Abstract
ABSTRACT The newly discovered Liuzhangshan (LZS) Rb deposit is a large granite-type deposit in the West Qinling Orogenic Belt (WQOB), spatially associated with biotite monzogranite. Previous research has focused on the geological characteristics and metallogenic conditions of the LZS Rb deposit; however, its geochronology and petrogenesis remain unclear. In this study, monazite U-Pb dating of biotite monzogranite in the LZS deposit yielded a U-Pb age of 200.8 ± 0.9 Ma via laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Combined with the age of magmatic rocks in the WQOB, we propose a potential mineralization event related to Rb around 200 Ma in the WQOB. The biotite monzogranite belongs to weakly peraluminous, high-K calc-alkaline serious, containing high SiO2, Na2O, K2O, and low FeO, MgO, CaO, and P2O5. Compared with primitive mantle and relatively unfractionated granodiorites found in the WQOB, the biotite monzogranite enriched in Rb, Th, U, and Pb, deleted in Ba, Sr, and Ti, and showed negative Eu anomalies, a high Rb/Sr ratio, and a low K/Rb ratio, an ∑REE of 31.3 ppm, an LREE/HREE ratio of 6.48, a LaN/YbN ratio of 2.59, an Mg# of 4.15, and a crystallization temperature of 760°C, the biotite monzogranite also had a high differentiation index (DI = 98.2), apparent tetrad effect (TE 1,3 = 1.12 ~ 1.15), characteristic of highly fractionated I-type granite. Monzoite from the biotite monzogranite in the LZS deposit has negative εNd(t) values ranging from −12.45 to −11.17, and TDM1 of 1569 ~ 2018 Ma, indicating that the LZS biotite monzogranite originated from the partial melting of a Mesoproterozoic ancient basement material, with a minor contribution from mantle-derived melts. Highly differentiated, low Sr and Yb contents, Sr/Yb ratios, and low crystallization temperature magma facilitated the enrichment of Rb.
Published Version
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