The Geology of Mining Areas

Abstract

MR. R. G. MCCONNELL has contributed to the “Annual Report of the Geological Survey of Canada,” vol. xiv., part B (1905, price 25 cents), a well-illustrated paper of wide interest on the Klondike gold-fields. The general topography and the communications with other regions are described, and the full-page landscapes convey an excellent idea of the conditions under which mining is carried on. Roads have been developed, the White Pass railroad is completed, and it now takes less than a week to reach Dawson City from Vancouver. In the latitude of only 60° N., the surface-stratum is continuously frozen, and unfrozen ground is reached at depths of from 60 feet to 200 feet. In summer, gravel-beds which are unprotected by moss thaw down to a depth of from 6 feet to 10 feet (p. 9). The gold-bearing quartz-veins are included for the most part in the Klondike series of schists. Microscopic evidence supports the view that these schists are of igneous origin, since a passage is traceable from uncrushed granitoid types to mylonitic sericite-schist (p. 19). Cainozoic rocks are found folded in with the schists in Last Chance Creek, thus proving the recency of earth-movement in this area. In the basin above Rock Creek these beds contain lignites of Upper Eocene age. The low-level gravels of the creeks, which are so important to the gold-miner, include bones of the mammoth, as well as of many existing northern animals (p. 29). The greater part, at least, of the Klondike gold is detrital, and is derived from the small but very numerous quartz-veins associated with the older schists (p. 61). Many of the grains of alluvial gold enclose quartz, and a few are themselves enclosed in quartz. The decay of the rocks must have been enormous to allo* of the vast accumulation of auriferous gravels. The quartz-veins are much younger than the schists in which they lie, but are older than the andesites and quartz-porphyries of the district. Lodemining has so far made little progress, but work among the gravels seems still, increasing.