There are no limits for natural occurrence of elements in rocks and minerals.

You will find answers (for selected mineral species) in the huge publication:

Handbook of Geochemistry by K.H. Wedepohl et al. (Editors) , publisher: Springer, Berlin (1969)

Best regards

Guenter Grundmann

If your question relates to the trace of radioactive elements in rocks and minerals, the answer can be found in the literature on NORMS (Natural Occuring Radioactive Materials).

http://www-pub.iaea.org/MTCD/Publications/PDF/Pub1326_web.pdf http://www-pub.iaea.org/books/IAEABooks/8557/Naturally-Occurring-Radioactive-Material-NORM-VI https://www.iaea.org/publications/10675/naturally-occurring-radioactive-material-norm-vii

Once trace elements are below detection level, their impact environmentally is minimal compared to when you have them in high concentrations within the rock or mineral especially in mining environments.

Hi,

another source of information is the UNSCEAR document about natural radioactivity in different materials, such as soil, rock, air, ecc...UNSCEAR 2000 is very complete. This document only for natural radioactivity.

About artifical radiaoctivity the best document are these of IAEA, like suggest by other colleagues.

Dear Mr. Masoud:

The technical term “trace element” is not very well defined as to the quantity ( < 1 wt % ?) and can only roughly be explained as an accessory element accommodated in the lattice or adsorbed on the surface of minerals without affecting the crystal structure or its morphology.

In host rocks the situation becomes vaguer and often depends on the effect such quantities of elements have as to the exploitation of these rocks (even ore is a rock!) or whether these elements may provoke a health issues for all living beings.

With this in mind I would like to confine my statement to the elements U and Th referred to in your question. To make the wheal full circle in this case I direct your thoughts to the brochures and publications of the IAEA (International Atomic Energy Agency) a sub-agency of the United Nations which takes care of all the various aspects of the use of radioactive material.

With kind regards

H.G.Dill