Ore genesis of the Baishizhang Mo(-W) deposit in the Nanling Range, South China: Constraints from wolframite geochronology and chemical composition

Abstract

The South China Block (SCB), as one of the most important molybdenum metallogenic provinces in China, contains >40 Mo deposits including porphyry, skarn, and quartz-vein systems. In this work, we examine the ore geology and wolframite chemistry of the Baishizhang (BSZ) quartz vein-type Mo(-W) deposit in the Nanling Metallogenic Belt, using in-situ laser ablation-inductively coupled plasma-mass spectrometric (LA-ICP-MS) analysis of U-Pb isotopes and trace elements. The hydrothermal history of the BSZ deposit can be divided into three stages (i.e., quartz-wolframite, sulfide, and calcite), the first two of which are the two main mineralization stages and wolframite shows petrological evidence for these two stages. Wol(I) yielded a U-Pb age of 154.0 ± 1.2 Ma (1σ; n = 20; MSWD = 0.86) and Wol(II) ages of 150.8 ± 0.5 Ma (Wol(II-1);1σ; n = 19; MSWD = 1.0) and 146.1 ± 2.3 Ma (Wol(II-2); 1σ; n = 12; MSWD = 2.6), bracketing the transition from the quartz-wolframite stage to the sulfide stage. The Wol(II-1) mineralization may be genetically related to emplacement of biotite K-feldspar granite (150.3 ± 1.1 Ma), and the large-scale Mo mineralization may be related to deep concealed granites at BSZ. Our results show that the composition of wolframite was constrained by both crystallochemical effects and the composition of the mineralizing fluid, and that the substitution mechanisms controlling the chemical compositions of Wol(I) and Wol(II) were different. Wol(II) exhibits changes in composition and Eu anomaly from the core to the rim, likely reflecting the influence of an external reducing fluid enriched in Sn and Mo from concealed granites that caused Mo mineralization. A metallogenic model of the BSZ deposit can be applied to better interpret the various formation processes of the two main mineralization stages.