Mineral Exploration Geochemistry: Soil Sampling Methodology
We evaluate “systematic soil sampling“, one of the most common geochemical methods used in mineral exploration activities, which is not talked about much. If we master the criteria and origins on this very relative issue, we can perform the sampling properly, make the interpretations correctly, and approach the conclusion we need to reach quickly.
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If the area where you work is dominatedly rocky or plowed fields, or if the mineralization probability you expect is at considerable depths and if it is stated by expert opinion that soil sampling will not work, it is strongly recommended that you do not waste time with soil sampling.
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1. Soil sampling will determine the scanning direction of the exploration methods you are going to apply in the area you focus on
If you have decided that “soil sampling will work” for your project, just mount the grid and do the sampling correctly.
2. Create your mineralization concept with general assumptions and element zoning at the source
If you are after an intrusion-based mineralization, evaluate the mineralization potential by considering the precipitation order of metal-containing volatiles from the magma, or in other words, the element zoning in the fertile magma.
Examine which elements move together proportionally in your analysis records.
Alkali (Li, Na, K, Rb, Cs), Alkali Earth (Be, Mg, Ca, Sr, Ba), and Sc, Y values will take you somewhere on a regional scale. Only if you direct your exploration project based on these will you be able to find element associations in multiple phases. You will ignore it.
Always keep in mind elements with high mobility after source intrusion (such as Mo).
If possible, you can estimate the direction of the mineralization by following the rock-forming element similarities of the source intrusion.
Keep the representation of lithophile, siderophile, chalcophile groups on the periodic table (Goldschmidt classification).
3 . The rock samples you reasonabily collect will point out the elements you should trace
Group the rock samples based on the lithology you collect, record the details on the sample form, and implement ore microscopy studies if necessary.
Examine which elements move together proportionally in your analysis results.
Keep the representation of lithophile, siderophile, chalcophile groups on the periodic table (Goldschmidt classification).
4. Important Notice: Make the legend manually, use histograms, determine the thresholds and ranges by testing
Let’s try a simple experimental method that anyone can implement to make an efficient legend for coloring the points, you just need to know how to open the “Excel” program (Check out section in the video for a few seconds). There is no formula for anomaly, there is no clear criterion. Determine the legend ranges and achieve results with your knowledge, experience and mastery of the project.
Examine the soil sample results that are automatically colored by the software and colored according to different legends made manually with geostatistical interpretation.
Abnormal values from faults and drainage channels should be excluded from evaluation, if necessary.
There may be metal enrichments in different phases that are at a perpendicular angle to your current mineralization trend. The structure generally develops a phase perpendicular to the mineralization, which is likely to be mineralized. You can also detect different trend directions by examining the statistical co-movement of elements.
Important Note: Incorporating statistics more and analyzing and interpreting experimental data can make such big differences that you have never thought of. Do not neglect, show your data to a competent person.
5. Evaluate soil sampling in 3D
Do not decide on your work without examining the samples on topography in 3D.
The location represented by the soil sampling you took from the sloping field will most likely be above the slope.
Draw conclusions from your sampling, taking into account meteorological conditions and topography (gravity).
6. Metals can be transported and mixed into the soil under the influence of topography - meteorological events and faults - drainages by groundwater
Study the dominant geomorphology of the region, soil formation will not be homogeneous at all levels until the actual topography, you must have certain assumptions for this.
Remember that the trace amounts of metal carried by groundwater moving along fault surfaces are even more effective than capillarity.
Also, young and narrow valleys where the soil is washed down will also drag metals into other drainage channels.
7. Understanding capillarity will be useful both before and after soil sampling
Just as the solubility of each metal in water is different, the metal concentration of groundwater in each region is also different. You will see this even when you look at the chart on the back of the plastic bottles of water you drink. Therefore, some metals associated with mineralization can help you trace even if they are not in the ore mineral.
Generally known and intended for the soil you sampled; the aim is to determine the places where the ore is thought to have eroded from the covered ore body after it has surfaced.
However, another element that is not well known but is very important will affect your entire evaluation: Capillarity.
It is quite possible that minerals belonging to an uneroded mass at depth will dissolve in groundwater and settle close to the surface by capillarity. With a similar logic, sampling in soils affected by groundwater in fault zones would also be quite misleading. Or from now on, when you look at it from this perspective, fault zones may lead you in the right direction.
We use the phenomenon of “capillarity” to represent the capillarity that carries groundwater upward in the vertical direction. Being able to predict what capillarity can do will allow us to achieve the optimum level during sampling and get closer to reality when evaluating all results.
8. More Important Notice: The one who picks up the pickax, say it loudly, and those who hear it should not move around.
Safety first, good luck.
Subjects discussed in this article may overlap with your mineral exploration, modeling, mining operation and business development issues and may provide solutions for those. However, remember that various factors specific to your business may bring about different challenges. Therefore, seek support from expert consultants to evaluate all data together in order to convert potential into profit most efficiently.
Should you have any questions regarding the articles or consulting services, please don’t hesitate to get in touch with us.
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