Texture and Geochemistry of Scheelites in the Tongshankou Deposit in Daye, Hubei, China: Implication for REE Substitution Mechanism and Multistage W Mineralization Processes
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Abstract:
The Tongshankou skarn deposit in the Edong ore district is a typical metasomatic deposit associated with adjacent granodiorite porphyry and carbonate rocks. Using comprehensive microscopic observations, mineralogical and geochemical analysis, scheelite grains in the skarns can be classified into three major types, showing multi-stage mineralization characteristics. In the redox fluid environment, scheelites that occur with garnets usually have affinity to garnets, while in later skarn phases others exist with oxides and sulfides. They can be subdivided by trace elements, such as Nb and Eu, to discuss the detailed ore-forming process. Scheelites have three typical substitution mechanisms including: 2Ca2 + ⇌ REE3 + +Na+ (1); Ca2 + + W6 + ⇌ REE3 + +Nb5+(2); and 3Ca2 + ⇌ 2REE3++ □Ca (□Ca = Ca site vacancy) (3). Plagioclase or various hydrothermal stages can cause Eu anomalies to fluctuate from positive to negative, and these processes can cause particular zonation in W and Mo contents in scheelites. This study highlights the use of texture and geochemistry of scheelites in skarn deposits, depicting the W mineralization processes.Keywords:
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Sulfide Minerals
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The Los Santos mineralization is the largest tungsten-bearing skarn of the Iberian Peninsula. Its is a complex skarn that share many features with equivalent tungsten-bearing calcic mesozonal reduced ones elsewhere. The mineralization is related with a hedenbergite-rich skarn superimposed by a younger amphi-bole-rich one in the contact with monzogranites, that are also pervasively replaced by a plagioclase-rich endoskarn; all these metasomatic rocks host disseminated scheelite. δ18O composition of the silicate minerals indicates that homogeneous deep fluids of likely magmatic/metamorphic origin were dominant in the formation of both the early and late skarns. The Sr and Nd isotope composition and the REE contents of the scheelite suggest that the tungsten derived from the nearby rocks (granitoids and siliciclastic sediments) and a deep, unexposed, highly evolved granite equivalent to those hosting the widespread W-Sn mineralization in the Variscan Belt of Iberia.
Scheelite
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Scheelite
Andradite
Grossular
Mineral redox buffer
Rare-earth element
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Metasomatism
Scheelite
Phlogopite
Pegmatite
Hornfels
Amphibole
Ore genesis
Diopside
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Greisen
Scheelite
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The Tongshankou skarn deposit in the Edong ore district is a typical metasomatic deposit associated with adjacent granodiorite porphyry and carbonate rocks. Using comprehensive microscopic observations, mineralogical and geochemical analysis, scheelite grains in the skarns can be classified into three major types, showing multi-stage mineralization characteristics. In the redox fluid environment, scheelites that occur with garnets usually have affinity to garnets, while in later skarn phases others exist with oxides and sulfides. They can be subdivided by trace elements, such as Nb and Eu, to discuss the detailed ore-forming process. Scheelites have three typical substitution mechanisms including: 2Ca2 + ⇌ REE3 + +Na+ (1); Ca2 + + W6 + ⇌ REE3 + +Nb5+(2); and 3Ca2 + ⇌ 2REE3++ □Ca (□Ca = Ca site vacancy) (3). Plagioclase or various hydrothermal stages can cause Eu anomalies to fluctuate from positive to negative, and these processes can cause particular zonation in W and Mo contents in scheelites. This study highlights the use of texture and geochemistry of scheelites in skarn deposits, depicting the W mineralization processes.
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Scheelite
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