Geology & GeoMetallurgy

Geology & GeoMetallurgy 2017-03-23T09:44:23+00:00
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MMI Anomaly Definition (9 replies)

Rahil Khan
1 year ago
Rahil Khan 1 year ago

How much ppb to ppm can be considered as MMI anomaly for gold soil Geochem?

Bob Mathias
1 year ago
Bob Mathias 1 year ago

There are a few things you need to think about before trying to answer the question. You need to understand whether the gold occurrence is likely to be coarse or fine, whether the soil material plays nicely with the digestion method, how large the sample you have taken is, how large the analytical subsample is, whether the soil type varies in the survey area.

An anomalous result is a relative value really, so a threshold for an 'anomaly' depends on the background abundance you are trying to discern the anomaly from. Of course, if you get abundance close to a ppm, it is probably worth having a look at! 🙂

MMI can give quite variable results too, so have a look at how variable your field duplicate results are before getting excited over spot highs. Spatially clustered high results are more encouraging, but whether you see them will depend on your sample spacing relative to the likely target size.

Sturmbann
1 year ago
Sturmbann 1 year ago

Difficult question to answer. It will vary depending on your background values. One rule to follow is 10 times the background values (as seen in Canada) in other environment we have seen anomalies as high as 100 times background (Colombia).

Rahil Khan
1 year ago
Rahil Khan 1 year ago

Let me add something samples spacing is 50m interval by 100m and 150gm of samples need to send to the lab for analysis. How much really reliable of MMI for gold? Any good pdf or reading material would help Thanks!

Sturmbann
1 year ago
Sturmbann 1 year ago

MMI analyses are carried out on 50 gm unprepared soil sample. Please go to http://www.sgs.com, under Mining and Analytical Services you will find lots of info on MMI. Sampling is the 1st critical step in any survey.

Kumar Choudhry
1 year ago
Kumar Choudhry 1 year ago

"Anomaly" is a relative term. Converting ppb to ppm when sampling by indirect means is not very meaningful. Sampling of soil, in and of itself, is an indirect sampling process, as is MMI. When I was in school, the threshold for "anomaly" was the mean plus one standard deviation. "Highly anomalous" was the mean, plus two standard deviations.

It has been my experience that the absolute value of an element is not as useful as are combinations of anomalous elements in the same area. In one project in Africa, our soil sample team found gold in excess of 30 ppm in soil that had no gold mineralization in the underlying bedrock. The absence of (or highly variable concentrations of) As-Sb-W-Bi-Cu-Pb-Zn was an indication that things were not right, but you have to drill +30 ppm gold in soil to "see" what's there.

Carmen Ibanz
1 year ago
Carmen Ibanz 1 year ago

Depending on the geology of the area, absolute figures or numbers do not matter in soil anomaly. However, do not ignore point anomaly, but further field investigations should be conducted before any follow-ups. There is no point of converting ppb to ppm before deciding what to do. Once there is a trend or unusual anomaly after analysis, it is worth investigating.

Rahil Khan
1 year ago
Rahil Khan 1 year ago

I agree with you. I have also notice that some time anomaly zone fail to prove the Mineralization below.

Hauptsturm
1 year ago
Hauptsturm 1 year ago

It's interesting discussion. Where would come anomalies without mineralization?

Rahil Khan
1 year ago
Rahil Khan 1 year ago

Before you do or conduct any exercise in exploration you should really know about it. And specially in MMI or Geochemical samples some time it happen it show anomaly on the ground (top Soil) while you drilled you may miss out or you cannot get that anomaly. Shallow geochemical surveys to detect mineralisation beneath thick transported cover is a substantial challenge. There is no general agreement on mechanisms that are effective in vertical mobilisation of ions, especially through a thick unsaturated zone, and many factors may affect ion movement.

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