This handbook provides a summary of activities undertaken in the Geoscience Australia (GA) Geochronology Mineral Separation Laboratory, an in-house facility dedicated to the production of high quality mineral separates for isotopic analysis.
Significant resources are expended acquiring isotopic geochronology data; money, time and effort are invested from the earliest stage of identifying a need to date a geological sample, followed by planning and sample collection, mineral separation processes, data acquisition, data processing, report writing and data management. The researcher and end-users need assurance that the best sample possible has been obtained and analysed.
The chain of quality control required for good isotopic analysis begins with field sampling and continues with detailed attention to mineral separation and final sample preparation. Issues faced include finding fresh samples, minimisation of contamination risks, efficiencies in sample preparation and digital documentation of samples. Skimping on sampling and preparation can produce erroneous results just as surely as any systematic instrument problem, potentially leading to inaccurate reporting, low confidence in data quality and a loss of reputation for the laboratory, researchers and organisation. Therefore, it is essential that measures are taken through all stages of processing to ensure the sample remains contaminant free, labelling is correct and that data entered into information and archiving systems are accurate.
Rock samples collected for geochronological analysis from outcrop, drill core or dredges can range in size from 100 grams to 30 kilograms. Variations in sample type, sample size and target minerals affect the approach to sample preparation.
Minerals most frequently separated for isotopic analysis are zircon, monazite and potassium-rich rock forming minerals including K-feldspar and micas. Other minerals separated include titanite, rutile, apatite, xenotime, sulphides, tungstates and gold.
Cleaning processes throughout the laboratory are very rigorous due to the risk of contamination between samples. The higher the level of sample concentration, the greater the risk of contamination; it only takes one grain from a previous sample separation to contaminate the next sample a grain that, if analysed, must be reported and explained in the interest of scientific transparency.
