Browsing by Author "Boerboom, Terrence J."

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C-19 Geologic atlas of Carlton County, Minnesota [Part A]
(Minnesota Geological Survey, 2009) Boerboom, Terrence J.
C-38, Geologic Atlas of Kanabec County, Minnesota
(Minnesota Geological Survey, 2016) Boerboom, Terrence J.
Surface and bedrock geology of Kanabec County, Mn., also includes data-base information, bedrock topography, depth to bedrock in GIS and image formats, as well subsurface interpretations of sand distribution between the land and bedrock surfaces.
Information Circular 26. Scientific Core Drilling in Parts of Koochiching, Itasca, and Beltrami Counties, North-Central Minnesota, 1987-1989: Summary of Lithological, Geochemical, and Geophysical Results
(Minnesota Geological Survey, 1989) Boerboom, Terrence J.; Jirsa, Mark A.; Southwick, D.L.; Meints, Joyce P.; Campbell, Frederick K.
This report summarizes the results of scientific core drilling undertaken primarily to gain a better understanding of the bedrock geology in north-central Minnesota. The drilling and concomitant mapping were supported by the Minerals Diversification Program of the state legislature. The study area lies in southern Koochiching, northern Itasca and east-central Beltrami Counties. This region was selected because data are suggestive of mineral resource potential, but existing geologic maps were too generalized to guide private minerals exploration efforts. The thick cover of glacial deposits in this region requires bedrock geologic mapping to be based largely on the interpretation of geophysical maps. Core drilling and outcrop mapping identify the rock types responsible for the geophysical patterns. It is hoped that geologic mapping by this method will encourage private minerals exploration. In addition, this mapping is an acceleration of on-going efforts by the Minnesota Geological Survey to produce accurate geologic maps of the state to meet existing and future societal, academic and economic needs. The resulting bedrock geologic map at 1:250,000 scale has been released as Minnesota Geological Survey Open-File Report 89-1 which is being reviewed before formal publication. In the course of the drilling program much information was acquired regarding the thickness and lithology of Quaternary surficial deposits and the locally thick weathered bedrock materials (regolith). No formal plans exist at this time to publish an interpretation of these data, but the data are presented here on the geologic logs.
Information Circular 31. Scientific Test Drilling in West-Central Minnesota Summary of Lithologic and Stratigraphic Results, 1987-1988, and Some Preliminary Geological Conclusions
(Minnesota Geological Survey, 1990) Southwick, D.L.; Setterholm, Dale R.; Boerboom, Terrence J.
In 1980 the Minnesota Geological Survey (MGS) began a program of scientific test drilling designed to acquire a better understanding of the complex Precambrian bedrock of Minnesota. A research approach that combined selective test drilling with geophysical surveying of the Precambrian terrane was dictated by the fact that the Precambrian rocks are covered by substantial thicknesses of Quaternary glaciogenic sediment in most places and therefore are not amenable to standard mapping and sampling techniques. This circular is the fourth to report basic results from the drilling program. It contains data from four separate studies that were undertaken in central and western Minnesota in 1987-1988 (Fig. 1). The drilling summarized here, like that in previous projects (Southwick and others, 1986; Mills and others, 1987; Boerboom and others, 1989), was closely coordinated with geophysical surveys, and the selection of drilling targets was guided by geophysics to the maximum extent practicable. Our standard procedure was to formulate regional interpretations of the buried Precambrian geology from the geophysical data and then drill to verify, modify, or otherwise constrain the geophysical interpretation. Earlier applications of this approach have contributed to regional-scale geologic maps of the Penokean orogen (Early Proterozoic) in east-central Minnesota (Southwick and others, 1988) and an Archean greenstone belt in north-central Minnesota (Jirsa and Boerboom, 1990); the data tabulated in this circular will eventually contribute to new geologic maps for west-central Minnesota.
Information Circular 40. Scientific and Exploration Drilling in Northwestern Minnesota
(Minnesota Geological Survey, 1993) Jirsa, Mark A.; Boerboom, Terrence J.
Scientific test drilling in northwestern Minnesota was undertaken by the Minnesota Geological Survey (MGS) primarily to elucidate the geology of Precambrian and Phanerozoic bedrock in this area where the bedrock is buried beneath several hundred feet of Quaternary glacial sediment. The results of this drilling of 23 holes, and of selected logging, and analyses of the approximately 80 archived records and core from previous drilling, are presented in this report. These data, in conjunction with various geophysical maps, were utilized by the authors and others to construct a series of new geologic maps of northwestern Minnesota that are part of MGS Open-File Report 93- lA (Jirsa and others, 1993). Parts of that report will soon be published in the MGS Miscellaneous Map Series. An important secondary objective of this project is to describe the Quaternary deposits that overlie bedrock, though no systematic regional interpretation of those deposits has been undertaken to date. This is the seventh information circular since 1980 to report the results of test drilling by the Minnesota Geological Survey. Figure 1 shows the areas covered by those earlier studies in relation to this study area in northwestern Minnesota.
M-189 Bedrock Geology of the Grand Marais Quadrangle, Cook County, Minnesota
(Minnesota Geological Survey, 2010) Boerboom, Terrence J.; Green, John C.
M-190 Bedrock Geology of the Kadunce River Quadrangle, Cook County, Minnesota
(Minnesota Geological Survey, 2011) Boerboom, Terrence J.; Green, John C.
M-195 Bedrock Geology of the Marr Island and Hovland Quadrangles, Cook County, Minnesota
(2013-11-01) Boerboom, Terrence J.; Green, John C.
Bedrock geologic map of Marr Island and Hovland Quadrangles, northeastern Minnesota, northshore of Lake Superior.
M-197 Bedrock Geology of the International Falls and LittleFork 30' x 60' Quadrangles, northern Minnesota
(Minnesota Geological Survey, 2014-09-25) Jirsa, Mark A.; Boerboom, Terrence J.; Chandler, V.W.
The map depicts a complex history of volcanism, sedimentation, intrusion, multiple events of migmatization involving partial melting and melt dispersion, and several periods of deformation and metamorphism. It lies within the southern exposed extent of the Archean Superior Province. In northern Minnesota, the province is divided into three major tectonomagmatic terranes known as the Wabigoon, Quetico, and Wawa subprovinces. The publication shows the locations of mapped bedrock outcrops, structural measurements, interpreted bedrock geology in both map and cross-section views, and associated explanations. Ancillary imagery includes maps of regional geologic setting, index of archived mapping incorporated into this interpretation, and schematic depiction of geologic history.
M-198 Bedrock Geology of the Devil Track Lake Quadrangle, Cook County, Minnesota
(Minnesota Geological Survey, 2015) Boerboom, Terrence J.; Green, John C.
Portrays the bedrock geology of the Devil Track Lake quadrangle which prior to this effort was largely unmapped. The map shows the distribution of the various rock types, locations of bedrock outcrops, and structural attributes of the bedrock. Mapped outcrops were used to constrain the geology for the most part, but mapping was augmented by the use of geophysical maps, and lidar imagery. Lidar was especially useful in locating bedrock outcrops during field work, and also for delineating the various bedrock units during the map compilation stage following fieldwork.
Minnesota at a Glance Precambrian Geology
(Minnesota Geological Survey, 2020; 1994) Boerboom, Terrence J.
What do the cliffs along the North Shore of Lake Superior, the smooth outcrops in the Boundary Waters Canoe Area Wilderness, the immense iron mines on the Mesabi Iron Range, and the knobby outcrops within the Minnesota River valley have in common? They are part of the very old bedrock that underlies all of Minnesota. Minnesota is situated at the southern edge of the Canadian Shield (Fig. 1)—the nucleus of the continent of North America that formed during Precambrian time. This period of time encompasses about 85% of Earth's history. Geologists consider Precambrian time to have begun with the formation of planet Earth about 4,550 million years (Ma) ago and to have ended about 541 Ma, when organisms with hard parts, such as shells, rapidly diversified. The rocks formed in Minnesota during this enormous span of time record a complicated geologic history that involved volcanoes, ocean islands, mountain chains, earthquakes, and unstable geologic conditions that were very different from the Minnesota of today. Precambrian Minnesota resembled modern-day Indonesia for a while; later, it resembled modern-day California; and still later it resembled parts of the Middle East and eastern Africa.
RI-38 Tourmaline in Early Proterozoic Metasedimentary Rocks Near Philbrook, Northeastern Todd County, Central Minnesota
(Minnesota Geological Survey, 1989) Boerboom, Terrence J.
RI-51 Geologic Setting and Descriptive Geochemistry of Archean Supracrustal and Hypabyssal Rocks, Soudan-Bigfork Area, Northern Minnesota: Implications for Metallic Mineral Exploration
(Minnesota Geological Survey, 1998) Southwick, D.L.; Boerboom, Terrence J.; Jirsa, M.A.
Geochemical data are presented for a suite of samples chosen to represent as nearly as possible the compositions of unaltered rocks within the Archean greenstone belt of the Soudan-Bigfork area in northern Minnesota. These data are interpreted within the stratigraphic and structural framework provided by geologic mapping, and are used to deduce probable depositional and tectonic environments for the volcanic and sedimentary sequences described. In addition, the data indicate regional differences in intrinsic mineral potential, as judged from the presence or absence of geochemically favorable rock types associated with economic deposits of metallic minerals elsewhere in the Superior Province. The greenstone belt as a whole has attributes consistent with development in an oceanic volcanic-arc setting that is broadly analogous to modern arcs of the western Pacific basin. Supracrustal rocks in the Soudan belt (southern portion of the Soudan-Bigfork area) include a lower volcanic cycle that consists of the upper parts of a calc-alkaline volcanic edifice which evolved with time from a submarine basaltic pile into an emergent or nearly emergent dacitic eruptive center, and an upper cycle that represents submarine fan deposits mingled in time and space with tholeiitic basalt of possible back-arc origin. The Newton belt (northern portion of the Soudan-Bigfork area) consists of several fault slices made up chiefly of tholeiitic basalt and pyroclastic and epiclastic dacitic rocks. Because of structural shuffling and imbrication, the rock sequences within the Newton belt cannot be reliably correlated from slice to slice, which handicaps paleotectonic interpretation. Geochemically they are consistent with a back-arc origin. Basaltic sequences in the Soudan belt are evolved to iron-enriched compositions and exhibit very low background values for gold. Basaltic sequences in the Newton belt are moderately more magnesian and auriferous, and therefore may be somewhat better candidates for harboring economic gold deposits. The dacitic rocks of the Soudan belt fall into the least favorable geochemical category for hosting massive- sulfide deposits, based on empirical associations throughout the Superior Province, whereas the geochemical attributes of dacitic rocks in the Newton belt remain inadequately characterized in this respect. Differentiated gabbro-pyroxenite-peridotite sills are absent from the Soudan belt but are characteristic of the Newton belt. Peridotite sills within the Deer Lake Complex contain subeconomic amounts of magmatic Cu-Ni sulfide minerals and are petrologically reasonable, but untested, candidates for hosting platinum-group minerals. On the basis of these broad lithogeochemical criteria, the mineral potential of the Newton belt would appear to warrant serious further investigation.
RI-70, Characterization of the Franklin Peridotite and Other Similar Intrusions in East-Central and Southwestern Minnesota
(2014) Boerboom, Terrence J.
Outcrops of peridotite adjacent to the Minnesota River near the town of Franklin in Renville County were sampled and petrographically characterized as part of a small study funded by the Minnesota Department of Natural Resources in 1997. That study obtained mineral separates with the intent of examining them for kimberlite indicator minerals. The results were not formally published, but rather summarized in an unpublished final report to the Minnesota Department of Natural Resources titled "Mineral Investigations of Franklin Kimberlites." In addition to petrographic and geochemical characterizations, ground magnetic traverses were made across the outcrop area in order to quantify the size and shape of the peridotite body. Based on simple ground magnetic surveys, the peridotite body is approximately 1 square kilometer (0.4 square mile) in area. The peridotite in the outcrops is extensively silicified, most likely by low-temperature alteration associated with lateritic weathering beneath Cretaceous sedimentary strata. Peridotite that is not silicified is composed of olivine (serpentinized), orthopyroxene, hornblende, magnetite, and minor spinel, phlogopite, ilmenite, and sulfide minerals; all the silicate phases are Mg-rich. The silicified peridotite contains abundant secondary quartz and chalcedony, but the silicification did not affect the Fe/Mg ratio, as both silicified and unsilicified peridotite have Mg numbers of 87 to 88. The Franklin peridotite is similar to ultramafic peridotite and pyroxenite bodies in east-central Minnesota, as well as the Cottonwood peridotite body intersected by drilling in northern Lyon County, 55 kilometers (34 miles) west–northwest of the Franklin peridotite and south of the Minnesota River valley. The peridotites in east-central Minnesota are between 1,770 and 1,791 Ma in age, whereas the age of the Franklin and Cottonwood peridotites is unknown.
S-21 Geologic Map of Minnesota-Bedrock Geology
(Minnesota Geological Survey, 2011) Jirsa, Mark A.; Boerboom, Terrence J.; Chandler, V.W.; Mossler, John H.; Runkel, Anthony C.; Setterholm, Dale R.
This map is a new construct that incorporates existing geologic maps where prior mappers had adequate ground control, and new interpretations based on drill hole, geophysical, and unpublished data where they did not. The interpretation differs significantly from previous maps to reflect new data and accommodate scale. It portrays our current geologic understanding of the temporal and geographic distribution of units within major Precambrian terranes and of the Phanerozoic strata. The western part of the mapped Precambrian terrane is inferred largely from geophysical maps, anchored locally by drilling. In many places, contacts are drawn between units of the same or similar apparent rock type (and same unit label); these are recognized as geometrically distinct, though geophysically or lithologically similar. Digital files corresponding to this map allow removal of Cretaceous, Paleozoic, and some parts of Mesoproterozoic strata to reveal an interpretation of the underlying Precambrian bedrock. For additional data see: (http://hdl.handle.net/11299/98043 [select, copy and paste into browser]) which contains files associated with Bedrock Topography, Depth to Bedrock, and locations of Outcrop and Geochronologic analyses.

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Browsing by Author "Boerboom, Terrence J."