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MMI™ Introduction
MMI™ (Mobile Metal Ions) is a proprietary SGS geochemical survey technique used to accurately locate deep ore deposits at depth. During the MMI™ procedure, we use sophisticated chemical processes and instrumentation to measure mobile metal ions (charged metal atoms and molecules) that have migrated into surface soils from mineralization below. MMI™ geochemistry strips mobile metal ions from the exterior of soil particles using a partial dissolution without digesting the soil itself, to measure metal ion concentrations in the parts per billion range.
By measuring only mobile metal ions in surface soils, SGS MMI™ surveys produces sharp responses (anomalies) over buried ore deposits. Significant reductions in your exploration costs may be realized as traditional exploration techniques such as geophysics and drilling can be focused into smaller, prioritized exploration zones, saving you both time and money. Trust SGS, the global technical leader and proprietary owner of MMI™ for your survey needs.
MMI™ Orientation Surveys
Before a full MMI™ exploration project is undertaken, it is important that you test the technique using a properly designed Orientation Survey at a small scale over a known area of mineralization. This will ensure MMI™ applicability, and will help determine optimum survey parameters. MMI™ Orientation Surveys are valuable in all geologic settings but are strongly recommended in areas of highly transported and/or depositional soils.
An MMI™ Orientation Survey consists of a single transect over a known target, with dense site spacing and multiple samples collected from each sample pit. The primary reasons for performing this survey are to: - Determine a site spacing that is sufficiently dense to identify mineralization
- Identify which elements fingerprint the mineralized zone
- Establish the appropriate depth below live organic material at which to collect samples
- Establish the appropriate elements to use as a reduced MMI-M package, or whether to do a complete package
MMI™ Orientation Survey Design
The MMI™ Orientation Survey, consisting of a single transect, must be done over a known exploration target such as an identified mineralized zone, structure, or geophysical anomaly. After this consideration is met, the following guidelines should be followed to ensure the proper design of your Orientation Survey: - The survey spacing should be 15 – 25m generally and then reduced below 15 m when directly over the mineralization target.
- Samples should be taken over the target’s center and beyond to include the hanging footwalls or edges of the mineralized zone.
- Sampling must to be extended at least 150m beyond the targets edges to capture the background levels of mobile metal ions.
- 25 sampling sites are required (at least 3 must be over the target) to ensure sufficient coverage to properly design an effective MMI™ survey for your exploration program.
- Each site must expose at least 40 cm of soil profile.
The final, optimal distance between sample sites will be dictated by the type and size of mineral deposit being explored. For example, fault-hosted gold deposits will likely have closer sample spacing than a porphyry copper deposit. Our consultants can advise you on details of specific orientation surveys or data interpretation.
Sample Collection Procedures
Normal Environments - In normal soil environments samples should be collected 10 to 25 cm below the surface at a consistent depth.
- The initial step in taking an MMI soil sample requires the 10cm surface soil layer to be scraped away eliminating loose organic matter, debris, and any possible contamination.
- The sample is then taken between 10 and 25 cm depth. The sample should be a “composite” taken over this 15 cm interval.
- Using a plastic scoop or shovel take a cross section of the material between the 10 to 25 cm depth and put into clean, properly labelled plastic bags. Collect approx. 250 to 350 grams of material.
Boreal Environments - Scrape away any extensive organic horizon (O or Ao) and eliminate loose non-decomposed matter, debris, and any possible cultural contamination.
- Penetrate the leaf litter and organic material that still has structure (i.e. decomposing leaves, bark, twigs and peat). Once through to a true A-horizon (where the soil resembles a decomposed mass without any obvious leaf or vegetation visible), discard the top 10cm of this A-horizon material.
- This is the true interface at which to begin your measurements.
- Collect the sample between 10 to 25 cm below this interface. The sample should be a continuous composite taken from the 15 cm interval.
- Using a plastic scoop take a cross section of the material between the 10 to 25 cm depth and put into clean, properly labelled plastic bags. Collect approx. 250 to 350 grams of material.
Guidelines - Ensure not to mix organic and inorganic soils in the collected sample. For example, if the material within the 10 to 25 cm zone has a mixture of humus and inorganic soil then proceed to the base of this “mixed zone” and collect the sample from the inorganic material.
- Do not vary depth beneath the true soil interface, or target a specific layer/feature of a soil profile when sampling. Extensive research has shown that mobile element concentrations are linked to the process of capillary rise and the depth at which water is removed from a soil by evaporation and evapo-transpiration (i.e. expect to see tree roots). Any significant variation in sampling depth and technique can cause severe problems for interpretation. It is imperative that all samples are collected in a consistent manner. In most tropical terrains, the true soil interface is the ground surface. In terrains with deep organic overburden, the true soil interface is the position where plant matter and debris ceases and organic soil material with an obvious mineral content becomes evident.
- Before actually taking the sample, brush sampling equipment to eliminate residue from previous samples and flush it with soil from the new sample site.
- Samples DO NOT have to be completely free of organics but should have a dominant mineral fraction. During sample collection and handling, no jewellery (watches, rings, bracelets, and chains) should be worn, as this can be a major source of contamination.
- Moist Samples – Damp samples should be collected in a similar manner to soils in dry environments. Samples should not be dried in ovens or pulverised in crushers or mills. In the case of dry plastic clays, sample material can be desegregated by crushing with a mallet between disposable plastic sheets. Sieving should be avoided if there is any possibility of serious cross-contamination during sample collection via the sieve. In this case, larger rocks and twigs/leaves etc. can be removed carefully by hand.
- Organic Material – Organic material in the form of fine roots and hairs, decomposing leaf material and other fine organic debris WILL NOT adversely affect MMI analyses. Experimental work has shown that variability in sampling depth has a more significant impact on element responses.
- Contaminated Sites – Where there is a potential contamination problem, samples should be collected as to avoid any contaminated material and the sampler’s judgment must be relied upon. Again, it is extremely important to keep good note of all the potential factors that may affect the sampling and interpretation.
Equipment - A 30-cm diameter plastic garden sieve or kitchen colander with minus 5-mm apertures, available from hardware and super markets, is ideal for sample collection. This is used only to remove large pebbles or roots.
- Plastic collection dish with similar diameter and a kitchen floor brush used for cleaning the sieve and dish between samples;
- A bare steel (no paint) garden spade; and
- Plastic snap seal bags; do not use calico or brown paper.
- Proper labelling of all samples is critical. Do not use water soluble markers or paper inside wet bags.
Other Assistance
SGS has a number of case studies and technical bulletins to help with all your sampling needs. Please visit our web site at www.sgs.com/geochem for further details or to contact our local SGS representatives. Consultants are available for sampling assistance and/or interpretation. |
