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Bauxite Ore Analysis: Aluminum & Associated Impurities


The DELTA couples an ultra high resolution SDD detector with a powerful 4W X-ray tube, delivering the fastest, most precise analysis available today in a handheld X-ray Fluorescence (XRF) analyzer. The introduction of new SDD technology has significantly advanced the application of Field Portable XRF for the Mining & Mineral Exploration Industry.

The key benefits include:

  • Significantly increased speed
  • Higher count-rates mean shorter testing times
  • In-Air Light Element Ability with Xpress Mining Mode for Al, Si, P, Ca, & S
  • Lower detection limits (LOD's) and higher precision across the entire periodic table
Delta Handheld XRF analyzing ore

Unprecedented Performance in Bauxite Ores

In its mineral form Bauxite, Aluminum is the most abundant metal in the earth's crust. Bauxite contains one of a variety of hydrated aluminum oxides (gibbsite, boehmite or diaspore), which are often expressed as Al2O3xH2O but are more commonly regarded as impure Al2O3. Bauxite is claylike and earthy, and ranges in color from white to deep brown or red according to the nature and quantity of its components. The major impurities in Bauxite are iron oxides (goethite & hematite), silicon dioxide, the clay mineral kaolinite as well as small amounts of anatase (TiO2). Consequently, its composition varies considerably with alumina constituting from about 50% to about 70%. The DELTA analyzer, with SDD technology, now enables the determination of ALL important phases of Bauxite ores. Aluminum content can be accurately and precisely determined over a broad analytical range simultaneously along with Si, Fe, Mn, Ti , Zr and up to 20+ other elements.

Pisolitic Iron-Rich Bauxite Ore sample
Pisolitic Iron-Rich Bauxite Ore

Light Element Analysis & Sample Preparation

In FPXRF analysis, light elements (LE ) are generally regarded as those with Atomic number (Z) less than 18 (Argon) and usually refer to the group: Mg, Al, Si, P, S & Cl. The investigation of Bauxite deposits is dominated by this LE suite, particularly Al, Si + Ca & K, and the mineralization style is often hosted in a coarse crystalline matrix. Therefore, they are significantly influenced by high sample heterogeneity and in order to achieve meaningful (decision level) analytical quality it may be necessary to undertake some form of sample preparation. This can involve a coarse crush and if necessary, pulverizing of the sample to < 200um and then placing into an XRF sample cup using Polypropylene film supports (as opposed to Mylar film which cannot be used for looking at LE ).

Data sample graphs
Typical Al, Fe, Si, Ti & Zr Performance on GeoStat's Bauxite Certified Reference Materials (90 second test IN AIR on prepared, powdered ores in Mining Mode using an Olympus DELTA SDD HHXRF Analyzer)

Why Use FPXRF?

The aspect of "True Portability" with the latest generation of XRF essentially enables the ability to bring a "miniaturized version of the laboratory" into the field, with obvious limitations. Olympus is clear and transparent about these limitations: (1) Higher LOD's than lab-based techniques; (2) Lower precision than lab-based techniques (higher +/- values but no compromise on accuracy above LOD's; (3) Less repeatable results. FPXRF should not to be seen as a replacement for the laboratory and should be used in conjunction with laboratory and industry standard reporting protocols such as determined by the ASX (JORC CODE ) & the TSX (43-101). The main advantage of FPXRF lies in the ability to generate dynamic, real-time, spatially registered geochemical data sets, rapidly. The Geoscientist can now immediately postulate the elemental characteristics of the observed regolith or lithology dynamically, making informed decisions while still in the field, at the exact location of the sample of interest. Instant and interactive approaches to exploration project management, target delineation and associated vectoring towards mineralization are now possible. This results in significantly reduced time-frames with less time intensive reiterations, such as excavating samples & sending them to the lab with the associated "normal" lengthy turnaround times and lags. FPXRF can be thought of as being a pre-screening tool used to select the best and most appropriate sample to submit to the Laboratory for comprehensive and more detailed analysis. Additionally, the ability to refine your sampling program in the field real-time means that you can easily increase sample density & resolution instantaneously. These field based efficiency gains are advancing project time-frames and assisting companies to better utilize their time in the field and maximize their exploration budget.

LOD's: The 1 Million Dollar Question

The determination of the analytical limit of detection (LOD's) depends on many aspects, not directly related to the instrumentation of choice. Some of these influences include (influential factor denoted in brackets):

  • The energy of excitation or X-Ray source (instrument) Note: This is not all about obtaining the maximum voltage (or keV). It is reliant on the process of fine-tuning both the X-Ray voltage and current to maximize the received count rate and therefore analytical precision (instrument).
  • The Atomic Number and associated response of element(s) being analyzed (sample).
  • Concentration of elements present (sample).
  • Relative density & matrix composition (sample).
  • Sample size, granularity & surface geometry (sample & user).
  • Length of test run (user).
  • The quality of the instrument calibration & QC samples used to "tweak" the instrument (user & instrument).
Delta Handheld XRF testing ore
Olympus IMS
Products used for this application

Combining a Silicon Drift Detector (SDD) and a 4W optimized X-ray tube, the DELTA Professional provides superior performance in speed, LODs, and elemental range. It analyzes Mg and higher for Alloys and Mining. The DELTA Professional is the best value solution from Olympus for handheld XRF.
DELTA Mining and Geochemistry Handheld XRF Analyzers provide immediate results to help determine the next course of action for the entire process – exploration, ore grade/process control, environmental sustainability. On-site detection of metals, minerals and contaminants. GPS-GIS-XRF for instant metal mapping, time, cost savings.
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