Geological Environments for PGE-Cu-Ni Mineralization in the East Bull Lake Gabbro-Anorthosite Intrusion, Ontario

Abstract The East Bull Lake gabbro-anorthosite intrusion is one of several Early Proterozoic layered mafic intrusions occurring along the Southern Province - Superior Province boundary in the Elliot Lake - Sudbury region, Ontario. The base of the East Bull Lake intrusion comprises abundant plagioclase cumulates (Leucogabbronorite Zone) hosting two distinct styles of sulfide mineralization: (1) disseminated magmatic sulfides, and (2) disseminated to massive, structurally controlled sulfides. Both types of mineralization are enriched in Pd, Pt, Au, Cu and Ni. The host rocks to the sulfide mineralization display a range of interesting features including nodular textures, dendritic-pegmatitic mafic pods, inclusion-rich zones (pyroxenite, anorthosite and granitic inclusions) and magmatic breccias. Disseminated chalcopyrite, pyrrhotite and pentlandite occur in concentrations of up to 10% within erratically distributed gossan pods near the base of the intrusion. The sulfides were originally precipitated from intercumulus liquids, but were subsequently recrystallized and locally remobilized along fractures during the major period of metamorphism and deformation that affected the East Bull Lake intrusion. The base- and precious-metal tenor of the structurally controlled sulfides can be explained by extensive remobilization and reconcentration of the pre-existing magmatic sulfides in the vicinity of a major shear zone. Both styles of sulfide mineralization locally contain ppm abundances of PGE + Au and are generally Pd- and Cu-rich, although both display large variations in Pd:Pt and Cu:Ni ratios. The magmatic sulfides are more strongly enriched in PGE and contain up to 1470 ppm Pd in 100% sulfide. Several factors, including source characteristics, magmatic processes (crustal assimilation, fractional crystallization) and post-magmatic interaction with hydrous fluid, have influenced the present distribution of PGE, Cu and Ni in the East Bull Lake intrusion.
The magmatic sulfide occurrences from the East Bull Lake intrusion compare favorably with marginal-type deposits from rift-related intrusions (Noril'sk-Talnakh region, Siberia; Duluth Complex, U.S.A.) in terms of their distribution, but are most similar to reef-type PGE deposits with respect to their base- and precious-metal geochemistry. The combination of high PGE tenors and large tonnages that is observed for the PGE-Cu-Ni mineralization from the East Bull Lake intrusion suggests that a good potential exists for the presence of economic concentrations of Pd, Pt, Au, Cu and Ni in the intrusion. On a global scale, the East Bull Lake intrusion is part of a suite of Early Proterozoic plutons, many of which contain significant volumes of stratiform and/or marginal-type PGE-Cu-Ni mineralization. The East Bull Lake intrusion is also one of the oldest mineralized intrusions derived from a sub-Superior Province mantle source region that has given rise to several significant magmatic PGE-Cu-Ni deposits during the period 2.5 Ga to 1.1 Ga.
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Summary: Regional and orientation geochemical stream sediment surveys were carried out by the Quebec Department of Energy and Resources in southwestern Quebec, over a part of the Mont-Laurier Terrane of the Grenville Province. The area contains some small stratiform zinc deposits. The response of Zn mineralization to geochemical surveys is weak; the known mineralization is not defined by anomalous samples and consistent patterns. This study uses a technique that increases the geochemical signature of...
Publication: Exploration & Mining Geology
Author(s): CLAUDE BELLEHUMEUR, MICHEL JEBRAK
Issue: 1
Volume: 2
Year: 1993
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Summary: The Corbet deposit is one of 17 proximal Cu-Zn massive sulfide deposits located within the Noranda Cauldron which occurs within the core of the Noranda Volcanic Complex. The deposit is located at the top of the Flavrian Formation, the lowermost formation of the 3000 m thick Mine Sequence; the deposit has yielded 2.75 M tonnes of ore grading 3% Cu, 0.96% Zn, 2.06 g/t Ag and 1.0 g/t Au. The multi-lens Corbet deposit formed within a 250 m wide crater that occurs within a localized breccia pile....
Publication: Exploration & Mining Geology
Author(s): H.L. GIBSON, D.H. WATKINSON
Issue: 1
Volume: 2
Year: 1993
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Summary: Electromagnetic surveys were conducted over the Yava sandstone-hosted lead deposit in Nova Scotia to evaluate the usefulness of such surveys for detecting and mapping sedimentary-hosted metallic ore deposits. Both transient and multifrequency systems were used for that purpose. The deposit consists of three zones of disseminated galena which also contain minor amounts of pyrite and sphalerite filling the interstices of the sandstone grains. Each zone overlies a basement depression and is...
Publication: Exploration & Mining Geology
Author(s): AJIT K. SINHA
Issue: 1
Volume: 2
Year: 1993
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Summary: The process of arriving at the size and grade of: (a) a newly-discovered body of mineralization, (b) a potential ore resource, (c) an orebody proposed for mining, or (d) the ore reserves in a mine, requires fundamental geological, and geometrical determinations as well as physical and chemical analyses. This paper outlines geological and geometrical features considered critical, in the authors' experience, in realistic reserve determination. These are discussed under the headings "The Four...
Publication: Exploration & Mining Geology
Author(s): OWEN OWENS, W.P. ARMSTRONG
Issue: 1
Volume: 2
Year: 1993
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Summary: The Jasper Gold mine in northern Saskatchewan produced a total mill feed of 140 127 tonnes at an average grade of 19.0 g/t Au. Both diamond drilling and chip samples from underground workings returned extremely high values, up to 12 851 g/t (375 oz/T) Au over 0.10 meter from a chip sample. In the presence of such extremely high grades, the accurate estimation of reserves is a major problem.
In the first part of this study, production data from the mine were used to evaluate the results of a...
Publication: Exploration & Mining Geology
Author(s): CHRIS M. HEALEY
Issue: 1
Volume: 2
Year: 1993
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Summary: Yidun Island Arc in Sanjiang Region is one of the important Kuroko-type volcano-genie massive sulfide deposits (VMS) districts in southwestern China. Tectonically, the region is situated in the eastern portion of the Tethys orogenic belt, and is a late Triassic extensional island-arc. The island-arc underwent earlier arc construction, intra-arc rifting, later arc construction and back-arc spreading during its evolution and formed a complete trench-arc-basin system, i.e., the Ganzi-Litang...
Publication: Exploration & Mining Geology
Author(s): ZENGQIAN HOU
Issue: 1
Volume: 2
Year: 1993
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Summary: The prospective Tulks volcanic belt hosts five significant massive sulfide deposits, Tulks Prospect, Tulks East, Jack's Pond, Daniel's Pond and Victoria Mine, as well as numerous showings and indications throughout its 70 km outcrop length. Regionally, the 498 Ma sequence consists dominantly of felsic pyroclastic rocks and flows with interbedded mafic volcanic units and finegrained sediments, commonly graphitic. Contemporaneous granitoid rocks occur in the south half of the belt. Rocks...
Publication: Exploration & Mining Geology
Author(s): C.B. McKENZIE, D.W. DESNOYERS, D. BARBOUR
Issue: 1
Volume: 2
Year: 1993
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Summary: The Laochang mine, located in the Sanjiang area of southwestern Yunnan Province of China, is a volcanogenic massive Pb-Zn-Cu sulfide deposit. It is hosted by a pyroclastic sequence of Early Carboniferous age, namely the lower member of the Yiliu Group, which was intruded by syenite and rhyolite porphyry. The volcanic suite is basaltic or basaltic-andesitic in composition, has alkaline affinities, and is associated with the initial rifting along the margin of the Baoshan-Shanstate continental...
Publication: Exploration & Mining Geology
Author(s): KAIHUI YANG, XUANXUE MO
Issue: 1
Volume: 2
Year: 1993
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