Geochemical Prospecting

Geochemical resource exploration is based on identifying anomalies in area; keeping in mind that the difference between the concentration an economic deposit is often more than 10-times higher the average concentration of the same element in a given area. Geochemical mapping could identify areas that may contain undiscovered resources.

Ideally, geochemical exploration is carried out in several phases, starting with a maximum surface area and low sampling density. The results of the first stage of sample will determine whether sampling proceeds to the next stage. If the results were promising, in the next phase, sample areas are considerably reduced, and the sampling density is correspondingly higher. A third stage may also be entered, where surface area and sample spacing change accordingly.

The choice of the sampling medium may change as the sampling density increases; flood sediments and mineral soil are among the natural choices in the initial phase, while the rocks, mineral soil, vegetation or water is often included in third phase sampling.

Avhengig av hvilke grunnstoffer man leter etter, velges metode for prøvebearbeiding og analyse. Pionerene i geokjemisk malmleting jaktet på forekomster med ett eller flere metallsulfider, hadde analysemetoder med langt mindre følsomhet og behov for innveiing av små prøver. De valgte arbeidsintensive metoder som utsikting av finstoff fra store prøver av bekkesedimenter eller mineraljord til materiale med partikkelstørrelse < 0,18mm eller < 0,06mm for å oppnå representativt uttak av små prøver, og benyttet salpetersyre (HNO3 – den løser opp alle sulfidmineraler) for å framskaffe en løsning for analyse.

The method of sample processing and analysis chosen depends on what element one hopes to find. The pioneers in the geochemical resource exploration searched for deposits with one to several metal sulphides, but their analytical techniques had less sensitivity and the weighing of small samples was challenging. They chose labour intensive methods such as utsikting of fine material from large samples of the Creek sediments or mineral soil to the material with particle size 0, 18 mm or < < 0, 06mm to achieve representative withdrawals of small samples, and used nitric acid (HNO3-it solves all of the sulphide minerals) in order to obtain a solution for analysis.

I dag benyttes oftest høyere partikkelstørrelse og innvekter, og analysemetodene er betydelig bedre med hensyn til følsomhet og antall grunnstoff som bestemmes er omtrent tidoblet.  Today, larger particle size and innvekter, and analysis methods are significantly better with regard to the sensitivity and the number of chemical elements that are determined is roughly tenfold.