ECONOMIC GEOLOGY.
With the knowledge acquired from exploitation of James township, and other of the more recently discovered silver-cobalt camps, prospectors in the Montreal River district gave exclusive attention to the diabase formation, recognizing it to be closely connected with mineralizations of this kind. Some work was done in 1907 and more in the following season, with the result that on August 4, the first native silver discoveries were made, almost simultaneously and at short distances apart, by Messrs. Mann and Dobie, in the diabase just west of Gowganda lake. The remarkably rich surface showings at once attracted the attention of the whole prospecting body in the Elk Lake country, and an activity began which, since the spreading of information to outside points, has developed into a ‘rush’ of large dimensions.
The known silver bearing area is restricted as yet to about ten square miles lying between Gowganda lake and the portage route from Elkhorn to Firth lakes, and is commonly known as Gowganda. Extensive prospecting only commenced in September, about the close of the field season, so that only the earlier discoveries are known to the writer, and a knowledge of the surface details could only be derived by examination of the few beginnings of patient and continued exploration by claim owners. The present account must accordingly be accepted as incomplete and by no means representing the present status of the Gowganda camp.
Conditions in the region are such as to demand exploration of the closest and most intensive order, for the indications of mineralization are negative rather than positive in character. The Gowganda area was entirely forested at the beginning of 1908, and a carpet of moss and vegetable mould covered most of the rock surface. Glacial materials are also fairly abundant, and sometimes thick enough to render surface exploration arduous and expensive. Added to this the veins are eroded more deeply than the country rock, and are represented at the surface by crevices filled with soil, and therebyrendered inconspicuous. Were the country a flat one the difficulties in the way of successful prospecting would be very serious, but fortunately it is rugged, especially near the diabase. Steep ridges of this material are a regular topographical feature. The sides of these ridges are bare or readily exposed and offer fine opportunities for examination. It is significant that the first silver discoveries were made in the sides of such rock walls. The pink bloom found at the surfaces of the veins and the adjacent country rock is also an indicator whose value is fully understood by those working in the region.
The deposits are in the form of well-defined veins occupying fissures in the diabase. The amount of surface work done in September was not enough to throw much light on the continuity of the veins, but a few had been traced for distances of 300 or 400 feet, and in one case across several contiguous mining claims, so that they may be said to occupy persistent fissures. They vary in width from 1ʺ up to 20ʺ. Little could be learned concerning their attitudes except where they traverse hillsides; in such cases they are approximately vertical. It is not yet known whether any regularity exists in their arrangement, but some extend east and west while others are north and south. The diabase shows no signs of extensive deformation, all geological evidence indicating that since its solidification its history has been uneventful, yet the cracks which the veins occupy appear too persistent to be the result of contraction by cooling. Besides the strong veins there are others of the gash type, but the latter are small, not very continuous and poorly or not at all mineralized.
COMPOSITION OF VEINS.
From comparison of veins at Gowganda, Duncan lake, and Wapus creek a general uniformity of structure, though not of mineralization, is found to obtain. The whole mineral association is not found in any one vein, nor are the relative proportions either of ore or gangue at all constant. The gangue minerals are quartz and calcite, always mutually arranged in definite manner. The sides of the veins are composed of white quartz, which may form only an insignificant coating on the walls or may occupy nearly the whole space, but in all cases there remains a central cavity into which the pointed ends of quartz crystals project freely. At the surface this central portion is empty owing to weathering, but farther down it is filled by calcite.Veins with predominant quartz filling seem especially abundant in the Huronian adjacent to the diabase. The rich veins near Gowganda, so far as ascertainable, are poor in quartz.
Practically all of them carry chalcopyrite either as diffuse grains or in considerable amounts. Pyrite is equally abundant but less constant. Galena is not uncommon. All these occur with the quartz; their presence in the calcite is not certainly known. Many of the veins show diffuse stains of reddish pink colour due to cobalt bloom, which though not in itself of value is important as a sign of the existence of smaltite from which it is formed by oxidation. The minerals enumerated thus far are widespread, but economically insignificant; the silver-cobalt association is present in some cases, however. Little opportunity existed in 1908 for favourable study of these minerals, so that only a list of those found at the surface can be given. There native silver, argentite, smaltite and cobalt bloom have been found, and a few feet down small lumps of native bismuth. Because they occur either in calcite or in loose decomposition materials filling the space which the calcite formerly occupied they are believed to be associated with that gangue. Infrequently gangue minerals are almost absent and the vein filled by massive ore.
Valuable argentiferous veins were known in 1908 only in the Gowganda district, and, so far as yet known, discoveries have been confined to the diabase west of that lake. Most of them occur in the southern portion of the central diabase strip which lies a short distance from the shore and extends northward for about seven miles from Elkhorn lake. On one of the Mann claims (T.R. 1966), now owned by Messrs. Foster, an east and west vein averaging 4ʺ or 5ʺ in width had been traced for 300 feet, the original discovery being made in the exposed face of a low diabase wall. At its surface the vein material had been weathered out for a depth of about 15ʺ and the cavity filled by a brownish mass of the decomposed matter mixed with vegetable mould and sand. Nuggets of mossy or arborescent silver were scattered richly through this dirt, and a fairly continuous spine of the same metal, sometimes an inch thick, extended along the middle of the crevice. A test pit sunk about 8 feet, but barricaded at the time of the writer’s visit, had exposed, according to Mr. Mann, silver and smaltite in a calcite vein. On the adjoining claim (T.R. 1982), a vein of massive smaltite about1ʺ wide was seen; a little silver had been found at its surface and streaks of argentite and disseminated grains of smaltite were seen in the wall rock. Aplite dikes on another claim were found to be stained by cobalt bloom, and full of disseminated chalcopyrite.
The properties owned by Messrs. Crawford and Dobie about half a mile farther south were not visited, but were generally reported to be of about the same richness as that in T.R. 1966. Immediately north of Hanging-stone lake Mr. F. A. McIntosh was conducting active prospecting in a coarse gabbroid, locally syenitic, form of the diabase, intersected by aplite dikes. A discovery of native silver has been made since then and the property sold to Messrs. F. R. Bartlett & Co., of Toronto, together with other claims located between the north-east and north-west arms. Other discoveries are reported just south-east, also a short distance north of Milne lake.
No silver had been obtained in the eastern diabase strip, although the geological conditions appear identical and calcite veins are abundant. An exceptionally large vein, about 18ʺ wide, and traceable across two adjoining claims was seen on the property of Messrs. McLaughlin and McIntosh, about half a mile north-east of the north-west arm. Mineralization in it near the surface was very slight. Several veins carrying small amounts of chalcopyrite, pyrite, bloom and smaltite were seen on the properties of Messrs. Elstone and Reilly (T.R. 1961, 1962 and 1903). In one of them small amounts of bismuth are present; another contains an unusually heavy black substance which proved to be calcite filled with minute crystals of magnetite.
In the western strip less exploration had been performed and little could be learned about the ore deposits. Loose pieces of native silver had been found by W. H. Margueratt in narrow fissures on M.R. 1798, but the vein material was not exposed.
Outside the Gowganda area systematic prospecting was in progress at only one point—Wapus creek. Under the management of Mr. Robert Lett a group of nine claims was being stripped and trenched, with the result that numerous calcite veins had been traced through a diabase showing the same complex intermingling of basic and acid phases and aplite dikes as at Gowganda. Chalcopyrite and cobalt bloom were abundant, and smaltite had been found as disseminations in the wall rock. Lumps of native bismuth weighing several ounces had been taken from a fissure in an aplite dike, analyses of which showed it to contain silver.
Tentative exploration was being conducted along Duncan lake and east of Firth lake, but not with the closeness and persistence which the topography of these veins require. In general the veins seen on Duncan lake are exceptionally rich in quartz, and gash veins are common. Chalcopyrite, pyrite and galena are the most noticeable metalliferous minerals, but cobalt bloom stains are frequently observable. So far as known no attention has been given to the large diabase body between Duncan lake and the West branch, although its size and varied composition are thought to make it a desirable prospecting ground.
The present knowledge of the Gowganda area indicates it to be highly mineralized, at least in so far as number of veins and surface showings are concerned. The number of discoveries within its area of ten square miles is steadily increasing. The area, character of the mineral association and the richness of the surface showings are comparable with those of Cobalt. There is a general similarity in the geological conditions. The mineralized veins in Gowganda occur in the diabase as do some of the good Cobalt veins. There are, it is true, local differences, but the resemblances are more pronounced than the differences and lead to the hope that exploitation will reveal similar underground conditions. The well mineralized veins are sufficiently long and uniform on the surface to suggest similarly persistent vertical dimensions. Further geological work may reveal something definite concerning the character and size of the diabase bodies which form the country rock, and thus afford a basis for predicting their subterranean distribution. While there are grounds for hoping that the veins will persist in depth, this has not yet been proved, nor, if this is the case, that the mineralization and values are also persistent.
The relative importance of Gowganda is therefore a matter of uncertainty as yet, but it may be confidently affirmed that for its state of development the outlook is very favourable, and the number of veins, area of mineralization and rich surface showings afford good grounds for hoping that some at least of the veins will be found to be commercially important.
The details of igneous intrusion, differentiation and mineralization may never be sufficiently understood to allow of accurate prediction regarding the location of silver deposits, but a general conception of the sequence of events culminating in their formation doespermit of the formulation of certain criteria useful in the search for ores. Evidence is accumulating to show that the silver-cobalt mineralizations in the Timiskaming region are connected with a late stage of differentiation in the magma which supplied the quartz diabase and aplite. It seems reasonable, therefore, to anticipate ore deposits in or near such bodies, especially if they are of large size and have undergone important chemical differentiation, that is, if they contain a varied and extensive association of basic and acid phases of the diabase. Pre-existing channels to receive the mineralizers are also necessary and their distribution a matter of vital importance, but in this region they appear to have been everywhere abundant.
These conditions appear to exist quite as fully at several other localities besides Gowganda. At Wapus creek they seem identical and, indeed, results obtained thus far indicate that some mineralization of the silver-cobalt type exists. Between Duncan lake and the West branch the conditions require further study, but, as now known, are not discouraging.
The chalcopyrite, which seems a much more constant constituent of the veins associated with the quartz diabase, is sometimes aggregated into bunches which yield ore specimens of such excellent appearance as to arouse interest. The ore is, however, confined to veins a few inches in width and so scattered as to render them valueless. Occurrences of this kind characterize most of the great diabase bodies, examples of which occur on Mosher lake, between the North-east and North-west arms of Gowganda lake and elsewhere. The chalcopyrite is sometimes superficially altered to malachite and azurite.
Hematite.—Excellent specular and kidney ore is known to exist a short distance east of Nest lake, but the locality was not visited owing to the more urgent requirements of other portions of the district. Specimens of the ore obtained, however, proved to be of excellent character, with little admixture of silica or other foreign matter. The ore body is thought to be of vertical tabular form, occupying a fissure-like space. Its limits are not known, consequently nothing can be yet stated regarding the commercial possibility of the deposit.
Specular ore was seen on mining claim T.R. 2009, near the north-east end of Firth lake, occupying a fissure in the Keewatin. The ore is of good quality, but the outcrop is of insignificant size, the fissure being only about 2 feet wide, and no ore occurring in either the chlorite schist or reddish granite which lie on either side.
Specular ore also occurs in the basal conglomerate of the Huronian series, filling the interstices between the pebbles where an original cement was deficient. At the south end of Kenisheong lake the conglomerate appears at the water’s edge, and the hematite may be observed while paddling near shore. The same thing occurs at the narrows on Duncan lake, just south of the central expansion. In neither case is the ore in commercially valuable quantity.
Magnetite.—Keewatin iron formation exists about one-half mile to the north-east of Gowganda lake. A brief visit was paid to some claims belonging to Mr. Cryderman where the formation is well exposed. The Keewatin, which is partially overlain by Huronian and traversed by diabase, consists of dark grey or black, banded chert or quartzite associated with chlorite schist. The dark bands, usually only a few inches in width, are full of disseminated magnetite grains. No concentrations were noticed and the richest bands would probably yield less than 30 per cent metallic iron, consequently the present showings cannot be considered valuable.
In the Keewatin area between Firth and Obushkong lakes there occur masses of a basic igneous rock through whose decomposition serpentine and asbestos have been developed. The localities given in connexion with the description of the Keewatin may be briefly restated. Two bodies were found. One of these, lying east of Foot lake and 20 chains from Obushkong was traced for a width of 4 chains, but nothing learned of its north and south extent. It consists very largely of green serpentine traversed by a network of fine, white weathering veins of asbestos. More extensive outcrops exist along the east shore of Firth lake. At somewhat more than a mile from the foot of the lake and near a small log shack at the water’s edge a considerable mass of partially decomposed wehrlite, serpentine, and asbestos is visible. The main mass is of dark green colour, the asbestos traversing it abundantly as a series of glistening brightgreen threads. The seams are small, none being found more than1⁄4ʺin width, but the asbestos fibres are fine and elastic. The serpentine is often coarsely fibrous but brittle.
Microscopic examination shows the serpentine and asbestos to be the product of decomposition of the wehrlite, a nearly black medium grained igneous type. Alteration has obscured its original character, but sufficient of the primary constituents remain to admit of its determination. It consisted of olivine, diallage, and common hornblende, with considerable ilmenite and apatite, but plagioclase is apparently absent. Hornblende and diallage form the basis of the section in which lie abundant rounded or idiomorphic grains of olivine. The latter is completely altered to a matted intergrowth of fibrous serpentine containing scattered grains of black iron ore. Diallage persists as colourless bi-refringent remnants enclosed by a felted mass of decomposition products, chiefly long scales of talc. The hornblende is fresher and strongly pleochroic, the tints being green; its alteration begins by bleaching, followed by development of colourless fibres of low bi-refringence, possibly serpentine. Primary ilmenite is replaced by irregular patches of leucoxene, showing gridiron structure. The final product of alteration is a soft green serpentine rock composed almost wholly of that mineral.
The limits of these masses are exceedingly difficult to define, owing to the fact that they are associated with other Keewatin rock and basic forms of the post-Huronian diabase, to which it presents considerable resemblance. The asbestos actually seen is probably too short and small in amount to be valuable, but the high commercial value of this material renders delimitation of the wehrlite masses advisable. Asbestos of very good quality has been found by Mr. George Rahn in the vicinity of Sinclair mountain, so that this mineral may be one of the district’s latent resources.
CANADADEPARTMENT OF MINESGEOLOGICAL SURVEY BRANCHHon. W. Templeman, Minister; A. P. Low, LL.D., Deputy Minister;R. W. Brock, Director.
CANADADEPARTMENT OF MINESGEOLOGICAL SURVEY BRANCHHon. W. Templeman, Minister; A. P. Low, LL.D., Deputy Minister;R. W. Brock, Director.
CANADA
DEPARTMENT OF MINES
GEOLOGICAL SURVEY BRANCH
Hon. W. Templeman, Minister; A. P. Low, LL.D., Deputy Minister;
R. W. Brock, Director.