LA-ICP-MS zircon U-Pb dating of important skarn type iron ( copper ) polymetallic deposits in Baingoin County of Tibet and geochemical characteristics of granites

With two important small skarn type iron (copper) deposits (Xueru and Chalangla) as the study objects, the authors made detailed field geological survey, collected samples and performed indoor rock appraisal, zircon LA-ICP-MS U-Pb dating and analysis of major and trace elements. The zircon LA-ICP-MS dating results of the metallogenic rocks are 79.72Ma±0.50Ma and 76.10Ma±0.40Ma, suggesting that late Cretaceous magmatism existed in Baingoin area. The contents of SiO2 are in the range of 70.45%～72.64%, the contents of K2O (4.62%～5.69%) are higher than that of Na2O (3.05%～3.75%), the contents of CaO (1.32%～2.03%) are somewhat lower, and the rock samples are rich in potassium. A/CNK ratios are lower than 1. The rocks belong to metaluminous series with A/NK ratios being 1.03～1.30. The rocks are characterized by high potassium. In the spider diagrams of rare elements, they are enriched in large ion lithophile elements such as Ra, Th, U and Nd and depleted in Nb. REE distribution curve is significantly rightly oblique. REE values range from 199.08×10－6 to 268.41×10－6, LREE/ HREE ratios range from 12.13 to 19.27 with medium negative Eu anomalies. The granites were formed in the same syn-environment and possessed favorable geological and geochemical conditions for iron copper polymetallic mineralization. Thus ore prospecting in this area is promising.