Dual-mineralization in the intracontinental Jiangnan Orogen, South China: Evidence from textures and in-situ trace elements and oxygen analysis of quartz from the Woxi Au-Sb-W deposit

Abstract

The Jiangnan Orogenic Belt (JOB), situated in the interior of the South China Block (SCB), harbors numerous gold-polymetallic deposits, but the ore genesis has been a long-standing controversy. This study examines the Woxi super-large gold deposit in the middle JOB, which is characterized by simultaneous large-scale antimony-tungsten mineralization. The investigation shows that the Woxi ore deposit have developed multiple-stage quartz, i.e., Qz1 (early quartz-carbonate, stage I), Qz2 (quartz-wolframite-scheelite, stage II), Qz3a (quartz-gold-pyrite, early stage III), Qz3b (quartz-stibnite-scheelite, late stage III) and Qz4 (late quartz-carbonate, stage IV). We conducted SEM-CL texture imaging, LA-ICP-MS trace element, and SIMS oxygen isotope analysis on the quartz samples from the main mineralization stages (mainly Qz2 and Qz3). The results reveal a dual mineralization process of the Woxi gold-antimony-tungsten deposit. In the initial stage, the quartz (Qz2) exhibits intense brightness in CL imaging and spiderweb-like texture, shows high concentrations of trace elements, especially Ge, Al and Ti, and has δ18Ofluid values ranging from 10.84 ‰ to 11.64 ‰. These characters are consistent with a magmatic fluid that is acidic (pH<3), reducing, and of relatively high-temperature. In the second stage, the quartz (including Qz3a, Qz3b and Qz4) shows relatively darker CL image and band texture or cobweb mosaic coexistence texture, low concentrations of trace elements, especially Al and Ti, and a low δ18Ofluid values (8.01 ‰ to 9.19 ‰ for Qz3a and 5.83 ‰ to 6.51 ‰ for Qz3b) consistent with characteristics of mantle-derived fluids. The results of this study supports an “intracontinental reactivation metallogenic model”, in which the gold-polymetallic deposits in the JOB formed from a dual-stage mineralization related to tectono-magmatic activities in a back-arc setting. The dual ore-forming processes revealed in this study provide important insights for a comprehensive understanding of the gold-polymetallic deposits in the JOB, and it may be a significant mechanism in the formation of large to super-large gold-polymetallic deposits in this region, which is indicative perspective for exploration of the gold-polymetal deposits. Our work also demonstrates that quartz is an effective tool for identifying the mineralization in the JOB.