Clark Fork District
Commodities: silver, lead, copper
The presence of copper, gold, and lead in this district has been known for a long time, but there was little production prior to 1913 and the principal development started with the discovery of some high-grade lead-silver veins in 1926. The mineralized area is bordered on the west by the Great Northern Railroad and on the south by the Northern Pacific Railroad, providing exceptionally convenient transportation facilities.
The district is underlain by the Belt series with intercalated quartz diorite sills, which, like the enclosing rocks, are regarded as pre-Cambrian. Both are cut by granodiorite of probable Mesozoic age accompanied by lamprophyre and pegmatite dikes. The Belt strata are folded and out by faults, some of which have displacements of several thousand feet. Some of the faults are closely related to the intrusion of the granodiorite, whereas others are later. Mineralization is in part localized along certain of the faults.
Mineral deposits are widely distributed throughout the district, but are especially abundant in a zone several miles long bordering the Hope fault, which has a westerly strike, transverse to many other faults of the region, and, like the Osborne fault in the Coeur d’Alene region, is supposed to have a large lateral shift.
Most of the productive deposits are in a small area near the town of Clark Fork, south of the Hope fault. Most of the lead deposits on the south side of the fault resemble those of the Coeur d’Alene region. They are replacement veins in Belt strata, mainly Wallace, containing galena, tetrahedrite, and lesser amounts of sphalerite, pyrite, arsenopyrite, and chalcopyrite in a gangue of siderite with some quartz and calcite. Some of these veins are rich in silver, a fact which has aided in the successful development of small mines.
On both sides of the area containing these lodes, and likewise south of the Hope fault, there are copper veins containing chalcopyrite in a gangue of quartz and siderite. North of the Hope fault there are veins in which replacement played a relatively subordinate part. These consist largely of quartz and pyrrhotite with variable amounts of galena, sphalerite, pyrite, arsenopyrite, chalcopyrite, calcite, and locally siderite. Those in which galena is abundant are principally valuable for lead. They contain less silver than the veins farther south, probably because of the paucity of tetrahedrite. Some of the veins contain insufficient base metals for profitable mining, and their value lies mainly in their gold content.
Lakeview District
Commodities: silver, lead, copper, zinc
This district borders Pend Oreille Lake on the southeast and is regarded by some as part of the larger district named for the lake. The original discovery of ore in the vicinity was made in 1888 at what is now the Webber mine in the Lakeview district. The rush that followed did not result in any production, but led to intensive prospecting in the area around Pend Oreille lake during which it is probable that all exposed lodes were noted. Mining has continued intermittently to the present time, but little has been done for several years. The ore is valuable principally for silver, although lead and lesser quantities of copper and zinc are recoverable.
The district is underlain by the Wallace and Striped Peak formations of the Belt series, covered locally by Cambrian quartzite, shale, and limestone, and intruded by granodiorite. There are a number of large faults, of which the Pack- addle fault is the most persistent within the district.
The principal development is on three vein systems; the Webber, 8,000 feet long; the Conjecture-Keep Cool, apparently 12,000 feet long; and the Hewer, 8,000 feet long. The vein systems are great shear zones, locally as much as 120 feet thick, containing lenses and chimneys of vein quartz, which is itself much sheared. The sulphide ore is associated with the quartz masses, the sheared country rook, even where silicified, being barren.
Lamprophyre dikes out sheared rook and ore intricately. The ore contains siderite (locally rhodochrosite), pyrite, arsenopyrite, quartz, sphalerite, galena, tetrahedrite, stibnite, chalcopyrite, boulangerite (?), hubnerite, and proustite, named in approximate order of deposition except that certain of the minerals crystallized at more than one point in the sequence.
Pend Oreille District
Commodities: silver, copper, gold, lead
This district, served by the Great Northern and Spokane International railroads and by lake boats, has been known and intermittently operated since 1888.
From 1889 to 1917, numerous small shipments of high-grade silver ore from this district and the nearby Lakeview district are estimated to have aggregated about $500,000. In 1917 to 1926 the Talache (formerly Blackball) mine is reported to have produced about $2,000,000 of which nearly 80 per cent was from silver and the rest about equally divided among copper, gold, and lead. Since then, there has been relatively little production in the district. Some term the part of the district on the west side of the lake the Blackball and that on the northeast the Hope district.
The district is underlain by Belt strata, out by granodiorite and locally overlain by patches of Cambrian sedimentary rocks.
The lodes are similar to those of the Lakeview district except that ore deposits are largely confined to the filling of clear-cut fissures, without the great shear zones characteristic of the Lakeview district. The minerals formed are about the same as in the Lakeview district, except that rhodochrosite is not recorded, polybasite (definitely hypogene) is more abundant than proustite, and in one mine hypogene metallic arsenic is present.
Priest Lake District
Commodities: lead, silver, copper
This large district, which includes much of western Bonner County and parts of Boundary County, contains a number of prospects, but no mines with large production records. Some include in it the adjacent Porthill district in Boundary County, p. 28 of this pamphlet. The southern end of Priest Lake is 25 miles by road from Priest River on the Great Northern Railroad, and the prospects are reached by branch roads and trails from that point or from roads in Boundary County
The district is largely underlain by granodiorite and kindred rocks with local areas of other rocks, presumably quartzite, limestone, and argillaceous Belt strata. In some areas, there are large amounts of gneiss and schist, presumably the result of injection and metamorphism of Belt strata in connection with batholithic intrusion, although other rocks may be included.
Most of the prospects are along the shores of Priest Lake. The only descriptions of these known to the writer are the two very brief ones mentioned below. These show that some prospects are on veins containing galena (low in silver) and some chalcopyrite; others are in pyritic replacements in limestone or dolomite. It appears from the annual reports of the State Inspector of Mines and news notes in Mining Truth that in 1930 to. 1932 some attempts were made to develop material in the so- called "Mystery Metal Belt" in this district.
It is claimed among other things that the material mined contains aluminum and beryllium. Silicate minerals containing aluminum are, of course, present in the rocks of this as of nearly all regions, but this fact is in no way an indication that aluminum can be profitably recovered from them.
