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Seismic amplitude vs. offset and attribute analyses for mine planning at the Hannukainen Fe-Cu-Au mine site

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Title: Seismic amplitude vs. offset and attribute analyses for mine planning at the Hannukainen Fe-Cu-Au mine site
Author(s): Galvin, Keith
Contributor: University of Helsinki, Faculty of Science, none
Discipline: none
Degree program: Master's Programme in Geology and Geophysics
Specialisation: Solid Earth Geophysics
Language: English
Acceptance year: 2020
A seismic reflection survey was carried out at the Hannukainen-Rautuvaara Iron (Fe), Copper (Cu), and Gold (Au) deposits as part of the HIRE (High Resolution Reflection Seismics for Ore Exploration, 2007-2010) project. The main discovery from this survey was a regional structure showing three reflective layers dipping to the southwest. The top of this package of reflectors is currently planned to be mined at Hannukainen. The deeper parts of this package may have potential continuation of the economically viable deposits seen at shallow depths. In this work, a target-specific, amplitude-preserving workflow for profiles E1 and V5 of the Hannukainen-Rautuvaara HIRE seismic data will be formulated and applied. Then seismic amplitude vs. offset (AVO) and attribute analyses will be used to analyse the reflective layers and identify potential areas of interest for further study. This is a burgeoning area of seismic research, AVO analysis is typically used in hydrocarbon exploration and has only been sparsely used in hard rock settings for mineral exploration. Attribute analysis is more common in hard rock environments, but still underutilised. The seismic reflection data were re-processed focusing on retaining the high-frequency content of the seismic signal, this is key for further analysis. The results of the AVO analysis consist of determining the AVO class of the responses seen across the CMPs of two selected AVO horizons. AVO product and Poisson’s ratio change across the horizons were calculated, and an area of interest was identified from the correlation of these parameters. Attribute analysis was done using the seismic attributes envelope, first derivative envelope, Hilbert Transform, relative impedance, phase, weighted instantaneous frequency and dip. The amplitude attributes (envelope, first derivative envelope, Hilbert Transform, relative impedance) were useful in determining the areas of the reflector package that showed the strongest amplitudes and selecting horizons on the uppermost reflector for AVO analysis. Phase and weighted instantaneous frequency helped determine the continuity of the reflector package which revealed a clear four-layer signature, differing form the earlier three-layer interpretation. The dip attribute showed vertical anomalies, some of which correlated with mapped faulting in the area. Detailed interpretation of the geophysical results requires better borehole coverage, and petrophysical work, to tie in the seismic data results to the alteration and mineralisation. With open pit mine planning ongoing in the study area, the identification of deep-seated mineral deposits will have direct impact on the planning of the mine and the future of exploration in Hannukainen-Rautuvaara.
Keyword(s): Seismic reflection Amplitude vs. offset Seismic attribute Mineral exploration Mine planning Hannukainen Mine

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