Affiliation:
1. Chengdu center, China Geological Survey (Geosciences Innovation Center of Southwest China) Chengdu 610081 China
2. MNR Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences Beijing 100037 China
3. Earth Sciences College, Chengdu University of Technology Chengdu 610059 China
4. No.6 Geological party, Tibet bureau of Geology and Mineral Exploration and Development Lhasa 851400 China
5. Tibet Shengyuan Mining Group Co., Ltd. Lhasa 851400 China
Abstract
AbstractMultistage tungsten mineralization was recently discovered in the Mamupu copper‐polymetallic deposit in the southern Yulong porphyry copper belt (YPCB), Tibet. This paper reports the results of cathodoluminescence, trace element and Sr isotope analyses of Mamupu scheelite samples, designed to better constrain the mechanism of W mineralization and sources of ore‐forming fluids. Three different types of scheelite are identified in the Mamupu deposit: scheelite A (Sch A) mainly occurs in breccias during the prograde stage, scheelite B (Sch B) forms in the chlorite‐epidote alteration zone in the retrograde stage, and scheelite C (Sch C) occurs in distal quartz sulfide veins. The extremely high Mo content and negative Eu anomaly in Sch A represent high oxygen fugacity in the prograde stage. Compared with ore‐related porphyries, Sch A has a similar REE pattern, but with higher ΣREE, more depleted HREE, and slightly lower (87Sr/86Sr)i ratios, and these features suggest that Sch A is genetically related to ore‐related porphyries, but the extensive interaction with carbonate surrounding rocks affects the final REE and Sr isotopic composition. Sch B shows dark (Sch B‐I) and light (Sch B‐II) domains under CL images. From Sch B‐I to Sch B‐II, LREEs are gradually depleted, and MREEs are gradually enriched. Sch C has the highest LREE/HREE ratio, which indicates that it inherited the geochemical characteristics of fluids after the precipitation of HREE‐rich minerals such as diopside, and garnet in the early prograde stage. The Mo content in Sch B and Sch C gradually decreased, indicating that the oxygen fugacity of the fluids changed from oxidation in the early stage to reduction in the later stage, and the turbulent Eu anomaly in Sch B and Sch C indicates that the Eu anomaly in the Mamupu scheelite is not only controlled by oxygen fugacity. The extensive interaction of magmatic‐hydrothermal fluids and carbonate provides the necessary Ca2+ for the precipitation of scheelite in the Mamupu deposit.