1. Hardrock Seismic Attribute Analysis and AVO modeling for Carlin-type Deposit Exploration Kyle T. Gray 1 Jared Townsend 2 John Louie 1 1 University of Nevada, Reno Seismological Laboratory 2 Barrick Gold Corporation Great Basin and Western Cordillera Mining Geophysics Symposium 11/23/2013

2. Overview Both petroleum and mineral exploration attempt to locate zones of increased porosity The CTD environment shares similarities with carbonate oil and gas reservoirs, which allows for adoption of oil and gas methodologies We cannot get all of the benefits of seismic data without abundant wire-line logs

3. Seismic Interpretation Methods 1.Conventional interpretation – Manual picking of horizons and faults 2.Seismic attributes – Analogous to filtering of potential fields data 3.Forward modeling – Synthetic data from wire-line logs 4.Inversion – Incorporation of wire-line logs to invert seismic data into elastic properties Petrophysical studies important in every step

4. Hardrock Seismic Structural complexity Crystalline environment – or close spatial association with magmatism Heterogeneous regolith zone High ambient noise – Haul trucks, mining operations Variable source- receiver couplings Ground relief

5. Seismic in Mining PREVIOUS HARDROCK SEISMIC STUDIES Bushveld, South Africa Witwatersrand, South Africa Flin Flon, Quebec Mount Morgan, Australia Bell Allard, Quebec Manitouwadge, Ontario St. Ives, Australia Mt. Isa, Australia Kristienberg, Sweden Pyhasalmi, Finland Half Mile Lake, Canada Voisey’s Bay, Labrador, Canada Previous seismic data for mining exploration is largely collected in the Proterozoic setting – No carbonates – No extant porosity – No direct analogies to petroleum industry (Harrison and Urosevic, 2012) (Salisbury et. al, 2003)

6. CTD Formation Ore genesis relates to structural and magmatic overprint on the platform- slope environment (Cook and Corboy, 2004)

7. Carlin Type Deposit paleo-stratigraphic setting: carbonate platform-slope http://www.beg.utexas.edu/lmod/_IOL-CM03/cm03-step01.htm (Cook and Corboy, 2004)

8. Seismic response in carbonate platform-slope environment (Jansen et. al, 2011 )

9. Alteration and Petrophysics Decarbonatization = decreased seismic parameters and increased porosity. Sample bias in drill-core petrophysics towards less altered rock.

10. Full wave-form Sonic Log Wire-line Logs Argillization Silicification Limestone Tertiary Limestone 3700 m/s 5700 m/s 3600 m/s Decarb. Intensity from geolog

11. Pseudo wire-line log Drill core sampled at high resolution Cannot sample heavily altered rock Stresses importance of wire-line logging

12. Case Study 1300 ft 150-250 ft

13. Seismic Attributes - potential field analogy Average frequency Instantaneous amplitude RTP Magnetics Total Horizontal Gradient

14. Intro to Pre-stack Data Sum all offsets Increasing offset Stacked trace http://subsurfwiki.org/wiki/Gather

15. Amplitude Versus Offset (AVO) Model DECARBON- ATIZATION. Offset Amplitude Gradient plot for base of decarbonatization Offset Far offset anomaly at base of decarbonatization

16. Pre-stack Migrated Gathers offset …

17. Inversion Pre-stack inversion using ONE wire-line log Tuff in geolog 2.6 g/cc 2.15 g/cc TERTIARY PALEOZOIC

18. Conclusions Decarbonatization produces distinct rock property contrasts but more wire-line data is needed to fully understand the system. Seismic attributes calculated in CTD environment can help reveal alteration features Inversion shows promise given that the case study only used one wire-line log.

19. References Salisbury, M., Harvey, C., Matthews, L., The acoustic properties of ores and host rocks in hardrock terranes In: D. Eaton, B. Milkereit & M. Salisbury, eds. Hardrock Seismic Exploration. Tulsa: Society of Exploration Geophyiscs, p. 141. Harrison, C. B. & Urosevic, M., 2012. Seismic processing, inversion, and AVO for gold exploration - Case study from Western Australia. Geophysics, 77(5), p. 235-243. Cook, H. & Corboy, J., 2004. Great Basin Paleozoic Carbonate Platform: Facies, Facies Transitions, Depositional Models, Platform Architecture, Sequence Stratigraphy, And Predictive Mineral Host Models, Field Trip Guidebook—Metallogeny of the Great Basin Project, August 17—22, 2003 :U.S. Geological Survey Open-File Report 2004-1078. Janson, X., Kerans, C., Loucks, R. Marhx, M., Reyes, C., Murguia, F., 2001, AAPG Bulletin, v. 95, No. 1 (January 2001) p. 105-146