Year: 1958
Type: report
Abstract: The calcite deposits of Park and Sweet Grass Counties, Mont., although mined locally for chicken grits, had yielded only slightly more than 600 pounds of optical spar and mineral specimens before World War II.During 1942 and 1943 the deposits were exploited extensively to obtain calcite for use in a new antiaircraft sight developed by the Polaroid Corporation.Records were not kept of the first production after the beginning of World War II, but it probably amounted to less than 1,000 pounds of acceptable optical calcite.Available records indicate that Calcite Operators, Inc., and Metals Reserve Company produced 9,217.5 pounds of optical material during the period of intensive mining.By the summer of 1944 the Polaroid Corporation had developed a synthetic substitute for optical calcite.The substitute was nearly as good as the calcite and could be mass produced.Mining of optical calcite ceased, therefore, in August 1944.Most of the optical calcite has been obtained from veins cutting sedimentary rocks of the Livingston formation, but some also has been obtained from veins in the Livingston igneous series of Parsons (1942).Sedimentary rocks of the Livingston formation are composed of andesitic sandstone, tuff, shale, conglomerate, and local intercalations of volcanic breccia and agglomerate.The Livingston igneous series of Parsons (1942) is made up of andesitic tuff, breccia, agglomerate, tuffaceous sandstone, volcanic conglomerate, and a few thin flows of andesite and basalt.Both the sedimentary rocks of the Livingston formation and the Livingston igneous series of Parsons (1942) are believed to be the stratigraphic equivalents of a number of Upper Cretaceous and lower Tertiary formations in areas nearby.In the calcite-producing area the Livingston formation has been folded into a broad, flat, synclinal trough trending about north.To the northeast, west, southwest, and south the Livingston formation has been turned up along the fronts of the surrounding mountains.The calcite veins occupy faults that trend northwestward and dip steeply either southwestward or northeastward.The calcite occurs as thick massive veins, as systems of branching smaller veins, or as stockworks of veinlets.A few veins also contain stilbite, and one occurrence each of laumontite and chalcedony was found.Some of the larger veins have been traced several thousand feet on the 431 432 CONTRIBUTIONS TO ECONOMIC GiEOIX)GY o surface and may have a maximum thickness of 20 feet.A thick vein about 100 feet below the surface on the bottom level of the Wade property is the deepest worked calcite vein in the area.Veins that cut both shale and sandstone tend to be thicker in the sandstone; and the steeply dipping parts of veins are generally thicker than the flatter parts.Many veins are conspicuously banded parallel to their walls, and the individual bands exhibit comb structure.The bands resulted from repeated movement on faults followed by deposition of calcite in the openings formed by the movement.Vugs created by incomplete filling of fissures have been the source of all optical calcite mined.The largest vug of record measured 70 feet long, 30 feet wide, and 3 feet thick.Most of the productive vugs were tabular in shape and had volumes of several tens to hundreds of cubic feet.Most of the usable material came from the clear crystal tips, though some came from the "root" material nearer the vein walls.In productive vugs crystals 3 to 8 inches across were the most numerous.The two most common crystal forms in all vugs were rhombohedrons and scalenohedrons.All crystal faces had been strongly etched by ground water.The principal defects causing rejection of crystals were excess opaqueness, twinning, and incipient cleavage fractures within the crystal.The calcite veins were deposited in open fractures by rising hydrothermal solutions of low temperature and pressure.The veins appear genetically related to the local igneous activity, and may have been deposited during an earlier hypogene period of carbonate mineralization by ancient hot springs similar to the .presentones in the area.All known optical calcite deposits in the counties are described here, including several other large veins that have not been exploited.Deer Creeks in the foothills of the Beartooth Mountains.Plate 23 is a map of the calcite-bearing area.The largest cities in the area, Livingston and Big Timber, are on the banks of the Yellowstone River.The main line of the Northern Pacific Railway passes through both places, and from Livingston a branch line runs north, up the Shields River valley through the small settlements of Grannis, Clyde Park, and Wilsall.Another branch runs 50 miles south to Yellowstone National Park.Small villages and many ranches lie near the streams and are connected to main highways by paved or graded Federal and State roads along the main rivers and by a system of dirt roads in the hinterland.Field work and acknowledgments.The field work for this report was done by the writers between November 18 and December 5, 1943, and during two weeks in May and five weeks in August and September 1944.The earlier work was done to determine the amount of optical calcite that could be produced by systematic mining of the deposits near Clyde Park and Wilsall.During the 1944 field work many mines were in operation, and the deposits were studied in detail underground.Field work included the examination and detailed mapping of veins and host rocks, and the assembling of data on production, excavation, and the economic value of the deposits.Large-scale planetable maps were made of selected surface areas, and compass and tape maps were made of the underground workings.Many veins other than those mined were visited and their location plotted in order to obtain a better knowledge of the geographic and geologic relations of the vein systems.Areal geologic mapping was not attempted.Land owners and personnel of mining organizations gave the fullest cooperation.Leo J. Coady, contractor, and Eric G. Ericson, mining engineer for Metals Reserve Company, provided maps, stope surveys, production data, and other necessary material.Information on local history, production, and location of outcrops was given by R. D. Hoffman and A. L. Anderson, manager and foreman, respectively, for Calcite Operators, Inc., W. H. Wade and J. B. Killorn, property owners, and Edwin Over, prospector and operator
DOI: 10.3133/b1042m
Authors: W.C. Stoll, Frank C. Armstrong
Language: English
Subfield: Geochemistry and Petrology
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: gold
OpenAlex ID: W4398540