The genesis of the rare-metal greisen Tigrinoe ore-deposit (Sikhote-Alin, Russia): Sm-Nd and Rb-Sr isotope constraints

Abstract

The Tigrinoe ore-deposit is a typical stockwork greisen Sn-W ore-deposit, which is supposed to be connected with typical Li-F rare-metal granites. The granites form two intrusive stocks: the early Upper stock of protolithionite granite and granite-porphyry and the late Lower stock of zinnwaldite granite. Due to the present Sr-Nd isotope study it was shown that the ages of protolithionite granite and zinnwaldite granite stocks are indistinguishable within age error limits and equal to 80-86 Ma. This age range corresponds to a magmatic intrusion and autometasomatic process. The granites were formed under mixing of the material of the crustal Proterozoic-Paleozoic basement and depleted subcontinental mantle, share of the mantle component for protolithionite granites amounts to 40-50%, for zinnwaldite granite >80%. The fluorite and wolframite vein mineralization dated by Sm-Nd isotope method at 82 Ma was soon after zinnwaldite granite stock crystallization. The fluorite and wolframite from the same ore veins have extremely different initial isotope composition of neodymium and strontium. The fluorite was formed from the same sources, as the source of rare-metal granites, but another sources took part in wolframite formation, including the host schist and some unidentified component, which may be represented by material from continental lithospheric mantle or some unexposed Mesozoic volcanic rocks.