Abstract: Shangshuiqiao fluorite ore is a newly discovered medium fluorite deposit with great exploitation prospect in northern Wuyi area in recent years. However, little research has been carried out on this deposit. In this paper, petrographic, zircon U-Pb chronological and whole-rock geochemical analyses have been carried out on the biotite quartz monzonite from the the Shangshuiqiao fluorite deposit. The zircon LA-ICP-MS U-Pb ages show that the biotite quartz monzonite was formed at  235~236 Ma, which is the product of Indosinian magmatism. According to the geochemical analyses, the biotite quartz monzonite samples are characterized by high alkali (Na2O+K2O), Mg and Fe contents and low P and Ti contents. They have high σ values (2.59 and 3.61) and low A/CNK ratios (0.96 to 1.16), belonging to the typical high-K series with metaluminous to weakly peraluminous. In terms of trace and rare earth elements, the biotite quartz monzonite is enriched in Rb, Th, U, K and light rare earth elements (LREEs), but depleted in Ba, Sr, Nd, Ta, P, Ti and heavy rare earth elements (HREEs), as well as high rare earth elements (ΣREE varying from 356×10-6 to 448×10-6) and weak negative Eu anomalies (Eu/Eu* between 0.61 and 0.76). Besides, the biotite quartz monzonite displays high Zr+Nb+Ce+Y content (varying from 381×10-6 to 546×10-6) and Ga/Al ratio (104×Ga/Al between 2.60 and 3.07), with lower Rb/Sr (0.31 to 0.82), Rb/Ba (0.11 to 0.18) and TFeO/MgO ratios (2.02 to 2.22), belong to post-orogenic (PA type) aluminous A-type granites. In addition, based on the results of geochemical mapping and characteristics of regional magmatism and sedimentation, we suggest that the biotite quartz monzonite from Shangshuiqiao fluorite deposit may be formed in the postorogenic extensional tectonic environment at the end of intracontinental orogeny under the background of multi-plate convergence. During the mineralization stage, the biotite hydrolysis and sericitization of plagioclase in biotite quartz monzonite may provide F and Ca sources for fluorite mineralization.

Key words: north Wuyi area, Shangshuiqiao fluorite deposit, Indosinian, aluminous A-type granite, petrogenesis