Abstract Structural data is vital for the understanding of the geometry and evolution of a deposit and feeds into geologic, structural, resource, and geotechnical models. Accurate models are critical for targeting, resource estimation, and geotechnical design and, if rapidly available, support real-time decisions on drilling and grade control. Structural drill core data add a high-resolution data set to traditional data from mapping or the structural interpretation of remote sensing and geophysical data and, therefore, add indispensable information to any integrated model. In this paper we propose standardized workflows for data collection, review technological advances and quality control processes accelerating structural data collection from both oriented drill core and televiewer techniques, and provide an overview of structures that may be observed in drill core and discuss their significance to record for the geometry of the deposit. Critical to the data collection process is an interpretative process that recognizes and identifies domain-based structures that ultimately are fundamental to developing 3-D structural models.

Abstract The ability to detect and quantify rock matrix porosity is explored using acoustic televiewer images and dolostone rock core samples. In particular, an empirical relationship between the acoustic televiewer amplitude response and core-derived total porosity is developed. The performance of the acoustic televiewer amplitude relationship was compared to neutron and gamma-gamma logs, which are traditional nuclear wireline tools commonly used for estimating porosity in dolostones. Acoustic televiewer amplitude results are consistent with the gamma-gamma (density) and neutron (porosity) logs, provide increased vertical resolution, do not require downhole radioactive sources and also provide oriented fracture information. Sample specific porosity and bulk density values from the calibrated acoustic televiewer datasets are then used to improve porewater concentration estimates from rock concentrations. Supplementary material: Physical properties determined from core samples and predicted from geophysical logs using linear regression are available at: https://doi.org/10.6084/m9.figshare.c.4085918

Abstract The Punchbowl is a large topographic basin in the rugged T'aebaek Mountains (T'aebaeksanmaek) of east-central Korea. Its steep northern rim is part of the Korean Demilitarized Zone (DMZ). This terrain was the target of various infiltration attempts in the postwar period and its potential to host clandestine tunnels was indicated by Allied intelligence studies of the early 1970s. In December 1989, at a depth of 145 m in intrusive granodiorite, a coherent cross-borehole electromagnetic anomaly with a signature indicative of an air-filled cavity was recorded by tunnel-search teams using continuous wave and pulsed ground-probing borehole-radar systems. Natural air-filled cavities at this depth were precluded by geological considerations and ground-water elevations. Target-evaluation drilling followed and, on December 24 at 0130 hours, a drill bit penetrated “Tunnel-4.” A borehole television camera provided clear images of artifacts of human tunnel-construction activity. Two and a half months later, Korean engineers, using a Wirth 3-m tunnel-boring machine (TBM), gained access to the tunnel and confirmed its nature and purpose. Mapping and surveying of the tunnel revealed that (1) the tunnel was constructed by drill and blast methods in Mesozoic intrusive granodiorite, similar to that hosting previously identified DMZ Tunnel-2 and Tunnel-3, and in Precambrian gneiss; (2) the tunnel slopes up to the south at an average grade of 2.3%, ranging from a low of 0.91% to a high of 3.5%; (3) the average cross-sectional dimensions of the tunnel, 1.6 m × 1.6 m, are somewhat smaller than other hardrock tunnels discovered elsewhere in the DMZ; and (4) standard rock-mass rating schemes do not accurately predict tunnel-construction difficulty for hardrock tunnels smaller than 2 m × 2 m in cross section.