Vertical Variations in the Mineralogy of the Yichun Topaz Lepidolite Granite, Jiangxi Province, Southern China

Abstract

The Yichun topaz-lepidolite granite is the latest and most evolved unit of the Yichun granitic complex, South China, and is well known by virtue of its unusual Ta-Nb-Li mineralization. A drill hole down to 300 m has intersected the granite from top to bottom, and revealed three petrographic zones: K-feldspar-rich facies in the lower part, albite-rich facies in the middle part, and Ab-and Kfs-rich facies in the upper part. Geochemically, the Yichun granite belongs to the phosphorus-rich type of rare-elementenriched granite. The phosphorus is concentrated in the feldspars, which contain up to 0.93 wt% P 2 O 5 . It is less enriched in feldspars in the middle part, where primary amblygonite is abundant. Principal accessory minerals include columbite-tantalite, cassiterite, zircon, and wodginite in all facies, and microlite in the middle facies. The composition of the columbite-group minerals corresponds to manganocolumbite and manganotantalite. Zircon contains mostly 4 to 8 wt% HfO 2 , but the HfO 2 contents may reach up to 22 wt% at the rim. From the lower part to the middle part of the drill hole, the progressive increases in Ta/(Nb + Ta) of columbite and Ta-rich cassiterite, and in Hf content of zircon, are strongly suggestive of magmatic differentiation. On the other hand, in the upper part of the drill hole, the decrease in Ta/(Nb + Ta) of columbite and cassiterite, in Hf content of zircon, and the increase in Fe of lepidolite, and especially marked enrichment in Fe and W in columbite (5.76% FeO, 7.28% WO 3 ) at the uppermost part of the drill hole, indicate another environment at the final stage of crystallization of the granite, influenced by fluid probably derived from the surrounding mica schist. SOMMAIRELe granite à topaze-lépidolite de Yichun, l'unité la plus tardive et la plus évoluée du complexe granitique de Yichun, du sud de la Chine, est bien connu à cause de son enrichissement inhabituel en Ta-Nb-Li. Un trou de forage de 300 m a intersecté ce granite pour révéler trois zones pétrographiques: faciès riche en feldspath potassique en profondeur, faciès albitique au milieu, et faciès enrichi dans les deux feldpaths vers le haut. En termes géochimiques, le granite de Yichun fait partie des granites enrichis en phosphore et en éléments rares. Le phosphore est concentré dans les feldspaths, qui contiennent jusqu'à 0.93% de P 2 O 5 (poids). La concentration diminue dans le faciès du milieu, qui contient beaucoup d'amblygonite primaire. Parmi les principaux minéraux accessoires se trouvent columbite-tantalite, cassitérite, zircon, et wodginite dans tous les faciès, et microlite dans le faciès du milieu. La composition des minéraux du groupe de la columbite atteint le champ de la manganocolumbite et de la manganotantalite. Le zircon contient en général entre 4 et 8% de HfO 2 (poids), mais peut en contenir jusqu'à 22% en bordure des grains. En passant de la partie inférieure au milieu de l'intervalle échantillonné par le trou de forage, nous documentons une augmentation progressive en Ta/(Nb + Ta) de la columbi...

Accessory Minerals in the Xihuashan Y-Enriched Granitic Complex, Southern China: A Record of Magmatic and Hydrothermal Stages of Evolution

“…The level of U generally is in the range of 0.08 to 4.81 wt% UO 2 , notably lower than contents found in zircon from the Beauvoir granite (up to 10.73 wt% UO 2 : Cuney & Brouand 1987) or the Yichun granite (up to 9.94 wt% UO 2 : Huang et al 2002). Thorite incorporates uranium relative to zircon.…”

“…This mineral has been recently noted in the Rutherford #2 pegmatite, in Virginia (Lumpkin 1998) and in the Laoshan A-type granite, China (Wang et al 2001). In rare-metal-enriched granites, uranmicrolite may be present where the granite has a high Ta:U ratio, e.g., in the Beauvoir granite (Cuney et al 1992) or in the Yichun granite (Huang et al 2002). In contrast, when Ta/U is low, a pyrochlore-group mineral forms instead, as in the case of the Xihuashan granites (0.27 < Ta/U < 0.57).…”

Geochemistry of Meso- and Neoproterozoic mafic-ultramafic rocks from northern Guangxi, China: Arc or plume magmatism?

“…Major element contents were determined by conventional wet chemistry (Liu et al, 1999;Huang et al, 2002) at the Central Laboratory of Department of Earth Science, Nanjing University (NJU). Rare earth and other trace elements were analyzed by ICP-AES (Liu et al, 1999) and ICP-MS (Finnigan MAT-Element 2: Zhu et al, 2001) respectively at the State Key Laboratory of Mineral Deposit Research, Nanjing University (NJU).…”

REE and Y Mineralogy of the Krudum Granite Body (Saxothuringian Zone)

“…Enrichment of non-formula elements such as P, Al, Ca, Y and REE in P-rich zircon was found also in some other high-P peraluminous granites worldwide [7,[34][35][36]. The entry of Y + HREE and P into the zircon structure is usually explained via xenotime substitution, whereas zircon and xenotime are isostructural [37][38][39].…”