World Placer Journal - 2000 - Volume 1, pages 160-174. | ||
Tantalum-tin placers are being shed by Ta-rich albitite plutons associated with tin granites.... | ABSTRACT The Urt Gozgor (‘Long Peak’) Placer near Ulaanbaatar is a Ta-Nb-Sn-Ti-REE-Au placer traceable up-valley to its source rocks (except for the problematic gold). The source rocks are with a multistage pluton, beginning with porphyraceous coarse-grained granites in the core, two-mica medium-grained granites and alaskites (K-feldspar alkaline biotite granite). Each granite is a different stage of magmatic differentiation, and are classed as S-type granites. The second stage of the pluton began with crystallisation of miarolic pegmatite, followed by tin (Sn) greisen and Sn-Ta-Nb-Li magmas. The magmas were highly differentiated and crystallised as amazonite-albite granite, microcline-albite granite and lepidolite-albite granite, collectively known as lithium-fluorine (Li-F) granite or tantalum (Ta) granite. These are classifiable as A2-type granitoids due to higher Y/Nb ratios of 1.2-7 and highly variable Sr87/Sr86 ratios. The Li-F granites were emplaced as the end members of magmatic differentiation after continent-continent collision between Siberia and Central Asia, and closure of the Mongol-Okhotsk Ocean in Mesozoic times. The source of the Urt Gozgor tantalite is coarsely-crystalline albitite, part of the multistage pluton. Past hard rock drilling is not adequate. The focus is the Urt-Gozgor Ta/Sn placer with proven reserves of tantalite and cassiterite ready to mine, plus some gold. | |
 | GRANITE TOR... typical of the tin zones of Mongolia. Outcrops are generally good, covered by thin mantle of colluvial. | |
 | OLD TRIAL PITS... the Soviets pitted the tanalite-tin placers but did not mine them. The pits are visible at Urt Gozgor decades later, and results are in the State archives. | |
 | OLD AIR PHOTOS... trial pits for tin and tantalite are visible. Old trial pits are easily found because the rate of landscape change is slow. | |
