Table 3. Base metal production in the Timmins District to the end of 2007.

Tisdale Assemblage Session

Targeting Komatiite-Associated Ni-Cu-(PGE) Deposits in the Abitibi Greenstone Belt

with an Emphasis on the Highly-Prospective Tisdale Assemblage

M.G. Houlé1 and C.M. Lesher2

1 Precambrian Geoscience Section, Ontario Geological Survey michel.houle@ontario.ca 2MERC,

Department of Earth Sciences, Laurentian University

Targeting komatiite-associated Ni-Cu-(PGE) deposits relies on identifying areas of high magmatic flux within deformed and metamorphosed greenstone belts. This requires an understanding of the physical volcanology of magma/lava pathways and their geophysical-geochemical signatures. All of the komatiites in the Abitibi greenstone belt (AGB), regardless of petrogenetic affinity (Al-undepleted, Al-depleted, Ti-enriched), appear to have been undersaturated in sulfide prior to emplacement and therefore capable of forming mineralization. Only the two youngest of the four komatiite-bearing assemblages (2719-2711 Ma Kidd-Munro and 2710-2704 Ma Tisdale) are known to host economic nickel deposits, which are also the only assemblages that contain both abundant magma/lava pathways (magma conduits, feeder sills, lava channels, and channelized sheet flows) and external sources of S. Although most of the komatiites in the AGB have been previously considered to be extrusive, an increasing number of units have been shown to be intrusive and it now appears that komatiite-associated Ni-Cu-(PGE) mineralization in the AGB occurs within a spectrum of environments ranging from intrusive (Dumont, Sothman) through subvolcanic (Dundeal-Dundonald South-Kelex, Galata-McWatters) to extrusive (Alexo, C Zone-Thalweg, Hart-Langmuir-Redstone, Mickel, Marbridge, Texmont). The stratigraphy of some assemblages is now known to be more complex than was previously understood. Thus, komatiite-associated Ni-Cu-(PGE) mineralization is not restricted to specific stratigraphic contacts as previously believed, but may occur in any environment (intrusive, subvolcanic, or volcanic) throughout the stratigraphy where lava pathways have had access to external S. Mineralization in the Kidd-Munro assemblage is interpreted to occur near the base of the sequence at several stratigraphic levels in Dundonald Township (Alexo-Kelex-Dundeal-Dundonald South) and likely at higher levels in Munro Township (Mickel) and LaMotte Township (Marbridge). Mineralization in the Tisdale assemblage is interpreted to occur at several levels near the base of the sequence in the Shaw Dome (Galata-Langmuir-Redstone-McWatters), in Bannockburn Township (C Zone-Thalweg), and the Halliday Dome (Sothman), and stratigraphically higher in the Bartlett Dome (Texmont). Most komatiite-associated deposits in the AGB are hosted by relatively undifferentiated olivine mesocumulates (which normally have very distinctive geophysical/geochemical signatures), most are localized within footwall embayments, and many are associated with S-rich country rocks, but one is hosted by olivine adcumulates (Dumont) and one is partly hosted by autoclastic komatiitic breccias (C-Zone). A multidisciplinary approach including geological mapping, volcanic facies mapping, geophysical surveys, and geochemical studies is required to recognize favourable volcanic sequences that are potential hosts for Ni-Cu-(PGE) mineralization.

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Geological Survey of Canada 2

Ontario Geological Survey 3

Ressources naturelles et Faune Québec

The Abitibi Greenstone Belt has been flown by various electromagnetic (EM) systems and a series of government-funded surveys cover the whole area. They were flown to help base metal exploration and data are available in the public domain. Two modern time-domain EM surveys covering about 3000 km were flown in 2006 and 2007. A first one was flown in the Chibougamau area, Quebec, and a second one in the Bartlett Dome area south of Timmins, Ontario. These recent surveys allow assessment of the benefits of flying a state of the art EM system over previously surveyed areas. We use two criteria to quantify this assessment, firstly the identifications of conductors, or targets, not detected by the previous surveys; secondly the impact of the new survey on mineral exploration in the surveyed area. This impact is reflected in the staking of new claims and increased exploration spending. Both areas were flown by time-domain surveys, in the early 70's for the Chibougamau area and 1990 for the Bartlett Dome area.

In the Chibougamau area the objectives were to identify new base metal exploration targets, to increase mining exploration and to help geological mapping. Many deposits have been mined in this region that is considered to still have a high mineral potential and which is under-represented in term of VMS deposits and. In that area, a first comparison, strictly based on the number of EM anomalies, reveals that the recent survey detected 25% more anomalies than the older ones. A second comparison is based on interpreted depths derived from the recent survey data compared to what is known of the depth of penetration of older systems. More than 1000 anomalies are interpreted to have their sources deeper than 75 m, and more than 450 have sources deeper than 100 m. The Bartlett Dome survey is part of a multi-year project of bedrock geological mapping of the area which goals are to update the geological mapping south of Timmins, to clarify and characterise the major lithologic units, to better understand the stratigraphy of the Bartlett Dome and its correlation with the Shaw Dome, to improve our understanding of the relationship of geophysical features to bedrock geology and to evaluate the mineral potential of the area and generate new exploration targets. The new survey allows a re-evaluation of the conductors identified in the 1990 survey as some of them were likely due to surficial conductors. The total magnetic field map and the EM maps allow a better mapping of the geology of the area. For example, the decay rate of the EM response allows to easily map conductors (Figure 1). In addition to providing new exploration targets, results from these recent EM surveys allow to improve the geological mapping in the surveyed areas. Survey results were extensively used by the industry in the exploration rush following the Golden Chalice major Ni-Cu-PGE discovery. This work was done as part of the Abitibi Project of the Targeted Geoscience Initiative 3 of Natural Resources Canada in close collaboration with the Ministère des Ressources naturelles et de la Faune du Québec and the Ontario Geological Survey.

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All quoted From Table 3 and pp 40-41

Northeastern Ontario Mines and Minerals Symposium 2008

A Century of Mineral Discovery Abstract Booklet