PETROGENESIS, PALEOTECTONIC SETTING, METALLOGENY OF MASHHAD PALEO-TETHYS GRANITOIDS, IRAN
The total REE content of the tonalite is 101 -136 ppm, feldspar monzogranite 221-238, and leucogranite 130-170. (La/Yb)N = 37-124 for leucogranite, and 7- 22 for tonalite-granodiorite. The (Eu/Eu* = 0.55 to 1.1).
Tonalite magma originated from a mafic source, feldspar monzogranite from a deeper source, was contaminated in the crust, and leucogranite from a psammite source. High concentrations of Ba (850 - 1100 ppm) and MgO, and higher K2O/(CaO+Na2O) ratios in leucogranite indicate that the source rock was enriched in K-feldspar, muscovite, and biotite and that all K-feldspar, muscovite and some biotite were melted. The Sn, W, and Au contents of all intrusive rocks are low. For all intrusions, Au = 10 - 15 ppb, Ag < 40 ppb, W = 1.5 - 5.4 ppm, Mo = 1 - 2 ppm, Sn 1 - 15 ppm, and F = 700 - 800 ppm.
Since the Mashhad granitoids are S-type, but contain no Sn, W or Au, a comparison was made of major, trace and rare earth data for granitoids associated with Sn worldwide, including Australia, China, Brazil and Thailand. The latter were found to have Sm/Eu 10 - 100 ppm, whereas this ratio is <10 for all the Mashhad granitoids. This ratio should be useful for exploration.