The Ketchikan miner., 1908-11-21
TIN DEPOSITS OF SEWARD PEN
 INSULA, ALASKA.

(Report by Government Geologist.)
 Stream tin was discovered n the York region of Seward Peninsual during the fall of 1900 as heavy and constituent which ac- cumulated in the sluice boxes of the placer-gold prospectors. A. II. Brooks, of the United States Geologi- cal Survey, who was engaged in hasty reconnaissance of the region, brought some of this material back to Washington. where it was identified as cassiterite, an ore of tin, and the discovery was soon heralded by the public press.
 The true nature of the mineral once kpowp, search was directed toward finding a wider distribution of the tin-bearing gravels and toward locating the bedrock source of the cassiterite, the seach being stimulated by the failure of the gold placers at the region and the high market price of metallic tin in recent years. Ever since their discovery the Alaska tin deposits, as they are popularly known, have continued to attract considerable attention from the mining publican interest due in large part to the fact that there are no producing tin mines in the United States proper.
 The tin. deposits of this region have been briefly described in several re- ports issued by the United States Geo. logical Survey, hut all these reports have been based on investigations that were incidental to other work. In the spring of 1907, however, more thorough investigation was undertak- en, and Adolph Knopf, of the Survey, was assigned to the work, with in- structions to make careful study of the mineral deposits and, so far as time permitted, to determine the conditions of their occurrence and origin. In MT. Knopf's report, which has just been published by the Survey as Bulletin 35S, the more purely scientific phase of the investigation has been emphasized rather than the commercial phase, which can best be solved by the mining expert and | engineer; but it is believed that the presentation and analysis of the chie1 facts regarding the mineralogy and geology of the tin deposits will have more value to the district as a whole than any publication of statement: concerning the commercial featurs. of individual ore bodies. Moreover, it has become the established policy of the Survey not to attempt to sample ore bodies, for such work is believed to fall outside of the province of the federal geolog ists, and obviously with out careful sampling the valuation O
 any given deposit is impossible.
 Mr. knopf presents the following practical deductions as the result O his field work:
 Developments in this region havt been sufficient to demonstrate, al least, that the granite-limestone con tacts are not favorable places to hum for commercial bodies of cassiterits ore. In view of the wide spread belief in Seward Peninsul; that contact depusits are likely sources of tin ore, it is worth while to review here what is known of cassiterit' contact metamorphic deposits in othe parts of the world. There has beer actual production of tin from twt only-Pitkaranta in Finland ant Schwarzepberg in Saxony-and il amounts that are relatively small The ore at these localities contain pyroxene and other minerals common
 in the Alaska contact-metamorphit deposits, but the ore formation is con fined to certain definite strata that were evidently favorable to the pre- cipitation of the cassiterite.
 "Quartz porphyry dikes, locally known as lodes, or even as quartz veins, have been prospected to som C extent, owing to the fact that the original discovery of lode tin in Alas ka was made on mineralized or altered dike of this character. The value of any such dike depends or the number of casserite stringers which it contains and the closeness with which they are spaced. Of itself a quartz porphyry dike has DO value. The unwelcome fact should be speedily |realized that few of these dikes hold out any inducements whatever as prospective tin producers.
 ''Most of the developments through out the region are still in the pros- pecting stage, and many of the open cuts have not uncovered solid bedroc k No tonnage of tin bearing rock, ex- cept at one place on Lost river, has yet been blockd out. Small holes in the ground, which give no clue to either dip, strike, or persistence of the ore rock, are held at enormous figures. The great need of the country is less desultory prospecting. The -I. f,,1