Report of Investigations

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Browsing Report of Investigations by Author "Beltrame, R.J."

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    RI-24 Manganese Resources of the Cuyuna Range, East-Central Minnesota
    (Minnesota Geological Survey, 1981) Beltrame, R.J.; Holtzman, Richard C.; Wahl, Timothy E.
    The Cuyuna range, located in east-central Minnesota, consists of a sequence of argillite, siltstone, iron-formation, graywacke, slate, and quartzite of early Proterozoic age. Manganese-bearing materials occur within the iron-rich strata of the Trommald Formation and the Rabbit Lake Formation. Computer-assisted resource estimates, based on exploration drill hole information, indicate that the Cuyuna range contains a minimum of 176 million metric tons (MMT) of marginally economic manganiferous rock with an average grade of 10.46 weight percent manganese. The calculated 18.5 MMT of manganese on the Cuyuna range could supply this country's needs for this important and strategic metal for nearly 14 years. An additional resource of 6.9 MMT of manganese metal is available in the lower grade deposits. The vast majority of these calculated resources are extractable by current surface mining techniques.
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    RI-27 Geophysical Investigation of the Cedar Mountain Complex, Redwood County, Minnesota
    (Minnesota Geological Survey, 1982) Beltrame, R.J.; Chandler, V.W.; Gulbranson, Brian L.
    The Cedar Mountain Complex is a roughly circular composite intrusion, 500 to 600 m in diameter, in the Archean gneiss terrane of southwestern Minnesota. Emplaced during early Proterozoic time, the complex consists of a central core of monzonite surrounded by slightly older, compositionally layered dioritic rocks. Existing geophysical and geologic data indicate that the complex may reflect a widespread igneous event that also formed the granite-rhyolite terrane of central Wisconsin. A gravity and magnetic survey was conducted over the Cedar Mountain Complex to (1) delineate the contacts which are nowhere exposed; (2) interpret the configuration of the intrusion at depth; and (3) determine what relationships the complex may have with similar intrusions in the area and determine how they might be detected geophysically. Magnetic anomaly and rock property data indicate that the dioritic rocks are the principal sources of anomalies and that they are polarized near or along the present earth's field. Magnetic anomaly data indicate an angular and irregular configuration for the diorite-gneiss contact and a somewhat rectangular configuration for the monzonite-diorite contact. Model studies of the magnetic data imply that some contacts may dip steeply outward, but most are nearly vertical. The gravity anomaly data indicate that the core monzonite may be in part underlain by dioritic rocks. The configuration of the outermost contact and the density constraints indicate forceful injection as the mechanism for emplacement of the dioritic rocks. Similar emplacement is possible for the core monzonite, but the regular configuration of the inner contact, density constraints, and gravity interpretation favor stoping out of large blocks of diorite. Upward continuation of the magnetic data indicates that gross anomaly attributes of the complex and related intrusions would be detectable by aeromagnetic surveying using a flight-line spacing of 400 m and terrain clearance of 150 m.