Indosinian isotope ages of plutons and deposits in southwestern Miaoershan-Yuechengling, northeastern Guangxi and implications on Indosinian mineralization in South China

Abstract

The Miaoershan-Yuechengling complex pluton is the largest granitoid complex in the western Nanling metallogenic belt with a surface exposure of >3000 km2. The complex pluton is composed of an early stage granitoid batholith and late stage small intrusions. The early stage batholith contains mainly medium-grained porphyritic mica granite and porphyritic monzonite granite, whereas the late stage intrusions are composed of muscovite granite porphyry and muscovite monzonitic granite. There are many W-Sn-Mo-Pb-Zn-Cu ores in the contact zone between the batholith and strata, forming an ore-rich belt around the batholith. Based on zircon LA-ICP-MS U-Pb ages, the southwestern part of the early stage batholith formed at 228.7 ± 4.1 Ma (MSWD = 2.49), with slightly earlier magmatic activity at 243.0 ± 5.8 Ma (MSWD = 2.62). The Yuntoujie muscovite granite was associated with W-Mo mineralization and has a zircon LA-ICP-MS U-Pb age of 216.8 ± 4.9 Ma (MSWD = 1.44). The Re-Os isochron age of molybdenite from the Yuntoujie W-Mo ore was 216.8 ± 7.5 Ma (MSWD = 11.3). Our new isotope data suggest that the late stage intrusive stocks from the southwestern Miaoershan-Yuechengling batholith were closely associated with W-Mo mineralization from the Indosinian period. These new results together with previous isotope data, suggest that South China underwent not only the well-known Yanshanian mineralization event, but also a widespread Indosinian metallogenic event during the Mesozoic period. Therefore, South China has a greater potential for Indosinian mineralization than previously thought such that more attention should be given to the Indosinian ore prospecting in South China.