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Portable XRF for Gold (Au) and Au Pathfinders for Mineral Exploration and Ore Body Vectoring


Olympus’ X-ray Fluorescence (XRF) analyzers provide high performance, real-time geochemical data for rapid multi-element characterization of soil, rocks, and ores. Recent advances in XRF technology have increased the number of elements measured, improved the limits of detection, and reduced analysis test times.

Vanta™ XRF analyzers provide convenient and rapid measurement of many types of samples associated with Au exploration, within Au mines, Au mine labs, and refined Au products.

Benefits

  • XRF analysis of pathfinder elements in soil, drill cuttings, and drill cores enables rapid indication of potential Au mineralization.
  • XRF pre-screening enables priority sample selection for laboratory analysis, improved drill target generation, and maximization of analytical budgets.
  • XRF mapping of structural features and identification of alteration zones improves ore deposit understanding, modelling, and vectoring; often resulting in less dilution and better Au recovery.
  • Use of XRF for litho-geochemistry applications and rock typing enables rapid and inexpensive lithological classification of samples.

Portable XRF for Gold (Au) and Au Pathfinders for Mineral Exploration and Ore Body Vectoring

Deposit TypeGeochemical Signature
Orogenic Au S, As, CO2, K+/– Sb, Te, Mo, W, Cu, Pb, Zn, Hg
High Sulphidation Epithermal Ag, Cu, Te, Mo, Bi, Sn
Low Sulphidation Epithermal Zn, Hg, Se, K, As, Sb, Ag/Au
Carlin-type As, Sb, Hg, Tl
Porphyry Cu-Au Cu, Pb, Zn, Ag
Au Skarns Bi, Te, As, Co
Intrusive Related Au Bi, W, As, Sb, Mo, Te
VHMS Cu, Pb, Zn, Ag, Ba, K, Mg +/–CO2
Iron Oxide Cu-Au (U) F, P, Co, Ni, As, Mo, Ag, Ba, U, LREE
Supergene Au High Fineness Au +/– any of the above

Associated Geochemical Signature of Au Deposits
Source: Reflex Geochemistry

Pathfinder and Alteration Geochemistry

Most Au deposits have an associated geochemical signature (as shown in the table above). The XRF analyzer can detect these geochemical signatures, enabling geologists to better understand the geological system in which they are working. Typical Au pathfinder elements include As, Cu, Pb, Zn, Sb, Bi, Ag, and W.

Typical XRF LODs for Common Au Pathfinder Elements

Element LOD (ppm)* Element LOD (ppm)*
As 1-2 W 1-2
Cu 2-5 Bi 2
Pb 2-3 Sb 5-10
Zn 1-3 Ag 2-5

*120 s test time per beam, interference free SiO2 matrix; refer to Olympus LOD documents for further discussion on lower limits of detection (LODs)

XRF Analyzer for Detection of Gold

It is common knowledge that handheld XRF analyzers do not support direct low level measurement of Au in geological samples (e.g., low ppm and ppb). The lab-based fire assay technique is commonly recognized as the method of choice for Au analysis. Au L-level X-ray lines are located in a very crowded area of the X-ray fluorescence energy spectrum. In this part of the spectrum, interference from other elements (e.g., As, Zn, W, and Se) can yield a false-positive Au determination. Nevertheless, direct measurement of Au by XRF can be achieved in specific cases such as highgrade (> 5 ppm) quartz vein environments (relatively interference free) or within refined Au products (where Au is present in very high concentrations).

However, an increasing number of Au onsite mining laboratories are using XRF in place of, and as a supplement to, fire assays methods. Please refer to the Olympus Application Note “Use of Handheld XRF in Au Mine Laboratories.”

Portable XRF for Gold (Au) and Au Pathfinders for Mineral Exploration and Ore Body Vectoring
Portable XRF for Gold (Au) and Au Pathfinders for Mineral Exploration and Ore Body Vectoring

Portable XRF for Gold (Au) and Au Pathfinders for Mineral Exploration and Ore Body Vectoring
Portable XRF for Gold (Au) and Au Pathfinders for Mineral Exploration and Ore Body Vectoring

Portable XRF for Gold (Au) and Au Pathfinders for Mineral Exploration and Ore Body Vectoring
Portable XRF for Gold (Au) and Au Pathfinders for Mineral Exploration and Ore Body Vectoring

Images taken from: Arne et al. (2014) – The use of property-scale pXRF data in gold exploration – advantages and limitations, Geochemistry: Exploration, Environment, Analysis.
Contor plots of As, Cu, and Pb in surface soil using field XRF compared with ICP analysis from Au exploration project in Canada.

Olympus IMS

Products used for this application


DELTA Professional

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.

VantaNEW

Vanta handheld XRF analyzers are some of the toughest devices Olympus has ever made. These rugged, powerful, and intuitive instruments provide rapid, accurate element analysis and alloy identifications to customers who demand laboratory-quality results in the field.

Vanta for Mining & Geochemistry

Vanta handheld XRF analyzers for mining and geochemistry provide immediate on-site elemental analysis for geochemical exploration, mining grade control, ore processing, and remediation.
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