NATURAL GEOCHEMICAL ENRICHMENTS OF ELEMENTS

1. 1 NATURAL GEOCHEMICAL ENRICHMENTS OF ELEMENTS GLY 4241 - Lecture 3 Spring, 2011

2. 2 Important Low-Abundance Elements Elements used in steel alloys Vanadium, chromium, nickel, niobium Elements used in rechargeable batteries Nickel, cadmium, lithium Jewelery Gold, silver, platinum, palladium Nuclear fuels Uranium, thorium Miscellaneous Copper, used in wiring, plumbing, alloys Mercury, used in electrical switches, pesticides, fluorescent bulbs, etc.

3. 3 Definition of Ore The naturally occurring material from which a mineral or minerals of economic value can be extracted at a reasonable profit (from the Glossary of Geology, 3rd edition)

4. 4 Factors Influencing Cost of Metals Exploration Mining Rights Acquisition Cost of mining, Includes cost of compliance with existing environmental regulations Ore separation and processing Transportation of ore to consumer

5. 5 Frank Wigglesworth Clarke Early career involved teaching, including a year at Howard University Later, Chief Chemist, USGS Source: http://www.chem.howard.edu/~mfeldman/clarke.htmSource: http://www.chem.howard.edu/~mfeldman/clarke.htm

6. 6 Definitions Clarke = the average abundance of an element in the crust of the earth Clarke of concentration = the concentration of an element in a rock compared with its average concentration in the earth's crust, or of an element within a particular mineral

7. 7 Clarke of Concentration Clarke of copper is about 55 ppm, or 0.006% In the mineral chalcocite, Cu2S, the Cu concentration is 79.8% Thus, the clarke of concentration within this mineral is 79.8/0.006, or 13,300

8. 8 Clarke Values

9. 9 Exchange Reactions M + Fe silicate ? M silicate + Fe M + Fe sulfide ? M sulfide + Fe

10. 10 Goldschmidt Element Affinities Siderophile: Elements concentrated in the metallic phase, along with metallic iron Chalcophile: Elements concentrated in the sulfide phase Lithophile: Elements concentrated in the silicate phase Atmophile: Elements concentrated in the atmosphere

11. 11 Meteorite Phases Iron-nickel metal Troilite (sulfide) Silicate

12. 12 Geochemical Classification of Elements

13. 13 Siderophile Characteristics Elements whose valence electrons are not readily available for combination with other elements Positive charge on the nucleus, at least under certain conditions, exerts a strong attraction on the outer electrons, preventing combination These elements usually occur in the native state

14. 14 Chalcophile Characteristics Elements whose valence electrons may be shared, but are not electropositive enough to donate electrons or electronegative enough to accept electrons Thus, the bonds formed are predominantly covalent Since sulfur is much less electronegative than oxygen, sulfur is prone to form covalent bonds with these elements Generally the chalcophile elements have their valence electrons outside a shell of 18 electrons

15. 15 Lithophile Characteristics Elements that are strongly electropositive or electronegative and thus typically donate or accept electrons, forming ionic bonds Most silicate minerals have oxygen ions that can form ionic bonds to metal cations Generally the lithophile elements have their valence electrons outside a shell of eight electrons

16. 16 Atmophile Characteristics Elements that do not readily combine with other elements, or which form diatomic molecules held together in the solid or liquid states only by very weak Van der Waal forces All of the inert gases, with completed shells or subshells, fall into this category

17. 17 Oxygen Secondary atmophile element would not occur in the atmosphere of the earth if the earth were at chemical equilibrium Oxygen is maintained in the atmosphere only by the continual photosynthesis within the biosphere Indeed, the presence of oxygen in an atmosphere is often regarded as an indicator of life on the planet

18. 18 Atomic Volume vs. Atomic Number Vertical scale should be atomic volume Source: http://kr.cs.ait.ac.th/~radok/physics/fig844.gifSource: http://kr.cs.ait.ac.th/~radok/physics/fig844.gif