Geology and petroleum potential of the Norton Basin area, Alaska
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Geology topics
Publications and source records attributed to William Wallace Patton.
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A small contact-metasomatic magnetite deposit was discovered in the Medfra quadrangle, Alaska, in 1976. It occurs at the contact between a Cretaceous or early Tertiary quartz monzonite stock and Paleozoic limestone and dolomite. The ore is a magnetite-clinohumite-hematite rock that contains up to 60 volume percent magnetite and 76 weight percent total iron expressed as FeO. Computer modelling of data derived from a ground-level magnetometer survey yielded an estimate of the shape and volume of the deposit. The volume is grossly estimated at 11,600 3 m .
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Numerous hot springs occur in a variety of geologic provinces in west-central Alaska. Granitic plutons are common to all the provinces, and the hot springs are spatially associated with the contacts of these plutons. Of 23 hot springs whose bedrock geology is known, all are within 4.8 km (3 mi) of a granitic pluton. The occurrence of hot springs, however, appears to be independent of the age, composition, or magmatic history of the pluton. Most of the analyzed hot springs appear to have chemical and isotopic compositions indicating that they were derived from deeply circulating meteoric water. About 25 percent of the analyzed hot springs show a distinct saline character with high concentrations of chloride, sodium, potassium, and calcium indicating either much more complex water-rock reactions than in the other hot springs or the addition of another type of water. Chemical geothermometers suggest subsurface temperatures in the general range of 70° to 160°C. If the hot spring waters have derived their heat solely from deep circulation, they must have reached depths of 2 to 5 km (6,000-15,000 ft), assuming geothermal gradients of 30° to 50°C/km. If a shallow igneous heat source exists in the area or if dilution or mixing has occurred, these depths may be shallower. The geologic and chemical data, although preliminary, suggest that most of the hot springs of west-central Alaska have relatively low subsurface temperatures and limited reservoir capacities in comparison with geothermal areas presently being utilized for electrical power generation. :The springs may, however, have some potential for limited power generation locally, if and when heat-exchange technology becomes available, as well as for space heating and agricultural uses.
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Reconnaissance mapping on St. Lawrence Island, Alaska has revealed seven epizonal granitic plutons of mid-Cretaceous age with a combined outcrop area of about 350 square miles. The plutonic rocks are dominantly quartz monzonite, but include minor amounts of granodiorite, monzonite, syenite, syenodiorite, and alaskite. The plutons are structurally and petrologically similar to and about the same age as plutons on the Chukotsky Peninsula, U.S.S.R. and in western Alaska. They suggest tectonic continuity between Siberia and Alaska since at least Cretaceous time. Several mineralized areas containing molybdenum, copper, lead, and zinc sulfides are associated with the plutonic bodies in the western part of the island.
The recent discovery of major oil resources on Alaska's North Slope has rekindled interest in the petroleum possibilities of the Yukon-Koyukuk province, a vast tract of Cretaceous rocks stretching along the west coast of Alaska from the Brooks Range to the Yukon delta. Attention was first focused on this region in the early 1950's, after oil and gas were discovered in the Cretaceous of the North Slope by the U.S. Navy. The presence of similar Cretaceous strata in the Yukon-Koyukuk province and the possibility that some of the broad alluviated lowlands within the province might be underlain by Tertiary basins were pointed out by Gryc and others (1951) and Payne (1955). Between 1954 and 1961 large parts of the province were reconnoitered by oil company surface parties and a small amount of geophysical work was carried out in the Nulato-Kateel and Bethel areas. The explorational activity culminated in 1960-61 with the drilling of two deep tests, a 12,000-foot hole near Nulato on the Yukon River and a 15,000-foot hole at Napatuk Creek in the Yukon-Kuskokwim Coastal Lowland. Apparently neither test revealed oil shows or favorable reservoir rocks, as exploration and leasing activity in the province declined sharply thereafter. Since 1954 the U.S. Geological Survey has maintained a modest but continuing program of reconnaissance geologic mapping of the province and its borderlands. Nearly all parts of this vast area have been visited either by helicopter or river boat. Although information in many places is still sketchy, the broad outlines of the surface geology are now known. Subsurface data, however, are almost totally lacking. The mapping indicates that the petroleum possibilities over most of the province are limited because of complex structure and scarcity of promising reservoir rocks. Two areas where further exploration seems warranted are the Yukon-Kuskokwim Coastal Lowland and the western part of the Kobuk-Selawik Lowland.
Analytical data for 207 stream-sediment samples from western St. Lawrence Island are presented in this report, together with a statistical treatment of the data. The samples were collected in 1968 and 1969 as part of the Heavy Metals Program of the U.S. Geological Survey. This report is intended to supplement Geological Survey open-file report entitled "Preliminary geologic investigations of western St. Lawrence Island, Alaska" (Patton and Csejtey, 1970) which describes the general geology of the area and discusses several localities where anomalous amounts of metals were found.
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