Petrology and Cu-Ni-PGE Mineralization of the Bovine Igneous ...

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dating of the BIC intrusion has, as of yet, not been successful, the lithologic and geochemical similarities between BIC and other early ultramafic intrusion (Schulz and Nicholson, 2009) strongly implies that it is also part of the early magmatic stage of the MCR. Figure 5. Generalized map of the Lake Superior region with simplified geology and location of mafic and ultramafic intrusions. Location of small ultramafic intrusions shown with red dots (Modified from Paces and Miller, 1993). 8
1.1.4 Bovine Igneous Complex The (BIC) is a small basin-shaped mafic/ultramafic intrusion emplaced in the southwestern part of the Baraga Basin (Figs. 1 and 2). Approximately 1200 meters long and 450 meters wide, the BIC is well exposed along its margins but moderately to poorly exposed in its interior. Based on reconnaissance mapping and core logging, Rossell (2008) subdivided the intrusion into three basic rock units: wehrlite at the base, clinopyroxenite in the midsection, and oxide gabbro at the top (Fig. 6). The intrusion cross-cuts Paleoproterozoic rocks of the Michigamme Formation, beginning in the north with the upper slate, followed by the sulfidic Bijiki Iron-formation member, and ending in the south with the lower slate. At depth, the intrusion is in contact with either the lower slate or granitic gneiss of the Archean Northern Complex. Rossell (2008) also speculated that the intrusion may cross-cut or be cut by an eastwest trending Keweenawan mafic dike. Rossell (2010, pers. comm.) also pointed out that aeromagnetic data seems to imply that the BIC may cross-cut a northeast trending dike that has a similar trend to Abitibi dike swarms in Ontario. The BIC intrusion has been found to be weakly to moderately mineralized with Cu-Ni- PGE-enriched sulfides. Metal tenors provided by initial drilling averaged less than .5% Cu and Ni, and less than 350 ppb Pt and Pd (Fig. 6)(Rossell, 2008). Although metal tenors in most of the intrusion are lower than other early stage ultramafic intrusions, a 16.5m-thick interval in the associated Little BIC intrusion (Fig. 2) contains 0.88% Cu, 1.0% Ni, 679 ppb Pt, and 104 ppb Au. Within this interval, sulfide metal tenors increase even more in a 2.8 meter section below the contact in surrounding country rocks, which averaged 1.66% Cu, 4.23 % Ni, 1380 ppb Pt, 2520 ppb Pd. Metal tenors when calculated to 100% sulfide are comparable to 9
Page 1 and 2: Petrology and Cu-Ni-PGE Mineralizat
Page 3 and 4: Acknowledgements I would like to th
Page 5 and 6: While this cumulate stratigraphy of
Page 7 and 8: 4.6.1 Little BIC...................
Page 9 and 10: Figures 1 Geologic Map of Southwest
Page 11 and 12: 1.0 Introduction The failed rifting
Page 13 and 14: 08BIC044 • Figure 2. Geology of t
Page 15 and 16: 1.1.2 Baraga Group Collision of an
Page 17: lithosphere and the lower crust (Ni
Page 21 and 22: and a sulfur isotope study is under
Page 23 and 24: those goals will be to characterize
Page 25 and 26: 2.1 Core Logging and Sampling Three
Page 27 and 28: exporting data layers from ArcMap a
Page 29 and 30: Figure 7. Modal rock type classific
Page 31 and 32: were chosen from each rock type whi
Page 33 and 34: outcrops are very coarse-grained an
Page 36 and 37: Figure 12. Bedrock geologic map of
Page 38 and 39: The feldspathic wehrlite is in turn
Page 40 and 41: unit to subprismatic at the top (Fi
Page 42 and 43: Figure 15. Stratigraphic variation
Page 44 and 45: 3.2.2 08BIC044 This 731m long hole
Page 46 and 47: The lower feldspathic wehrlite unit
Page 48 and 49: the dramatic increase in clinopyrox
Page 51 and 52: Figure 17. Generalized lithostratig
Page 55 and 56: Figure 21. Lithostratigraphy of dri
Page 57 and 58: Figure 23. Modal mineralogy of plag
Page 59 and 60: A B Figure 25. A.) Photomicrograph
Page 61 and 62: A B Figure 27. A.) Photomicrograph
Page 63 and 64: 3.3 Mineral Chemistry and Cryptic L
Page 67 and 68: All values in parts per million (pp
Page 69 and 70:
4.0 Discussion The petrographic, mi
Page 71 and 72:
the lower feldspathic wehrlite unit
Page 73 and 74:
would expect from the fractional cr
Page 75 and 76:
Cumulate Stratigraphy Pl+Cpx+Ox Cpx
Page 77 and 78:
orthocumulate zone similarly increa
Page 79 and 80:
upper slate of the Michigamme forma
Page 81 and 82:
C. Emplacement of upper ultramafic
Page 83 and 84:
Figure 34. Normalization spider dia
Page 85 and 86:
aluminum but higher titanium, iron,
Page 87 and 88:
B. QFM C. QFM-2 Figure 36. Mineral
Page 89 and 90:
Figure 37. Mineral paragenesis calc
Page 91 and 92:
Figure 38. Plot of Cu, Ni, Pd, and
Page 93 and 94:
wehrlite followed by a feldspathic
Page 95 and 96:
Johnson, R.C., 2007, Petrography an
Page 97 and 98:
Appendix A Petrographic Description
Page 99 and 100:
Appendix A-1 Bulk Rock Petrography
Page 101 and 102:
044-414.7 fwer med crs to crs wehrl
Page 103 and 104:
Appendix A-2 SILICATE MINERAL PETRO
Page 105 and 106:
044-497.5 fwer med to med crs calci
Page 107 and 108:
Appendix B Mineral Chemical Data Py
Page 109 and 110:
Spectrum 3 53.26 0.94 2.43 7.6 0 15
Page 111 and 112:
Average 86.1 50.1 8.1 41.8 SD 0.37
Page 113 and 114:
Spectrum 3 54.15 0.84 1.64 5.3 0 16
Page 115 and 116:
Spectrum 5 55.36 1.56 5.96 0 19.97
Page 117 and 118:
Ol.2 40.99 16.16 0 42.84 100.0 82.5
Page 119:
Spectrum 6 53.95 0.95 2.41 6.92 17.
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Petrology and Cu-Ni-PGE Mineralization of the Bovine Igneous ...

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