Magma mixing and gold mineralization in the Maevatanana gold deposit,Madagascar |
| |
| Institution: | 1. Fundamental Science on Radioactive Geology and Exploration Technology Laboratory, East China University of Technology, NanChang, Jiangxi 330013, China;2. National Research Center for Geoanalysis, Chinese Academy of Geological Sciences, Beijing 100037, China;3. MLR Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China;4. State Key Laboratory of Geological Process and Mineral Resources, China University of Geosciences, Beijing 100083, China;1. Earth Science Institute, St. Petersburg University, Universitetskaya Embankment 9, 199034 St. Petersburg, Russia;2. All-Russian Geological Research Institute (VSEGEI), 199106 Sredny pr. 74, St. Petersburg, Russia;1. MLR Laboratory of Metallogeny and Mineral Resource Assessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China;2. China Geological Survey, CGS, Beijing 100037, China;3. Centre for Exploration Targeting, ARC Centre of Excellence for Core to Crust Fluid Systems, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia;1. Tianjin Center, China Geological Survey, Tianjin 300170, China;2. College of Geosciences, East China Institute of Technology, Nanchang 330000, China;1. MLR Laboratory of Metallogeny and Mineral Resource Assessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China;2. Centre for Exploration Targeting, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia;3. Development and Research Center, China Geological Survey, Beijing 100037, China;1. School of Earth Sciences, University of Melbourne, VIC 3010, Australia;2. School of Earth, Atmosphere and Environment, Monash University, Clayton, VIC 3800, Australia |
| |
| Abstract: | The Maevatanana gold deposit in Madagascar is hosted by Archean metamorphic rocks in quartz–sulfide veins that are structurally controlled by NNW–SSE trending shear zones. Fluid inclusion data show that the trapping conditions in quartz range from 0.87 to 2.58 kbar at temperatures of 269–362 °C. Laser Raman spectroscopy confirms that these inclusions consist of CO2, SO2, and H2O. The δ34S values of the pyrites range from 1.7‰ to 3.6‰, with an average of 2.25‰, supporting a magmatic origin. Noble gases (He, Ne, Ar, Ke, Xe) are chemically inert, thus will not be involved in chemical reactions during geological processes. Also due to the low concentration of He in the atmosphere and the low solubility of He in aqueous fluids, the atmosphere-derived He is unlikely to significantly affect He abundances and isotopic ratios of crustal fluids, ensures that He production should have the typical crust 3He/4He ratios. The 3He/4He ratios of fluid inclusions in pyrite from the deposit range from 0.06 to 0.12 Ra, while the 40Ar/36Ar ratios range from 6631 to 11441. We infer that the ore-forming fluids could have been exsolved from a granitic magma. The oxygen and hydrogen isotope compositions of the ore-forming fluids (1.5‰ ≤ δ18OH2O ≤ 7.8‰; –72‰ ≤ δD ≤ –117‰) indicate they were derived from a granitic magma. Four pyrite samples from the gold deposit yield a precise Re–Os isochron age of 534 ± 13 Ma. Given that the post-collisional granites in northern and central Madagascar were derived by melting of sub-continental lithospheric mantle and formed between 537 and 522 Ma, we can state that the gold metallogenesis was coeval with the crystallization age of these parental magmas. These data could be accounted for the formation of the Maevatanana gold deposit. First, the shear zones hosting the deposit formed around 2.5 Ga, when the Madagascan micro-continental blocks collided with other continental blocks, triggering large-scale tectono-magmatic activity and forming NNW–SSE trending shear zones. The gold mineralization at Maevatanana is coeval with the crystallization age of the Cambrian post-collisional A-type granitoid plutons in northern and central Madagascar, implying that this deposit is associated with extensional collapse of the East African Orogen. This extension in turn induced asthenospheric upwelling, melting of sub-continental lithospheric mantle. These magmas underplated the lower crust, generating voluminous granitic magmas by partial melting of the lower crust. The mixing magma during tectono-thermal reactivation of the East African Orogen produced large volumes of volatiles that extracted gold from the granitic magma and produced Au–S complexes (e.g., Au(HSO3)2?). The shear zones, which were then placed under extensional collapse of the East African Orogen in the Cambrian, formed favorable pathways for the magmatic ore-forming fluids. These fluids then precipitated gold-sulfides that form the Maevatanana gold deposit. |
| |
| Keywords: | Fluid inclusions Isotope geochemistry Re–Os geochronology Magma mixing Maevatanana gold deposit Madagascar |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
