Geochemical Prospecting: Trace Element Dispersion, Pathfinders and Sampling Methods for Mineral Exploration
Classified in Spanish
Written on in 
English with a size of 4.27 KB
Objective of prospecting: to discover anomalous spatial distribution patterns of chemical elements related to concealed mineralizations.
Primary dispersion: occurs during the formation of the deposit, through the processes of dispersion.
Secondary dispersion: erosion and transport.
Indicator element: the use of the presence of geochemical animals.
Contrast: the concentration of the element of the anomaly.
Mobility and Behavior of Key Elements
As: mobile, []xFe, indicator of Au.
Ba: low mobility; used in panning studies.
Cr: low mobility; panning to search for chromite.
Co: moderate mobility; absorbed by Mn hydroxides.
Cu: low mobility at pH > 5; moderately low below.
Pb: low mobility.
Mn: moderately mobile and highly mobile at acidic pH; [] Co, Zn and Ag.
Hg: high mobility; search for sulfides.
Mo: moderate to high mobility, especially in basic media (pH > 10).
Ni: low mobility; may be [] by Fe and Mn oxyhydroxides; found in ultramafics.
Sn: very low mobility; cassiterite via panning.
W: low mobility; scheelite; fluorescent under UV.
U: in 4+ state not mobile; in 6+ state very mobile and soluble in water; absorbed by organic matter; used in water analysis.
Zn: high mobility; absorbed by Mn oxyhydroxides.
Fine Fraction Sampling
Fine fraction: average and representative; presents greater contrast between anomaly and background for metals.
Fluvial Sediment Sampling
The elements most analyzed are:
- Semi-mobile: Zn, Ni, Cu, Co
- Immobile: Au, Sn, W (panning is used)
Ao horizons: reflect the chemical composition of the vegetation, which is of interest.
A1 horizon: clay minerals, Fe and Mn oxyhydroxides.
Chernozems: no leaching; Cu accumulates in A1 and A2 horizons.
Laterites: direct B horizon.
Water Sampling
Water study: mobile dissolved elements are studied.
Zn, Cu: form soluble cations.
U, Mo, W: anions.
Filtration: studied mainly over Zn and Cu anomalies.
Geobotanical and Biogeochemical Methods
Geobotany: identify plant species that grow preferentially on soils with certain metals (plant indicators).
- Changes in morphology, color and diseases.
- Biogeochemistry: chemical analysis of plant parts.
- Always study the same plant and part; [] depends on the species and the part.
- Age.
- Phreatophytes: large root system.
- Seasonal variations.
Gas Studies
- Sulfur prospecting: study of Hg vapor and volatile S compounds.
- Natural gas and petroleum: study of methane.
- Uranium: study of radon emanation.
Problems of Representativeness and Individual Sampling
Analytical errors are well controlled; the most serious problems are due to sampling errors.
- Biased sampling: the composition of the sample is not representative of the outcrop.
- Unbiased sampling: the mean composition of the population coincides with the mean of the sample taken.
Procedures:
- Composite sampling: 5-8 samples are collected and the mean and variance are calculated, or everything is mixed and the mean composition is determined (the variance cannot be determined in this case).
- Duplicates: 2 samples of each of about 30 and statistical analysis of the variance.
- Unbiasedness: if the sampling variance is much smaller than the population variance.