Browsing by Author "McSwiggen, Peter L."

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    Information Circular 22. Analytical Results of the Public Geologic Sample Program, 1983-1985 Biennium
    (Minnesota Geological Survey, 1985) Morey, G.B.; McSwiggen, Peter L.; Kuhns, Mary Jo P.; Jirsa, Mark A.
    In 1983 the Minnesota Geological Survey, in conjunction with the Minnesota Department of Natural Resources, Division of Minerals, began a geologic sample program whereby the general public was encouraged to submit samples of geologic material for identification and possible analysis. The program was roughly patterned after a similar program in Finland. The Finnish program has resulted in a heightened public interest in the mineral potential of that country and has resulted in the discovery of several ore deposits. It was for those reasons, as well as the potential increase in geologic knowledge that could result, that a similar program was initiated in Minnesota. As originally conceived, the geologic sample program was to focus on samples submitted to the Minnesota Geological Survey by the general public. As part of its public service function, the Survey was to identify and classify rock or mineral samples that were collected in the state. If any of the samples were thought to have potential scientific or economic interest, they were to be submitted for chemical analyses or other appropriate tests. A copy of a brochure that was prepared to advertise the program is shown in Figure 1, and the sample submittal form that sets forth the operating conditions for the program is shown in Figure 2. The brochure and other publicity about the program led to requests for 238 submittal forms and to approximately 500 walk-in and telephone requests for additional information. Unfortunately, of the more than 700 inquiries, only 9 samples were ultimately judged suitable for additional chemical analysis (Table 1). The "suitability" rate of only slightly more than 1 percent was due to a number of factors. Many people only became aware of the program very late in the biennium. Other people who had samples of scientific or economic interest were unwilling to submit those samples to the Geological Survey for several reasons, including (a) the expense of mailing samples, (b) an unwillingness to part with a "prized" specimen, or (c) a lack of knowledge about mineral rights (i.e., a fear of jeopardizing their rights by revealing the location of a sample). However the great majority of samples were submitted by individuals who simply wanted them identified without concern as to possible scientific or economic value. Because of the sluggish public response, the program was modified in early 1985 to include samples of scientific or economic interest that were submitted by personnel of the Minnesota Department of Natural Resources, Division of Minerals, or the Minnesota Geological Survey. This programmatic change led to the additional analysis of 304 samples from various components of the Early Proterozoic Animikie basin on the Mesabi and Cuyuna ranges and in east-central Minnesota (Tables 2, 3, 4, and 7) and from various poorly known rock units in southwestern (Tables 5 and 8) and southeastern Minnesota (Tables 6 and 9).
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    Information Circular 28. Graphite in Early Proterozoic Rocks of East-Central Minnesota
    (Minnesota Geological Survey, 1989) McSwiggen, Peter L.; Morey, G.B.
    The Penokean orogen and southern Animikie basin of cast-central Minnesota contain numerous carbonaceous units. The carbon content of these units ranges from as little as 1-2 wt.% to as much as 44 wt.%; the thickness of these units ranges from a few inches to over 500 feet. By using published values for the energy content of some Finnish and Swedish carbonaceous rocks, it is possible to estimate the energy content in samples from this study. These values indicate that a ton of rock with 44 wt.% graphite contains approximately as much energy as one ton of lignite or a half ton of bituminous coal. This suggests that such a rock contains roughly $13.50-19.00/ton worth of energy. In certain localities, the carbonaceous units also contain significant precious and base metal concentrations. Values of as much as 350 ppb gold and 6 ppm silver were recorded.
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    RI-45 Iron-Formation Protolith and Genesis, Cuyuna Range, Minnesota
    (Minneota Geological Survey, 1995) McSwiggen, Peter L.; Morey, G.B.; Cleland, Jane M.
    The Cuyuna iron range in east-central Minnesota is unique in the Lake Superior region because of its large manganiferous iron ore resource. The protolith to the ore has traditionally been considered a Lake Superior-type iron-formation similar to other Early Proterozoic iron-formations in the region. However, recent stratigraphic, mineralogical, and geochemical studies show that the Trommald Formation-the principal iron-formation of the Cuyuna North range-is not the product of a simple sedimentological regime. The presence of the minerals aegirine, barite, Ba-feldspar, and tourmaline within or associated with the iron-formation shows that hydrothermal and exhalative processes were very important during deposition of the iron-rich strata. This new interpretation has significant implications for mineral exploration in this part of Minnesota. It implies that parts of the Cuyuna range may be likely areas for exploration for sediment-hosted, submarine exhalative, PbZn- Ag deposits.
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    RI-46 Hydrothermal Systems in Manganese-Rich Iron-Formation Ofthe Cuyuna North Range, Minnesota: Geochemical and Mineralogical Study of the Gloria Drill Core
    (Minnesota Geological Survey, 1996) Melcher, Frank; Morey, G.B.; McSwiggen, Peter L.; Cleland, Jane M.; Brink, S.E.
    The iron-rich Trommald Formation of Early Proterozoic age on the Cuyuna North range in east-central Minnesota is the largest resource of manganese in the United States. To better elucidate the complex history of the manganese oxides and to investigate their compatibility with in situ leaching techniques, the U.S. Bureau of Mines drilled a core near the Gloria mine (sec. 28, T. 47 N., R. 29 W.) to an inclined depth of about 1200 feet. It intersects a complete section of Trommald Formation 553 feet thick, as well as short intervals of the overlying Rabbit Lake and underlying Mahnomen Formations. At the Gloria site the lowermost part of the Trommald Formation consists of chlorite-bearing hematite iron-formation, and contains features indicative of syndepositional reworking-possibly under shallow-water conditions that include granule-rich layers and pebble-size conglomerate. Much of the overlying thin-bedded facies consists of carbonate-silicate iron-formation broken in places by beds of breccia. In the breccia, sulfides--especially pyrite filled interstitial voids or form discordant composite veins along with quartz, manganese oxides, carbonates, and stilpnomelane. Pyrite contains included pyrrhotite, chalcopyrite, and arsenopyrite, and is replaced by magnetite, in turn replaced by martite. The silicate-carbonate iron-formation contains little manganese <2 wt. percent MnO), but the breccias are marked by elevated values of Mn, as well as Cu, As, Sb, S, Sr, Y, Ca, and P. Within the thin-bedded facies, a transitional interval of about 15 feet separates silicate-carbonate iron-formation below from oxide iron-formation above. Isocon analyses show that oxidized strata can be derived from unoxidized strata by a variety of decomposition reactions, all essentially removing Mg, K, Ca, Na, P, and resulting in a mass loss of 40 to 50 percent. Manganese oxides appear in oxidized strata as discordant veins and as concordant, massive layers and lenses, where they are admixed with goethite and hematite. Massive layers are partly enveloped by brecciated oxides of several kinds, have maximum MnO values of 12 wt. percent, and are enriched in Ba, Sr, Ag, and U. Manganese values increase markedly just above the contact between the thin-bedded facies and the overlying thick-bedded facies. Manganese oxide-rich layers just above the contact have brecciated or "gnarled ore" textures and are conformably interlayered with intervals of decomposed oxide iron-formation containing abundant secondary limonite. The manganese oxide-rich layers are intercalated with thick beds of admixed chert and hematite; they have a relict micronodular texture and discordant textural features, involving manganese minerals such as manganite, cryptomelane, and pyrolusite. Whole rock assays show that they can contain as much as 50 wt. percent MnO. They also have elevated Ca, Mg (attributed to secondary carbonates), and P values and are enriched in Ba (as much as 1.8 percent), Pb, Sr, Ag, As, and the LREE. The uppermost part of the thick-bedded facies consists of oxide iron-formation where primary hematite is abundant but where manganese oxides are lacking. The overlying Rabbit Lake Formation is an epiclastic unit that contains thick beds of carbonaceous shale, thin layers of tuffaceous material, and intercalated beds of sulfide (pyrite) and oxide (hematite) iron-formation. The sulfide iron-formation (35.7 wt. percent Fe203, 26 percent S) contains elevated values of Au (31 ppb), As, Cu, Co, Ni, Pb, Sr, V, Mo, and Se (230 ppm). Many of the textural and mineralogical features observed in the Gloria core are consistent with hydrothermal fumerolic processes that started in late Mahnomen time and persisted into early Rabbit Lake time.