Genesis of the Nanyangtian scheelite deposit in southeastern Yunnan Province, China: evidence from mineral chemistry, fluid inclusions, and C–O isotopes

• Published in: Acta geochimica 2018-08, Vol.37 (4), p.614-631
• Main Authors: Cai, Qianru, Yan, Yongfeng, Yang, Guangshu, Jia, Fuju, Li, Chao
• Format: Article
• Language: English
• Subjects: Calcite; Calcium magnesium silicates; Chemistry; Diopside; Earth and Environmental Science; Earth Sciences; Fluid inclusions; Fluids; Geochemistry; Homogenization; Isotopes; Lasers; Magma; Magmatic water; Meteoric water; Mineralization; Minerals; Original Article; Quartz; Scheelite; Veins (geology)
• ISSN: 2096-0956; 2365-7499
• DOI: 10.1007/s11631-017-0257-0

The Nanyangtian skarn-type scheelite deposit is an important part of the Laojunshan W–Sn polymetallic metallogenic region in southeastern Yunnan Province, China. The deposit comprises multiple scheelite ore bodies; multilayer skarn-type scheelite ore bodies are dominant, with a small amount of quartz vein-type ore bodies. Skarn minerals include diopside, hedenbergite, grossular, and epidote. Three mineralization stages exist: skarn, quartz–scheelite, and calcite. The homogenization temperatures of fluid inclusions in hydrothermal minerals that formed in different paragenetic phases were measured as follows: 221–423 °C (early skarn stage), 177–260 °C (quartz–scheelite stage), and 173–227 °C (late calcite stage). The measured salinity of fluid inclusions ranged from 0.18% to 16.34% NaCleqv (skarn stage), 0.35%–7.17% NaCleqv (quartz–scheelite stage), and 0.35%–2.24% NaCleqv (late calcite vein stage). Laser Raman spectroscopic studies on fluid inclusions in the three stages showed H 2 O as the main component, with N 2 present in minor amounts. Minor amounts of CH 4 were found in the quartz–scheelite stage. It was observed that the homogenization temperature gradually reduced from the early to the late mineralization stages; moreover, δ 13 C PDB values for ore-bearing skarn in the mineralization period ranged from − 5.7‰ to − 6.9‰ and the corresponding δ 18 O SMOW values ranged from 5.8‰ to 9.1‰, implying that the ore-forming fluid was mainly sourced from magmatic water with a minor amount of meteoric water. Collectively, the evidence indicates that the formation of the Nanyangtian deposit is related to Laojunshan granitic magmatism.