U-Pb dating of columbite-bearing ores with a new columbite reference material

VON QUADT, A.; GILLONG, M. ; LAURENT, O.; PEYTCHEVA, I.; GALLISKI M. A.; BERMUDEZ, A.

Barcelona

Conferencia; Goldschmidt 2019 Barcelona; 2019

European Association of Geochemistry

Columbite-bearing ores are very difficult to date byconventional LA-ICP-MS U-Pb geochronology usingtechnique as there are no matrix matched standard referencematerials known (SRM). Several publications recentlypresented LA-ICP-MS ages of columbite, using zircon as theprimary SRM (Che et al., 2019), however zircon, monazite orother usual SRMs are most often lacking in columbitetantaliteore bearing veins and rocks.We investigated several SRMs to date columbite by theLA-ICP-MS U-Pb method, including zircon GJ-1 and theNIST610 glass. Due to differences in laser-induced elementfractionation and/or matrix effects, we observed inaccuracy ofcolumbite U-Pb dates by up to 10% appling these non-matrixmatched SRMs. Our project therefore aims at characterizing anew homogenous columbite reference material for U-Pbdating using the LA-ICP-MS and ID-TIMS techniques.Preliminary results show that 2 to 4 homogeneous singlecrystals (selected out of more than 20 localities) arepotentially suitable columbite SRMs. These show Pbrad/Pbcomratio and U content of 12.5 - 0.85 and 44 - 420 ppmrespectively. The 206Pb/238U ratios and corresponding agesreveal a 1 % uncertainty (SD). Our new SRM was tested oncolumbites from several deposits in Colombia and Argentina.The results show that using the new SRMs the columbite UPbdates are concordant and well defined with usualuncertainty less than 2%. They encourage the potentialapplication of this techniques and SRMs for dating of similartype of deposits over the world.Che, X.D. et al. (2019), Ore Geolpgy Reviews, 105, 71-85.