A Qualitative Examination of the Iron Boomerang and Trends in Spectral Metrics across Iron Ore Deposits in Western Australia

Andrew Rodger,Carsten Laukamp,Ian Lau,Erick Ramanaidou

doi:10.3390/app12031547

Abstract

There are two major types of iron ore deposits in the Pilbara Province of Western Australia—banded iron formation (BIF)-hosted iron ore deposits and bedded iron deposits (BID), respectively, named martite–goethite and martite–microplaty hematite and the channel iron deposits (CID). These deposits consist mainly of iron oxides such as magnetite, hematite and goethite; the latter have been subdivided into vitreous and ochreous goethite. Combining spectral scanning of diamond drill core, drill chips and pulps collected from these deposits provides a rapid and relatively inexpensive means of assessing the potential mineral makeup within a deposit to make informed qualitative decisions. Additionally, the full width half maximum (FWHM) of the 900 nm 6A1à4T1 crystal field absorption feature within the goethite-dominated region is shown to be related to the type of goethite, namely ochreous and vitreous. The assessment capabilities of the combined metrics are presented in a visual format named as the iron boomerang because of its distinctive manifold. This provides the identification of at least two spectral endmembers comprised of hematite and vitreous goethite, the identification of samples that are moving from a pure hematite to mixed hematite/goethite and lastly into a goethite-dominant-driven regime.

Highlights

The use of hyperspectral reflectance spectra (“spectral data”) in the iron ore resources industry is well established and continues to be a valuable tool to aid orebody characterisation, mineral classification, and quantification [1,2,3,4]
This study focuses primarily on the F900 absorption feature and on how calculation of the full width half maximum (FWHM) of the feature, when combined with the wavelength of the point of maximum absorption of the F900 absorption wavelength, adds a strong qualitative aspect to spectral datasets collected in bedded iron deposits (BID) and channel iron deposits (CID) formations
Utilising a simple combination of two spectral metrics, namely the Fe oxide wavelength and the Fe oxide FWHM, it is demonstrated that a large collection of spectral samples from banded iron formation (BIF), BID and CID of the Pilbara Province of Western Australia fall within a distinctive manifold

Summary

Introduction

The use of hyperspectral reflectance spectra (“spectral data”) in the iron ore resources industry is well established and continues to be a valuable tool to aid orebody characterisation, mineral classification, and quantification [1,2,3,4]. The use of spectral data for characterisation purposes is dependent on the wavelength region in which the reflectance spectra were collected. This has led to spectral region-specific metrics that are used to leverage the strength of each spectral region and, in many cases, is deposit specific [1,5,6,7]. 350 and 2500 nm, the 1300–2500 nm spectral region has alteration mineral assemblages associated with hydrothermal base and precious metal deposits which can often be defined by the absorption features present [8,9,10,11,12,13], while absorptions in the VIS and NIR between. The Moh hardness scale has a range of 5–5.5 but the yellow ochreous goethite is much lower due to its porosity

Methods

Results

Conclusion