Spectral discrimination of dolerite in crushed rock road aggregate, Perth, Western Australia

Abstract

Reflectance spectroscopic analysis, covering the visible to short‐wave infrared wavelength range (400 to 2500 nm), was tested on 56 light granite, dark granite and dolerite chips that typically comprise crushed rock aggregate quarried for use as road‐surfacing within the Perth, Western Australia (WA) metropolitan area. The technique was evaluated as a means of identifying and quantifying the proportion of dolerite within a bulk sample of granitic road aggregate. The ratio of the absorption depth at 2350 nm to the absorption depth at 2200 nm, for log‐space difference spectra (R2350 : 2200), successfully identified and discriminated with 100% accuracy all dolerite versus granitic rock chips tested. It is recommended that reflectance spectroscopy replace the current testing methodology (Colour of Aggregate Test) as the standard method of quantifying dolerite content in road surface aggregate.

Acknowledgements

The authors gratefully acknowledge the help of Travis Naughton of the Visual Resources Unit (VRU), CSIRO Exploration and Mining for drafting figure 1. Dr. Robert Hewson is thanked for his assistance with initial processing of the raw reflectance data using Envi^® version 4.2 software. Finally, the authors gratefully acknowledge the Commissioner of Main Roads WA for permission to publish this research. The chrysoprase spectra presented in figure 5 was kindly reproduced from the ASTER Spectral Library through the courtesy of the Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, copyright © 1999, California Institute of Technology. All rights reserved.