Browsing by Subject "Duluth Complex"

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The Babbitt Copper-Nickel Deposit: Part A: Digital Drill Hole Data Files for the Babbitt and Serpentine Copper-Nickel Deposits
(University of Minnesota Duluth, 1994-09) Patelke, Richard L
The main objective of this investigation is to assist Arimetco International, Inc. in their evaluation of establishing a non-ferrous mine in northeastern Minnesota. This portion of the report presents data compilation work done on the Babbitt and Serpentine Cu-Ni deposits by the NRRI. The purpose was to put all available copper-nickel-sulfur assays, precious metal assays, RQD (Rock Quality Designation) information, and down hole drill hole survey data into a uniform digital format.
The Babbitt Copper-Nickel Deposit: Part B: Structural Datums
(University of Minnesota Duluth, 1994-09) Severson, Mark J; Patelke, Richard L; Hauck, Steven A; Zanko, Lawrence M
This portion of the investigation concentrated on determining specific structural and stratigraphic datums within the Babbitt Cu-Ni deposit of the Partridge River Intrusion, Duluth Complex, northeastern Minnesota. Structural datums and footwall lithologies were obtained by relogging the footwall portions of all surface drill holes (391) within the confines of the deposit. Specific lithologies recorded during relogging included depth to: 1) basal contact of the Duluth Complex with the footwall rocks; 2) distinctive units within the footwall Virginia Formation; and 3) top of the underlying Biwabik Iron-formation and the specific iron-formation submembers intersected in drill hole. In addition, 100 surface drill holes were relogged in detail and compared with 166 previously relogged drill holes. The top of Unit I, the main sulfide-bearing igneous unit of the Babbitt deposit, was determined for all 266 drill holes that were relogged. The top of the first significant sulfide-bearing zone (not always the top of Unit I) was also determined for the relogged drill holes. All these datum points are used to generate several contoured surface maps to gain a better understanding of the main structural features present within the Babbitt deposit. The contoured surface for the top of the Biwabik Iron-formation is an excellent means of displaying the major structural features, i.e., the Local Boy Anticline, Bathtub Syncline, and Grano Fault. These same features are evident in the contoured surface of the basal contact and indicate that pre-existing structures in the footwall were important to how the basal portion of the Duluth Complex was emplaced. Datum points within the upper portion of the Duluth Complex also suggest that these structures were reactivated throughout the emplacement history of the Duluth Complex (see discussion in Part C). Some of the structures were also important controls of Cu-Ni mineralization. A contoured surface of the bedrock ledge is also presented for the Babbitt deposit. Several structural features are outlined by the bedrock ledge. A crude subsurface geologic map is also portrayed for the bedrock ledge. In addition, an isopach map of glacial overburden thickness is included in this report.
Bulletin No. 44. Geology of the Duluth Gabbro Complex near Duluth, Minnesota
(Minnesota Geological Survey, 1964) Taylor, Richard B.
Multiple intrusions at Duluth, Minnesota, form a rock series that is here called the Duluth Gabbro Complex. Each of the principal rock types transgresses one or more of the older units. The oldest rock, a coarsegrained anorthositic gabbro that was intruded into the Keweenawan flows, makes up the upper part of the complex. It was intruded by basaltic magma of a second period of magmatic activity which formed rocks that commonly are banded, and hence called the layered series. The gabbroic rocks of the layered series as well as the older anorthositic gabbro are cut by intrusive bodies of ferrogranodiorite and granophyre and by late dikes of basalt and aplite. The lower two-thirds of the complex, the layered series. is composed chiefly of troctolite, olivine gabbro, feldspathic gabbro, and syenogabbro. About 15,000 feet of layered rocks is exposed, locally with rhythmic banding, fluxion structure, and gravity stratification demonstrating bottom accumulation by crystallization under conditions of active magma circulation. A series of samples collected from bottom to top of the layered series shows only limited development of cryptic layering. This lack of cryptic layering may be explained as the result of periodic renewal of magma in the crystallizing chamber or by multiple small intrusions. Cross-cutting relations between the different types of gabbro in the layered series show that the mass originated by multiple intrusion. The lack of chilling effects indicates that the successive intrusions were not greatly separated in time. Near the top of the series a transition exists from gabbro to syenogabbro, and a similar transition may exist from syenogabbro to ferrogranodiorite. The rock series is similar in many respects to that of the Skaergaard Intrusion, but there are important differences that can be explained by dissimilar tectonic history. The poor development of cryptic layering and the absence of ferro gabbro at Duluth, in contrast to their remarkable development in the Skaergaard Intrusion, can be explained by differing tectonic stability. The Skaergaard magma apparently crystallized in a chamber under stable conditions, whereas the Duluth magma seems to have crystallized in an environment of tectonic instability manifested by multiple intrusions of magma. The various rocks of the Duluth Gabbro Complex can be explained by crystallization-differentiation of basaltic magma, although the origin of some, such as the anorthositic gabbro and intrusive peridotite, is puzzling. The rocks of the layered series probably were derived from a basaltic magma approaching the composition of analyzed late basalt dikes. Compared with the analyses of "marginal olivine gabbro" from the Skaergaard Intrusion, the Duluth parent magma seems to have been notably richer in K2O, TiO2, MnO, and P2O5. The Duluth Gabbro Complex is an immense sill-like mass that extends for 150 miles northeast from Duluth, and relations in other parts may differ from those at Duluth.
Copper-Nickel Grade Maps for the Spruce Road Deposit, South Kawishiwi Intrusion, Duluth Complex
(University of Minnesota Duluth, 2002-02) Peterson, Dean M
This report describes the Cu-Ni mineralization of the Spruce Road area in the northern portion of the South Kawishiwi intrusion. The mineralization in the area is defined by > 9,500 assays from approximately 140,000 feet of core from 232 exploration holes drilled by INCO (220 holes), Bear Creek (6 holes), U.S. Bureau of Mines (3 holes), Hanna Mining (2 holes), and Wallbridge Mining (1 hole). Drilling in the Spruce Road area largely occurred during two time periods: the middle 1950s, following the original discovery of Cu-Ni mineralization, and from 1966 to 1973. Assay data from all of the drill holes within the South Kawishiwi intrusion have been compiled by the author into a comprehensive geological and geochemical database. Drill hole assays for the Spruce Road area have been exported out of this database and form the geochemical basis for this report. Preliminary analysis of the drill hole assay data for all of the deposits of the South Kawishiwi intrusion has led to the identification of two main styles of mineralization associated with the base of the intrusion. These mineralization types include: 1) “Open” – vertically extensive (> 450 meters) mineralization with moderate Cu-Ni grade and low Au+PGE grades. Examples of this open style include the Spruce Road, Serpentine, and Dunka Pit deposits. 2) “Confined” – vertically restricted (< 150 meters) mineralization with high Cu-Ni grades and moderate to very high (locally) Au+PGE grades. Examples of the confined style include the Maturi, Maturi Extension, and the Birch Lake deposits. Regional crosscutting relationships indicate that the “Open” style mineralization preceded the “Confined” style. Moreover, the curvilinear nature of the contact between the styles of mineralization is similar to the regional contacts of most of the intrusions of the Duluth Complex and adds further support to this theory.
Geologic Map Mesabi Iron Range, Minnesota, second edition
(Mesabi Range Geological Society (MRGS) and Minnesota Geological Survey, 1999) Meineke, David G; Buchheit, Richard L; Dahlberg, Henk E; Morey, G B; Warren, LeRoy E
Historic strip-map of a 100 mile-long, 10 mile-wide area covering portions of St. Louis and Itasca counties, and enclosing the Mesabi Iron Range and parts of the Duluth Complex. Scale 1: 62500. First compiled and released in 1993, this map has never been formally published with a cite-able reference. Data and assistance for the compilation was provided by numerous companies, individuals and organizations which are listed on the map plate. The map has been in the charge of the Mesabi Range Geological Society and they have provided the MGS permission to host a scanned version of this map under the MGS holdings on the University of Minnesota Digital Conservancy (2019). The original map of 1993 has been superseded by the 1999 edition to correct certain errors in the cartographic base. The geology portion of the map was not altered.
Geology and Mineralization in the Dunka Road Copper-Nickel Mineral Deposit, St. Louis County, Minnesota
(University of Minnesota Duluth, 1990-03) Monson Geerts, Stephen D; Barnes, Randal J; Hauck, Steven A
The Dunka Road Cu-Ni deposit is within the Partridge River Intrusion (T. 60 W., R. 13 W.), which is part of the Duluth Complex, and is approximately 1.1 b.y. (Keweenawan) in age. Relogging of 46 drill holes at the Dunka Road Cu-Ni deposit identified four major lithologic units and several internal ultramafic subunits that can be correlated over two miles. The ultramafic subunits (layers of picrite to peridotite) exhibit relative uniform thicknesses and are present at the same relative elevation within the major lithologic units. The major lithologic units, the same as delineated by Severson and Hauck (1990), and upward from the basal contact are: Unit I, a fine- to coursegrained a sulfide-bearing troctolite to pyroxene troctolite (450 ft. thick) with associated ultramafic layers I(a), I(b), and I(c); Unit II, a medium- to coarse-grained troctolite to pyroxene troctolite (200 ft. thick) with a basal ultramafic layer II(a); Unit III, a finegrained, mottled textured troctolitic anorthosite to anorthositic troctolite (150 ft. thick) with one minor ultramafic layer III(a); and Unit IV, a coarse-grained troctolite/pyroxene troctolite to anorthositic troctolite with associated ultramafic layers IV(a) and IV(b). Most sulfide mineralization occurs within Unit I. Within Unit I the sulfide mineralization is both widespread but variable in modal percentage (rare to 5%), continuity and thickness (few inches to tens of feet). Sulfide mineralization is somewhat related with proximity to: hornfels inclusions, the basal contact with the footwall Virginia Formation, and some of the internal ultramafic layers within Unit I. Precious metal mineralization (Pd+Pt+Au) is associated with fracturing and alteration of the host rocks. The alteration assemblage is chlorite, bleached plagioclase, serpentine and uralite. Pd+Pt values range from 100 to >2400 ppb over 10 foot intervals. These intervals can occur independently as 10 to 50 foot zones, or as part of a larger correlatable occurrence/horizon. Two mineralized subareas within the Dunka Road deposit are: 1) an area which is peripheral to a highly anomalous Pd occurrence (reported by Morton and Hauck, 1987; 1989) herein termed the "southwest area", and 2) the "northeast area" which contains several drill holes that have near surface intercepts of >1% Cu. There are four somewhat large mineralized occurrences within the study area that carry >300 ppb combined total Pt+Pd+Au. These mineralized zones appear to be stratigraphically controlled by the ultramafic subunits within Unit I. Three of the four correlatable zones are found within the southwest area, and range from 40 to 130 feet thick. High Pd values within these zones range from 10 to 20 feet thick with values of 800 to 1650 ppb Pd. In the northeast area, the fourth mineralized zone appears continuously throughout Unit I. This zone ranges from 120 to 300 feet thick. High Pd values within this zone range from 10 to 40 feet thick with values of 800 to 1500 ppb Pd. Many 5 to 30 foot intersections of >1 ppm Pd+Pt+Au occur throughout the mineral deposit. Geostatistical analysis based on 72 vertical holes and 12 angle holes suggests: 1) the base of the complex is a critical datum with the higher grade intercepts located between 100 and 400 feet above the base; 2) high inter-element correlations support local redistribution/concentration of primary mineralization by a secondary hydrothermal process and thus, polymetallic mining selectivity is possible; 3) the available drilling gives a spacial range of geologic influence at 400 foot centers, but sufficient angle drilling is not available to assess the potential of high grade, steeply dipping mineralized zones; 4) additional vertical in-fill drilling will almost certainly not discover any additional quantity of ore within the volume of rock studied; but 5) additional angle drilling to assess the potential of high grade, steeply dipping, mineralized zones would benefit a more complete geostatistical analysis.
Geology and Mineralization of a Cyclic Layered Series, Water Hen Intrusion, St. Louis County, Minnesota
(University of Minnesota Duluth, 1990-03) Strommer, James; Morton, Penelope; Hauck, Steven A; Barnes, Randal J
The Water Hen intrusion is an oxide-bearing (ilmenite + magnetite) ultramafic intrusion (OUI) that is emplaced along a pre-basement fault into the troctolitic series rocks of the Duluth Complex. The intrusion consists of medium-grained dunite and peridotite and local pegmatitic pyroxenite approximately 1,600 ft. x 500 ft. x 700 ft. in size. Oxide (>90% ilmenite) composes from 5-50% of the various lithologies. Sulfides are minor, about 2-5%, and are predominantly pyrrhotite with minor cubanite, chalcopyrite and pentlandite. Concentrations of 5-80% graphite also occur within the intrusion. Surrounding the Water Hen intrusion is a zone of mixed lithologies (Mixed Zone) consisting of the host rock troctolites, apophyses of OUI and local inclusions of footwall rocks. The Mixed Zone (M) is dominated by >60% troctolitic rocks with OUI composing the remainder. The OUI apophyses vary from 1-50 ft. thick and have sharp contacts with the country rock. The troctolitic host rocks for the Water Hen intrusion consist of medium- to coarsegrained troctolite to anorthositic troctolite (TA unit) and a troctolitic cyclically layered series (TL unit). The cyclically layered series is similar to troctolitic layered rocks at Bardon Peak. The individual cyclic layers are 6 in. to 10 ft. in thickness and the entire unit is over 300 ft. thick. The An content decreases from An80 at the bottom of the unit to An60 near the top of the unit. The individual cyclic layers are composed of ilmenite-dunite at the base and grade upward to anorthositic troctolite. The bottom contacts are sharp and each successive layer within the individual unit is identified by the occurrence of biotite or clinopyroxene. In the bottom olivine-rich layer, the oxides (<5%) are ilmenite >> magnetite. The sulfides in this same layer (3-5%) are coarse-grained with cubanite > chalcopyrite > pentlandite >> pyrrhotite. In the more feldspathic layers, the sulfides (1-3%) are fine-grained with chalcopyrite >> pentlandite = cubanite + pyrrhotite. The oxides (1- 5%) are also fine-grained with ilmenite >> magnetite. The footwall rocks in the Water Hen area consist of very fine-grained metamorphosed Virginia Formation and fine-grained hornfelsed basalt and/or troctolite. There are >100 ft. of basalt or chilled margin rocks within the footwall. This mafic hornfels commonly occurs between the Virginia Formation and the TA unit. Orthopyroxenite dikes and dikelets also occur in the mafic hornfels. These dikes contain anomalous PGEs and secondary sulfide mineralization. The copper-nickel sulfides are primary igneous sulfides associated with the troctolitic rocks. Violarite, pyrite and secondary magnetite in cross-cutting veinlets and other secondary sulfides indicate that the primary sulfides were altered and remobilized by a later event. Cu:Ni ratios have a bimodal distribution that is not followed by the PGEs. However, Cu, Ni, Ag, Au, Pt, Pd are all highly correlated with each other. This high interelement correlation suggests that the late-stage (secondary) remobilization locally redistributed and reconcentrated these elements.
Geology and petrogenesis of the Tuscarora Intrusion of the Duluth Complex, Gillis Lake 7.5’ quadrangle, northeastern Minnesota
(2010-09) Costello, Daniel Edward
The Tuscarora Intrusion is a layered mafic intrusion located at the base of the 1.1 Ga Duluth Complex in northeastern Minnesota. Detailed field mapping (1:12,000) and follow-up petrographic and geochemical analyses were conducted to evaluate the troctolitic igneous stratigraphy of the Tuscarora Intrusion, as well as to understand the petrologic relationship between the troctolitic cumulates and the plagioclase-rich gabbros of the overlying Anorthositic Series. Previous studies have interpreted the two lithologies as being interlayered, a relationship that would be unique within the Duluth Complex. Field mapping has identified two lithologically distinct stratigraphic zones within the Tuscarora Intrusion. The lower zone is composed of olivine gabbro to augite troctolite that is typically heterogeneous in mode and texture and locally displays modal layering and foliation. Most notably, it contains abundant, large (>100m) basaltic hornfels inclusions. The upper zone is composed of homogenous, foliated troctolite to leucotroctolite, which grades upward from melatroctolite at the base of the zone. Inclusions in the upper zone are mostly large, often elongate blocks of anorthositic rocks and are especially abundant near the contact with the Anorthositic Series. No field evidence was found for an interlayered relationship between the two lithologies and geochemical studies imply distinct parent magma compositions. This study concludes that the Tuscarora Intrusion and Anorthositic Series are two separate intrusive suites, as found in other areas of the Duluth Complex. Furthermore, the lower and upper zones of the Tuscarora are interpreted to have formed successively from major emplacement episodes of moderately evolved tholeiitic mafic magma. The emplacement model proposed has plagioclase porphyritic magmas intruding at some level above the base of the North Shore Volcanic Group to create the Anorthositic Series. This was followed by emplacement of lower zone magmas closer to base of the volcanic pile. This resulted in the incorporation of abundant volcanic inclusions and in strong contamination of the magma by interaction with pre-rift rocks of the footwall. Emplacement of upper zone magmas occurred above the newly crystallized Lower Zone and below the Anorthositic Series cap, which contributed anorthositic inclusions.
Geology and Petrology of the Wilder Lake Intrusion, Duluth Complex, Northeastern Minnesota
(2016-07) Leu, Adam
Abstract The Wilder Lake Intrusion (WLI) is a well differentiated, northward-dipping, sheet-like mafic layered intrusion that is part of the 1.1 Ga Duluth Complex exposed in northeastern Minnesota. While several reconnaissance studies of the well exposed western quarter of the WLI have shown it to have several distinctive petrologic characteristics compared to other layered intrusions in the Duluth Complex, its relative inaccessibility within the Boundary Waters Canoes Area Wilderness precluded a detailed study of its field and petrologic attributes along its entire 10 km strike length. This changed in the Fall of 2011 when an intense forest fire (the Pagami Creek Burn) created easy access to excellent exposure of the WLI. Through field mapping, petrographic observations, and geochemical analysis, this study sought to document the igneous stratigraphy of the WLI along its entire strike-length with the goal of better understanding the petrogenesis of its unique petrologic attributes. These attributes, noted by others and confirmed here, include the up-section stratigraphic changes characterized by 1) a cumulus reversal from a olivine oxide gabbroic cumulate of Pl+Cpx+Ox+Ol to a troctolitic (Pl+Ol) cumulate; 2) a reversed cryptic variation of Fo in olivine and En’ in clinopyroxene; and 3) the cumulus arrival of Fe-Ti oxide before augite (Miller and Ripley, 1996). Detailed mapping conducted in 2012 and 2013 revealed that most cumulate units of the WLI can be followed along its entire strike length, but with some notable exceptions. Remapping in the western part of the WLI has confirmed that the 2 km-thick igneous stratigraphy exposed here starts with a basal unit of heterogeneous, intergranular olivine oxide gabbro that is in sharp contact with Anorthositic Series rocks. This marginal gabbro is overlain by a troctolitic unit of Pl+Ol cumulates, which can be subdivided into a heterogeneous subunit, a layered subunit and an anorthosite inclusion-rich subunit. The troctolite unit is overlain by a thin (20-100 m thick) oxide troctolite unit of Pl+Ol+ Ox cumulates that abruptly gives way to an olivine oxide gabbro unit of Pl+Cpx+Ox+Ol cumulates. This four-phase cumulate is abruptly overlain by another troctolitic cumulate unit demarking a cumulus reversal back to Pl+Ol cumulates. Mapping of the excellent exposures created by the Pagami Creek Burn reveal that the upper troctolite unit cross-cuts and locally scoured out the four-phase gabbro and part of the oxide troctolite unit. Thus it is interpreted as a recharge of more primitive magma into the upper part of the WLI chamber rather than a downward crystallizing roof zone unit as speculated by Miller (1986). Detailed mapping by overland traverses in the central and eastern extents of the WLI show it to thin from 700 m in the west to 500 m in the east. Moreover, several units pinch out in the eastern section of the intrusion. The oxide troctolite pinches out just east of center, but swells back to about 20 meters in stratigraphic thickness before pinching out again farther east. The lower gabbro also pinches out around the same place and is replaced by a taxitic unit that dominates at the eastern margin; a similar heterogeneous unit also can be found at the western margin. Petrographic study of 223 thin sections collected along three profiles across the WLI at its western, east-central and eastern extents helped to confirm and refine the stratigraphic variations in mineralogy and texture noted from field observations. In addition, olivine and pyroxene from many of the samples were analyzed by University of Minnesota Duluth’s SEM/EDS (Scanning Electron Microscope/Energy Dispersive X-Ray Spectroscopy) to document cryptic variation of mg# (=Mg/(Mg+Fe), cation %). This mineral chemical data was acquired to verify the reversed cryptic variation previously documented in the west and to determine if this variation persists along strike to the east. Reversed cryptic variation of upwardly increasing magnesium number (mg# =MgO/(MgO+FeO), mol %) in olivine (Fo) and pyroxene (En’) was confirmed in the west and shown to persist in the eastern profiles. However, the data also reveal that the mg# tends to decrease at a particular stratigraphic horizon from west to east. The reversed cryptic variation up-section is interpreted to reflect a trapped liquid shift within the oxide troctolite and olivine oxide gabbro units. Trapped liquid shift occurs where high mg# cumulus olivine re-equilibrates with low mg# intercumulus liquid. As evidenced by their strong foliation and the low abundance of augite in the oxide troctolite unit, these rocks are clearly adcumulates with very little postcumulus minerals (i.e., representing the trapped liquid component) and thus retain their high-mg#. The lateral decrease in mg# to the east, as well as the disappearance of the oxide troctolite unit, is thought to be caused by the thinning of the intrusion which in turn would result in the eastern portion of the intrusion to cool more rapidly than the west. This more rapid cooling would have trapped intercumulus liquid (and thus a stronger trapped liquid shift) and promoted oxide and pyroxene to crystallize more synchronously since their liquidus temperatures are not very different. Finally, whole rock geochemical analyses of the basal intergranular gabbro samples were evaluated to determine if they may be representative of a parental liquid composition. One piece of evidence that this is the case is that the WLI marginal gabbro composition is comparable to other tholeiitic magma compositions occurring in the North Shore Volcanic Group (NSVG). Another method used to evaluate the parental composition of the marginal gabbro is to apply its composition to a MELTS-based phase equilibrium program, Pele (Boudreau, 2006). This modelling indicates that the phases in equilibrium with the fractional crystallization of the marginal gabbro compositions can replicate the cumulate stratigraphy observed in the WLI with normal to reduced fO2 conditions (between QFM and 3 log units below QFM). These modeling results indicate that the cause of early oxide crystallization relative to augite was largely the result of an Fe-Ti enriched parental magma composition, and not elevated oxygen fugacity. References Joslin, G.D., and Miller, J.D., Jr., 2003, Stratiform Pd-Pt-Au mineralization in the Sonju Lake Intrusion, Minnesota. Geological Society of America Abstracts with Programs, v.34, no. 7, p. 101. Miller, J.D., Jr. 1999, Geochemical evaluation of platinum group element (PGE) mineralization in the Sonju Lake intrusion, Finland, Minnesota. Minnesota Geological Survey Information Circular 44, 32 p. Miller, J.D. Jr., Green, J.C., Severson, M.J., Chandler, V.W., Hauck, S.A., Peterson, D.E., and Wahl, T.E., 2002, Geology and mineral potential of the Duluth Complex and related rocks of northeastern Minnesota. Minnesota Geological Survey Report of Investigations 58, 207p. w/ CD-ROM Phinney, W.C., 1972. Northwestern part of Duluth Complex. In: Sims, P.K. & Morey, G.B. (eds.) Geology of Minnesota -A centennial volume. Minnesota Geological Survey, p. 335-345
Geology, Mineralization, and Geostatistics of the Minnamax/Babbitt Cu-Ni Deposit (Local Boy Area), Minnesota: Part I: Geology
(University of Minnesota Duluth, 1991-06) Severson, Mark J
The Minnamax Cu-Ni deposit (also called the Babbitt deposit) is situated within what has been informally referred to as the Partridge River intrusion (or Partridge River Troctolite) of the Duluth Complex (1.1 Ga), northeastern Minnesota. The deposit has been subdivided into five contiguous ore zones; the Local Boy area and Bathtub area are two ore zones described in this report. Within the deposit are a wide variety of troctolitic, ultramafic, and footwall rock types, and hornfelsed inclusions (both footwall and hanging wall). Many specific rock types are correlative between drill holes and can be grossly categorized into seven sub-horizontal troctolitic units, three types of hornfelsed inclusions, and a late cross-cutting pegmatitic phase. Also present are correlative units within the footwall rocks. All rock units were identified by detailed relogging of 61 surface drill holes (117,605 feet of core) and are portrayed on nine cross-sections that extend through various portions of the Minnamax deposit. Severson and Hauck (1990) described the stratigraphy of the troctolitic rocks of the Partridge River Troctolite to the west of the Minnamax deposit; the stratigraphy is referred to as the Partridge River Troctolite Series (PRTS). Most of the PRTS rock units defined at the Dunka Road Cu-Ni deposit (located to the immediate SW of Minnamax) by Severson and Hauck (1990) are present at Minnamax. However, the overall picture at Minnamax is more complicated than Dunka Road due to rock type changes that are manifested by: 1) pinch-out and reappearance of specific marker bed units; 2) down-strike gradational changes of ultramafic horizons; 3) extremely limited areal extent of some ultramafic horizons; and 4) gradational changes in the troctolitic rock types between drill holes. In some areas a particular marker horizon may "disappear" laterally and then reappear at the same stratigraphic level in another group of drill holes. In spite of these local difficulties, a gross stratigraphy of seven subhorizontal igneous units is present at Minnamax and consists of (from bottom to top): Unit I - heterogeneous, sulfide-bearing augite troctolite and troctolite with abundant metasedimentary inclusions; Unit II - homogeneous troctolite with a basal picrite horizon (Unit II is present only in the SW portion of the Minnamax deposit); Unit III - mottled textured anorthositic troctolite to troctolite with characteristic olivine oikocrysts (Unit III is present mainly in the SW portion of Minnamax and is enveloped by Unit I to the NE); Unit IV - mixed homogeneous troctolite and augite troctolite (augite troctolite is at the top of Unit IV in localized areas) with a semipersistent basal ultramafic horizon termed the "± picrite"; Unit V - homogeneous anorthositic troctolite that exhibits a gradational contact with Unit IV; and Units VI and VII - homogeneous troctolites with persistent basal ultramafic horizons. More abundant and thicker ultramafic horizons are present in Units VI and VII in the Bathtub area of the Minnamax deposit. Specific marker horizons utilized in drill hole correlations include: Unit III, "± picrite," "pocket picrite," top of Unit IV (augite troctolite), and the ultramafic base of Units VI and VII. The troctolitic stratigraphy is cut by pegmatitic orthopyroxenite and peridotite bodies that are referred to as OUI - Oxide-bearing Ultramafic Intrusions. Pegmatitic hybrid hornblendite and granophyre also cut the stratigraphy and are often related to the OUI bodies. Rusty chlorine-rich drops may commonly coat the core of the ultramafic horizons and OUI bodies. Several enigmatic hornfelsed inclusions are present in Units VI and VII at Minnamax. These are grouped in two categories that include: 1) CC-type inclusions that are similar to outcrops of the Colvin Creek hornfels; and 2) "pic"-type inclusions that are similar to nearby outcrops of basalt inclusions. Both inclusion types are similar in that they contain fine-grained plagioclase-filled ovoids or wisps that may represent vesicles, and they exhibit the same chemical signature. However, they exhibit a different mineralogy (the CC-type inclusions are oxide-rich). Their stratigraphic position in the troctolitic rocks suggests that they are probably hanging wall material (North Shore Volcanic Group). While these two inclusion types are readily correlative between drill holes, the nature of their different mineralogy remains unknown. Another enigmatic rock type is present within the lower portion of the Virginia Formation footwall rocks. The rock is unique in that it contains hornblende ± olivine and locally grades into serpentinized picrite with hornblende. It is generally concordant with the overall bedding of the Virginia Formation and is referred to as the sill(?) unit. Whole rock geochemistry indicates that this unit locally exhibits: high Cl contents that are similar to Cl values of ultramafic horizons in the troctolitic rocks; MG numbers that are more primitive than the ultramafic horizons; and high Cr contents that are much higher than anything sampled in the overlying troctolitic section. If the unit was a sill, it now exhibits gradational contacts with the metasedimentary rocks and is characterized by a granoblastic texture with superimposed euhedral hornblende. These data may indicate that the sill was intruded before, and hornfelsed during, emplacement of the majority of the Partridge River Troctolite Series.
Geology, Mineralization, and Geostatistics of the Minnamax/Babbitt Cu-Ni Deposit (Local Boy Area), Minnesota: Part II: Mineralization and Geostatistics
(University of Minnesota Duluth, 1991-06) Severson, Mark J; Barnes, Randal J
The Minnamax/Babbitt Cu-Ni deposit, located within the Partridge River Troctolite Series (PRTS) of the Duluth Complex, northeastern Minnesota, contains both troctolite-hosted disseminated ore and footwall-hosted massive sulfide ore. This report pertains to the massive sulfide ore zone, which is restricted to a small portion of the deposit, and is referred to as the Local Boy area. Studies conducted in the Local Boy area include: 1) detailed geologic relogging of drill core; 2) sulfide petrography and microprobe analysis; 3) assaying for Pt, Pd, Au, and Ag in the high-grade Cu ore zones; and 4) geostatistical analysis of the Cu-Ni ore (plus PGEs and precious metals). Detailed relogging of 76 underground drill holes, along with pertinent surface drill holes, has been completed within the Local Boy area (from drifts B, C, and D). The data indicates the highly undulatory nature of the basal contact of the Duluth Complex with the footwall Virginia Formation. Intrusive rocks of the Duluth Complex (Unit I of the PRTS) consist of augite troctolite, troctolite, and norite. All exhibit gradational contacts with each other, and all may occur at any stratigraphic position relative to the undulatory basal contact. However, norite is the most common rock type adjacent to sedimentary hornfels inclusions and at the basal contact due to contamination of the magma. The spatial configuration of the intrusive rocks indicates that Unit I was intruded as multiple pulses along bedding planes of the Virginia Formation. The Virginia Formation hosts the majority of the massive sulfide ores that are present within hornfels inclusions positioned above the basal contact, and within the footwall rocks at and below the basal contact. Massive sulfide ore is not as common within the intrusive rocks, and when present, is generally associated with, or in close proximity to, hornfels inclusions. Ore/host rock textures are extremely varied, but all are indicative of structural control in the footwall rocks. Overall, the massive sulfide ores are spatially distributed in a spotty manner in an east-west (EW) direction that corresponds to a major EW-trending anticline present within the footwall rocks. All these factors suggest that an immiscible sulfide melt was injected into structurally prepared footwall rocks along the anticlinal axis in a "vein-like" setting. At some later period, the footwall-hosted massive sulfide ore zone was re-intruded by multiple sills (which collectively make up a portion of Unit I) along bedding planes of the Virginia Formation. The end result is a disjointed zone of mineralized inclusions and mineralized footwall rocks separated by "barren" intrusive rocks. Sulfide textures indicate that the sulfides formed by cooling of a monosulfide solid solution (MSS) followed by limited replacement at very low temperatures. Minerals contained within the sulfide ore are dominantly pyrrhotite, chalcopyrite, cubanite, and pentlandite. Locally present are maucherite, sphalerite, bornite, talnakhite, mackinawite, and an unknown Cu-sulfide ("Cp"). Also present in minor amounts are native silver (primary and secondary), parkerite, chalcocite, covellite, godlevskite, violarite, magnetite, and zincian hercynite. Although no discrete PGE minerals were identified, analytical results of the high-grade (>1% Cu) massive sulfide ore confirms the presence of several anomalous PGE values. These spot values are mainly confined to an EW-trending zone that also roughly corresponds to the EW-trending anticline. Maximum values obtained within the Local Boy massive sulfide ores include: Pd = 11,100 ppb; Pt = 8,300 ppb; Au = 10,900 ppb; and Ag = 34 ppm. Native silver (primary) was found within several maucherite grains in this investigation, and PGE mineral inclusions have previously been found in maucherite (Ryan and Weiblen, 1984). Generally, the drill holes that contain the anomalous PGE values also contain the native silverbearing maucherite; whereas, homogeneous maucherite is more characteristic of drill holes with little to no anomalous PGE values. This suggests that PGEs were scavenged from the sulfide melt by early-formed maucherite, and thus the PGEs are related to a primary (magmatic) process. However, a hydrothermal origin for the PGEs is also indicated. Anomalous PGE values are commonly associated with Cl-drop encrusted massive sulfide drill core. The spatial distribution of the Cl-drop encrusted drill core also coincides with the EW-trending anticline. Presence of the Cldrops indicates that the rocks of the Local Boy area were invaded by Cl-bearing solutions that may have been capable of transporting and concentrating PGEs. Therefore, both primary/magmatic (sulfides injected into a "vein-like" setting) and later secondary/hydrothermal processes appear to have been factors in controlling PGE distribution in the Local Boy area. However, it is difficult to separate the primary and secondary processes. This is due to the coincidence of several features within the EW-trending zone, which include: 1) anticline in the footwall rocks; 2) overall massive sulfide spatial distribution; 3) spatial distribution of anomalous PGE values; and 4) spatial distribution of Cl-drop encrusted core. Reactivation of structures that controlled the initial "vein-like" massive sulfide distribution could have been responsible for channeling later hydrothermal solutions. Geostatistical analysis of the underground drill holes (Drifts B, C, and D), and pertinent surface drill holes, yields five main conclusions: 1) the top of the Biwabik Iron-formation (BIF) is a critical datum, with the higher grade Cu-material located between 100 and 400 feet above the BIF (mainly within the Virginia Formation near the basal contact); 2) inter-variable correlations between Cu and Ni are high, indicating that selective mining of Cu and Ni is physically possible; but, selection on ore grade Cu and Ni will not necessarily capture all the ore grade PGEs and other precious metals; 3) the available drilling gives a spacial range of geologic influence of about 150 feet; 4) potentially economic ore reserves do exist in the Local Boy area; and 5) the property is under-valued due to the inclusion of many "barren" (unassayed) intervals into the compositing process. A coarse block model, and in situ geologic reserves, are presented for the Local Boy area.
Igneous Stratigraphy of the South Kawishiwi Intrusion, Duluth Complex, Northeastern Minnesota
(University of Minnesota Duluth, 1994-12) Severson, Mark J
The Middle Proterozoic (1,099 Ma) intrusive Duluth Complex contains numerous smaller sub-intrusions that collectively comprise the Complex. Two of these sub-intrusions are informally known as the South Kawishiwi intrusion (SKI) and Partridge River intrusion (PRI). A correlative igneous stratigraphy has been documented in the PRI by Severson and Hauck (1991) and Severson (1991). In this investigation, detailed relogging of drill holes within the SKI (136 drill holes totalling 214,461 feet of core) also defines an intrusion-wide stratigraphic sequence along a 19-mile strike length that is referred to as the South Kawishiwi Troctolite Series (SKTS). The stratigraphic sequences of the SKI and the PRI are completely dissimilar. At least 17 correlative subhorizontal igneous units are defined within the SKTS; however, they are not equally present in all areas of the SKI. The SKTS units, from the bottom to the top (roughly), are referred to as: BAN = Bottom Augite troctolite and Norite; BH = Basal Heterogeneous troctolites (sulfide-bearing); U3 = Ultramafic Three (sulfide-bearing); PEG = Pegmatitic Unit of Foose (1984); U2 = Ultramafic Two (sulfide-bearing); U1 = Ultramafic One (sulfide-bearing); AT-T = homogeneous Anorthositic Troctolite to Troctolite; UW = Updip Wedge (sulfide-bearing); LOW AGT = homogeneous Lower Augite Troctolite zone; MAIN AGT = homogeneous Main Augite Troctolite zone; AT&T = homogeneous Anorthositic Troctolite and Troctolite; AT(T) = homogeneous Anorthositic Troctolite with lesser amounts of Troctolite; AN-G Group = intermixed Anorthositic and Gabbroic rocks; UPPER GABBRO = oxide-bearing gabbroic rocks; "INCL" = large shallow-dipping inclusion of magnetic basalt(?); UPPER PEG = Upper Pegmatitic zone; and T-AGT = Troctolite to Augite Troctolite (the latter five units are restricted to a small area referred to as the Highway 1 Corridor area). The lowest units of the SKTS are the most varied with respect to textures, rock types, and sulfide content. They are very unevenly distributed along the strike length of the SKI in a "compartmentalized" fashion suggesting a complicated intrusive history. The lowest units were emplaced early into several restricted magma chambers via repeated and close-spaced magmatic pulses. The effects of contamination from assimilated and devolatized country rocks were the most pronounced in these units. Three ultramafic-bearing packages (U1, U2, and U3 units) are also present within the lower portion of the SKTS. These units are characterized by alternating layers of troctolitic and ultramafic (olivine-rich) rock. The ultramafic-bearing units represent periods of rapid and continuous magma injection that crystallized more primitive ultramafic layers before mixing with the resident magma. The U3 Unit is the most unique in that it contains several massive oxide (magnetite-rich) pods along its strike length. An empirical relationship between the U3 Unit and the Biwabik Iron-formation (BIF) suggests that the massive oxides were derived from intruded and assimilated BIF. The U3 Unit also contains the majority of high Platinum Group Elements (PGE) values sampled to date in the SKI. In contrast, the upper SKTS units reflect an entirely different intrusive history. Each unit is characterized by monotonous sequences of texturally homogeneous and sulfide-free rocks. Gradational contacts are present between each of the units. In contrast to the lower SKTS units, the upper SKTS units are generally distributed throughout the SKI. Ultramafic members are restricted to only two thin horizons referred to as High Picrite #1 and #2. All of these features are indicative of a quiescent and open magmatic system. Thus, the upper SKTS units appear to have been emplaced as widely-spaced pulses into a progressively developed, single magma chamber with little interaction with the country rocks. An entirely different package of rocks is present in six extremely deep drill holes that were drilled within the Highway 1 Corridor (H1C). The H1C represents a large inclusion of older Anorthositic Series rocks. It appears that the H1C rocks were underplated by the younger intruding SKI magmas. Several drill holes within the PRI were also relogged to better understand the nature and location of the contact between the SKI and PRI. One important feature noted is that as the contact between the two intrusions is approached, the upper units of the PRI become heterogeneous and indistinguishable from each other. The same heterogeneity is not evident in the adjacent SKI. The presence of the "heterogenous zone" within the PRI adjacent to the SKI suggests that the PRI was intruded before the SKI. Also present near the PRI/SKI contact zone is a major north-trending fault (down to the east). Associated with this fault are voluminous amounts of steeply-inclined lenses of late granitic/felsic material that cross-cut the PRI stratigraphic section. This fault is named the Grano Fault because the late lenses consist of varied granitic to pyroxenitic material. Though the Grano Fault trends through both the PRI and SKI, the late granitic lenses are not particularly common within the SKI. This fact also suggests that the PRI is older than the SKI. Offset units within the footwall rocks suggests that movement along the Grano Fault was initiated before emplacement of the PRI. All geochemical data pertaining to previously sampled SKI drill core is compiled and correlated with the SKTS units. An additional 80 geochemical samples collected from SKTS units in this investigation are added to this database. The grouping of the SKTS units on the geochemical plots supports the geologic correlations of this investigation. Some of SKTS units also show geochemical overlap with footwall units and indicate the effects of contamination of the magma due to assimilation of the country rocks during intrusion. PGE analyses conducted on a multitude of rock types and igneous units within the SKTS indicate that the U3 Unit, and to a lesser extent the PEG Unit, show the most promise of hosting a PGE deposit. The PGE origin model of Boudreau and McCallum (1992) is invoked to explain why anomalous PGEs are common to the U3 Unit. The Boudreau and McCallum model envisions the upward migration of chlorine-rich, late, magmatic fluids that were capable of transporting PGEs and concentrating them at stratigraphic traps. However, a straightforward application of the model does not explain why significantly higher PGEs are restricted to certain areas, e.g., the Birch Lake deposit. A variation of the "Boudreau and McCallum model" is proposed to explain this difference. This revised model is similar except that upward-moving, Cl-rich, PGE-pregnant hydrothermal solutions are envisioned to have been concentrated in fault zones. When fluids associated with fault zones encountered a proper stratigraphic trap (ultramafic horizon), more PGEs were deposited relative to areas outside of the fault zones. An intersection of the proper stratigraphic trap (U3 Unit with massive oxides, sulfides and high Cr contents) and the proper channelway to concentrate the PGE-pregnant Cl-rich solutions (Birch Lake Fault) reasonably explains the significant PGE values in the Birch Lake deposit. The Birch Lake Fault is defined by a zone wherein drill holes commonly encountered either: massive sulfide mineralization within the footwall granitic rocks; and/or "voluminous" amounts of late granitic/felsic lenses that cut the troctolitic rocks of the SKI.
Incorporation of Duluth Complex Maps into GIS Platform
(2014) Lentsch, Nathan
Incorporation of Duluth Complex Maps into GIS Platform
(2014) Lentsch, Nathan; Miller, James
Information Circular 10. Copper and Nickel Resources in the Duluth Complex, Northeastern Minnesota
(Minnesota Geological Survey, 1974) Bonnichsen, Bill
The Ely-Hoyt Lakes region, in northeastern Minnesota, contains very large quantities of disseminated copper and nickel sulfides that are potentially minable. The principal sulfides are pyrrhotite, chalcopyrite, cubanite, and pentlandite, and the average copper-nickel ratio in the sulfide concentrations is approximately 3:1. The sulfides are associated with the northwestern margin of the Duluth Complex, a large mafic igneous pluton of Late Precambrian age, and occur principally within the basal zone of the intrusion. A conservative estimate of the metal resources in the Ely-Hoyt Lakes region, based on assay data available from 24 drill holes, and a cutoff grade, or lower mining limit, of 0.5 percent combined copper and nickel indicates 13.8 million tons of copper and 4.6 million tons of nickel having a gross value of $27 billion. Although the copper and nickel deposits in the Ely-Hoyt Lakes region are marginal economically, they constitute one of the United States' principal metal resources.
An Investigation of Ni and Cu Isotopic Fractionation in Basal Duluth Complex Cu-Ni-PGE Mineralization, Northeastern Minnesota
(2016-05) Asp, Kristofer
Cu-Ni-PGE magmatic sulfide-style mineralization occurs along the western margin of the Duluth Complex in northeastern Minnesota. Previous studies have demonstrated a notable fractionation of 60Ni and 58Ni in terrestrial materials, including both primary and secondary phases, with a total range of up to 2.1 ‰. Other work has indicated a fractionation of 65Cu and 63Cu, with pronounced differences between primary copper sulfides and secondary copper phases in a variety of deposit types. Prior to this study, no δ60/58Ni or δ65/63Cu values have been measured in Duluth Complex rocks. The primary goal of this study is to measure Ni and Cu isotope values in a variety of Duluth Complex samples, and develop a possible model for the δ60/58Ni isotopic system in this geologic terrane. Based on the findings of previous studies, samples were collected to determine the isotopic differences between sulfide-bearing and sulfide-barren material. Samples were collected from a variety of locations in the basal Duluth Complex, including glacial till beds and surface outcrops in the vicinity of the I, II, Serpentine, Mesaba, and NorthMet deposits. Additional drill core material was obtained from the III, Wetlegs, and Wyman Creek deposits. A detailed characterization of till, weathered surface, and primary drill core samples revealed three main sources of nickel in Duluth Complex material: silicate, sulfide, and secondary oxide. The 24 δ60/58Ni values have an overall range from -0.97 to 0.22 ‰, but are correspondingly distinct in each type of material: silicate (-0.03 ‰ average), sulfide (-0.36 ‰ average), secondary oxide (-0.50 ‰ average). Further geochemical and microprobe work, along with the isotopic values, indicate two main stages of Ni fractionation in basal Duluth Complex rocks: a high temperature stage during crystallization, and a low temperature stage during surficial weathering. High-T fractionation is defined by a preferential incorporation of 58Ni into sulfide, while silicates, especially olivine, are reflective of the Bulk Silicate Earth value. Low-T fractionation results in a preferential incorporation of 58Ni into secondary oxide, while 60Ni possibly enters solution and leaves the system. The 22 measured Duluth Complex δ65/63Cu values have an overall range from -1.28 ‰ to 0.36 ‰, with an overall average of -0.35 ‰. Further work is necessary to better define and interpret the involved fractionation processes in the Duluth Complex.
Minnesota Ilmenite Processing Using High Pressure Rolls
(University of Minnesota Duluth, 2001-08-09) Benner, Blair R; Hendrickson, David W
With funding from the Minnesota Department of Natural Resources through the Minerals Coordinating Committee, a study was undertaken to determine the potential for the use of High Pressure Rolls (HPR) grinding to improve recovery and reduce grinding energy in the processing of ilmenite bearing material from the Duluth Complex. Several deposits in the Duluth Complex have been identified, and the potential ore reserves have been estimated at 50 million tons. Previous work on this material showed the potential for making a low-silica ilmenite concentrate; however, the recovery was only about 50 percent. Relatively low recovery was due to losses in the minus 200 mesh fraction. HPR has been shown to produce less minus 200 mesh material than the conventional rod mill that had been used previously. Two HPR grinding flowsheets were tested. The first involved two stages of HPR, with the first stage being closed by a three mesh screen. The second stage, which treated the minus 3 mesh material from stage one, was closed with a 14 mesh screen. The second flowsheet involved a single HPR stage closed by a 14 mesh screen. Both flowsheets produced significantly less minus 200 mesh material than the rod mill, with the single stage producing the least. Grinding energy for the single stage HPR was 3.28 kWh/mt of new feed, compared to the previous rod mill energy consumption of 13.59 kWh/mt. The minus 14 mesh material from the HPR grinding was concentrated in two stages of spirals with recirculation of the cleaner tails to new feed. The cleaner concentrate was passed through a single drum magnetic separator to remove any magnetite. The nonmagnetic fraction was dewatered in a screw classifier and stored for future upgrading. Ti02 recovery in the nonmagnetics averaged about 61 percent, compared to the average Ti02 recovery of about 50 percent in the previous study. Clearly, the HPR grinding resulted in improved recovery. The amount of Ti02 reporting to the magnetic concentrate was essentially the same for both this study and the previous study using the rod mill; 25. 07 percent and 25 .19 percent respectively. To determine the potential for recovering a portion of the Ti02 in the magnetic concentrate, a series of grinds followed by laboratory magnetic separation tests were run. Even a 90.6 passing 270 mesh grind was not sufficient to produce a magnetic concentrate suitable for pellet production. Elutriation tests run on selected size fractions from the nonmagnetic material from the 84.9 percent passing 270 mesh grind indicated that the Ti02 was well liberated in the plus 500 mesh fractions. A study funded by the Permanent University Trust Fund is currently under way to explore ways of reprocessing the primary magnetic concentrate to increase Ti02 recovery and to produce a suitable pellet feed material.
Origin and Occurrence of Platinum Group Elements, Gold and Silver in the South Filson Creek Copper-Nickel Mineral Deposit, Lake County, Minnesota
(University of Minnesota Duluth, 1990-03) Kuhns, Mary Jo P; Hauck, Steven A; Barnes, Randal J
The South Filson Creek Cu-Ni-PGE-Au-Ag mineral occurrence is located on the western margin of the Duluth Complex in Lake County, northeastern Minnesota. The occurrence of primary magmatic and late-stage, structurally controlled mineralization is located in the South Kawishiwi intrusion of the Duluth Complex, approximately 2200 feet above the basal contact. The primary host rock for the mineralization is a medium-grained augite troctolite. Petrographic studies indicate that there were at least two episodes of mineralization. Deposition of primary, coarse-grained, interstitial pyrrhotite, pentlandite, and chalcopyrite occurred in "cloud zones". Primary mineralization was followed by the introduction of hydrothermal fluids along fracture zones, as evidenced by the formation of hydrous minerals, sulfide replacement textures and geochemical signatures suggestive of remobilization. These late-stage fluids deposited secondary sulfides at redox boundaries created by the primary sulfides. The secondary assemblage includes chalcopyrite, bornite, chalcocite, digenite, covellite, violarite, sphalerite, mackinawite, valleriite, and the platinum group minerals, all which occur in extremely fine, discontinuous veinlets that are rarely recognizable in hand specimen. The veinlets were created by hydrofracturing of silicate minerals due to a volume increase initiated by serpentinization of olivine. These veinlets are always proximal to highly serpentinized fractures and are possibly associated with a proposed NE-trending fault zone along the south branch of Filson Creek. The copper-nickel ratio for the deposit is about 3:1. Platinum + palladium correlates with high copper and sulfur. Also, high inter-element correlation between Cu, Ni, Pd, Pt and Au suggests that secondary enrichment of these elements is local in extent and related to faulting and redox boundaries. Statistical analysis suggests, given the available data, that infill drilling could discover a significant quantity of mineralization. The alteration assemblage associated with the secondary mineralization is serpentine, biotite, stilpnomelane, iddingsite, chlorite, sericite, and clay minerals. The alteration is very subtle and is best recognized in thin section. Both alteration and mineralized zones range in thickness from less than one foot to 90 feet.
The petrology, petrogenesis, and metallogeny of the South Kawishiwi intrusion in the Nokomis deposit area, Duluth Complex, northeastern Minnesota.
(2010-08) White, Christopher Reed
A recent flurry of minerals exploration in northeastern Minnesota has legitimized the Duluth Complex as one of the largest deposits of base and precious metals in the world. These activities have facilitated both the need and the means for academic studies geared toward developing and defining the numerous Cu-Ni-PGE resources in the Duluth Complex. This study focuses on Duluth Metals‟ Nokomis deposit, taking advantage of huge volumes of new drilling and associated data to examine previous work conducted by Severson (1994), and Peterson (2001) with regard toward the petrology, stratigraphy, and genesis of the South Kawishiwi intrusion in the Nokomis deposit (formerly known as Maturi Extension) area. Through the examination of recently drilled core, and bedrock mapping in the study area Severson‟s (1994) igneous stratigraphy was evaluated and largely adopted with several additions and minor modifications. Analyses of geochemistry allowed for confirmation of several stratigraphic attributes alluded to by Severson (1994). Whole-rock, major-element geochemistry showed progressive re-charge trends through the upper parts of the intrusion, while whole-rock, major-element geochemistry and mineral chemistry data seemed to show order through chaos in the basal contact area of the intrusion. Major-element, whole-rock geochemistry also confirmed a large block of exotic rocks within the intrusion. As such, the intrusion has been broken into several major zones (basal contact zone, and upper zone) with a third zone consisting of a large block of remnant anorthositic series rocks (anorthositic inclusion block). iv Testing Peterson‟s (2001) open versus confined style mineralization model for the South Kawishiwi intrusion was the prime objective of this study. Petrographic and chemical analysis of samples collected from recently drilled core, as well as the analysis of available whole-rock and assay geochemical data led to the exploration and development of answers to several questions related to Peterson‟s (2001) model. Analyses geared toward testing for lateral flow in the basal contact area of the intrusion ultimately led to the determination that magma flow was likely prominent in the basal contact area of the South Kawishiwi intrusion, and that channelized flow may have resulted in significant upgrading of metals. This study ultimately results in the presentation of several petrogenesis and metallogenesis models for the South Kawishiwi intrusion in the Nokomis deposit area, which are largely founded on Peterson‟s (2001) mineralization model, and Severson‟s (1994) ideas regarding petrogenesis of the South Kawishiwi intrusion.
Precious Metals (Pt-Pd-Au-Ag) in Three Copper-Nickel Deposits in the Duluth Complex
(University of Minnesota Duluth, 1989-11) Hauck, Steven A
The research work on the precious metals in the three copper-nickel deposits centered on: 1) defining the lateral and vertical extent of the precious metals; and 2) the controls on mineralization, e.g., lithology, structure, etc. While these objectives were the same for each deposit, the methods of investigation at each deposit were dependent upon the amount and quality of previous data available.

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