The molybdenite Re-Os isotope chronology, in situ scheelite and wolframite trace elements and Sr isotope characteristics of the Chuankou tungsten ore field, South China

Abstract The Chuankou tungsten ore field, situated in the central area of the Qing-Hang ancient suture zone in South China, is characterized by predominantly quartz vein-type tungsten mineralization that formed near the contact between the Chuankou granite and slightly metamorphosed silt-bearing sericite slate. Based on field work, cathodoluminescence, molybdenite Re-Os dating and in situ laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis, the Chuankou tungsten ore was formed at 230.6 ± 2.9 Ma to 229.4 ± 2.6 Ma in a typical Indosinian metallogenic event. In addition, three distinct generations of scheelite and two types of wolframite can be clearly distinguished. Type 1 wolframite has a semiautomorphic grain or brecciated vein structure with a high heavy rare earth element (HREE) content and an obvious negative Eu anomaly. Type 2 wolframite grains are strongly altered as residual-pseudomorphic structures by ore-forming fluids and have relatively low REE contents. Sch-1 scheelite is present in the interior of the type 2 wolframite grains. The Sch-1 scheelite grains have an elevated REE content and low 87Sr/86Sr ratios with a strongly negative Eu anomaly, which suggests an inheritance signal of the host rocks. Comparatively, Sch-2 and the altered Sch-1 scheelite have characteristic extremely low REE contents and remarkably strong positive Eu anomalies. These scheelites also have increased 87Sr/86Sr ratios and low 88Sr signals. Sch-3 is idiomorphic with perfect oscillating zoning. The REE content of Sch-3, which typically has the lowest 87Sr/86Sr ratios, is higher than those in Sch-1 and Sch-2, and the extremely high 88Sr signals indicate a distinct thermal fluid event that was directly derived from the host rock. The correlations between the REE and Nb of scheelite imply a type B-substitution of Sch-1 and Sch-2 but a type C-substitution for Sch-3. The correlation of EuN and EuN* shows an Eu3+ substitution process for stages Sch-1 and Sch-2 and an Eu2+ substitution process for stage Sch-3. Thus, we confirm that ore-bearing hydrothermal rocks must undergo early-stage metasomatism and filling, middle-stage fluid mixing between wall rocks and magmatic hydrothermal activity, and refilling of late-stage magmatic hydrothermal activity during the metallogenic process. During the Indosinian period, the mineralization stages of polymetallic deposits in the Indosinian were composed of Stage 1 (240 to 220 Ma) and Stage 2 (220 to 200 Ma). The Chuankou tungsten ore field can be considered as the typical representation of the Stage 1 metallogenic event in South China. This ore field is derived from remelting of the ancient basement and was reduced by regional extension under the dominant compression regime in the South China Block.