Browsing by Subject "Partridge River intrusion"

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Finish Logging of Duluth Complex Drill Core
(University of Minnesota Duluth, 2007-10) Severson, Mark J; Hauck, Steven A
From 1988 through 2005, NRRI personnel had logged 955 drill holes from the basal zone of the Duluth Complex. The major result of all this effort was the establishment of igneous stratigraphic packages, which in turn, were used to improve our understanding of the mineralization controls on the Cu-Ni deposits and the distribution of Platinum Group Elements (PGE). However, at the beginning of the biennium there were still over 220 drill holes (226,000 feet of core) that remained to be re-logged from portions of the Partridge River and South Kawishiwi intrusions. The main objective of this proposal was to complete a logging campaign of these remaining holes and establish a complete stratigraphic section for these two intrusions of the Duluth Complex. To date, 224 holes have been relogged for this project totaling 198,979 feet of drill core. This total includes several holes that were recently drilled in the Maturi Extension/Nokomis deposit by Duluth Metals, and several recently found drill cores from the Dunka Pit deposit. All of the newly logged holes, see appendix, are located in eight deposits within the Partridge River and South Kawishiwi intrusions; including a few scattered holes in the Cloquet Lake and Tuscarora intrusions. The vast majority of relogged holes were from the Babbitt/Mesaba deposit due to the incredibly large number of drill holes drilled there in the first place. While this project made a significant dent in the total amount of holes logged at the Babbitt deposit, there are still about 20 holes that yet remain to be logged. In an addendum to this report, these drill holes at the Babbitt deposit will be logged, and an unknown number of additional drill holes at the Maturi Extension will be logged.
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 Structure of a Portion of the Partridge River Intrusion: A Progress Report
(University of Minnesota Duluth, 1988-09) Severson, Mark J
Studies of the basal contact of the Partridge River intrusion, as deduced by compilation of all drill hole data and relogging of 37 drill holes, has indicated more structμre than previously recognized. Structure contour maps of the footwall rocks have been prepared showing the nature of the basal contact, the top of the Biwabik Iron-Formation, and the thickness of the Virginia Formation beneath the Partridge River intrusion. These data indicate that preexisting folds in the basement rocks at both Minnamax and Dunka Road exerted a strong control over the form of the base of the intrusion. Several northeasttrending normal faults and northwest-trending strike-slip(?) faults were al so delineated in this study which supports the half-graben model proposed by Weiblen and Morey (1980). A northeast~trending pre-Keweenawan fault has also been located in the Wetlegs area. Along this fault an inferred window of Biwabik Iron Formation is in direct contact with the Partridge River intrusion. Three oxidebearing ultramafic bodies {Longnose, Longear, and Section 17) are exposed at the surface along this zone. The spatial location of oxide-bearing ultramafics to areas where the iron formation is in direct contact with the Duluth Complex suggests that they may be genetically related. At least five major units within the basal portion of the Partridge River intrusion have been delineated for the Wetlegs area. They are present in 23 drill holes at Wetlegs and extend northeast into the Dunka Road Cu-Ni deposit and southwest into the Wyman Creek Cu-Ni deposit. From the base up, these units are characterized by: sulfide-bearing augite troctolite {175-1570 ft. thick); troctolite with abundant layers of picrite (melatroctolite), peridotite and dunite (450 ft. thick); a 250 ft. thick, fine-grained, mottled-textured troctolitic anorthosite ("marker bed" for the area); augite troctolite (400 ft. thick); and augite-bearing anorthositic troctol ite (250 ft. thick). To the northeast and southwest of Wetlegs, most of these units are present but the omission of particular units in either direction indicates an irregular stacked pattern. Establishment of an internal stratigraphy has provided an excellent opportunity to: 1) study the nature of any structural discontinuities present within the intrusion, 2) determine the extent and variability of intrusive lithologic units, 3) more fully understand any background geochemical variations that may be present within and between the l i tho logic units, and 4) better understand the origin of the Partridge River intrusion, the various Cu-Ni, CuNi- Ti and Fe-Ti deposits and their relationship to the origin of the Duluth Complex.
Geology of the Southern Portion of the Duluth Complex
(University of Minnesota Duluth, 1995-12) Severson, Mark J
The Duluth Complex (Middle Proterozoic - 1,099 Ga) is a large intrusive body that contains numerous smaller intrusions that collectively comprise the Complex. Recent work has shown that igneous stratigraphic sections can be delineated within these intrusions through detailed relogging of drill core, e.g., for the Partridge River intrusion (Severson and Hauck, 1990; Severson, 1991) and the South Kawishiwi intrusion (Severson, 1994). This report pertains to the igneous geology of the South Complex area. More than 140 drill holes are located in the "South Complex" area. Most of these holes are relogged (112 holes, 88,000 feet of core) and are correlated into several troctolitic to gabbroic stratigraphic units for several specific areas in the South Complex that have abundant drill holes. While each individually drilled area exhibits good correlative units, these correlative units do not extend into an adjacent drilled area that is located only a few miles distant. This lack of large-scale continuity suggests: 1) the South Complex study area constitutes an area that actually includes several smaller intrusive bodies; 2) drilling is not detailed enough to delineate large-scale correlative units; 3) because most of the drill holes are located close to the basal contact, the effects of contamination to the magma, via assimilation of footwall rocks, hampers large-scale correlations; or 4) combinations of the above. Most of the holes within the South Complex were drilled during exploration for Cu-Ni sulfide mineralization. Only weak sulfide mineralization is present in these drill holes. However, many of the holes intersect small plug-like bodies of Oxide-bearing Ultramafic Intrusions (OUIs) that are intrusive into the troctolitic rocks of the Complex. The OUIs are characterized by coarsegrained to pegmatitic clinopyroxenite, picrite, peridotite, and dunite. Oxide content in the OUI varies from disseminated (15%-20%) to thick massive oxide zones. Ilmenite is the dominant oxide in some OUIs; whereas, titanomagnetite is dominant in others. In almost all instances, the OUIs are spatially arranged along linear trends, suggesting that structural control was important to their genesis. At some localities (northern end of the South Complex), an empirical link between ironformation assimilation near the basal contact and OUI formation is apparent. This relationship suggests that the OUIs were initially formed at depth followed by upward injection of OUI material along fault zones. However, other OUI (southern end of the South Complex) are situated within, or immediately below, layered oxide-rich gabbroic rocks, suggesting that the OUIs formed from a differentiated iron-rich melt that drained down into the cumulate pile along fault zones. These two different OUI groups (north and south) also show some corresponding differences in chemistry. The north OUIs are characterized by relatively higher chromium contents and the south OUIs have relatively higher vanadium contents. All of the OUIs contain titanium mineralization and some sulfide mineralization. A model of origin for the OUIs involving metasomatic replacement of preexisting igneous rock is not considered to be plausible. Also present within the South Complex area are fine-grained granular rocks that are hornfelsed inclusions of basalt and troctolitic-gabbroic-noritic rocks. One of these inclusions, referred to as the FN Unit, is only observed in drill holes in the southern half of the South Complex area. The unit exhibits vesicle-like features in drill core and has often been referred to as a hornfelsed basalt. However, several features argue against a basalt protolith for the FN Unit. These features include the presence of abundant footwall hornfels inclusions within the unit, common gradations into medium-grained intrusive rock, and a "rind-like" overall pattern of the unit at the basal contact at Water Hen. These characteristics suggest that the FN Unit represents an earlier pulse of magma (chilled?) into the footwall rocks that was later hornfelsed by subsequent intrusions of the Complex. The Bear Lake Inclusion, present in numerous outcrops and one drill hole, probably represents a large inclusion of magnetic basalt. The inclusion is a massive rock with no distinct volcanic features, but is similar to magnetic basalt inclusions described elsewhere in the Complex (Colvin Creek Inclusion, and "INCL" unit within the South Kawishiwi intrusion; Severson and Hauck, 1990; Severson, 1994; Patelke, 1996). The Bear Lake Inclusion is over 500 feet thick and dips gently to the southeast. It is located well into the interior of the Complex and is not related to the basal contact (as is the FN Unit). Geochemical plots are constructed for many of the igneous units of the South Complex area. These plots are not particularly instructive in discriminating between the units because many of the spider profiles are fairly similar, and in the X-Y plots only a few units cluster within distinct fields. However, some conclusions can still be drawn from these data. First, similarities in geochemistry indicate that some units of the nearby Partridge River intrusion are present as far south as Water Hen. Second, the FN Unit is chemically similar to both troctolitic to gabbroic rocks, even in the same drill hole. This relationship supports an earlier intrusive protolith rather than a basalt protolith. Third, the north and south OUI can be separated into two groups based on similarities in spider diagram profiles. However, the profiles for the north OUI show similar profiles that alternate with geographic location. The reason for this "leap frog" alternation in profiles is unknown at this time, but may be related to more than one OUI-forming event along a fault zone. Last, rocks of the Bear Lake Inclusion are chemically similar to rocks of the Colvin Creek inclusion (Severson & Hauck, 1990; Patelke, 1996) and the "INCL" unit of the South Kawishiwi intrusion (Severson, 1994); all of which have been inferred to be magnetic basalts. A sample of a semi-massive oxide horizon (0.8 ft. thick), associated with subhorizontal, ultramafic layers (picrite, peridotite, etc.) near the Water Hen area (drill hole SL-19A) has been found to contain anomalous PGE and chromium values (Pt = 737-786 ppb, Pd = 63-106 ppb, Cr = 46,000 ppm). This semi-massive oxide horizon is similar in many respects to PGE- and Cr-enriched semi-massive to massive oxide horizons located elsewhere within the Duluth Complex (Birch Lake and Fish Lake areas). The data suggest that the PGE in SL-19A are magmatic and have not been redistributed by hydrothermal fluids, as has been suggested for other areas within the Complex. Additional targets of vein-like PGE-enriched Cu-Ni ore are also present in the Skibo and Water Hen areas. These targets could potentially have formed via fractional crystallization of a sulfide melt in a vein-like setting.
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.
Igneous Stratigraphy and Mineralization in the Basal Portion of the Partridge River Intrusion, Duluth Complex, Allen Quadrangle, Minnesota
(University of Minnesota Duluth, 1997-12) Severson, Mark J; Hauck, Steven A
Geologic mapping of the igneous rocks of the Partridge River intrusion (PRI) within the Allen Quadrangle was conducted during the 1996-1997 period by Severson and Miller (1997). In addition to the surface geology, drill holes were logged in order to gain a better understanding of the third-dimensional geology and Cu-Ni mineralization of the quadrangle. Drill hole correlations of igneous units, along with cross-sections and a discussion of Cu-Ni±PGE enriched zones, are presented in this report. Detailed logging of drill core from over 400 drill holes indicates that there are at least seven major igneous units (Units I through VII) within the basal 3,000 feet of the PRI. These units, starting with Unit I at the base, are described in Severson and Hauck (1990) and are reiterated herein for drill holes within the Allen Quadrangle. Also present within the quadrangle and described in this report are late plug-like bodies of Oxide-bearing Ultramafic Intrusions (OUI), a Keweenawan sill within the Biwabik Iron-Formation (K-Sill), and a small Keweenawan(?) intrusive within the Archean rocks near a major fault zone. Establishment of an igneous stratigraphy for the PRI provides a framework that can be used to determine the nature and location of fault offsets between drill holes. The tenor of Cu-Ni mineralization is often locally increased along some of these faults. Fault zones, with or without increased mineralization, that are discussed in this report include faults in the Wetlegs Cu-Ni deposit, faults in the Wyman Creek Cu-Ni deposit, the Siphon Fault, and the Donora Fault. Many of these fault zones are depicted on the cross-sections that accompany this report. Enrichments in Platinum Group Elements (PGE) occur at several stratabound horizons within the Allen Quadrangle (using an arbitrary cutoff of >90 ppb Pd). All of these PGE-enriched horizons are present in sulfide-bearing troctolitic rocks that are positioned immediately below, and in some cases within, laterally continuous ultramafic layers. However, the overall Pd content in some of the horizons shows a definite decrease in an east-to-west direction. This trend suggests that as the magma of the PRI was intruded, in an east-to-west direction(?), it became progressively impoverished with respect to PGEs.
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.

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