Gold itself is non-magnetic. Magnetic exploration in the search for gold is used to search for zones in which gold correlates with the content of a magnetic mineral, rock.

In this case, there may be cases that exclude this correlation. Therefore, in order to exclude false anomalies, additional data obtained by other methods are needed: electrical prospecting, gravimetry, metallometry, nuclear geophysics, and others.

Generally, more than two methods are used to validate and reconfirm information that has been obtained with some main method. A method by itself could be accepted, but geophysical exploration reduces risks and will reveal much more reliable anomalies for the next stage of drilling. Therefore, at least 2 methods should be chosen that can be used and respond with sufficient contrast to the characteristics of the deposit.

A magnetic survey will only find gold in special circumstances, where gold is associated with a magnetite-rich rock, where gold is associated with pyrrhotite, or where gold occurs in a de-magnetised zone. There are so many non-gold bearing rocks that create a magnetic anomaly, that using magnetics with no other technique is likely to be a money-waster, unless you are in a special area where gold is known to be associated with magnetic rocks.

Gold is not magnetic, and gold is often associated with pyrite or arsenopyrite that are also non-magnetic.

Magnetic surveys respond to pyrrhotite, magnetite, maghemite and native iron. Apart from them also non-ferromagnetic minerals like ilmenite, hematite, chromite and olivine intergrown with these ferromagnetic minerals may give a weak readout. You have first and foremost to determine how gold is related to lithologies rife with the afore-mentioned minerals and how the contrast is between barren wall/country rocks and host rocks. Unless this is done it is a bit of trial and error or poking in the fog. I suggest better to precisely investigate the host rocks of gold and then select the proper method from the classical methods such as gravimetry, electro-magnetic, electric, radiometric or seimsic methods. Another apprroach can be taken by using remote sensing techniques covering the full spectral range. Even in this case it is only the host rock or host structures which you can expect to receive a positive signal from.

HGD

Magnetic surveys are principally used in mapping lithologies and structural zones of deformation. The latter are critical in providing pathways for hydrothermal fluids, particularly around dilation zones creating by reactivated or intersected faults. Magnetic surveys are therefore principally used to determine the structural deformation history of an area and pin point structural exploration targets. Additional geophysical techniques are then employed to determine the presence of sulphides which commonly are associated with gold. Of particular use are for example IP, ERT surveys and the in-phase component of EM Surveys.

Dear all, so many thanks for your generous answer. Now I am very clear about why do we need supportive geophysical survey.

For those who still want to answer to this question, please do not hesitate to leave your answer. I really appreciate your knowledge contribution.

Thank you very much. Regards, Ong.

In general, geophysical surveys are always recommended to be complemented with eachother and ground truth data, as you are scanning the subsurface which is extremely heterogenous. In case of magnetometry survey of gold you need to keep in mind that magnetometry is sensitive to anomalies that have magnetic signatures. This means objects/materials that are comprised of Iron, Nikel Cobalt, etc. Now Gold is non-magnetic and actually this is one of reasons that it is expensive. Under these circumstances you do the Magnetic survey to look for gold-related anomalies such as partnered or Para genesis minerals of Gold and then you can relate that to gold. Thereafter you are advised to correlate your data with other techniques to clarify further. Methods such as: gravimetry, ERT, and specially induced polarization.