Next Article in Journal / Special Issue
Analysis of Au-Ag Mineralization in the Caribou Base-Metal VMS Deposit, New Brunswick; Examination of Micro-Scale Inter- and Intra-Sulphide Distribution and Its Relation to Geometallurgy
Previous Article in Journal / Special Issue
Trace Element Analysis of Minerals in Magmatic-Hydrothermal Ores by Laser Ablation Inductively-Coupled Plasma Mass Spectrometry: Approaches and Opportunities
Article Menu

Export Article

Open AccessArticle
Minerals 2016, 6(4), 112; https://doi.org/10.3390/min6040112

Focused Ion Beam and Advanced Electron Microscopy for Minerals: Insights and Outlook from Bismuth Sulphosalts

1
School of Chemical Engineering, The University of Adelaide, Adelaide 5005, SA, Australia
2
FEI Company, Achtseweg Noord 5, P.O. Box 80066, Eindhoven 5600 KA, The Netherlands
3
Adelaide Microscopy, The University of Adelaide, Adelaide 5005, SA, Australia
4
BHP Billiton Olympic Dam, Adelaide 5000, SA, Australia
*
Author to whom correspondence should be addressed.
Academic Editor: Paul Sylvester
Received: 2 August 2016 / Revised: 27 September 2016 / Accepted: 11 October 2016 / Published: 20 October 2016
(This article belongs to the Special Issue Advances in Mineral Analytical Techniques)
View Full-Text   |   Download PDF [12097 KB, uploaded 20 October 2016]   |  

Abstract

This paper comprises a review of the rapidly expanding application of nanoscale mineral characterization methodology to the study of ore deposits. Utilising bismuth sulphosalt minerals from a reaction front in a skarn assemblage as an example, we illustrate how a complex problem in ore petrology, can be approached at scales down to that of single atoms. We demonstrate the interpretive opportunities that can be realised by doing this for other minerals within their petrogenetic contexts. From an area defined as Au-rich within a sulphosalt-sulphide assemblage, and using samples prepared on a Focused Ion Beam–Scanning Electron Microscopy (SEM) platform, we identify mineral species and trace the evolution of their intergrowths down to the atomic scale. Our approach progresses from a petrographic and trace element study of a larger polished block, to high-resolution Transmission Electron Microscopy (TEM) and High Angle Annular Dark Field (HAADF) Scanning-TEM (STEM) studies. Lattice-scale heterogeneity imaged in HAADF STEM mode is expressed by changes in composition of unit cell slabs followed by nanoparticle formation and their growth into “veins”. We report a progressive transition from sulphosalt species which host lattice-bound Au (neyite, lillianite homologues; Pb-Bi-sulphosalts), to those that cannot accept Au (aikinite). This transition acts as a crystal structural barrier for Au. Fine particles of native gold track this progression over the scale of several hundred microns, leading to Au enrichment at the reaction front defined by an increase in the Cu gradient (several wt %), and abrupt changes in sulphosalt speciation from Pb-Bi-sulphosalts to aikinite. Atom-scale resolution imaging in HAADF STEM mode allows for the direct visualisation of the three component slabs in the neyite crystal structure, one of the largest and complex sulphosalts of boxwork-type. We show for the first time the presence of aikinite nanoparticles a few nanometres in size, occurring on distinct (111)PbS slabs in the neyite. This directly explains the non-stoichiometry of this phase, particularly with respect to Cu. Such non-stoichiometry is discussed elsewhere as defining distinct mineral species. The interplay between modular crystal structures and trace element behaviour, as discussed here for Au and Cu, has applications for other mineral systems. These include the incorporation and release of critical metals in sulphides, heavy elements (U, Pb, W) in iron oxides, the distribution of rare earth elements (REE), Y, and chalcophile elements (Mo, As) in calcic garnets, and the identification of nanometre-sized particles containing daughter products of radioactive decay in ores, concentrates, and tailings. View Full-Text
Keywords: High Angle Annular Dark Field Scanning Transmission Electron Microscopy; FIB-SEM; nanoscale; bismuth sulphosalts; neyite High Angle Annular Dark Field Scanning Transmission Electron Microscopy; FIB-SEM; nanoscale; bismuth sulphosalts; neyite
Figures

Figure 1

This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

Supplementary material

SciFeed

Share & Cite This Article

MDPI and ACS Style

Ciobanu, C.L.; Cook, N.J.; Maunders, C.; Wade, B.P.; Ehrig, K. Focused Ion Beam and Advanced Electron Microscopy for Minerals: Insights and Outlook from Bismuth Sulphosalts. Minerals 2016, 6, 112.

Show more citation formats Show less citations formats

Note that from the first issue of 2016, MDPI journals use article numbers instead of page numbers. See further details here.

Related Articles

Article Metrics

Article Access Statistics

1

Comments

[Return to top]
Minerals EISSN 2075-163X Published by MDPI AG, Basel, Switzerland RSS E-Mail Table of Contents Alert
Back to Top