Preliminary Report, Geology of Lake Assinica Area, Abitibi Territory

RP 550(A) PRELIMINARY REPORT, GEOLOGY OF LAKE ASSINICA AREA, ABITIBI TERRITORY

P.R. NO. 550

DEPARTMENT OF NATURAL RESOURCES

Honorable GASTON BINETTE PAUL-EMILE AUGER Minister Deputy Minister

Geology of

LAKE ASSINICA AREA

ABITIBI TERRITORY

PRELIMINARY REPORT

L.B. Gillett

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QUEBEC

1966 P.R. NO. 550

P.R. NO. 550

QUEBEC DEPARTMENT OF NATURAL RESOURCES

Honorable GASTON BINETTE PAUL-EMILE AUGER

Minister Deputy Minister

GEOLOGICAL EXPLORATION SERVICE

ROBERT BERGERON, Director

Geology of

LAKE ASSINICA AREA ABITIBI TERRITORY

PRELIMINARY REPORT

L.B. Gillett

QUEBEC 1966 P.R. NO. 550

Preliminary Report

LAKE ASSINICA AREA

Abitibi Territory

L.B. Gillett

INTRODUCTION

The Lake Assinica area, mapped during the summer of 1964, comprises 381 square miles bounded by latitudes 50°30' and 50°45' and by longitudes 75000' and 75030'. Lake Assinica itself straddles the southern boundary of the area and is approximately 55 miles northwest of Chibougamau.

Floatplanes can land on many lakes within the area and were used exclusively as a means of access. The nearest commercial floatplane base is at Caché lake, 6 miles south of Chibougamau. The area can also be reached by canoe from the Chibougamau-Senneterre highway, but all water routes involve a series of portages and are generally impractical. The area lies entirely within the drainage basin of Broadback river. The Broadback (North Broadback) drains the northern part of the area; Assinica river (South Broadback) drains Lake Assinica. Both rivers, together with their associated lakes, provide good canoe routes for travel within the area. Assinica river joins the Broadback, which ultmately flows into James bay, 150 miles west of the junc- tion. - 2 -

The major topographic features of the area reflect the underlying geology. Discontinuous ridges mark two major bands of metavolcanic rocks that trend easterly through the central part of the area. These ridges, on the average, rise about 300 feet above the intervening lowland which is on metasedimentary rocks. In general, the gneiss-amphibolite complex north and south of the volcanic-sedimentary zone is low and is covered by drift. Large masses of alaskitic granite or of pegmatite are relatively resistant and account for the hilly topography near the eastern boundary of the area. On the other hand, the porphyritic granite and porphyritic syenite have no distinctive topographic expression.

The smaller features of the topography are, in most cases, the direct result of glaciation, whereas eskers, drumlins and low morainic ridges are abundant throughout much of the area.

Large outcrops are virtually restricted to hilltops. Small outcrops occur on or near hilltops and along some shorelines. The search for outcrops was conducted along traverse lines spaced at half-mile intervals, but intervening areas of abundant outcrop were also visited. The shorelines of all large lakes, streams and rivers were examined.

GENERAL GEOLOGY

All bedrock in the area is Precambrian in age. The gneisses and amphibolites exposed in the north and south are tentatively considered to be the oldest rocks present. According to this interpretation, the pre-Broadback Group of metasedimentary rocks lies in a syncline that trends easterly across the middle of the area. Most of the lenticular bodies of metagabbro and metadiorite are probably related to the pre-Broadback Group, though some occur in the Broadback Group. Late- and post-orogenic masses of alaskitic granite, porphyritic granite and granitic pegmatite have invaded the gneisses extensively, but are rare in the volcanic-sedimentary zone. The only large intrusive body in the latter is a porphyritic syenite. Younger tourmaline- and, locally, spodumene-bearing pegmatites are closely associated with this syenite and are probably genetically related to it. Dikes of diabase that cut gneiss near the southwest corner of the area are probably the youngest rocks represented. 3

Table of Formations

PLEISTOCENE Moraine, outwash; eskers AND RECENT Gravel; sand; silt

Diabase

Granitic pegmatite

Alaskitic granite Post-Broadback Intrusive Rocks Porphyritic granite

Tourmaline-spodumene pegmatite

Porphyritic biotite- hornblende syenite

PRECAMBRIAN Gabbro and diorite

S Conglomerate Broadback Group Graywacke ROCK Black shale Andesite and basalt Pre-Broadback Group Layered rocks (chiefly pyroclastics?)

Amphibolite

Mesocratic hornblende Pre-Broadback (?) and biotite gneiss METAMORPHIC Leucocratic biotite and hornblende gneiss - 4 -

The present map differs chiefly from the older one by Shaw (1942) in that the Broadback Group is now recognized in this area. Shaw's map showed the Broadback rocks only in the adjoining area to the west.

PRECAMBRIAN

Pre-Broadback(?)

Leucocratic Biotite and Hornblende Gneiss

Gneisses ranging in composition from granitic to granodioritic comprise the major part of the bedrock in the northern and southern thirds of the area. White feldspar is the major constituent of most of the gneisses, but pinkish feldspar is locally dominant. Colorless quartz typically forms 25-35% of these rocks. Biotite is much more common than hornblende, but the total mafic content of the gneisses rarely exceeds 10%. No rocks of undoubted sedimentary origin were recognized, though paragneisses may be common in both the southern and northern gneiss complexes.

In the south, the gneissosity is generally out- lined by quartz lenticles and flakes of biotite. Mineral lineations are inconspicuous, but weak horizontal lineations may be detected in some of the gneisses near Lake Assinica and dip lineations are fairly common in the more massive gneisses west of Lake Assinica near Triart (Puzzle) lake.

In the north, the gneisses tend to be relatively heterogeneous. Irregular compositional layering is more common and textures are more variable.

The ages of the gneiss zones relative to the intervening volcanic-sedimentary zone and relative to one another are conjectural. However, the northern and southern gneisses are tentatively correlated and are assumed to underlie the volcanic-sedimentary rocks. Contacts between the major zones were not seen. 5

Mesocratic Hornblende and Biotite Gneiss

A distinctive type of gneiss crops out in a zone 2,000-5,000 feet wide extending 5 miles southwest from Labeau (Jonigill) lake. It is characterized by a high mafic content which ranges from 15% to 55% and averages about 35%.

The more mafic varieties are composed essentially of hornblende and white feldspar. With decreasing mafic content, quartz forms up to 25% of the rock and biotite also commonly becomes abundant. The gneisses of this unit are all relatively coarse grained. Gneissic fabric ranges from weak in the mafic varieties to strong in the less mafic varieties. Compositional layering is generally absent. The relationship of these gneisses to the sur- rounding rocks is unknown.

Amphibolite

Discontinuous layers or lenses of amphibolite occur at a number of localities, within the leucocratic gneisses, but are sufficiently wide or abundant to be mapped as a unit only near the northwestern and southwestern corners of the area. The amphibolite contains about equal amounts of hornblende and plagioclase and is finely grained,weakly foliated and layered. It is thought to be metavolcanic. Near the southeast corner of the area, similar amphibolite forms a contorted layer enclosed by pegmatite and gneissic granite. It may be an inclusion or a relic of ungran- itized wall-rock.

Pre-Broadback Group

Metamorphosed Layered Rocks

A diverse assemblage of layered rocks is interbedded with metalavas of the pre-Broadback Group. Much of the layered rock forms bodies that are too small or too discontinuous 6 to be mapped as distinct units, but scattered exposures within the southern zone of pre-Broadback rocks indicate that here the layered series predominates across a band up to 8,500 feet wide. The layers range in thickness from a fraction of an inch to several feet. Some of the fine layering may be the result of metamorphism, but the coarser layers are inter- preted as relic beds.

In the mapped band of layered rocks, the most common rock type is a fine-grained schist composed of chlorite, amphibole,, feldspar, quartz and minor garnet. It resembles the graywackes farther north, but generally is greenish rather than gray. Structures suggesting crossbedding occur 2,500 feet south of Bruine (Drizzle) lake. Other rock types in this unit include very fine-grained, pale gray, mica schist; pale gray, cherty argillite; medium-grained meta-arkose; and schis- ose agglomerate or conglomerate. None could be traced for more than a few tens of feet along strike.

Minor amounts of layered rocks occur throughout the areas mapped as pre-Broadback metalava. The most common type is similar in composition to the lavas with which it is associated, but is thinly layered owing to differences in content of green minerals. Such rocks are thought to be tuffs, though the layering may be a result of metamorphic segregation. In general, they appear to lack quartz, though this is difficult to determine because of their fine grain. The other types of layered rocks mentioned above are relatively rare in areas where lavas predominate.

Meta-andesite and Metabasalt

Metalavas form an important part of the two pre-Broadback Group volcanic bands that trend easterly across the middle of the area. The northern band has a relatively uniform width of about 6,000 feet and contains only minor amounts of intercalated layered rocks. The southern band is 10,000-18,000 feet wide and contains as much as 50% layered rocks. Questionable top determinations based on distorted pillows suggest that the two bands are on opposing limbs of a syncline.

Probably both meta-andesites and metabasalts are present. Some of the more massive types are sufficiently coarse grained to show an original pyrobole content of 30-55%. - 7 -

The pyrobole has been altered to secondary amphiboles and chlorite, and the plagioclase has been partly replaced by epidote. Locally, small red garnet crystals are abundantly disseminated through schistose phases of the lava. They range in shape from well-formed dodecahedra to sheared lenticles. Their presence may indicate a slightly higher than usual grade of metamorphism.

Broadback Group

Black Shale

The Broadback Group forms an easterly-trending band of metamorphic sedimentary rocks in the central part of the area. The band increases in width from about 1,500 feet at the eastern boundary to about 15,000 feet at the western boundary. It is thought to lie in a major syncline, and, if this is so, the metamorphosed black shale is near the base of the Broadback Group. The shale is exceptional in several ways. Although it is probably only about 200 feet thick, it has been tentatively identified along strike for 7 miles. It appears to be the only rock in the map-area containing sig- nificant amounts of carbonaceous material. Much of it has the characteristics of a hornfels, although it is not adjacent to any intrusive body, and much is not schistose. Chiastolite, a mineral generally considered to be a product of contact metamorphism, occurs locally as one-inch porphyroblasts. Porphyroblasts of garnet, as well as ovoidal, highly-altered grains of staurolite (?), are common. The matrix is dark gray to black and appears to be composed mainly of quartz, micas, and carbon. Pyrite or marcasite is a characteristic accessory and is locally abundant.

Graywacke

Graywacke is the most common rock type of the Broadback Group. It is highly susceptible to frost wedging and as a result appears most commonly in fields of angular blocks. It has been eroded into a broad valley trending easterly across the middle of the area. The graywacke is thought to rest conformably upon the lavas which crop out to the north and south. - 8 -

The designation of this rock as graywacke is based primarily on its poor sorting, overall fine grain, and gray color. Mineralogically, much of it could be classed as arkose or feldspathic sandstone, because the matrix, like the larger grains, is chiefly quartz and feldspar. Biotite, the characteristic mafic mineral, rarely exceeds 15%, whereas amphibole, epidote, chlorite and muscovite are generally minor or absent. The weathered surface is a distinctive pale brown and commonly shows an inconspicuous, fine lamination. However, this lamination may be simply a result of metamorphism, as these rocks are invariably somewhat schistose.

Conglomerate

On the basis of a few outcrops near Savournin (Jig Saw) lake and the wide distribution of conglomerate boulders to the south, a band of conglomerate about 8 miles long and up to 1/2 mile wide is mapped near the middle of the Broadback metasedimentary band. The conglomerate is thought to occupy the axis of a syncline and to overlie conformably the graywackes of the Broadback Group.

The conglomerate is composed of well-rounded phenoclasts, ranging up to one foot or more in diameter, set in a graywacke matrix. The phenoclasts are chiefly siliceous volcanic rocks, granite, and metasedimentary rocks. Thin layers of non-conglomeratic graywacke are interbedded locally. The lithology of the conglomerate is quite similar to that of other Timiskaming-type conglomerates of the region. Both the conglomerate and the graywacke closely resemble Opemisca rocks exposed in the Vienne-Blaiklock area north of Chibougamau.

Post-Broadback Intrusive Rocks

Metagabbro and Metadiorite

Small lenticular to tabular bodies of metamorphosed gabbro and related rocks are common in the metalava bands. They are rare in the Broadback Group graywackes, and were seen at only one locality (eastern side of Lake Assinica) in the pre-Broadback leucocratic gneisses. The intrusive nature of some of these bodies is demonstrable, but good exposures are rare and it is possible that many of the masses associated - 9

with the lavas are merely the interiors of thick flows. Only the larger bodies within the lava bands are shown on the map. The thicker lenses near Perdu (Lost) lake and Gariteau (Charlish) lake appear to have undergone differentiation, for their northern parts are relatively feldspathic and potassic. This has been taken as evidence of their pre-folding age. The metagabbros cutting the Broadback Group are dike-like and post-date the major interval of folding, although their metamorphic state is similar to that of most of the other metagabbros.

The rocks have been classed as dioritic or gabbroic on the basis of relic igneous textures and color indices which range from 30 to 60. More mafic or more feldspathic rocks are locally present, but are thought to be genetically related and have not been distinguished on the map (No. 1608) complementing this report. The Lake Assinica body is chiefly a coarse-grained metapyroxenite which still retains a considerable amount of primary pyroxene. The other mafic rocks are now essentially amphibolites. The plagioclase is generally only slightly altered to epidote and the amphibole has a shredded appearance. Biotite and potassic feldspar are important constituents only in the differentiated masses near Gariteau lake. Ilmenomagnetite is a common accessory. Many of the amphibolites have a blastoporphyritic texture with mafic phenocrysts up to 1/4 inch in diameter. Others range in grain size from medium to coarse, and coarser-grained types predominate in the more mafic varieties. Foliation is weakly developed or absent.

Porphyritic Hornblende-biotite Syenite

A stock about 5 miles in diameter cuts lavas and graywackes near the western boundary of the area. It is mapped as nearly circular. However, its true shape cannot be determined because of the scarcity of outcrops.

The feldspar of the syenite is medium to coarse and generally white; locally a pink feldspar predominates. The feldspar content ranges from 50% to 90%, but about 70% is most typical. The major mafic minerals, biotite and hornblende, generally occur together in nearly equal amounts, but locally one occurs to the virtual exclusion of the other. The grain size of the hornblende is about the same as that of the associated feldspar. Most of the biotite forms phenocrysts, which are the characteristic feature of this rock. The phenocrysts te,.d co have euhedral basal faces, are up to an inch in diameter and are probably primary. - 10 -

Tourmaline-spodumene Pegmatite

A number of granitic pegmatite dikes with distinctive accessory minerals cut rocks of the volcanic-sedimentary zone near the western boundary of the map-area. Most occur in graywacke, but some are in volcanic rocks and porphyritic syenite. They are typically quite irregular and many split into subsidiary dikes.

In addition to quartz and feldspar, the pegmatites contain pale greenish to cream-colored spodumene, black tourmaline, pale greenish to yellowish mica (perhaps in part lithium-bearing), and lesser amounts of garnet, beryl and apatite. Molybdenite was seen at one locality.

More detailed descriptions of the pegmatites are given in the section on economic geology.

Porphyritic Granite

About 25% of the granitic stock near the northwest corner of the map-area is porphyritic. The relationship between porphyritic and equigranular facies of the granite is not clear. Locally, porphyritic granite forms a zone a few thousand feet wide along the margin of the stock, and there is some porphyry near the center of the stock. Possibly the "phenocrysts" are actually porphyroblasts developed during pegmatitization, as there appears to be a relation between the abundance of pegmatites in an area and the development of "porphyry" in the adjacent granite. The matrix of the porphyritic granite is composed of medium-grained, pink and/or white feldspar, clear to pale gray quartz, and minor amounts of biotite or, less commonly, hornblende. The phenocrysts are pinkish feldspar from 1/2 inch to 3 inches long. Although locally they comprise up to 30% of the rock, they are generally rather widely disseminated. The rock is commonly massive, but near wall- rock contacts the groundmass tends to be slightly gneissic. Typically, the phenocrysts are randomly orientated and are euhedral. Alaskitic Granite

Large masses of equigranular granite containing less than 5% mafics, mainly biotite, occur in the eastern and northwestern parts of the area. Both white and pink feldspar occur in the granite, and either one may be dominant. Where white and pink granites are in contact, the pink granite is generally the younger. The white feldspar is probably sodic plagioclase and, therefore, the white "granites" should probably be classified as granodiorites. Quartz is abundant in all the alaskitic rocks, averaging about 30%.

The pink granites are typically medium to fine grained and massive. They are most common in areas remote from wall-rocks. Closer to the boundaries of the granite masses, the rocks tend to be richer in white feldspar, coarser grained, and weakly gneissic. Some of the gneissic varieties may be leucogneisses coarsened by recrystallization.

Granitic pegmatite

Dikes of simple granitic pegmatite, ranging in thickness from a few inches to several feet or tens of feet, are exceptionally common throughout most of the area. Almost every outcrop of leucogneiss is cut by pegmatite dikes, which are very common in the mesocratic gneisses, the fine-grained amphibolites and the porphyritic granites. The pegmatite dikes within the alaskitic granite are relatively large, up to 100 feet or more thick. On the other hand, simple pegmatite is rarely seen in the volcanic-sedimentary zone.

The simple pegmatites are thought to be magmatic differentiates of the alaskitic granite. Locally, they grade into the granite, and the largest dikes are in the marginal facies of the granite. Apparently none of the pegmatites originated by metamorphic differentiation or partial melting, as the dikes are dilational and their compositions are not affected by the lithology of the wall-rock. The scarcity of simple pegmatites in the volcanic-sedimentary zone is probably related to the virtual absence of granite in this zone, perhaps because the metalavas served as a high melting-point shield to granite intrusion.

The feldspar crystals in the pegmatites range from 1 inch to 3 feet in diameter, the coarsest grain sizes - 12 -

being in the thickest dikes. Both white and pale pink feldspar are common within the same dike. Quartz rarely forms giant crystals, but is abundant as rods or irregular intergrowths within the larger feldspar crystals. Muscovite is a common though very minor accessory, and biotite is local.

Diabase

Two definite outcrops and, possibly, a third outcrop of diabase occur near the southwestern corner of the area. They would have been mapped as parts of a single northerly-striking dike, were it not for the fact that a dike contact exposed 2,000 feet north of the south end of Lafargue (Lake 007) lake trends northeasterly. The dike at this point is vertical and is at least 20 feet thick. Maximum grain sizes in the three occurrences of diabase are similar. The diabase is composed of about 60% black pyroxene and 40% pale green plagioclase. These minerals form an ophitic texture which is conspicuous on the fresh as well as on the weathered surface. Ilmenomagnetite is a minor constituent and traces of sulfides are present. The coarsest diabase contains feldspar laths about 1/4 inch long. Adjacent to the one intrusive contact seen, the diabase is uniformly fine grained, though the plagioclase crystals remain lath- like.

CENOZOIC

Pleistocene

Till in the form of ground moraine, washboard moraines, and drumlins covers most of the area. Washboard moraines are the most distinctive, occurring as series of abrupt ridges about 20 feet high, a few thousand feet long, and several hundreds of feet apart. They are common in all but the eastern fifth of the area. As hundreds of such ridges are present, no attempt was made to plot them individually. However, their generalized trends are indicated on the map by lines spaced 3 or 4 miles apart. The ridges are thought to be recessional moraines marking positions of the front of an - 13 - ice sheet retreating towards the northeast. Cigar-shaped drumlins averaging 1,000 to 2,000 feet long and a few tens of feet high trend generally southwestward at right angles to any associated washboard moraines. The best developed drumlins are within the northernmost 3 miles of the area; particularly about 4 miles east of the western boundary and also about 4 miles west of the eastern boundary.

Outwash occurs in, and adjacent to, the several southwesterly-trending eskers. Most of the eskers are of the beaded type, with gravelly hills as much as 100 feet high developed every few hundred feet along their length. The esker extending discontinuously southwest from Labeau lake developed in a reentrant of the former ice front, as indicated by the changed trends of moraines near this esker. An ice sheet retreating by calving into a lake would tend to have a reentrant in such a position.

Glacial striae, friction cracks and crescentic gouges occur on many outcrops. Generally, their orientation confirms the southwesterly glacial flow as evidenced by moraines and drumlins. However, on the south side of a small island in Lake Assinica they record an older southeasterly ice flow as well.

STRUCTURAL GEOLOGY

The volcanic-sedimentary zone trending easterly through the middle of the map-area is believed to be pre- served in a syncline. If so, folding is practically isoclinal, as bedding planes characteristically dip steeply and foliation is generally parallel to bedding. Unfortunately, top determinations based on pillows or bedding plane structures are unreliable because of the strong deformation. The dissim- ilarities in lithology and thickness of the rocks on either side of the proposed synclinal axis may possibly be explained by assuming that the southern limb was closer to the volcanic centers. The gneisses are thought to underlie unconform- ably the volcanic-sedimentary sequence. The attitude of the foliation in the gneisses is relatively irregular though northeasterly trends are locally dominant, particularly near Lake Assinica. - 14 -

Small, nearly vertical faults trending northeast or northwest were seen at a number of places in the volcanic-sedimentary zone, but displacements along these faults were a few feet at most. The easterly trending ridges of the northern band are interrupted by northwesterly-facing cliffs at four localities between 75°12'W. and 75°21'W. Jags in the ridges adjacent to the cliffs give the impression that the cliffs are fault-line scarps with left-hand separations in the order of 1,000 feet. However, no geological evidence of the fault origin of the cliffs was found.

An important north-northeast-trending fault is inferred near the eastern boundary of the area to explain the more northerly occurrence of the volcanic-sedimentary zone mapped by Rondot in the adjoining area to the east. The fault is thought to follow an esker whose position was determined by a valley developed along this fault. The esker continues for many miles to the northeast in the adjacent area and may conceal a fault throughout much of its length. Rondot's map shows other faults whose traces approximately parallel the fault proposed here.

ECONOMIC GEOLOGY

Lithium

In 1959 and 1960, Sirmac Mines Limited did considerable exploratory work on the lithium-bearing pegmatites northwest of the porphyritic syenite stock. A base line (shown on map No. 1608) was cut across the principal showing, — namely, a northwest-striking ridge along which a pegmatite dike up to 450 feet wide is exposed for about 1,500 feet. A dozen lines spaced at 400-foot intervals were cut at right angles to this base line for about 4,000 feet to each side. Sirmac's geological map in the area of these cut-lines, available in the assessment files of the Department of Natural Resources, shows numerous smaller exposures of pegmatite, several of which contain spodumene. In 1961, the property was optioned to, and drilled by, Consolidated Mining and Smelting Co. of Canada. The spodumene-bearing zone of the principal dike was found to be about 900 feet long and 56 feet wide at the surface and to average 2.7% lithia. However, the zone gradually narrows downward, pinching out at depths between - 15 -

200 and 400 feet (Quebec, 1962). Other minerals of economic interest in these pegmatites include green to white beryl, columbite-tantalite, and some rare phosphates (Wright, 1960).

Granitic pegmatites, which in common with those described above contain tourmaline, garnet, and greenish mica, are exposed on and near the western boundary of the area, about 2 miles west-southwest of Daloguy (Intestine) lake. A molybdenite-bearing grab sample assayed at the laboratories of the Department of Natural Resources contained 0.27% Mo. No spodumene was observed in these dikes.

Several spodumene-bearing pegmatite dikes less than 30 feet wide occur 3,500 feet north of the west end of Clapier (Bladder) lake. Two grab samples from these dikes were assayed at the laboratories of the Department of Natural Resources. One sample, assayed for lithium alone, was found to contain 0.64% Li. The other sample was assayed for both lithium and beryllium and was found to contain 0.13% Li and 0.034% Be. All the tourmaline-spodumene pegmatite dikes occur within 11,000 feet of porphyritic syenite outcrops; the dikes tend to trend radially with respect to the porphyritic syenite stock; and syenite elsewhere is commonly associated with pegmatites of the complex type. For these reasons, a genetic relationship between the tourmaline-spodumene pegmatites and the porphyritic syenite seems probable. Therefore, further prospecting for elements such as lithium, beryllium, molybdenum and tantalum should be near the syenite stock. To date, exploration has been concentrated on a relatively small area on the northwest side of the stock. The present survey indicates that the same type of pegmatite occurs to the west and to the north of the stock; perhaps similar pegmatites occur on all sides.

Sulfides

Sulfides occur in minor quantities at a few places. The metamorphosed black shale contains up to 25% pyrite or marcasite, but no base-metal mineralization appears to be associated. F, few specks of chalcopyrite are disseminated in the metavolcanic rocks in the vicinity of the tourmaline- spodumene dikes 3,500 feet north Clapier lake. Traces of chalcopyrite were also observed near the base of the meta- gabbroic lens at the south end of Gariteau lake, about 2 miles - 16 - south of the middle of the map-area. An unidentified, white, metallic mineral forms abundant half-inch pods in silicified rock in a small outcrop 2 miles southeast of the southeast corner of Clapier lake. A grab sample assayed by the Depart- ment laboratories gave: 0.00% arsenic, 0.01% nickel, 0.000 ounce of gold a ton, and 0.007 ounce of silver a ton.

Feldspar

Some of the pegmatites are potential sources of feldspar. The largest and coarsest dikes, apart from the principal spodumene pegmatite already described, occur in the border zone of the granitic batholith in the eastern part of the area. Only two of the numerous exposures will be mentioned. One is a mass of undetermined shape which crops out at an approximate longitude 75°1.1'W. and latitude 50°31.7'N. Both the white and the pink feldspars are up to 1 foot in diameter and are commonly intergrown with 1/4-inch diameter rods of quartz. A second pegmatite forms an easterly-trending dike at longitude 75°9.8'W. and latitude 50°41'N. This dike is unusual in that it contains up to 10% mica, mainly muscovite but locally biotite. The feldspar crystals are up to 3 feet in diameter. Quartz occurs both as rods intergrown with the feldspar and as irregular masses about 1 foot in diameter. Zoning is inconspicuous or absent in most of the dikes. The quartz-feldspar intergrowths are common and probably would make it difficult to produce a pure feldspar product.

Geochemistry

Samples of stream sediment were taken as part of a program intended to establish whether or not it would be desirable to carry out limited geochemical exploration during the geological mapping of an area. The following pro- cedure was adopted: - When a stream was crossed on a traverse, two samples of sediment were taken several feet apart from the stream's active zone. Pertinent information, such as the dimensions of the stream, speed of the current, etc., was recorded on sheets of paper prepared in advance. The samples were sent to the laboratories of the Department of Natural Resources in Quebec, where they were analysed for copper, zinc, lead, and molybdenum. - 17 -

The major factor complicating an evaluation of the results is that a broad range of materials was samples, from fine quartz sand to almost pure humus. Equipment for sampling was available during only a part of the field season, so that a broad coverage of the area was not possible.

REFERENCES

QUEBEC, 1962 Outline of Progress of the Mining Industry in the Province of Quebec during the Year 1961. Que. Dept. Nat. Res.

SHAW, George, 1942 Assinica Lake, Abitibi and Mistas- sini Territories, Quebec: Geol. Surv. Canada, Map 712A.

WRIGHT, C.M., 1960 Mineralogical Examination of a Suite of Pegmatite Samples from Sirmac Mines Ltd., Quebec: Unpub- lished Report, Univ. of Wisconsin.