Petrology and Geochemistry of Drill Core AT-14-01
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Petrology and Geochemistry of Drill Core AT-14-01 FINAL REPORT prepared for Canadian Continental Exploration Prepared by Alexander Kawohl & Hartwig E. Frimmel Bavarian Georesources Centre Dept. of Geodynamics and Geomaterials Researc Institute of Geography and Geology University of Wuerzburg Am Hubland D-97074 Wuerzburg Germany March, 2018 A. Kawohl (MSc) is a project scientist. Prof. Dr. Hartwig E. Frimmel holds the Chair of Geodynamics and Geomaterials Research. He is a Competent Person who is a Fellow of the Geological Society of South Africa (GSSA), Fellow of the So- ciety of Economic Geologists (SEG) and an Executive Council Member (incl. Past President) of the So- ciety for Geology Applied to Mineral Deposits (SGA). He has close to 30 years of experience that is rel- evant to the topic of this research project and to the activity being undertaken to qualify as a Competent Person as defined in the 2012 Edition of the Joint Ore Reserves Committee (JORC) ‘Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves’ as well as the ‘South Afri- can Code for the Reporting of Exploration Results, Mineral Resources and Mineral Reserves’ (the SAMREC Code). II Table of Contents 1. Preamble............................................................................................................................. 2 2. Geological Background ..................................................................................................... 4 Location .................................................................................................................................. 4 Temagami Greenstone Belt .................................................................................................... 4 Huronian Basin ....................................................................................................................... 5 Sudbury Igneous Complex...................................................................................................... 5 Other Magmatic Events .......................................................................................................... 7 3. Results................................................................................................................................. 8 Stratigraphy ............................................................................................................................. 8 Petrography ............................................................................................................................. 9 Whole-Rock Geochemistry................................................................................................... 17 Rock Classification ............................................................................................................... 21 Trace Element Patterns ......................................................................................................... 29 4. Alteration and Metamorphism....................................................................................... 37 Assessment of Element Mobility .......................................................................................... 37 Metamorphism ...................................................................................................................... 46 5. Discussion ......................................................................................................................... 50 Correlation with Temagami Greenstone Belt ....................................................................... 50 A New Sudbury Offset Dyke .............................................................................................. 555 6. Outlook ........................................................................................................................... 622 7. References ……………………………………………………………………………... 63 III Executive Summary The Temagami magnetic anomaly is similar in size and extent to the geophysical anomaly that marks the 1.85 Ga Sudbury Igneous Complex (SIC) in its immediate vicinity but its geological cause and poten- tial link to the Sudbury impact structure have remained elusive. A first analysis of the lithology and alter- ation of diamond drill core intersecting the area of maximum magnetic anomaly (bore hole AT-14-01) revealed that the units intersected below Huroninan sedimentary cover can be correlated with those of the 2.7 Ga Temagami Greenstone Belt. Much of the intersected rock types experienced extensive alteration, in places completely obliterating original protoliths. Different styles and stages of alteration could be distinguished based on petrographic, mineral chemical and whole rock geochemical analyses. Much of the alteration in the Temagami Greenstone Belt-equivalent units is similar to VMS-type alteration, prob- ably on the Neoarchaean seafloor. Two igneous units in the drill core escaped that alteration. These are mafic rocks that bear all the hallmarks of the 2.2 Ga Nipissing Diabase elsewhere in the region and two diorite bodies, either sills or dykes, near the bottom of the bore hole. Both of these rock types experienced low-grade metamorphic overprint but with relatively little element mobility. This makes it possible to reconstruct their protolith composition. New geochemical data for the diorite indicate that it has a com- position that is very similar to that of quartz dioritic offset dykes in and around the SIC and that is very distinct from all other kown igneous units in the region. A correlation of the diorite with the SIC is further supported by Sr, Pb and most notably Nd whole rock isotope data. The latter are in perfect agreement with new and published data for the SIC. Consequently, it is speculated that the Temagami magnetic anomaly could be caused by a larger body of such magnetic diorite, representing offset dykes at an even greater distance from the SIC than has been known so far. This new finding considerably increases the exploration potential of the area representing the Temagami magnetic anomaly for SIC-type sulfidic Cu- Ni-PGE deposits. 1 1. Preamble The principle goal of the project, as outlined in the project proposal approved on 8th May 2016, has been to determine whether mafic rocks, intersected by diamond drill hole AT-14-01, which targeted the Temagami magnetic anomaly, are equivalent to rocks of the 1850 Ma Sudbury Igneous Complex (SIC). The motivation for this is based on a first preliminary petrographic and geochemical assessment as re- ported by A. Bite in an internal report from 30th December 2014 as well as a first attempt to date these rocks by D.W. Davies (Internal Report from 1st September 2015), which yielded a highly imprecise U-Pb monazite age of 1775 ± 76 Ma. Although this age is within analytical error of the age of the SIC, its poor quality and uncertainty about the actual genesis of the dated monazite grain leaves the result inconclusive. A critical unit in the drilled section is a rock at the bottom of the drill hole, logged as gabbronorite by Joerg Kleinboeck, as it is the most likely candidate for being a possible correlative of the SIC. The project to be reported on here was designed as a MSc thesis project to be carried out by the MSc student A. Kawohl under the supervision of H.E. Frimmel. To this effect, both A. Kawohl and H.E. Frimmel visited Sudbury for two weeks from 18th to 30th July 2016. During that time, representative samples of the various rock types within drill core AT-14-01 could be taken, complemented by some samples from the Emerald Lake deposit and other units of and around the SIC. In addition to sampling the drill core, an introduction to the regional geology was provided through field visits under the guidance of A. Bite and W. Whymark. Brief discussions were also held with P. Lightfoot. The sampled material was shipped to Würzburg, Germany, where it arrived by the end of September 2016. In the meantime A. Kawohl commenced his petrographic analyses, first on thin sections provided by A. Bite, subsequently on thin sections prepared in Würzburg. Since then A. Kawohl conducted a series of analyses on this material. First petrographic observations have been summarized in the first interim report, submitted in January 2017. Without a proper understanding of the alteration history of the rocks of interest, any interpretation of the protoliths’ geochemistry in terms of magmatic provenance would be futile. Consequently, the first work step focused very much on characterizing the style and extent of al- teration, which was found to be extensive and widespread throughout most of the core. Since then, A. Kawohl expanded on the alteration study by investigating the mineralogy of various alteration phases, using electron microprobe and XRD techniques and the trace element distribution within different gener- ations of magnetite. The latter provided evidence of a hydrothermal magnetite generation and these results were presented at the 14th Biennial SGA Meeting, held in Quebec City from 20-23 August 2017. Up to that stage, no evidence could be found to support a genetic link between the rocks intersected in the drill core AT-14-01 and the SIC but much of the intersected rocks could be correlated with those of the Neo- archaean Temagami Greenstone Belt (Kawohl et al. 2017). Subsequently, this situation changed when we eventually obtained the complete geochemical data set for some 80 samples analyzed by XRF and ICPMS. Seventeen of these samples represent two diorite (previously logged gabbronorite)