Bayesian subsampling of time-domain electromagnetic data using kernel density product

The Bayesian method is a powerful tool to estimate the resistivity distribution and associate uncertainty from time-domain electromagnetic (TDEM) data. As the forward simulation of the TDEM method is computationally expensive and a large number of samples are needed to globally explore the model space, the full Bayesian inversion of TDEM data is limited to layered models. To make high-dimensional Bayesian inversion tractable, we propose a divide-and-conquer strategy to speed up the Bayesian inversion of TDEM data. First, the full datasets and model spaces are divided into disjoint batches based on the coverage of the sources so that independent and highly efficient Bayesian subsampling can be conducted. Then, the samples from each subsampling procedure are combined to get the full posterior. To obtain an asymptotically unbiased approximation to the full posterior, a kernel density product method is used to reintegrate samples from each subposterior. The model parameters and their uncertainty are estimated from the full posterior. The proposed method is tested on synthetic examples and applied to a field dataset acquired with a large fixed-loop configuration. The 2D section from the Bayesian inversion revealed several mineralized zones, one of which matches well with the information from a nearby drill hole. The field example shows the ability of Bayesian inversion to infer reliable resistivity and uncertainty.

The geological framework for Hvideklint, south-east Denmark, using glaciodynamic sequence stratigraphy

Glaciodynamic sequence stratigraphy provides a practical model for grouping and classifying complex geological data to aid interpretation of past climatic and environmental development in Quaternary successions. The principles of glaciodynamic sequence stratigraphy are applied here to summarise the complex glacial geological framework of Hvideklint on the island of Møn, south-east Denmark. The framework of the superimposed deformed Hvideklint is presented in a reconstructed geological cross-section of Hvideklint. For the construction of the architecture of the glaciotectonic complex, the interpretation of structures below sea level was based on a detailed new survey of the cliff section combined with construction of successive approximation balanced cross-sections. The new description is supported by drill hole data from the Jupiter database. Where chalk is not glaciotectonically deformed, the constructed depth to the top-chalk-surface is generally located about 30 m below sea level. In Hvideklint, thrust sheets with chalk are exposed 20 m above sea level, and the balanced cross-section constructions indicate that the décollement surface for a Hvideklint glaciotectonic complex is located about 80 m below sea level. Between the décollement level and the top of the complex, two or more thrust-fault flat-levels and connecting ramps add to the complex architecture of Hvideklint.

Wall rock alteration in part of the Sarnak gold deposit, SE Bulgaria. Preliminary data

This short communication presents preliminary data on а wall rock alteration in part of the Sarnak epithermal gold deposit based on host rock samples from drill hole cores. Methods used are powder X-ray diffraction as well as optical and scanning electron microscopy. The most pronounced alterations related to the epithermal mineralization are vein silicification, adularization and pyritization.

Simulation of control and stabilization of the lubricant-coolant flow

The subject of the research is a control system of coolant supply. The results of system simulation in MathLab application program package for solving problems of technical calculations are presented and the analysis of transients is carried out. Reliability and productivity of a machine tool module depends on the quality of coolant supply control. This problem is actual for CNC machines, used for drilling holes with hard-alloy drills. of cutting fluid through the cutting zone depends on the state of chips in the drill hole channels. In the article the simulation of pump control as a function of changing flow rate is performed. The conclusion of the conducted research is the proposed model of the system of supply and flow of lubrication-cooling fluid, which allows analyzing the performance of the object under study.

The first true millipede—1306 legs long

The name “millipede” translates to a thousand feet (from mille “thousand” and pes “foot”). However, no millipede has ever been described with more than 750 legs. We discovered a new record-setting species of millipede with 1,306 legs, Eumillipes persephone, from Western Australia. This diminutive animal (0.95 mm wide, 95.7 mm long) has 330 segments, a cone-shaped head with enormous antennae, and a beak for feeding. A distant relative of the previous record holder, Illacme plenipes from California, it belongs to a different order, the Polyzoniida. Discovered 60 m below ground in a drill hole created for mineral exploration, E. persephone possesses troglomorphic features; it lacks eyes and pigmentation, and it has a greatly elongated body—features that stand in stark contrast to its closest surface-dwelling relatives in Australia and all other members of its order. Using phylogenomics, we found that super-elongation (> 180 segments) evolved repeatedly in the millipede class Diplopoda. The striking morphological similarity between E. persephone and I. plenipes is a result of convergent evolution, probably for locomotion in similar soil habitats. Discovered in the resource-rich Goldfields-Esperance region and threatened by encroaching surface mining, documentation of this species and conservation of its habitat are of critical importance.

<i>dh2loop</i> 1.0: an open-source Python library for automated processing and classification of geological logs

A huge amount of legacy drilling data is available in geological survey but cannot be used directly as they are compiled and recorded in an unstructured textual form and using different formats depending on the database structure, company, logging geologist, investigation method, investigated materials and/or drilling campaign. They are subjective and plagued by uncertainty as they are likely to have been conducted by tens to hundreds of geologists, all of whom would have their own personal biases. dh2loop (https://github.com/Loop3D/dh2loop, last access: 30 September 2021​​​​​​​) is an open-source Python library for extracting and standardizing geologic drill hole data and exporting them into readily importable interval tables (collar, survey, lithology). In this contribution, we extract, process and classify lithological logs from the Geological Survey of Western Australia (GSWA) Mineral Exploration Reports (WAMEX) database in the Yalgoo–Singleton greenstone belt (YSGB) region. The contribution also addresses the subjective nature and variability of the nomenclature of lithological descriptions within and across different drilling campaigns by using thesauri and fuzzy string matching. For this study case, 86 % of the extracted lithology data is successfully matched to lithologies in the thesauri. Since this process can be tedious, we attempted to test the string matching with the comments, which resulted in a matching rate of 16 % (7870 successfully matched records out of 47 823 records). The standardized lithological data are then classified into multi-level groupings that can be used to systematically upscale and downscale drill hole data inputs for multiscale 3D geological modelling. dh2loop formats legacy data bridging the gap between utilization and maximization of legacy drill hole data and drill hole analysis functionalities available in existing Python libraries (lasio, welly, striplog).

Rare Earth Elements Distribution in Weathered Volcanic Rock from Mamuju Area, West Sulawesi

The study on the distribution of rare earth elements (REE) was carried out from bedrock and its weathering profile at North Botteng Village, Simboro District and Kelapa Tujuh Village, Mamuju District, Mamuju Regency, West Sulawesi. This study aims to determine the potential and distribution of REE in the bedrock and its weathering profile and to identify the REE-bearing bedrock type. In addition, the relationship between REE and Zr element as one of REE associated elements is also discussed. The analytical method used include petrographic observations to identify the REE-bearing host rock and the ICP-MS (Inductively Coupled Plasma Mass Spectrometry) method to determine the REE content. Samples were taken from drilled hole samples in three different locations and classified into three groups, namely Group 1 (K-01 drill hole sample) and Group 2 (K-62 drill hole sample) from Kelapa Tujuh while Group 3 taken from the P-05 drill hole sample from North Botteng Village. Petrographic observations on the bedrock show that the REE are hosted by phonolitic leucitite composed of mainly leucite as phenocryst set in K-feldspar, plagioclase, pyroxene and opaque groundmass. REE content (expressed as TRE2O3 or total rare earth oxides) show a high concentration values ranging from 2000 - 6400 ppm and display variations enrichment in depth. The highest total REE content in Group 1 found in samples from 9 - 11 meters depth, which is 4600 ppm, while in Group 2 the highest concentration is from 4 - 5 meters depth with a total REE value of 2380 ppm and in Group 3 the highest value of REE content encountered at a depth of 6 - 7 meters, which is 6400 ppm. Zr content in Group 1 samples shows value range between 1780 - 2870 ppm whereas in Group 2 ranges from 1670 - 2380 ppm with the highest Zr concentration at a depth of 4 meters while in Group 3 the Zr content show values ranging from 2100 ppm - 4480 ppm with the highest concentration encountered a depth of 11 meters. The study results suggest that the relationship between REE and Zr element in Group 2 samples showed a positive relationship. Meanwhile, the Group 1 and 3 samples show a varied relationship. The REE concentration is controlled by elevation, in which areas with higher REE concentrations are encountered at elevations above 359 meter above sea level (masl) while low REE content concentrates in areas with elevations below 365 masl. REE enrichment is caused by weathering process that occurs on phonolitic leucite in the study area.

Interface Sampling and Indicator Minerals for Detecting the Footprint of the Lancefield North Gold Deposit under the Permian Glacial Cover in Western Australia

Areas under a thick Permian glacial cover in Western Australia formed as glaciers gouged fresh bedrock and deposited diamictites in disconnected valleys and basins. These areas now present the greatest challenge for mineral exploration in the northeast Yilgarn Craton. At the Lancefield North gold prospect, in the southern part of the Duketon Greenstone Belt, Permian diamictites on average 40 m thick cover unweathered basalt hosting gold mineralization. The basal Permian diamictites consist of fresh, very poorly sorted, angular to rounded, pebble- to boulder-sized, polymictic clasts supported by a matrix of coarse-grained sand and mud. The framework and matrix are cemented by calcite, dolomite, chlorite, and pyrite. These diamictites are stable under alkaline and reducing conditions below the water table. Detrital; fresh sulfides; gold; and opaque oxides, such as pyrite, pyrrhotite, chalcopyrite, sphalerite, arsenopyrite, gersdorffite, cobaltite, pentlandite, scheelite and galena, chromite, ilmenite, and magnetite, are identified in the framework and matrix of the fresh diamictites, and these are identical to those in the primary gold mineralization. Weathering of diamictites and oxidation of detrital and diagenetic sulfides above the water table produced several Fe- and Mn-rich redox fronts and secondary chalcocite and bornite. Interface sampling across the Archean–Permian unconformity shows Au, As, Zn, Ni, Co, and Cd anomalism over the mineralization compared to the background. However, these elements are low in concentration in the redox fronts, where Fe is correlated with As, Cu, Mo, and Sb and Mn is correlated with Co, Ni, and Ba. Gold shows elevated levels in the fresh basal diamictites and decreases in the weathered diamictites over the mineralization. A sampling at or near the Archean–Permian unconformity (interface sampling) only delineates gold mineralization, with no hydromorphic dispersion halo beyond the peripheries. At the Lancefield North prospect, the detrital indicator sulfides are mechanically dispersed up to 500 m to the east of the mineralization in the direction of ice flow. This dispersal distance is controlled by the rough topography of the Archean–Permian unconformity, and it may be greater, but the estimation of the actual distance of transport is limited by the distribution of drill hole locations.