Analytical Infrastructure and Research Facilities

The Institute of Geology of the Mongolian Academy of Sciences (MAS) operates an integrated laboratory and field infrastructure dedicated to petrological mapping, mineral exploration, and tectonic reconstructions. This specialized research workflow is carried out across three core institutional units: the Laboratory of Sample Preparation, the Laboratory of Electron Probe Microanalysis (EPMA), and the Field Infrastructure for Paleomagnetic Investigation. Together, these facilities bridge classical field exploration with advanced micro-analytical characterization, providing the foundational framework necessary to evaluate geochemical data, map mineral phases, and reconstruct deep-time regional tectonic histories.
 
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The Laboratory of Sample Preparation constitutes the primary mechanical and physical processing stage within the analytical pipeline. It converts macro-scale, unweathered lithological field specimens into highly constrained, precise geometries and grain separates required for optical petrography, bulk-rock geochemistry, and micro-beam mass spectrometry.

Core Methodological Sub-Units and Capabilities:

• Mechanical Comminution & Sizing (Rock Sawing): Equipped with heavy-duty diamond-blade circular and precision trim saws designed to isolate unaltered rock matrices. This process mechanically strips outer weathered surfaces to eliminate surficial contamination prior to downstream processing.

• Ultra-Fine Pulverization (Rock Powdering): Utilizes primary jaw crushers followed by specialized agate and tungsten carbide planetary ball mills. Samples are reduced to a homogeneous whole-rock powder (<60 μm) optimal for X-ray Fluorescence (XRF) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) configurations.

• Petrographic Thin Section Fabrication: Incorporates automated precision lapping, grinding, and polishing systems. This unit produces standard petrographic thin sections calibrated to a uniform thickness of 30 μm for polarized light optical microscopy, as well as highly polished, flat-surface epoxy pucks necessary for electron-beam microanalysis.

• Mineral Separation (Geochronological Processing): Employs an integrated processing line consisting of wet-shaking tables (Wilfley tables), density-gradient heavy liquids, and Frantz isodynamic magnetic separators. This workflow isolates pure heavy mineral fractions—primarily zircon, monazite, apatite, and titanite—essential for U-Pb and specialized isotopic geochronology.

The EPMA Laboratory delivers non-destructive, high-spatial-resolution chemical characterization and micro-imaging of solid inorganic materials. The facility is anchored by the JEOL JXA-iSP100 Electron Probe Microanalyzer, an advanced analytical instrument capable of sub-micron chemical mapping and localized major and trace element quantification.
 
Primary Analytical Systems and Modalities:
 
• Quantitative Micro-Chemical Quantification:
 
– Major Element Screen (EDS): Utilizes integrated Energy-Dispersive X-ray Spectroscopy for high-throughput elemental identification, mineral phase discrimination, and rapid standardless compositional screening.
 
– Trace Element Resolution (WDS): Configured with five automated Wavelength-Dispersive Spectrometers (WDS) equipped with high-sensitivity analyzing crystals. This optimized geometry resolves severe spectral peak overlaps and achieves highly precise detection limits extending down to low parts-per-million (~10 ppm) for trace elements and rare earth elements (REEs).
 
• High-Resolution Elemental Mapping:
 
Executes automated, multi-element X-ray intensity mapping via stage-and-beam synchronization software. This maps spatial elemental distribution to resolve complex intra-crystalline chemical zoning, metasomatic reaction fronts, and micro-inclusion phases.
 
• Micro-Imaging Configurations:
 
– Backscattered Electron Imaging (BSE): Capitalizes on atomic number (Z) contrast to immediately visualize spatial chemical heterogeneity. Brightness variations correspond directly to mean atomic weight differences, revealing cryptic growth zoning, dissolution-reprecipitation textures, and phase transitions.
 
– Secondary Electron Imaging (SEI):
 
Evaluates nanoscale surface topography, morphology, and sample microstructures, ensuring precise beam placement on pristine, pit-free polished surfaces.
 
– Mineral Cathodoluminescence (CL):
 
Features an integrated panchromatic CL detector that records visible-light photon emission stimulated by electron bombardment. This mode isolates internal crystalline growth structures, inheritance cores, and structural defects in quartz, carbonates, and accessory zircons—providing the spatial context required for targeted in-situ microprobe and laser ablation analyses.

Pomeroy Rock Coring Drills (Gasoline-Powered Field Hand-Drilling)

To obtain pristine, structurally oriented sub-surface core samples from remote outcrops across Mongolia’s complex terrain, researchers deploy Pomeroy Rock Coring Drills (such as the Pomeroy EZ Core D261-C series):

• The Hardware: These portable field hand-drilling machines are heavily modified from lightweight, high-performance Stihl two-stroke gasoline engine blocks. They are engineered with customized omni-directional fuel pick-up configurations, allowing the operator to drill smoothly at any angle—horizontal, vertical, or angled into a cliff face.

• Core Extraction: Using water-lubricated diamond core drill bits powered by manual, pressurized water-can cooling pumps, they extract highly uniform 1-inch to 1⅛-inch diameter rock cylinders directly from dense igneous, metamorphic, or sedimentary basements.

2. Paleomagnetic Orientation and Structural Context

Taking the core out of the rock is only half the battle; its exact position in the earth must be logged before it is broken free. Field teams couple the Pomeroy drill with specialized field fixtures:

• Core Orienting Fixtures: Before snapping the core sample from the outcrop using a slot-chisel, a specialized Pomeroy orienting fixture is slid over the in-situ cylinder.

• Azimuth & Dip Mapping: Geologists fix a Brunton pocket transit or a sun compass directly onto the orienting wand to accurately measure the precise magnetic/solar azimuth and structural dip of the core axis.

© Institute of Geology

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