciated protoliths. All of the large «2.0mm) clasts are angular to sub­angular, and some are intergrown with plagioclase.

Most plagioclase are sub-angular and interstitial to the subrounded quartz clasts. Their morphology suggests derivation from different sources.

Most microcline and perthite are strained, angular and deformed clasts and some are small fragments interstitial to the larger

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,) .,

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Biotite + 9 muscovite

Carbonate 1

Av.O.2

Up to 0.4

clasts. They are generally more coarse­grained than the subrounded quartz clasts. Some microcline are attached to coarse­grained quartz.

Fine-grained biotite and muscovite are interstitial to the matrix and form part of the fine-grained matrix to the sediment, or occur in aggregates. Biotite is more abundant, and most are pleochroic green.

Fine-grained anhedral carbonate is interstitial to the matrix. Some occur in aggregates with the micas .

Accessory minerals: opaque minerals, titanite/rutile, apatite, zircon

33

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22320-A. Sediment. Width of photo: 2.3mm. XN.

22320-8. Relict microcline (cross-hatched tvvinning) in sediment. Width of photo: 2.3mm. XN.

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Sample Number: 22323 (10)

Location: IRM: L8S + 6 + OOW

Rock Type: Footwall Breccia (+dacite?)

Petrographic Description:

A very fine-grained rock that consists of microcrystalline quartz-rich matrix (80%), broken quartz and feldspar clasts (10%) and carbonates (10%). The texture resembles of an altered porphyritic dacite.

However, a small igneous fragment in the thin section (2x5mm) having mineralogy and texture comparable to the footwall breccia as described by McCormick et al. (2002), is, in sinuous contact with the fine-grained quartz-rich matrix. In addition, in the fine-grained quartz-rich matrix some of the broken plagioclase clasts have an unusual morphology (see photomicrograph of 2 grains of annealed plagioclase: 22323-B), whereas some are extensively brecciated (photomicrograph 22323-A).

Anhedral, blocky opaque minerals are relatively common and they are disseminated through the matrix.

Mineral %

Quartz 70

Plagioclase 20

Biotite 2

Detailed mineralogy

Grain size(mm) Comments

Minute to 2.0 Microcrystalline quartz makes up most of the matrix, and anhedral and broken quartz phenocrysts or clasts that occur in the matrix range from 0.5 to 2.0mm. They are generally strained and have uneven grain boundaries. Some recrystallized and form interlocking aggregates with the carbonates.

<0.3-2.0 Anhedral, angular and sub-angular plagioclase (oligoclase) are mostly present as broken phenocrysts or clasts. Some broken clasts are annealed, several are strained, some are brecciated and some are granulated at the grain boundaries.

<0.5 Fine-grained biotite is interstitial to the matrix quartz. It also occurs as rims on some of the plagioclase and quartz clasts, suggesting a metamorphic origin.

35

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Opaque minerals

Carbonate

3

5

up to 0.4

<0.2-1.0

Anhedral I subhedral and blocky opaque minerals are disseminated through the matrix. They are often rimmed by biotite.

Anhedral carbonate occurs within the quartz-rich matrix, and as aggregates interstitial to quartz and plagioclase clasts.

Accessory minerals: chlorite, sericite, apatite, zircon (2), rutile

36

..

. •

22323-A. Brecciated plagioclase (rimmed by carbonate) in fine-grained quartz+sericite matrix. Width of photo: 2.3mm. XN .

--22323-B. Two separate grains of plagioclase, annealed. Width of photo: O.4Smm. XN .

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Sample Number: 4883 (11) Rock Type: Brecciated granite fragment

Location: IRM: L8S + 4 + 60E + 30S

Petrographic Description:

A fragmented and granulated granite that consists of aggregates of coarse­grained quartz, plagioclase and perthite. The coarse-grained mineral aggregates are fractured, fragmented. The quartz and feldspar grains have sutured grain boundaries, and the deformed and fragmented lamellae in the feldspars is consistent with extensive deformation and brecciation of the rock. The different feldspar fragments and the quartz are annealed into clumps. One large (mafic?) phenocryst is completely recrystallized to fine-grained biotite and titanite. Fine-grained biotite is interstitial to quartz and the feldspars, and also occur in fractures. Pleochroic halos in biotite that contain inclusions of titanite suggest, that the titanite grains probably contain some REE and Th or U. A few small, fine-grained fragments between the coarse-grained quartz and feldspars, that consist of intergrowths of fine-grained feldspars and quartz have texture similar to the matrix of some footwall breccia that has been described by McCormick et a!. (2002).

Small fluid inclusions, containing halite daughter minerals were identified in recrystallized quartz, suggesting that the quartz crystallized from highly saline fluids. Saline fluids have been reported earlier from several ore zones at the SIC (cf. Farrowet aI., 1994, Molnar et aI., 2001).

Mineral %

Quartz 70

Plagioclase 10

Perthite 15

Detailed mineralogy

Grain size(mm) Comments

<0.3-4.0 avo 2.5 Anhedral quartz are strained, fractured, and fragmented. Several of the grains have sutured grain boundaries. In the granulated matrix, quartz occur as sub­angular grains with em bayed and ragged grain boundaries.

<0.5-3.0 avo 2.0 Due to deformation of the twin lamellae, the composition of plagioclase cannot be properly determined. They appear to be in the range of albite-oligoclase. Several of the grains are fragmented and granulated. Some recrystallized to semi-granoblastic aggregates with quartz.

0.5-4.0 avo 2.5 Perthite is the most abundant feldspar in the granite. It is also the most susceptible to granulation and recrystallization. The

38

•

Biotite 5 Up to 0.5

grains are often fragmented and form aggregates with quartz. The sutured and embayed grain boundaries suggest disequilibrium recrystallization.

Biotite occurs as replacement after a large (2.5mm) mafic phenocryst, as aggregates within recrystallized domains, and as veinlets interstitial to the coarse-grained quartz and feldspars.

Accessory minerals: chlorite, titanite, sericite, carbonate, apatite, zircon

39

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4883-A. Cubic halite daughter minerals in fluid inclusion in quartz of brecciated granite. Ppl.

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4883-B. Brecciated and fragmented granite. Width of photo: 2.3mm. XN .

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4883-C. Partly recrystallized perthite in granite. Width of photo: 2.3mm. XN.

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/~. ; .. '~ ... '

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,TI .~ , I ~ .... 'I - ..........

4883-0. Fine-grained titanite (colorless) with inclusions of relict titanomagnetite (blk) in chlorite-biotite-altered granite. Width of photo: O.45mm , PpL

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Sample Number: 22324 (12) Rock Type: Quartz diorite or fractionated gabbro?

Location: IRM: 450365 5170196

Petrographic Description:

An amphibolitized coarse-grained quartz diorite or a highly fractionated quartz­rich gabbro. The rock consists predominantly of uralitized hornblende, zoned and unzoned calcic plagioclase, interstitial quartz, biotite aggregates, acicular stilpnomelane (?), fine-grained clinozoisite, and several grains of skeletal ilmenite and other opaque minerals. Intergrowth of graphic quartz with alkali feldspars is common and it variably contains aggregates of stubby biotite. The graphic quartz assemblage is generally interstitial to the amphibole and plagioclase. Apatite is coarse-grained and abundant. Replacement minerals include fibrous actinolite, biotite and stilpnomelane(?). Minor sericite and fine-grained epidote/clinozoisite aggregates occur as inclusions in some of the plagioclase.

Mineral %

Amphibole 55

Plagioclase 20

Graphic qtz.+ 10 alkali feldspars

Detailed mineralogy

Grain size(mm)

0.5-4.0 avo 2.5

Comments

Several amphibole generations were identified. The relict amphibole are highly pleochroic hornblende. They occur as large, stubby and prismatic grains interstitial to plagioclase. Much of the hornblende has been partly replaced by blue-green actinolite at the selvages and along fractures and cleavages. Some of the amphibole recrystallized to acicular, fibrous and semi-radiating actinolite. Fine­grained actinolite also occurs as inclusions in plagioclase.

Av.2.0 Plagioclase are extensively altered, and most twin lamellae has been destroyed. Therefore, their composition cannot be estimated. Some plagioclase grains are zoned and they contain fine-grained inclusions of actinolite, clinozoisite and sericite.

Coarse up to 1.5 Intergrowth of graphic quartz and alkali feldspars±biotite is relatively abundant. Some of the quartz recrystallized.

42

Biotite 10

Stilpnomelane 1

Ilmenite / 4 magnetite

<0.3-0.6

Up to 2.0

Up to 1.0

Biotite aggregates partly replaced some of the actinolitic amphibole, and relict K­feldspars. They also occur as aggregates within the graphic quartz and alkali feldspars.

Dark brown pleochroic needles that cross­cut all other minerals are probably stilpnomelane (too narrow for optical measurements to positively identify).

Skeletal ilmenite and titanomagnetite are associated with the amphiboles. Many are rimmed by fine-grained titanite and/or biotite.

Accessory minerals: alkali feldspars, sericite, titanite, apatite, clinozoisite

43

· 22324-A Graphic quartz (light) interstitial to amphibole. Width of photo: 2.3mm. XN.

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22324-8. Skeletal ilmenite in amphibole grain. Width of photo: 2.3mm. XN .

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Sample Number: 22325 (13) Rock Type: Diabase-textured gabbro(?)

Location: IRM: L4S + 8 + 10E + 15N

Petrographic Description:

An amphibolitized medium-grained diabase-textured gabbro. The rock consists predominantly of partly uralitized hornblende, zoned plagioclase, skeletal ilmenite­titanomagnetite, fine-grained epidote and clinozoisite (after plagioclase), and a few grains of anhedral, interstitial quartz. The replacement assemblage in this rock is significantly different from the previous sample (332324), as it contains an abundance of epidote-group minerals, and fine-grained titanite (most opaque minerals were replaced by fine-grained titanite). Biotite and graphic quartz however, are sparse. The abundance of clinozoisite inclusions in plagioclase laths suggests that the original plagioclase had a calcic composition.

Mineral

Amphibole

Plagioclase

Epidote / clinozoisite

%

60

25

10

Detailed mineralogy

Grain size(mm)

0.5-4.0

0.5-2.5

Minute - up to 0.6

45

Comments

Amphibole occur as long, prismatic phenocrysts and stubby grains. Some of the large grains are hornblende, but most were partly replaced by actinolite, as suggested by the blue-green pleochroism of the secondary grains. Textural evidence suggests that some of the plagioclase were also partly replaced by blue-green actinolite (amphibolitized), and several of the amphibole grains contain opaque minerals (titanomagnetite or ilmenite) that were partly replaced by fine-grained titanite.

Plagioclase occur as lath-shaped grains, most of which are partly replaced by clinozoisite and some by actinolite. Zoning is common, but the twin lamellae in most grains were destroyed by alteration and by strain. Thus, their composition cannot be determined.

Clinozoisite aggregates crystallized at the expense of plagioclase and fine-grained epidote occur as granular aggregates

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Titanite+opaques 5 Variable

Quartz <0.5 variable

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within or around the rims of altered amphibole.

Opaque minerals were more or less replaced by fine-grained titanite. The almost pseudomorphic replacement of ilmenite or titanomagnetite resulted in the preservation of the skeletal form of some grains.

Quartz occurs as anhedral, interstitial grains to plagioclase and the amphiboles. Some have weakly graphic texture.

Accessory minerals: biotite, sericite, chlorite, apatite

46

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~ ---I-33235-A. Prismatic amphibole and plag ioclase (diabasic texture).

Width of photo: 2.3mm. XN .

- . 22325-8. Skeletal ilmenite or titanomagnetite in amphibole. With of photo: 2.3mm. Ppl.