Multiple generations of titanites and their geochemical characteristics record the magmatic-hydrothermal processes and timing of the Dongguashan porphyry-skarn Cu-Au system, Tongling district, Eastern China

• Published in: Mineralium deposita 2021-02, Vol.56 (2), p.363-380
• Main Authors: Xiao, Xin, Zhou, Taofa, White, Noel C., Zhang, Lejun, Fan, Yu, Chen, Xuefeng
• Format: Article
• Language: English
• Subjects: Copper; Crystallization; Dating; Earth and Environmental Science; Earth Sciences; Enrichment; Feldspars; Fluorapatite; Geology; Gold; Hydrothermal activity; Ilmenite; Inclusions; Lava; Mafic magma; Magma; Magma chambers; Magnetite; Mineral Resources; Mineralogy; Porphyry copper; Radiometric dating; Tin; Titanite; Vanadium
• ISSN: 0026-4598; 1432-1866
• DOI: 10.1007/s00126-020-00962-0

Dongguashan is one of the largest porphyry-skarn Cu-Au deposits in eastern China and titanite is found in the ore system. Five types of both magmatic and hydrothermal titanites are distinguished, based on their textural and chemical characteristics. Types 1 and 2 titanites are magmatic in origin whereas types 3, 4, and 5 are hydrothermal. Magmatic titanites are wedge-shaped and display concentric and sector zoning, whereas hydrothermal titanites show a wide range of textures that vary with different alteration stages. REE, Sn, Mo, and Cu are enriched in magmatic titanites (types 1 and 2). In contrast, vanadium and HFSE are enriched in hydrothermal titanites, especially in type 4 titanite from the propylitic alteration zone. Magmatic titanite (type 1) coexists with magnetite and K-feldspar and crystallized in oxidized and H 2 O-rich magma at 730–760 °C. Type 2 titanite contains ilmenite inclusions reflecting changes in the f O 2 of the magma chamber, possibly caused by input of mafic magma. The mobility and enrichment of HFSE and association with fluorapatite reflect the F-rich composition of the magmatic-hydrothermal fluid at Dongguashan. The relationship between titanite textures and chemistry indicates that titanite can serve as a recorder of magmatic-hydrothermal processes in porphyry copper systems. U-Pb dating of type 4 titanite from the propylitic alteration zone and type 5 titanite from skarn yielded ages of 139.0 ± 2.6 Ma and 137.0 ± 2.0 Ma, respectively, indicating that it formed synchronously with the associated quartz monzodiorite.