Abstract:

IOCG deposits usually preserve evidence of multiple hydrothermal events and superimpose processesdue to their prolonged geological history. Consequently, establishing precise constraints on the sourcesand ore-forming processes of IOCG deposits is challenging. Recently, the in-situ Laser Ablation MultiCollector Inductively Coupled Plasma Mass Spectrometry (LA-MC-ICPMS) technique has been widelyused in dating and tracing hydrothermal ore deposits with complex evolutionary histories. In this study, weapply in-situ LA-MC-ICPMS Nd isotope analysis to two types of titanite from the Sin Quyen IOCG depositin northwestern Vietnam to decipher the origin and ore-forming processes of the giant rare earth element(REE) and Fe-Cu deposit. Type 1 titanite (Ttn1) consists mainly of euhedral to subhedral crystals, withdiameters ranging from 0.5 to 2 mm, closely associated with amphibole and allanite. In contrast, type 2titanite (Ttn2) is characterized by uniform, fine grains closely associated with magnetite and chalcopyrite.Ttn1 displayed εNd(t) values ranging from −6.4 to −5.7‰, overlapping with the Nd values of the meta-sedimentary basement rocks at Sin Quyen deposit. Conversely, Ttn2 yielded values within the range of−4.3 to −2.0‰, similar to felsic intrusions in the region. The significant variation in Nd isotopes betweenthe two types of titanite at Sin Quyen indicates different sources contributing to the REE and Fe-Cumineralization at the Sin Quyen deposit. This finding may inspire other IOCG deposits with complexevolutionary histories.