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A PETROGRAPHIC AND GEOCHEMICAL STUDY OFTHE POTTER MINE AND INTERPRETATIONS ON IT'S VOLCANIC ENVIRONMENT

MUNRO TOWNSHIP, ONTARIO

FOR
MILLSTREAM MINES LTD.

BY
HAROLD GIBSON
SEPTEMBER 1998

SUMMARY

Appendix 1, to view Element Analyses on Potter Core

Massive Cu, Zn, Co, Ag VMS mineralization at the Potter mine occurs within a tholeiitic volcanic centre contained within a largely ultramafic komatiitic volcanic succession. The mineralization is hosted within a package of transported, basaltic hyaloclastite breccias and minor sediments intruded by synvolcanic basaltic sills and dikes that occupy a volcanic subsidence structure - basin or graben - on the flat, komatiitic lava plain. The mineralization occurs as either massive to semi massive, subseafloor replacement deposits within the hyaloclastite or as massive sulphide lenses, associated with carbonaceous and argillaceous sediments, that formed on the seafloor. The stacked, multi-lens nature of the mineralization indicates that hydrothermal activity responsible for the mineralization was active throughout, and interrupted by, deposition or the hyaloclastite deposits. The semi-massive and massive sulphide lenses are enveloped by an aerially restricted, semiconformable black chlorite alteration characterized by a depletion in SiO2, Na2O, CaO and MgO and an enrichment in Fe2 O3 and metals. The lack of an extensive, pervasive and/or discordant chlorite alteration zone strongly suggests that the mineralization encountered is either a product of a small, intermittent hydrothermal system or is fringe to a larger system which may have formed a larger sulphide lens or lenses. The mineralization is open at depth (along the plunge of the subsidence structure) and to a lesser extent along strike, this coupled with its stacked character, indicate that the potential for discovery of additional sulphide lenses is high.
 


RECOMMENDATIONS

l. Results of the orientation study indicate that lithogeochemistry is useful in defining areas of altered chloritized-rock associated with mineralization and in "finger-printing" the host stratigraphy which is useful when tracing mineralization outside of the mine area and in the resolution of structural problems. It is recommended that core from all drill holes within and outside of the mine area be systematically sampled for major elements plus Cu and Zn. Samples should be taken every 30m or at a change in rock type and each sample should consist of 6-8, 2-4 cm long pieces taken over a 2 m interval. Major element data should be examined visually and statistically arid plotted on plans and sections where the data can be contoured. The orientation study suggests that oxides such as Na2O, CaO, K2O, MgO and Fe2O3 may adequately define chlorite alteration which is intimately associated with the mineralization. The immobile and incompatible nature of Al2O3 and TiO2 make them useful monitors of alteration and fractionation and removes the need to analyze for expensive trace elements during "routine" exploration.

2. As recommended in a previous memo, all sulphide intersections regardless of visible tenor or width should be assayed for Cu, Zn, Co, Ag and Au. This new data, plus that generated from previous mining, should be compiled onto sections and plans where the raw data for each element and selected ratios (ex. Cu/Cu+Zn x 100; Cu x thickness etc..) are contoured. Trends within the contoured data may indicate primary metal zoning variations that can be tested by drilling. In particular, trends of Cu-enrichment coupled with low Na2O and CaO and high MgO and Fe2O3 may be particularly important in defining "core areas" within the paleohydrothermal system which may be associated with larger and higher grade deposits.

3. A limited SEM study should be completed to: a) determine the sulphide mineralogy, particularly how and where the Au, Ag and Co occur in the sulphides (this may have metallurgical/recovery implications); b) verify silicate mineralogy; and 3) quantify variations in alteration minerals that may be useful in targeting mineralization (ie. Fe and metal content of chlorite).

4. It may be worth while to examine the geology around the Potterdoal mine as it appears to have a similar stratigraphic/structural setting and it may provide some additional "clues" to controls on mineralization at Potter.
 


A PETROGRAPHIC AND GEOCHEMICAL STUDY OF THE POTTER MINE
AND INTERPRETATIONS ON IT'S VOLCANIC ENVIRONMENT
 MUNRO TOWNSHIP, ONTARIO
 FOR
MILLSTREAM MINES LTD.

INTRODUCTION

This report summarizes the results of a petrographic and lithogeochemical study of the Potter mine host rocks and base metal mineralization as represented in drill hole S97-9 (Figure I), as well as observations of other drill core and surface exposures. Hole S97-9 was chosen on the recommendation of Dave Gamble, Millstream Mines Consulting geologist, as representative of the host rocks and mineralization. A total of 66 thin sections were examined and 33 samples were analyzed for major and trace elements (XRF-fused and pressed pellets) at the Central Analytical Laboratory, Laurentian University. Samples were collected by Dave Gamble and myself during an initial visit to the property in March and during a subsequent visit in June. Samples were also collected to examine apparent silicification of ultramafic footwall rocks (Table 3).

OBJECTIVES

The main objectives of this petrographic and geochemical study were to: 1) describe and characterize the komatiitic and tholeiitic host rocks, particularly the hyaloclastite units which host the base metal mineralization; and 2) determine the alteration mineralogy and associated compositional gains and losses. It was anticipated that results of the study, and a summary of observations to date, would help to further characterize/clarify the volcanic environment which hosts the Potter volcanic associated massive sulphide (VMS) deposit and provide an orientation study for a more extensive and systematic lithogeochemical sampling program designed to target/prioritize areas for future drilling.

ORGANIZATION

The report is divided into three parts. The first part is a description of the komatiitic and tholeiitic succession which contains the mineralization as well as a discussion of its geochemical characteristics (chemostratigraphy). The second part focuses on the base metal mineralization, and the third part is a discussion of the alteration types recognized and their geochemical signatures. Appendix I contains a table of geochemical analyses (including those of Coad, 1976) as well as all geochemical diagrams referred to in the text. Appendix II is a photographic atlas of thc various rock and alteration types and, for documentation purposes, contains a least one photomicrograph of each sample that was submitted for major and trace element analysis.(Appendix II has been omitted from this particular copy due to file size. Contact Millstream if interested.)

PART I: THE KOMATIITIC -THOLEIITIC VOLCANIC SUCCESSION

Potter mine (477,572 tonnes @ 1.67% Cu; 1967-72), located within Munro Township, occurs within an east-southeast trending Archean (2714 Ma) succession of mafic to ultramafic komatiitic to tholeiitic volcanic and intrusive rocks referred to as Kidd-Munro Assemblage. The Kidd-Munro Assemblage also hosts the world class Kidd Creek Cu-Zn-Ag VMS deposit (> 138.7 million tonnes of 2.35%Cu, 6.50% Zn, 0.23% Pb and 89 g/t Ag) located some 80 kilometres to the east, near the town of Timmins.

The Komatiitic -Tholeiitic volcanic succession which comprises the Kidd-Munro Assemblage at the Potter mine is divisible into 3 lithostratigraphic and chemostratigraphic units, which from oldest to youngest, includes: 1) a Lower ultramafic komatiite unit, 2) a Middle tholeiitic basalt unit; and 3) an Upper ultramafic komatiite unit (Figure 1; Gamble, 1998). Basaltic hyaloclastite of the Middle tholeiitic unit hosts mineralization at the former Potter mine as well as mineralization encountered during the recent deep drill programs which lies below the 8th underground level (1100 ft).

The Komatiitic-Tholeiitic volcanic succession strikes east to east-southeast and dips steeply (85 deg.) to the north. The volcanic succession faces north and is interpreted to lie on the south limb of a west plunging regional synclinal structure whose fold axis lies north of the mine (Coad, 1976; Gamble, 1998). Base metal mineralization at the former Potterdoal mine is interpreted to lie on the north limb of this synclinal structure and The Centre Hill Complex, a layered mafic-ultramafic tholeiitic intrusion, which intrudes the Middle unit may be the stratigraphic equivalent of Theo's flow or the Munro-Warden intrusive complex on the north limb of the structure (Coad, 1976).

THE LOWER AND UPPER ULTRAMAFIC KOMATIITIC

The Lower and Upper komatiitic units, as well as Komatiitic flows within the Middle tholeiitic unit, are described together as they consist of massive periodititic and spinifex-textured flows. Spinifex-textured flows are characterized by an upper chilled and polygonal fractured flow top, an underlying spinifex zone and a base of massive pyroxene peridotite as described for komatiitic flows at Pyke Hill, located east of the Potter mine. These "layered" or "organized" spinifex flows are interpreted as a distal or levee facies to more massive komatiitic flows that are interpreted to represent a channelized facies (Hill et al., 1995 ). Spinifex texture results from the parallel growth of large blade-like olivine crystals which attain lengths of up to 2.5 cm, comprise up to 60% of the flow and are invariably altered to serpentine (Plates 3,6,8,9,10 and 14). Skeletal crystals of clinopyroxene are altered to fibrous amphibole arid locally massive chlorite, presumably replacing original glass, occupies inter-olivine areas (Plates 3,6,8,9,10 and 14). Samples of massive peridotite, either from the base of spinifex flows or from massive, non-spinifex bearing flows consist of closely packed, serpentinized, equant olivine crystals (up to 3mm in size) that comprise up to 80% (+) of the flow. The intercumulus groundmass consists of acicular clinopyroxene altered to amphibole, with massive chlorite presumably after original glass (Plates 1,2 arid 5 ). Locally the intercumulate groundmass consists of subhedral clinopyroxene (lesser orthopyroxene) crystals up to 3mm in diameter that poikilitically enclose smaller equant crystals of serpentinized olivine (Plates 4,7,11,12 and 13).

The komatiitic affinity of both the massive and spinifex texture flows is clearly indicated in Figures 2 and 3. The MgO content of the flows range from 18 to 34 %, and the flows can be classified as pyroxenitic and peridotitic komatiites. The spinifex textured flows typically have a lower MgO content (<20 wt%) than the more massive flows (up to 34 wt%) as illustrated in Figure 4. Variations in Fe, Mg and Ca, as illustrated in Figures 6,7,8, and 9, can be accounted for by olivine and lesser clinopyroxene fractionation.

Paleoenvironment Interpretations

Komatiitic flows because of their low viscosity, a function of high eruption temperature and composition, are interpreted to have constructed extensive low relief lava plains (Hill et al., 1995). Flows proximal to their vent they may have flowed turbulently and had a viscosity akin to water and voluminous eruptions such as those responsible for the Kidd-Munro Assemblage likely extended for a 100 or more kilometers from their feeding fissure to essentially produce a broad lava plain analogous to lava plains formed during flood-type basalt eruptions.

THE MIDDLE THOLEIITIC BASALT UNIT

The Middle Tholeiitic Basalt unit consists of hyaloclastite, intact and autobrecciated sills (dikes) of massive quench-textured basalt, thin discontinuous deposits of argillaceous and carbonaceous sediments, chert, massive sulphide and komatiitic flows. The basalt sills and hyaloclastite are identical in composition (Figure 5) and are chemically distinct from the Upper and Lower komatiitic units as they have higher SiO2, TiO2, Fe2O3 and lower MgO contents and display a pronounced Fe-enrichment trend typical of tholeiites. Framework supported units of densely packed, angular to subrounded fragments (<lmm to 5mm) of altered basalt glass are referred to as hyaloclastite by Coad (1976) and Gamble (1998). Certainly the blocky equant shape of the fragments, the paucity of amygdules within the fragments and near ubiquitous perlitic cracks supports an origin through passive quench fragmentation of basaltic magma in contact with water and/or explosive hydrovolcanic eruptions. The dominant fragment type is a grey-green coloured, chloritized aphyric basaltic glass that is distinctly massive (Plates 16,19,20 22,23, and 37). Chloritized sideromelane shards with relict palagonite rims and a more irregular morphology arc also common (Plates 15,17,24,27,36,38,39). Fragments of olivine porphyritic basalt, amygdaloidal aphyric basaIt and plagioclase microlitic basalt are less common (Plate 22). Microslaggy textured (skeletal clinopyroxene needles) basalt fragments described by Coad as the most dominant clast type were not observed in the samples examined. Accessory fragments of chert, black carbonaceous mudstone, argillaceous mudstone, and massive sulphide are common but account for <1% by volume of the breccia (Plate 17).

The matrix ,which rarely exceeds 20% by volume of the hyaloclastite, consists of: 1) fine ash-sized grains of quartz, plagioclase and carbon interpreted by Coad (1976) as tuff; 2) coarse carbonate (dominant matrix observed; Plate 37; 3) broken crystals of quartz, plagioclase and pyroxene (Plates 23 and 26); 4) fine, massive chlorite (Plate 39); 5) black carbonaceous sediment (Plate 44); and 6) massive sulphide (Plates 41). Whether derived through either passive and/or explosive fragmentation of basaltic magma the hyaloclastite deposits represent resedimented, syneruptive deposits. Evidence in favour of this interpretation includes:

1) distinct bedding, although not apparent in surface exposures; bedding defined by variations in clast size and matrix content are well displayed in drill core; 2) good size sorting; 3) near ubiquitous occurrence of argillaceous mudstone clasts and occasional sulphide clasts (indicates mineralization, in part, was emplaced during deposition of the hyaloclastite unit); 4) rounding of hyaloclastite grains and granules; 5) occasional "felsic" clasts"; 6) interbedded argillaceous mudstone beds (source of argillaceous and carbonaceous mudstone clasts); and 7) absence of and gradational contact with, massive autobrecciated basalt flows typical of proximal, primary hyaloclastite. A more accurate term for this unit is "resedimented hyaloclastite" or the non-genetic "volcaniclastic deposit", alternatively the terms volcanic sandstone and granule conglomerate stress the resedimented character of the deposit.

Sills (and perhaps dikes) of massive and autobrecciated basalt intrude hyaloclastite, mineralized hyaloclastite, massive sulphide and argillaceous and carbonaceous mudstone. The basalt sills exhibit a distinct quench texture characterized by equant, serpentinized olivine microphenocrysts that sit in a groundmass of randomly orientated skeletal clinopyroxetie (variably altered to amphibole/chlorite) occasionally intergrown with skeletal plagioclase, and fine grained massive chlorite presumably after devitrified glass (Plates 18,25,31 and 35). Coad (1976) referred to this texture as a "microslaggy", typified his Broken Pillow Breccia and Quench-textured Tholeiitic units.

The basalt sills are interpreted as high level, synvolcanic intrusions emplaced into wet, unconsolidated hyaloclastite and sediment. Evidenced for this interpretation includes: 1) their fractured and autobrecciated upper and lower contacts with massive hyaloclastite, massive sulphide and or argillite injected along fractures that penetrate the massive sill interior; 2) locally chilled and sharp upper and lower contacts; and 3) the development of hyaloclastite along chilled and perlitic textured sill contacts and the mixing of this hyaloclastite with enclosing argillaceous mudstones and sulphide to form peperitic breccia - typical of subsurface magma/wet sediment interaction (Plates 30 and 34). Hyaloclastite developed at the margins of the basalt sills differs from the surrounding transported hyaloclastite in that the former are invariably perlitic textured, are typically angular and locally have delicate wispy forms displaying relict palagonite textured margins. Where sills are in contact with carbonaceous sediments or massive sulphide autobrecciation and quench fragmentation of the sill margins result in the formation of "mixed" zones where massive intact globules of basalt and hyaloclastite intimately mix with carbonaceous sediment to form a perperite breccia (Plates 28 ,29 ,32,ancl 34 ).

The obvious textural and mineralogical similarity along with identical chemical composition as illustrated in Figure 5 between the basalt sills and Coad's Broken Pillow Breccia and Quench-texture Tholeiitic units suggests that they are the same. The Broken Pillow Breccia arid Quench-Textured Tholeiitic units observed by Coad at surface are now interpreted as autobrecciated and intact, massive tholeiitic basalt sills respectively.

Paleoenvironment Interpretations

The hyaloclastite deposits may have been derived by quench fragmentation and autobrecciation of basalt flows, however the lack of larger lapilli and block-sized clasts of basalt, and the shear volume of hyaloclastite does not support this interpretation. Instead, the production of large volumes of lapilli-size hyaloclastite granules may best be explained by quench fragmentation within a subaqueous lava fountain where the rapid eruption of low viscosity magma into a water column resulted in localized lava fountains where the magma was literally torn apart by rapid and quench-fragmented to produce hyaloclastite. This mechanism of magma fragmentation has been proposed by Smith and Batiza (1989) to explain hyaloclastite deposits (hyaloclastite sands) on deep water seamounts. Irregardless of their origin the hyaloclastite units were probably transported from their vent area(s) as high particle concentration mass or grain flows and redeposited in a paleotopographic depression within the underlying komatiitic flow topography. Assuming that the komatiitic lava plain topography was essentially flat or horizontal the paleotopographic depressions were likely fault controlled and may have formed during subsidence of the volcanic pile during the tholeiitic volcanism. The basalt sills and dikes may represent the last aliquot of tholeiitic magma that was emplaced into hyaloclastite presumably along the same synvolcanic structures that accommodated subsidence?

Thin, discontinuous deposits of argillaceous and carbonaceous sediment and chert within the hyaloclastite deposits signify breaks in hyaloclastite deposition that were dominated by fine suspension sedimentation and hydrothermal discharge (chert, sulphides). Clasts of these sediments within the hyaloclastite deposits probably represent rip-tips from underlying sediments that may have been completely removed during emplacement of subsequent mass/grain flows. The occurrence of massive sulphide clasts indicates that hydrothermal discharge and sulphide deposition occurred during breaks in hyaloclastite deposition, although the majority of the sulphide may have formed below the seafloor within the hyaloclastite deposits as discussed below.

The origin of carbon within the sediments, and as a matrix to the hyaloclastite is unknown. It could be organic, or alternatively, it could be the product of the reduction of magmatic CO2, a common volatile associated with mafic volcanism.

The Centre Hill Complex

The Centre Hill Complex is a large differentiated peridotite-gabbro sill-like (?) intrusion that has a strike length of approximately 1 km and ranges up to 400m in thickness. It may be correlatable with the Munro-Warden intrusive complex located on the north limb of the synclinal axis. The Centre Hill Complex consists of a layered ultramafic (peridotite/pyroxenite) base and an upper gabbroic part, up to 200m thick, that intrudes tholeiitic hyaloclastite and sills of the overlying volcanic succession (Coad, 1976). The gabbro has a subophitic texture characterized by subhedral clinopyroxene intersticial to plagioclase laths with an interstitial groundmass of finer plagioclase, clinopyroxene, quartz and chlorite (Plate 46). The Centre Hill Complex is significant in that it was interpreted by Coad (1976) to be a high-level synvolcanic intrusion emplaced into its own volcanic pile, an interpretation supported by its compositional similarity to tholeiitic sills and hyaloclastite. It essentially defines a tholeiitic volcanic centre and, as such, is important in volcanic reconstruction.

Volcanic centres are typically characterized by subsidence and the formation of fault controlled topographic depressions or basins such as the basin or graben inferred to have localized the hyaloclastite deposits at the Potter mine. They are also areas of high heat flow and cross-stratal permeability which are requirements for the generation of a high temperature, seawater dominated hydrothermal system that may account for the alteration observed within the volcanic pile, and perhaps the sulphide deposits themselves.

PART II. BASE METAL MINERALIZATION

Two basic types of base metal sulphide mineralization are recognized, subseafloor sulphide and seafloor sulphide. In both types the predominant sulphide is pyrrhotite with lesser sphalerite and chalcopyrite. Subseafloor sulphide consists of disseminated and semi-massive sulphide mineralization (10-80% sulphides) which occurs within the matrix to hyaloclastite. Mineralization ranges from disseminated sulphide, often replacing an earlier carbonate cement (Plate 45), to semi-massive sulphide where black, chloritized, wispy hyaloclastite shards sit in a massive sulphide matrix (Plates 40 and 41). The delicate wispy nature of the chloritized hyaloclastite shards within semi massive sulphide lenses is not a primary feature but a product of their replacement along shard margins and perlitic cracks (Plates 42 and 43). Thus, the hyaloclastite host acted as a trap for sulphide mineralization and the lenses grew through processes of cementation and replacement where metals were trapped and not dispersed via plumes into the water column. Subseafloor replacement is a mechanism common, but not restricted to, the formation of many large massive sulphide deposits. Lenses of subseafloor sulphide are interpreted to have grown by the precipitation of sulphides within the permeable hyaloclastite matrix and by replacement of the matrix and, to some extent, the hyaloclastite shards.

Seafloor sulphide consists of massive sulphide lenses that are devoid of hyaloclastite and range from a few decimeters to metres thick. They are typically associated with argillaceous or carbonaceous mudstone beds (Plate 33). These massive sulphide lenses are interpreted to have formed by exhalative activity on the seafloor during hiatuses in hyaloclastite deposition marked by the deposition of argillaceous sediments. Alternatively, the massive sulphide lenses may have formed below and within argillaceous mudstones that acted as an aquiclude. Sulphide clasts within the hyaloclastite unit are interpreted to have been derived from seafloor sulphide deposits.

Paleoenvironment Interpretations

Without a doubt hydrothermal activity responsible for the formation of massive sulphide deposits at and below the seafloor occurred throughout the depositional history of the hyaloclastite units. This implies a relatively long-lived, sustained hydrothermal event which favours the formation of numerous stratigraphically stacked sulphide deposits. Although textural and field evidence is limited to a few cross-cutting relationships it is tentatively interpreted that early formed massive and banded pyrrhotite and sphalerite is replaced by chalcopyrite. This paragenetic sequence is typical of many VMS deposits, and by analogy, may reflect original temperature gradients and sequential replacement during formation of thc sulphide lenses where an early, "lower temperature" pyrrhotite/sphalerite mineralization was progressively replaced by "higher temperature" chalcopyrite.

PART III. ALTERATION

The typical "alteration assemblages" recognized within mafic and ultramafic rocks of the Potter volcanic succession could be ascribed to hydration during regional greenschist facies metamorphism. Regional metamorphism can result in the pseudomorphic replacement of olivine and clinopyroxene by serpentine and amphibole/chlorite respectively, and the replacement of glass, both within the flows and hyaloclastite, by chlorite, amphibole and minor quartz. These mineralogical changes are not textually destructive and can generally be assumed to have been isochemical. A quick glance at the analysis in Tables 1 and 2 indicate compositions that are typical, for the most part, of least altered flows.

There is, however, evidence of hydrothermal alteration and this is best displayed within the hyaloclastite shards which record a complex alteration history that is not always apparent in the flows. A tentative paragenetic sequence for alteration of the glass shards is as follows:

1) Initial palagonitization, which resulted in the development of both fibrous and gel palagonite on any free surface in contact with water such as shard boundaries or perlitic cracks (Plate 27). Palagonitization is a low temperature alteration (<150°C) that result in the hydration of glass, oxidation of Fe to form minute oxide granules which define palagonite textures in older rocks and, possibly, minimal removal of SiO2 or MgO from the glass. In most cases palagonitization is assumed to be isochemical.

2) Chloritization, which resulted in the replacement of glass shards and palagonite by chlorite (+/- amphibole, quartz) overprints palagonitization. Chlorite may be a synvolcanic alteration, a result of complete hydration of the glass during diagenesis/spilitization or it could be a product of later greenschist facies metamorphism. In either case it is not textually destructive as even the delicate textures of former palagonite are preserved. Chlorite alteration may or may not be accompanied by spilitization which results in the removal of Ca and addition of Na. Na2O values >3.0 wt%, such as in samples S97-9-342.1,-368.1, -569.5 and S98-2-357.5, may be a product of spilitization that accompanied an early, synvolcanic regional chlorite alteration.

3) Carbonate alteration, which is more common in the ultramafic flows but is also present in the basalt sills and hyaloclastite, appears to overgrow serpentine, pyroxene and chlorite which suggests that it may be syn- to post-greenschist facies metamorphism. Carbonate cement, a common matrix to the hyaloclastite breccias, represents an earlier synvolcanic, hydrothermal event. Whether or not any of the carbonate found within the flows and sills is a product of this earlier carbonate event is uncertain.

4) Black chlorite alteration which resulted in the replacement of shards by chlorite (Fe-rich chlorite?) and the destruction of former palagonite textures is the alteration type which is spatially associated with the sulphide mineralization (Plates 40 to 43). Black chlorite alteration is most evident in the core where the hyaloclastite shards take on a distinct black colouration , as opposed to their normal green-grey colour, immediately adjacent (within decimeters to meters) to massive and semi-massive sulphide. Assuming constant TiO2 mass balance calculations indicate that black chlorite alteration is accompanied by a loss of SiO2, CaO, Na2O and MgO and an addition of Fe2O 3 (Table 3). Some of the Fe2O3 enrichment is attributable to matrix sulphide. These chemical changes and textures are typical of chlorite alteration associated with VMS deposits.

Interpretations

Palagonitization, early chloritization/spilitization and, to some extent carbonitization, are all typical of regional semi-conformable alteration zones found in most VMS districts (Noranda, Mattagami, Snow Lake, Sturgeon Lake....). They typically occur in the footwall, but also the hanging wall, to VMS deposits. They are interpreted to be a product of large scale, regional hydrothermal systems akin to modern day geothermal fields. Their genetic relationship, if any, to base metal deposits is uncertain, however they are an indicator of large hydrothermal systems which are a key requisite for the formation of VMS deposits.

The black chlorite alteration is typical of chlorite alteration zones that typify proximal discordant, and often pipe-like footwall, and to a lesser extent hanging wall, alteration zones to VMS deposits, such as those in the Noranda Camp. The chlorite is interpreted to be the product of high temperature fluid rock interaction within discordant, structurally controlled, fluid discharge channelways that acted as the principal conduits for ascending hydrothermal fluids which formed massive sulphide deposits at and below the seafloor. The restricted distribution and apparently semiconformable character of black chlorite alteration at Potter is not typical of proximal; discordant chlorite alteration zones and may suggest a more fringe or distal environment

Appendix 1, to view Element Analyses on Potter Core

REFERENCES
 

Arndt, N.T., 1976. Ultramafic rocks of Munro Township and their volcanic setting. Unpublished PhD thesis, Univ. Of Toronto.

Coad, P.R., 1976. The Potter Mine. Unpublished Msc thesis, Univ. Of Toronto.

Hill, RET., Barnes, S.J., Gole, M.J. And Dowling, S.E., 1995. Thc volcanology of komatiites as deduced from field relationships in the Norseman-Wiluna greenstone belt, Western Australia. Lithos, v.34, p.1-25.

Jensen, L.S., 1976. A new cation plot for classifying subalkalic volcanic rocks. Ontario Div. of Mines Misc. Publication 62.

Smith, T.L., and Batiza, K., 1989. New field and laboratory evidence for the origin of hyaloclastite flows on seamount summits. Bull of Volcanology, V.51, p. 96-114.

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