Zirconium (Zr) is an important element in chemostratigraphy, due to its immobility and mineral links. So, which are the element-mineral links of Zr?
Zirconium (symbol Zr; atomic number 40; relative atomic mass 91.224) [Link to webelements.com]
Zr has one oxidation state, +4.
Zirconium is present in five naturally occurring isotopes (90Zr, 91Zr, 92Zr, 94Zr, and 96Zr), of which 90Zr is the most abundant one.
A common element substitution for Zr is hafnium (Hf) (both elements have very similar chemical behavior due to almost identical ionic radii: Zr4+ = 72 pm, Hf4+ = 71 pm).
In geochemical analysis, zirconium is commonly reported in its element form in parts per million [ppm]. Nevertheless, some analyses report it in its oxide form as ZrO2 (a.k.a. zirconia).
Common element-mineral links of Zr
Most common element-mineral link of Zr: zircon (ZrSiO4).
Zr in siliciclastic rocks
Zircon (ZrSiO4) is the most common Zr-mineral. Baddeleyite (ZrO2) is much rarer.
Zr can substitute for Ti in ilmenite, rutile, and sphene, and may be present in traces in amphibole, clinopyroxene, mica, and garnet.
Zircon, as a heavy mineral (density = 4.6 – 4.7 g/cm3, average = 4.65 g/cm3), is commonly most abundant in the silt to fine-sand size fraction.
Zr in carbonate and evaporite rocks
In carbonates, Zr concentrations are commonly very low and hosted in the non-carbonate fraction. It possibly can get enriched in stylolites. It may also be present as part of volcanic ashes. Hence, Zr may have a high potential for chemostratigraphic correlation (marker horizon).
Zr in igneous rocks
Zr enrichment is more common in felsic (particular intrusives) than mafic igneous rocks.
As mentioned above, Zr can substitute for Ti in ilmenite, rutile, and sphene. It may also enter the crystal lattices of amphibole, clinopyroxene, mica, and garnet during magmatic processes. It thus may be present in trace amounts in these minerals.
Although Zr is incompatible with the crystal lattice sites of most common rock-forming minerals. Limited Zr remobilization may happen during intense metasomatism and granite-related hydrothermal alterations.