On-Site Mineral and Rock Measurements

Table of Contents

Introduction
Rock and Mineral Analysis
Agilent’s Diffuse Reflectance Sample Interface
Diffuse Reflectance Geolibrary
Conclusion
About Agilent Technologies Inc.

Introduction

Agilent’s handheld battery operated Fourier transform infrared (FTIR) analyzers are not only robust but also deliver superior performance in challenging field environment, especially in the field of geosciences.

This article covers the application of the Agilent 4100 ExoScan and 4200 FlexScan FTIR systems to create an optimized rock and mineral library for a field FTIR analyzer (Figure 1).

Figure 1. Agilent FTIR analyzer with diffuse reflectance sampling interface rapidly records the molecular spectrum of the sample with no preparation required

Rock and Mineral Analysis

Rock and mineral analysis has been performed using FTIR spectroscopy for the past several years. The commercially available libraries consisting of geological samples are typically measured in classical absorbance/transmittance mode. The process involves taking and grinding a small mineral sample in KBr or nujol to produce a suspension in order to acquire its spectrum. Another common feature is recording all of these spectra in a laboratory using a conventional benchtop FTIR spectrometer.

Agilent’s Diffuse Reflectance Sample Interface

An at-site infrared (IR) analyzer can acquire a spectrum with minimum or no sample preparation, thus enabling to obtain the IR spectrum of an area of interest irrespective of whether it is an ore body, inside a mine, drill core or outcrop. The development of a diffuse reflectance sampling interface by Agilent enables its handheld FTIR systems to perform direct sample measurement with no sample preparation.

These reflectance measurements involve acquisition of the diffusely scattered light from a sample and returning of scattered light to the IR detector. The difference between diffuse reflectance of neat rocks and minerals and transmittance spectra enables creating a unique library for this kind of analysis technique involving the analyzer on-board.

Igneous/plutonic, metamorphic and sedimentary rocks and minerals are added to the library consisting of different chemical compositions such as urinates, tungstates, vanadates, borates, sulfides, phosphates, aluminosilicates, silicates, oxides, sulfates and nitrates. A well-defined IR spectrum can often be recorded for a mineral having a chemical structure involving covalently bonded atoms.

The diffuse reflectance spectrum has a specular component based on the reflectivity of the surface of interest and crystallinity and particle size of the sample. This component has the tendency to modify the entire spectrum. Due to this reason, spectra have been added to the library of both the smooth reflective crystal surface and rough surfaces for some materials (Figure 2). Both types of spectra can be accessed using the analyzer algorithm to predict the ideal match for a given sample. The spectra were acquired at 4 cm-1 resolution and comprise 128 scans co-added interferograms, which require roughly one minute for collection and subsequent processing.

Figure 2. Stacked plot of spectra of calcite rock samples with a smooth flat surface (blue) and a rough porous or fractured surface texture (red) from representative mineral chemical composition classes.

Diffuse Reflectance Geolibrary

Users of the Agilent FTIR analyzers (Figure 3) can rapidly predict the identity of a mineral in the field, thanks to the instrument’s intuitive software (Figure 4). The full spectrum of the sample being analyzed is recorded for subsequent analysis. Agilent will keep on expanding the diffuse reflectance rock and mineral library as a higher number of referee samples become available. Besides the on- board Agilent library, uses of the 4100 ExoScan and 4200 FlexScan FTIR analyzers can build their own library depending on their requirements.

Figure 3. An Agilent FTIR analyzer

Figure 4. The IR spectrum of minerals measured neat may arise from diffuse and specular reflection and thus both types of spectra are included in the library, thereby maximizing the potential hit quality

Conclusion

The combination of a field-ready FTIR analyzer capable of performing molecular composition analysis of rocks and minerals with minimal or no sample preparation and an on-board library to facilitate the identification process provides geoscientists with a robust tool, and complements existing elemental analysis analyzers being used in the field.

About Agilent Technologies Inc.

Agilent is the proven leader in elemental analysis for geochemistry, mining, and metals industries. We offer the broadest atomic spectroscopy portfolio on earth, with AA, MP-AES, ICP-OES and ICP-MS solutions that solve your toughest challenges.

Our innovative and unique solutions also create opportunities for you to advance and define new levels of performance. From exploration and production to mine site rehabilitation, Agilent is the single source you require to achieve rock-solid minerals analyses with maximum speed, accuracy, safety and cost savings.

MP-AES Cost Savings Estimator

Agilent Solutions for Geochemistry, Metals & Mining

  • Rugged, reliable, low cost atomic absorption spectrometers ideal for challenging conditions
  • Revolutionary Microwave Plasma Atomic Emission Spectrometer (MP-AES), which runs on air, enabling unattended multi-element analyses without flammable and expensive gases
  • Robust, productive ICP-OES chosen by mining labs around the world for fast,
  • accurate and reproducible geochemical analysis
  • ICP-MS for ultimate confidence in trace analysis
  • Micro GC for the analysis of mine gas
  • Handheld FTIR for at-site rock and mineral measurement

This information has been sourced, reviewed and adapted from materials provided by Agilent Technologies Inc.

For more information on this source, please visit Agilent Technologies Inc.

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