Cost-Effective Seismic Exploration: 2D Reflection Imaging at the Kylylahti Massive Sulfide Deposit, Finland

Suvi Heinonen,Gardar Gislason,Michal Malinowski,Stefan Buske,Felix Hloušek,Marek Wojdyla,Emilia Koivisto

doi:10.3390/min9050263

Abstract

We show that by using an advanced pre-stack depth imaging algorithm it is possible to retrieve meaningful and robust seismic images with sparse shot points, using only 3–4 source points per kilometer along a seismic profile. Our results encourage the use of 2D seismic reflection profiling as a reconnaissance tool for mineral exploration in areas with limited access for active seismic surveys. We used the seismic data acquired within the COGITO-MIN project comprising two approximately 6 km long seismic reflection profiles at the polymetallic Kylylahti massive sulfide mine site in eastern Finland. The 2D seismic data acquisition utilized both Vibroseis and dynamite sources with 20 m spacing and wireless receivers spaced every 10 m. For both source types, the recorded data show clear first breaks over all offsets and reflectors in the raw shot gathers. The Kylylahti area is characterized by folded and faulted, steeply dipping geological contacts and structures. We discuss post-stack and pre-stack data processing and compare time and depth imaging techniques in this geologically complex Precambrian hardrock area. The seismic reflection profiles show prominent reflectors at 4.5–8 km depth utilizing different migration routines. In the shallow subsurface, steep reflectors are imaged, and within and underneath the known Kylylahti ultramafic body reflectivity is prominent but discontinuous.

Highlights

Seismic methods can be used to image subsurface geological features at high resolution down to several kilometers depth but are often considered expensive by the mineral exploration industry.The COGITO-MIN project (COst-effective Geophysical Imaging Techniques for supporting OngoingMINeral exploration in Europe) investigated and developed cost-effective seismic exploration techniques [1] including passive seismic interferometry [2] and distributed-acoustic sensing vertical seismic profiling [3]
Comprised the three main workflows, namely post-stack migration (PoSTM), pre-stack timedata migration (PreSTM), and pre-stack depth migration basedtime on migration (PoSTM), pre-stack time migration (PreSTM), and pre-stack depth migration based on Fresnel Volume Migration (FVM)
The COGITO-MIN data pre-processing was common for all imaging methods used and included data pre-processing was common for all imaging methods used included automatic gain control (AGC), bandpass filtering, deconvolution, and refraction staticand corrections

Summary

Introduction

Seismic methods can be used to image subsurface geological features at high resolution down to several kilometers depth but are often considered expensive by the mineral exploration industry.The COGITO-MIN project (COst-effective Geophysical Imaging Techniques for supporting OngoingMINeral exploration in Europe) investigated and developed cost-effective seismic exploration techniques [1] including passive seismic interferometry [2] and distributed-acoustic sensing vertical seismic profiling [3]. We discuss cost-effectiveness of active seismic reflection profiling for mineral exploration in crystalline rock environments. This includes the discussion about (1) the signature of Vibroseis vibroseis and dynamite sources, (2) the usage of different migration algorithms in data processing, and (3) the possibilities to record informative seismic data if source access is limited. Vibroseis was the main source type used in the COGITO-MIN 2D survey but dynamite charges were used in areas inaccessible for the Vibroseis trucks. Use of the two source types within the same area and survey motivates the comparison of Vibroseis and dynamite source signatures in hardrock mineral exploration

Methods

Results

Discussion

Conclusion