The MMI Process®

What is MMI™ Technology?

The MMI™ technology is an innovative geochemical process that uses a very different approach to the analysis of metals in soils and weathered materials. It involves sample attack using extremely weak solutions of organic and inorganic compounds rather than the conventional aggressive acid digest solutions or fusions. Conventional techniques digest soil substrates releasing metals that are chemically bound by strong atomic forces, either to each other or within and to the clay and other minerals and particles in the soil sample. In contrast to this MMI™ extractants, containing strong ligands, are used to detach and hold in solution metal ions which are loosely bound to soil particles by weak atomic forces. The extractants are formulated to avoid dissolving the bound forms of the metals. The metal ions held in solution are therefore the chemically active or 'mobile' component. These mobile forms occur in very low concentrations that are readily measurable by modern ICP-MS analytical instrumentation with considerable precision, provided that the solution delivered to the machine is very dilute. MMI™ extractants meet these criteria particularly well.

The mechanism of formation of MMI™ anomalies has been the subject of industry and government sponsored research between 1993 and 1997 at the Geochemistry Research Centre in Perth, Western Australia. Under the auspices of the Minerals and Energy Research Institute of Western Australia, this research has led to an improved understanding of how MMI™ soil geochemical anomalies form, for a wide range of weathered materials, climatic conditions and countries. Together with the results of many hundreds of unpublished case studies and exploration programs, this work suggests that metal ions are released from mineral deposits by oxidation process at depth, migrate essentially vertically and concentrate in the soil profile close to the surface, overlying their source. These 'mobile ion' anomalies are interpreted as the pre-cursors to the conventional or 'bound' geochemical responses that form broader patterns, usually with lower anomaly-to-background resolution, and in some cases transported from the primary source. By deliberately targeting only the recently arrived or mobile forms of metal elements, prior to chemical binding and their chemical and physical dispersion over the landscape, MMI™ analyses give a more focussed geochemical expression of buried mineralisation, even in many types of transported overburden at low detection levels.

MMI™ technology uses proprietary extractants. "MMI-M" is a new, single multi-element leach that now provides an option to measure the concentration of a broad selection of mobile elements in soils. With MMI-M, explorers can now create their own individual multi-element packages, using any or all of commodity elements, diamond host rock elements, lithological elements and pathfinder elements.

Development of MMI™ Technology

MMI™ technology was first made available to the exploration industry research sponsors in 1992. By 1994 it had been tested at over 74 different base metal or gold deposits with remarkable success (Mann et al., 1995). Sharp and responsive commodity metal anomalies over concealed deposits of copper, lead, zinc, nickel and gold were defined at all but 10 of these 74 sites, which occur in a range of geographical environments, from arid to high rainfall, and including deeply weathered terrains and areas covered by transported overburden. This is a success rate of 86%. The success rate of conventional soil geochemistry has not been accurately measured but, given the common failure of total digest analysis in alluvial and aeolian cover, is significantly less.

In addition, an extensive set of applications research data from many hundreds of mines, deposits and exploration camps around the world has been accumulated. The success rate remains above 80 percent. Most of this data is confidential to the mining companies involved. However those that are in the public domain illustrate the application of the technology in a wide range of geological, geographical and climatic environments. Currently the technology is being applied in numerous countries world-wide, and several companies have published results of surveys in what are geochemically difficult terrains in respect of conventional geochemical methods.

The MMI™ technology is particularly reliable and applicable in areas which have a well developed soil layer. In areas of certain Indonesian islands which are widely cov¬ered by metres of tephra, the technology has been tested at 28 sites of variable tenors of buried mineralisation defined by extensive drilling to about 150 metres depth (Fripp, 1999). The success rate for MMI™ was 90 percent. MMI™ gold results accurately located the site of the buried mineralisation at all the sites where it would rank as a resource. In particular it did not highly rank the weak and modest mineralisation which drilling had shown would not be sufficiently continuous or robust to warrant extensive drilling for a resource. This drilling was focussed at Total Digest gold-in-soil anomalies of similar strength to those at the strongly mineralised sites. Had MMI™ extractants been used initially the weakly mineralised sites would not have been drilled, leading to very significant cost savings. This is partly because the MMI™ technology is not prone to the nugget effect responsible for the misleading Total Digest anomalies. The incidence of false anomalies is very significantly less than that for conventional soil geochemistry.

In Manitoba, Canada, the technology has successfully identified a new VMS style base metal prospect (Assean Lake Prospect), and a new gold camp (Hunt Gold Project) which is adjacent to the base metal mineralization (Fedikow, 2002). Drilling has successfully tested both. Key to these successes has been the development of reliable ultra low levels of detection, particularly for gold, that allows definition of natural backgrounds in transported or exotic overburden. Field trialling in highly transported surface environments has been undertaken and includes salt lakes in the Eastern Goldfields, WA and glaciated till covered terrains in Canada. This work has shown that it is now possible to identify the very low 'natural background' levels expected from geochemical data in highly transported soils, rather than 'machine imposed' background levels previously available. The data is robust, repeatable and now routinely available commercially and provides explorationists with a tool to explore more confidently in transported soil terrains.

Sampling is simple but critical for successful application. Soil samples MUST NOT be processed, simply placed in plastic bags, and they MUST be collected as an integrated 'channel' sample from 10-25 cm below the organic-soil interface.

The Benefits of MMI™ Technology

• False and displaced anomalies may occur, but their occurrence is statistically very low compared to conventional geochemistry, thereby reducing drilling costs. By careful planning and interpretation of MMI™ multi-element geochemistry exploration programmes, it is possible to understand and limit the effect of misleading anomalism;
  
  
• Repeatability is excellent. Repeat samples taken at any particular site have very limited variance, less than 15 percent in the case of gold;
  
  
• Nugget effects are minimised. The results of all experiments and applications to date has shown that analyses of mixed samples return values very close to the arithmetic average of the separate samples analysed prior to mixing. This makes interpretation of anomalism and the statistical treatment of data more reliable, and reduces the incidence of false anomalies. It also enhances the application of less costly and more reliable composite reconnaissance sampling;
  
  
• Focused anomalies. Anomalies are commonly restricted and narrow, and tend to occur directly above buried primary mineralization, thus sharply defining the area of the drill target, and thus reducing the extent of early drilling programmes by approximately 30% to 50% compared to conventional geochemistry. Sampling is much more rapid and does not require auger drilling, so it is much more cost effective;
  
• Zonation and metal associations. MMI™ provides high-resolution data, which is capable of allowing the definition of metal zonation within buried deposits, lithochemical discrimination and specific metal associations, e.g. Zn and Cd in sphalerite, gold selvedges on base metal hanging walls.
  
  
• Deeply buried mineralisation is detectable, as demonstrated in many orientation surveys. These surveys done over known deposits have readily detected deposits up to 700 metres below surface;
  
  
• Background values are low. MMI™ anomalism over any deposit or mineralisation is more strongly defined than the corresponding conventional anomalism, with response ratios of signal to background much greater than for conventional analysis;
  
  
• Lower limits of detection for all of the commodity metals analysed are at least an order of magnitude better than conventional geochemistry, that is one tenth the value, at a comparable to slightly cheaper commercial cost. Accordingly the technology is commonly applicable in leached, deeply weathered terrains, and in areas covered by transported overburden such as sheet-wash, wind-blown sand and glacial overburden, the regions for which conventional geochemistry usually cannot detect a chemical signal at surface;
  
  
• Recent Developments MMI™ technology has been developing in the areas of:
  • Inferred geology, with the use of elements such as Ni, Ce and Fe, Ti for delineating sub-surface geology
  • Stream sediments and catchment overbank sampling, using very low density sampling to provide useful and predictive geochemical information in areas dominated by transported regolith
  • Regional style geochemical survey, where the importance of the lithological elements along with the commodity elements can provide data to help focus further detailed exploration

Application of MMI™ Technology

Application of the technology led to discoveries of economic gold mineralisation at the Golden Web Mine and of sub-economic mineralisation at the Forest Prospect, both near Coolgardie in Western Australia. At Nepean, also in Western Australia, MMI™ technology was able to define the location of buried nickel mineralisation where conventional geochemistry was ineffective. All of the above deposits occur in arid and deeply weathered laterite terrain, and sample media included soils associated with sheet wash sands, laterite duricrust and degraded lateritic colluvium. In addition the technology has successfully identified the location of buried gold mineralisation in laterite terrain which, rather than being arid, sparsely vegetated and of low relief like the gold fields of Western Australia, is the hilly, tropical humid jungle of Venezuela. This is the La Salle Prospect near Anococo.

In the rugged wet terrain of central west Scotland at Kilmelford, MMI™ technology has identified and discriminated between related bedrock deposits of copper-gold and lead-zinc-silver. Outcrop at Kilmelford is less than 10% despite the rugged terrain and the media sampled was mainly boggy clays, peats and glacial sands. At the Hunt Lake Prospect in Manitoba, Canada and at the Night-Hawk Lake Prospect near the famous Timmins mining camp in Ontario, Canada, MMI™ technology has successfully identified copper-lead-zinc and gold-silver mineralisation. At these Canadian examples there is no outcrop, conventional geochemistry was completely ineffective, and the results of drilling to date show "ore-grade" mineralisation intercepts which have encouraged the companies to continue deep diamond drilling. The new discoveries are buried beneath up to 30 metres of glacial gravels, sands and lake clays, and the media sampled were mainly wet sandy soils with a high organic content. Recent new Canadian discoveries of gold include the Avalon Dubenski prospect and Hunt Gold Camp, details of which are on our Case Studies page.

MMI™ technology has also successfully located buried mineralisation beneath 70 metres of the desert gravels and sands in the Andean foothills of Argentina, near Mendoza, at the San Jorge prospect. Systematic soil sampling has identified an Au-Cu porphyry deposit. This study also defined the metal zonation typical of these very large deposits.

The technology has also proven to be a very successful, cost effective and practical surface reconnaissance method for diamond explorers. In Australia, Botswana and Canada companies have used surface MMI™ geochemistry to prioritise geophysical and topographic targets identified as prospective for buried diamond-bearing intrusive pipes and dykes. The technique not only has a success rate in excess of 93% for correctly identifying potential hosts, but it has discriminated between different phases and compositional variations of the buried intrusives.

We have many examples of the use of MMI™ in various environments and commodities available on our Case Studies and Technical Bulletins pages.

Analytical Performances

The analytical protocols developed for MMI™ extractions control many variables that normally constitute sources of error in other analytical methods, and enables the technique to achieve very high levels of precision and accuracy. All extractants are produced from one location with strict control over the components used for manufacture. The performance of each is tested on standard soil samples prior to dispatch, to avoid any variation between the batches. All reagents have limited use-by dates and laboratories performing the analyses undergo frequent QA/QC testing. Weights, volumes, temperature, time, viscosity and solubility are closely monitored and all equipment is used once and discarded to avoid cross contamination. The solutions have been specifically designed to optimize the ICP-MS analytical method, and to present to the machine optimum analyte solutions for analysis thereby reducing interferences that can also introduce sources of error to the data.

Reproducibility

Numerous detailed studies have been undertaken to assess analytical reproducibility where repeat analysis of aliquot's of the same soil sample are tested and compared using the same analytical batch, and different analytical batches, over time. In both cases the technique has shown reproducibility characteristics as good as and usually far better than total and other partial digest techniques (Mann et al, 1997, Reproducibility of data in the MMI™ Process ®).

Data from individual soil samples collected pre- and post rainfall at two field sites, one over blind Au mineralization and the other a barren control site, also showed excellent reproducibility (MMI™ Technical Bulletin TB04, Repeat Sampling Study, Mt Gibson, Western Australia).

The MMI™ Process

The original concept of the MMI™ process was to provide a range of digest packages for specific commodities. For example, if an exploration company was exploring for base metals they would choose the MMI-A base metal package. The MMI-A package contained chemicals to specifically extract the following elements: Cu, Pb, Zn and Cd. However, there was no extraction of the adsorbed ions of Au. Hence, if a gold target was being explored, the client would then choose the MMI-B package. The MMI-B package contained chemicals to specifically extract the following elements: Au, Ag, Pb, Co and Ni. In many instances when clients were exploring for multiple commodity targets, two separate digests were required to provide information for all of the required elements.

As the technology progressed, various other extraction solutions were developed for other commodities: MMI-D for kimberlites (Ni, Cr, Co, Mg, Rb, Y, Nb and 8 REE elements); MMI-F for pathfinder elements (As, Sb, Bi, Hg, Te and Tl); and MMI-G for Granophiles and Pegmatites (U, Th, Pb, Ta, Sn and W).

Recently, a 45 element extraction solution was developed for multiple commodity exploration. This package is called MMI-M. The role of the MMI-M package is to provide exploration professionals with the flexibility to meet requirements for different commodities and geological settings. Examples include: particular commodity associations (Cu-Au mineralization); zonation patterns associated with mineralization (element halos around porphyries); alteration halos; specific lithological associations (geological set¬ting for Ni sulphides); and specific intrusive phases associated with diamond bearing minerals.

After several years of comparative testing between the commodity specific packages and MMI-M, as well as the added advantages listed above for the implementation as a successful geochemical tool, MMI-M is now the only digest package required for geochemical exploration. Therefore, use of the individual commodity specific packages has been discontinued. Furthermore, MMI-M is a more cost effective approach since it provides all client requirements with one package. This package can be further tailored to suit specific requirements with regard to choice of elements. Please consult your nearest laboratory for further details.

The table below shows the full list of elements ana¬lyzed in the MMI-M package (shown in red circle).

Research and Development

SGS Minerals Services is committed to the continued expansion and development of the MMI™ product, with respect to data interpretation and improvements to the analytical process. New research in the MMI-M technology has lead to lower detection limits as well as additional elements that have not previously been available due to parameters hindering the analysis. The improvements are based on advances in new instrumentation technology as well as the sample introduction phase. However, the chemical composition of the solution has not changed.

Certain exploration commodities require a lower detection level of chromium in order to effectively identify the MMI™ signature compared with background levels, e.g. nickel exploration or kimberlite deposits. This low level Cr (1ppb detection limit) is available under the package name MMI-ME. As there are additional costs associated with this analysis, prices will vary compared with the regular MMI-M package. Please consult your nearest laboratory for details.

For uranium exploration, the addition of vanadium to the MMI-M package can be valuable, since many uranium deposits are associated with particular vanadium bearing minerals. This add-on for vanadium is also available under the package name MMI-ME. As there are additional costs associated with this analysis, prices will vary compared with the regular MMI-M package. Please consult your nearest laboratory for details.

If required elements for the specific commodity of interest are not listed on our MMI-M table, or if you require recommendations on choosing elements for specific commodities, please contact Pierrette Prince, MMI™ Business Manager.

Sampling for MMI™

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 loose non-decomposed matter, debris, and any possible cultural contamination.
  
  
• Dig a small pit to penetrate the organic material that still has structure (i.e. decomposing leaves, bark, twigs and peat).
  
  
• Identify where the organics begin to decompose and you start to see soil formation. This is the true interface (organic / inorganic) at which to begin your measurements.
  
  
• Collect the sample between the 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 col¬lected 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 col¬lected 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, Journal and News Articles and Technical Bulletins to help with all your sam¬pling needs. Consultants are available for sampling assistance and/or interpretation.

Independent Comparisons

During the course of its development, many comparisons have been undertaken between MMI™ and many other techniques. Below are data reproduced from an independent study undertaken by CAMIRO over a Zn rich VMS deposit in Ontario, Canada. The full study can be obtained from CAMIRO or viewed on our Journal Articles page.

CAMIRO - Crosslake Soil Study, Line 40W, Ontario, Canada.

Comparison of Analytical techniques, Independent Report 8, 2001.



Contact Us

Pierrette Prince
MMI™ Business Manager
SGS Minerals Services
1885 Leslie St, Toronto, Ontario, Canada M3B 2M3

t: +1 416 445 5755
f: +1 416 445 4152
Email

MMI™ Laboratories

Canada
1885 Leslie Street, Toronto, Ontario, Canada M3B 2M3

t: +1 416 445 5755
f: +1 416 445 4152
Contact: Bernadette LeBoeuf

Peru
Avenue Elmer Faucett, 3348, Callao 1, Lima, Peru

t: +51 1 517 1970    
f: +51 1 574 1600
Contact: Maria Elena Napanga

Australia
10 Reid Road, Newburn, Western Australia 6106 Australia

t: +61 08 9373 3500    
f: +61 08 9373 3668
Contact: Michael Gerrard