What is Nugget Effect Gold Assay (NEFFA)?

To understand this new technique, it is important to know how the “nugget effect” works.

The nugget effect is a term used to describe the sampling problem that can occur when there are large gold particles (nuggets) in a sample. If a nugget is selected during a traditional sampling process, researchers can overestimate the amount of gold in the sample. But if the nugget is missed, the gold can be underestimated. For gold exploration and mining, this variability can lead to inaccurate results and costly mistakes.

The Nugget Effect Gold Assay (NEFFA) technique aims to turn the traditional challenge associated with the nugget effect into an opportunity. NEFFA attempts to measure the nugget effect through multiple nondestructive, systematic analyses of a geological material (typically crushed rock or crushed drill core) to identify the presence of gold or other precious metals based upon its distribution within the sample.

NEFFA completely redefines and reduces the traditional sample preparation procedure and aims to provide semi-quantitative gold results using portable XRF analyzers to identify samples of potential interest for further laboratory analysis.

Here’s how it works:

  • Representative samples of 20–30 g, depending on the nature of material, are isolated in a medium such as a clear sample bag or under plastic film to ensure that there’s no contamination from an external agent
  • The sample is distributed evenly over a 10 cm × 10 cm square with the depth of the material being no thicker than 2 mm
  • A grid or matrix is placed over the sample, with individual matrices measuring 1 cm × 1 cm
  • Measurements are performed within each square cm, and the average of all results is reported
  • The technique is most effective on crushed rock or crushed drill core samples with a grain size 3 mm, but not on homogenized pulp samples
  • Rotary air blast and reverse circulation (RC) samples can be analyzed directly

This method takes the throughput advantages of GERDA for general exploration projects and adds additional value for gold exploration by providing gold estimates using XRF.

Experience the future of gold assay technology with the Nugget EFFect Gold Assay by MEFFA Lab Oy revolutionise your exploration efforts and make informed decisions with the speed and accuracy offered by our innovative express-method.

UK Patent No. 1805456.9

To read more, please download NEFFA presentation