Alan R. Butcher

Rapid quantitative mineral and phase analysis using automated scanning electron microscopy (QemSCAN); potential applications in forensic geoscience

Abstract QemSCAN is a scanning electron microscope (SEM) system, initially designed to support the mining industry by providing rapid automated quantitative mineral analyses. The system is based upon Carl Zeiss SEMs fitted with up to four light-element energy dispersive X-ray spectrometers. Representative subsamples are mounted into either resin or wax blocks and polished prior to analysis, or can be mounted onto carbon tape. During analysis, X-ray spectra are collected at a user-defined pixel spacing and are acquired very rapidly (c. 10 ms per pixel). The measured spectra are automatically compared against a database of known spectra and a mineral or phase name is assigned to each measurement point by the QemSCAN computer software programs. In this way the near-surface qualitative elemental composition of each particle is systematically mapped, assigned to a mineral name or chemical compound/species, and digital pixel maps of each particle are created. Depending upon a range of parameters, including the particle size and the user-defined pixel spacing (which can vary between 0.20 μm and 25 μm), approximately 1000 particles, each 1–10 μm in size, can be measured per hour using a 1 μm pixel spacing. In addition to providing a qualitative elemental analysis and mineralogical or phase assignment for each particle, data relating to particle size, shape and calculated specific density are also generated. In this study, the potential application of this automated SEM system in forensic geoscience was evaluated by the analysis of: (1) a series of soil samples, and (2) a series of dust samples from an industrial complex. In both case studies, the mine-ralogy/phase composition of each sample analysed was found to be distinctive. In addition, textural data for the soil samples and particle shape data for the dust samples show that they can be clearly distinguished. Automated SEM using QemSCAN has clear potential application in the analysis of soil or other trace evidence in forensic case work.

Platinum-group mineralization in the Tertiary Igneous Province: new data from Mull and Skye, Scottish Inner Hebrides, UK

In recent years, platinum-group mineral deposits have been reported from several of the Tertiary igneous complexes in East Greenland. These intrusions form part of the same igneous province as the Tertiary igneous centres in northwest Scotland, and recent work confirmed the presence of abundant platinum-group minerals in the Rum Central Complex. In this paper we report for the first time the presence of abundant and diverse platinum-group minerals from the Tertiary Ben Buie intrusion on Mull and the Cuillin Complex of Skye, Inner Hebrides, Scotland. The platinum-group minerals in the Ben Buie intrusion are associated with chromitite layers in ultramafic cumulates. The grains are small (1–2 μm), locally very abundant, and dominated by Pd–Bi–Te–Sb phases. In the Peridotite Series of the Cuillin Complex, the platinum-group minerals are dominated by laurite commonly enclosed within chromite or silicate. A combined orthomagmatic–hydromagmatic origin is proposed for the mineralization. However, the style and type of mineralization differs between each of the igneous centres. Platinum-group element mineralization is a ubiquitous feature of the Tertiary Igneous Province in northwest Scotland and in Greenland and is intimately linked to the regional tectonic setting.

Petrological Reconstruction of the Subsurface Based on PDC Drill Cuttings: An Advanced Rock Typing Approach

Recent advances in automated scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDS) have transformed the petrological analysis of drill cuttings by replacing qualitative descriptions with ultra-fast, quantitative and repeatable analysis. In this study, 100 m of drill cuttings produced by Polycrystalline Diamond Compact (PDC) bits were mapped on a cutting-by-cutting basis, providing information on mineralogy and texture. The individual cuttings were classified into lithotype categories based on mineral composition and grain sizes. These lithotyping data complement bulk sample mineral and chemical assays, providing detailed information on the nature of cementation, intra-formational seals and changes in mineral grain sizes between reservoir sections. The petrological reconstruction generated from the cuttings analysis compares well with the gamma-ray well log. By combining automated SEM-EDS measurements with advanced digital image analysis, meaningful geological information can be generated from PDC drill cuttings, improving our understanding of lithostratigraphic subdivision and zonation.