Abstract
The Metal Earth project acquired 927 km of deep seismic reflection profiles from August to November of 2017. Seismic data acquired in this early stage of the Metal Earth project benefited greatly from recent advances in the petroleum sector as well as those in mineral exploration. Vibroseis acquisition with receivers having a 5 Hz response (10 dB down) generated records from a sweep signal starting at 2 Hz, sweeping up to 150 Hz or 200 Hz. Not only does this broadband signal enhance reflections from the deepest to the shallowest crust, but it also helps the use of full waveform inversion (e.g., to mitigate cycle-skipping) and related techniques. Metal Earth regional-scale transects using over 5000 active sensors target mineralizing fluid pathways throughout the crust, whereas higher spatial-resolution reflection and full-waveform surveys target structures at mine camp scales. Because Metal Earth was proposed to map and compare entire Archean ore and geologically similar non-ore systems, regional sections cover the entire crust to the Moho in the Abitibi and Wabigoon greenstone belts of the Superior craton in central Canada. Where the new sections overlap with previous Lithoprobe surveys, a clear improvement in reflector detection and definition is observed. Improvements are here attributed to the increased bandwidth of the signal, better estimates of refraction and reflection velocities used in processing, and especially the pre-stack time migration of the data.
Highlights
Innovative technology for conducting seismic exploration historically derives from petroleum exploration in sedimentary rock environments, but mineral exploration in crystalline rock environments requires different emphasis [1]
Major innovations and more incremental technical improvements have occurred simultaneously within the petroleum seismic exploration industry over the past decade and these were adapted into the Metal Earth seismic acquisition program [2]
Most of the R1 surveys were acquired with live receivers along the entire line. These very long offset recordings can be problematic for Common Mid-Point (CMP) binning of crooked lines, during processing the maximum offset for R1 surveys was restricted to 15 km
Summary
Innovative technology for conducting seismic exploration historically derives from petroleum exploration in sedimentary (soft) rock environments, but mineral exploration in crystalline (hard) rock environments requires different emphasis [1]. Major innovations and more incremental technical improvements have occurred simultaneously within the petroleum seismic exploration industry over the past decade and these were adapted into the Metal Earth seismic acquisition program [2]. Metal Earth, requires new observations and data over a broad range of scales, from craton- to deposit-scale and integration of information from seismic, magnetotelluric (MT), gravity and traditional geological mapping surveys. Minerals 2019, 9, 145 of transect surveying, deep seismic reflection profiling, will build upon previous regional-scale surveys conducted as part of the Lithoprobe and Discover Abitibi projects [3,4,5,6]. A few seemingly small improvements enable very significant new approaches to analysis and enhance our understanding of mineralization pathways and processes. The processing and analysis of high-resolution (R2) and full waveform inversion tailored (R3) seismic data is currently underway and will be discussed in future publications
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