MICROLITE AND TANTALITE IN THE LCT GRANITIC PEGMATITES OF LA CANALITA, NAVASFRIAS Sn-W DISTRICT, SALAMANCA, SPAIN

被引:16
作者
Llorens, Teresa [1 ]
Candelas Moro, Maria [1 ]
机构
[1] Univ Salamanca, Dept Geol, E-37006 Salamanca, Spain
关键词
microlite; columbite-tantalite group; tapiolite; cassiterite; granitic pegmatites; lepidolite subtype; La Canalita; Navasfrias district; Spain; RARE-ELEMENT; OXIDE MINERALS; COLUMBITE-TANTALITE; CHEMICAL EVOLUTION; FLUID INCLUSION; TA; NB; GEOCHEMISTRY; DEPOSITS; NIOBIUM;
D O I
10.3749/canmin.48.2.375
中图分类号
P57 [矿物学];
学科分类号
070901 ;
摘要
The La Canalita pegmatites in the Navasfrias Sn-W district, in Spain, are a group of Li-rich LCT rare-element pegmatites hosted by metamorphic rocks. It consists of several dikes up to 1 m thick, 16 m in length and of unknown depth that were mined during the 40s and 50s for tin. Here, we document the Ta-rich oxide minerals, such as those of the columbite-tantalite group, tapiolite-(Fe) and microlite. It is possible to distinguish a primary assemblage, formed of extremely Mn-rich columbite and tantalite, and microlite, the latter forming the host of columbite-(Mn) exsolution lamellae in the intermediate parts of the dikes. The influence of metasomatic fluids led to the formation of a lepidolite-albite late unit and the crystallization of a secondary assemblage consisting of tantalite-(Fe), tantalite-(Mn) and tapiolite-(Fe). Uranium-rich microlite (up to 6% wt. UO2) is present in this assemblage, replacing tantalite. Subsequently, the entrance of hydrothermal fluids, probably mixed with metamorphic fluids, caused a partial greisen-like alteration of the pegmatite bodies and formed a second generation of microlite replacing tapiolite, with high Ca and Ta and low F contents. The lack of a chemically suitable protolith in the surrounding metamorphic rocks, combined with the mineralogical paragenesis containing U-rich microlite, together with the composition of the Sn, Nb and Ta oxide minerals of the pegmatite dikes, suggest that the Cadalso - Casillas de Flores batholith is the most probable source of the melts forming the La Canalita pegmatite dikes.
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页码:375 / 390
页数:16
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