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Genesis of the Gold Deposit in the Indus‐Yarlung Tsangpo Suture Zone, Southern Tibet: Evidence from Geological and Geochemical Data
Author(s) -
ZHANG Xiong,
DENG Xueguo,
YANG Zhusen,
HOU Zengqian,
ZHENG Yuanchuan,
LIU Yingchao,
ZHAO Xiaoyan,
XU Bo,
PEI Yingru,
ZHOU Jinsheng,
ZHAO Miao,
YUAN Jianfei
Publication year - 2017
Publication title -
acta geologica sinica ‐ english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.444
H-Index - 61
eISSN - 1755-6724
pISSN - 1000-9515
DOI - 10.1111/1755-6724.13318
Subject(s) - diorite , geology , geochemistry , quartz , metamorphic rock , epidote , meteoric water , ultramafic rock , fibrous joint , mineralization (soil science) , zircon , chlorite , paleontology , medicine , soil water , soil science , hydrothermal circulation , anatomy
The Nianzha gold deposit, located in the central section of the Indus‐Yarlung Tsangpo suture (IYS) zone in southern Tibet, is a large gold deposit (Au reserves of 25 tons with average grade of 3.08 g/t) controlled by a E–W striking fault that developed during the main stage of Indo‐Asian collision (∼65–41 Ma). The main orebody is 1760 m long and 5.15 m thick, and occurs in a fracture zone bordered by Cretaceous diorite in the hanging wall to the north and the Renbu tectonic mélange in the footwall to the south. High‐grade mineralization occurs in a fracture zone between diorite and ultramafic rock in the Renbu tectonic mélange. The wall‐rock alteration is characterized by silicification in the fracture zone, serpentinization and the formation of talc and magnesite in the ultramafic unit, and chloritization and the formation of epidote and calcite in diorite. Quartz veins associated with Au mineralization can be divided into three stages. Fluid inclusion data indicate that the deposit formed from H 2 O–NaCl–organic gas fluids that homogenize at temperatures of 203°C–347°C and have salinities of 0.35wt%–17.17wt% NaCl equivalent. The quartz veins yield δ 18 O fluid values of 0.15‰–10.45‰, low δ D V‐SMOW values (−173‰ to −96‰), and the δ 13 C values of −17.6‰ to −4.7‰, indicating the ore‐forming fluids were a mix of metamorphic and sedimentary orogenic fluids with the addition of some meteoric and mantle‐derived fluids. The pyrite within the diorite has δ 34 S V‐CDT values of −2.9‰–1.9‰ (average −1.1‰), 206 Pb/ 204 Pb values of 18.47–18.64, 207 Pb/ 204 Pb values of 15.64–15.74, and 208 Pb/ 204 Pb values of 38.71–39.27, all of which are indicative of the derivation of S and other ore‐forming elements from deep in the mantle. The presence of the Nianzha, Bangbu, and Mayum gold deposits within the IYS zone indicates that this area is highly prospective for large orogenic gold deposits. We identified three types of mineralization within the IYS, namely Bangbu‐type accretionary, Mayum‐type microcontinent, and Nianzha‐type ophiolite‐associated orogenic Au deposits. The three types formed at different depths in an accretionary orogenic tectonic setting. The Bangbu type was formed at the deepest level and the Nianzha type at the shallowest.