Curtin/CSIRO Geophysics Group Seminar, 1st July 2021
Elemental Analysis via Prompt Gamma Neutron Activation For Diamond Drilling
Date: Thursday, 1st July, 2021
Time: 10:00 AM – 11:00 AM
Location: ARRC Seminar Room, 26 Dick Perry Avenue, Kensington
Presenter: Snezana Petrovic, PhD student, Exploration Geophysics, Curtin University
Abstract
The purpose of this research project is to conceptually design, and test the idea of a prompt gamma neutron activation (PGNA) logging-while-drilling tool that would reliably identify the elemental composition of rock units. The principle idea is to place a PGNAA system onto or behind the core-tube assembly. This configuration will allow us to gather data about the rock mass while drilling diamond core holes, which is the most widely used drilling method in mineral exploration and development. As the core is retrieved every 1.5 to 3m at a time the data can be stored in the tool and retrieved every time core is extracted. This near real-time elemental analysis could provide information that would improve almost every stage of mining and mineral processing.
Logging while drilling (LWD) is a technique that involves recording data from various sensors while the borehole is being drilled. Currently, elemental assay and petrophysical information is provided after the hole has been completed; often weeks afterwards. The key advantage in real time measurement is the possibility of making drilling decisions immediately when needed. Also, the borehole conditions during drilling are usually better compared to wireline logging; there is less drilling fluid invasion than during the logging (Crain’s Petrophysical Handbook). Although the LWD technique is in widespread use in oil and gas industry since the late 1980s, it has not been adopted in mining industry due to the lack of suitable tools. Australian scientists claim that adapting this method will improve efficiency and cut cost in mineral exploration industry (Mehta 2009).
Prompt Gamma Neutron Activation Analysis (PGNAA) offers a means to perform elemental analysis while drilling. It is a penetrative, non-destructive analytical method used for determining the presence and amount of many elements in the sample simultaneously. PGNAA is particularly suitable for borehole logging due to its large sampling volume (an order of magnitude greater sample than core assay, thus, statistically robust) and real-time analysis potential. This technique employs a neutron source as the main source of radiation. When the emitted neutrons enter a medium, they collide with nuclei in rock until they lose energy and slow down. Once “thermalised” various elemental nuclei capture these thermalized neutrons, producing unstable compound nucleus in excited state, which decays by the nearly instantaneous emission of one or more gamma rays (Molnár and SpringerLink 2004). The emitted gamma-rays have energies characteristic of the target nuclei, and measuring the relative intensities at various energies (spectral gamma analysis) with a gamma ray detector we may identify the neutron-capturing elements. Thus, neutron induced gamma ray spectrum analysis may be used to compute elemental concentrations in the rock in-situ..
Snezana Petrovic is a PhD candidate at the Discipline of Exploration Geophysics at Curtin University. Her research interests in developing a prototype of a prompt gamma neutron activation logging-while-drilling tool for slim-holes in mineral exploration. She received her B.Sc. and M.Sc. (2014) in Applied Geophysics from the Faculty of Mining and Geology, University of Belgrade (Serbia).
LinkedIn profile: https://www.linkedin.com/in/snezanapetrovic90/