Indicator mineral studies

‘Each heavy mineral grain is a unique messenger of coded data, carrying the details of its ancestry and the vicissitudes of its sedimentary history’

— Mange & Wright, 2007

 

Sieved till samples are processed by Knelson gravity concentrator for recovering indicator mineral-rich heavy mineral concentrates. Before microscoping, the concentrates are further processed by using micropanning techniques.

General information

The concentration of heavy minerals and recovery of indicator minerals from surficial sediments is one of the oldest exploration methods. For example, gold – the best possible indicator of gold – have been recovered from glacial and stream sediments for more than 100 years, in many cases by using hand pans. Currently the indicator mineral methods are applied worldwide to a broad spectrum of commodities and a variety of media, including stream sediments, glacial sediments, aeolian sediments and regolith in deeply weathered terrains. Clastic sediments are geological archives that record and preserve signatures of past geological events in source provinces, during transit, and at the site of deposition (Mange & Wright, 2007). Their high-density grains represent the detrital occurrence of essential rock-forming minerals (e.g. garnet, pyroxenes and micas) or accessories with densities larger than 2.8 and are thus called ‘heavy minerals’.

Typical accessory minerals include zircon, tourmaline and apatite, but in the case of gold- or base metal-mineralised terrains, also such mineral species as gold, pyrite and sphalerite are observed. In addition to clastic sediments, indicator minerals are also recovered directly from both fresh and weathered bedrock.

Our service package

Muon Solutions offers indicator mineral studies primarily for gold and base metal exploration sectors operating in glacial terrains. However, as the same methods are applicable to other types of terrains too, we are certainly interested to hear if you have something else in mind. Our service can commence from the study of historical or recent heavy mineral fractions, or we can step in in an earlier stage and participate in to sampling decisions and/or the sampling itself. We can handle your field samples and extract heavy mineral fractions for further studies, e.g. by using Knelson concentrator. Moreover, our team is very experienced in the use of the “micropanning” method that is remarkably effective in retrieving even the most minute gold grains. At the next stage we analyse the heavy mineral species and related grain morphologies with microscope (e.g. shape, angularity/roundness, colour, inclusions). Gold and other indicator mineral grains can also be digitally photographed. Observation statistics can then be used to interpret the properties of the provenance and to shed light on the likely distance of glacial transport. Indicator mineral studies are hence used to trace the heavy mineral dispersal trains back to their source.

Till samples are composed of fine-grained to coarse materials sourced from local to distal bedrock areas. However, the ratio of local and distally-transported debris varies significantly and can be anything between the two extremes. We study not only the heavy mineral fractions of the samples, but also their pebble-sized rock fragments (e.g. variation of rock types and their corresponding average roundness). Just like the accessory heavy mineral fractions these data improve our understanding on the transport distance of the sampled till and in some cases we are able to determine the most likely bedrock source areas.

Sampling procedures

The first-pass till sampling is usually conducted as a sparse reconnaissance-scale sampling and is followed by higher density sampling near anomalous samples. Sampling can be done either by shovels from the surface till or by percussion drill rig equipped with a flow-through bit from the basal till (or base-of-till, “BOT”). In the latter case the samples are commonly collected from or immediately above the till-bedrock interface. While most sulphide minerals are susceptible to degradation in the near-surface environments, the relatively unoxidised basal till may still contain well-preserved sulphides.

Muon Solutions can mobilise sampling teams to your project area. We can also conduct outcrop mapping, boulder hunting and/or geochemical sampling programs simultaneously with the ongoing heavy mineral studies. We can also help you to find an operator that has a BOT rig.