Geology topics
C.L. Sainsbury
Publications and source records attributed to C.L. Sainsbury.
Tungsten deposits of the Hyder district, Alaska
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Geochemical exploration for antimony in southeastern Alaska
Preliminary geochemical prospecting by the Geological Survey was carried out in 1952 in muskeg-covered ground at Caamano Point, Cleveland Peninsula, Alaska, in an effort to delimit areas of stibnite concentrations. It was conducted to aid, if possible, a prospecting project of the Defense Minerals Exploration. Samples were collected from soil and decomposed limestone-and-schist bedrock at depths ranging from 18 inches to 60 inches, by means of a pipe with an interior plunger. Initial sampling was followed by detailed sampling of the areas where the antimony content of the soils consistently averaged more than 300 ppm. These Areas of major soil concentrations were prospected by surface trenching and percussion drilling to depths of 20 feet which proved the existence of stibnite ore. Next a shaft and drifts made in the most favorable area proved disseminated stibnite ore to depths of 60 feet. This geochemical work of soil sampling to indicate hidden ore bodies in a typical Alaskan muskeg area is believed to be the first application in Alaska of such techniques in active ore exploration. The results show the economic feasibility of such exploration as a first step in extending the known boundaries of mineralized areas, and in directing initial exploration toward the most favorable areas of near-surface ore bodies. Data are presented to help establish values of soil content of antimony that may be considered as normal in this type of geologic terrain.
Geology of two areas of pegmatite deposits in southeastern Alaska
A pegmatite deposit about 600 feet in diameter crops on a high bluff less than one-half mile east of a small unnamed cove between Redfish and Byron Bays, on the west coast of Baranof Island, southeastern Alaska. The deposit which comprises several pegmatite bodies consists of quartz, albite-oligoclase, microcline and mica, listed in the order of their relative abundance. Feldspar and quartz crystals locally attain a length of more than 1 foot. Some muscovite mica up to 2 inches in diameter occurs, but the major part of the mica is contained in concentrations, containing mica flakes one-half inch across, that often are as large as 10 feet across. Ruby mica of strategic grade has been obtained from float from this deposit. None of the rarer minerals such as beryl, columbite-tantalite or cassiterite that often occur in pegmatites were observed in the preliminary examination; and small-size concentrate samples obtained by panning stream sands from the area did not contain recognizable amounts of these rarer minerals. One sample contained a few grains identified as cassiterite. No radioactive anomalies were detected in the pegmatites, or in the stream concentrates. The large tonnage of material available arid the favorable location by a good anchorage on an ocean route are favorable factors that should contribute to the development of the deposits. Other deposits of comparable size probably occur in the area.
Geology of the Olds Mountain-Clark Peak area, Juneau and vicinity, Alaska
The area under study lies about ten miles east of Juneau, Alaska, and includes the bedded rocks adjacent to the Coast Range batholith, and intrusive rocks related to the batholith. Deep glaciated valleys and glacially scoured rocks are the major topographic features. The relief is about 3,500 feet, and the highest mountain reaches an altitude of 4,453 feet. Remnants of larger glaciers and perennial snow fields cover many of the higher summits, and glacial erratics at elevations above 3,100 feet attest to a former thick ice cover. The bedded rocks are crystalline schists that locally reach katozonal metamorphic rank as indicated by biotite-garnet-kyanite-sillimanite mineral assemblages. The schists are believed to be dominantly a product of regional metamorphism predating the intrusion of rocks related to the Coast Range batholith. It appears, however, that stresses continued to be active during igneous and granitizing activity accompanying the Coast Range orogeny. The major intrusive bodies are a composite quartz-dioritic batholith and quartz-diorite sills that locally reach a thickness of more than two thousand feet. The sills usually are notably gneissic, and appear to have formed by intrusion rather than replacement. The batholith is a composite body formed by migmatization, replacement, and local fusion. A stressed environment during formation is suggested by a primary gneissic structure. A high quartz content and a paucity of potash feldspars is diagnostic of the intrusive bodies. In addition to the bodies of quartz-diorite, small sills and dikes of gabbro, quartz-pegmatite, and unmetamorphosed diabase intrude the schists. Overturned folds in the schists are nearly isoclinal, and some of the folds are large enough to cause repetition of beds in the Clark Peak schists. Two persistent northwest-trending strike faults of small displacement cut the schists. Two east-trending faults of larger displacement are marked by thick gouge zones locally containing graphite. The rocks near the faults are hydrothermally altered and pyritized, and at least two of the diabase dikes are crushed and hydrothermally altered near one of the northwest-trending faults. Faulting and hydrothermal activity probably continued at least into the early Tertiary.