红十字湖地区锂云母-透锂长石伟晶岩脉中锡锰钽矿的发现

The discovery of wodginite in the lepidolite petalite bearing pegmatitefrom Red Cross Lake area, northeastern Manitoba,Canada

锡锰钽矿(wodginite)理想式为MnSnTa2O8,Z=4,其结构为锡铁钽矿(ixiolite)结构的有序化形式。它是钽的主要工业矿物,是高度分异演化伟晶岩的标志矿物之一。在加拿大红十字湖地区锂云母-透锂长石伟晶岩脉中发现了这一钽矿物。矿物为黑褐色,呈半自形,颗粒达0.2mm,分布于由锂云母钠长石构成的条带中,与之共生的是一套典型的、高演化的花岗伟晶岩矿物组合。锡锰钽矿具有Mn/Fe、Sn/Ti、Ta/Nb比值高,杂质少的特点。矿物平均分子式为:Mn1.00(Sn0.64Ta0.24Ti0.04Mn0.04Zn0.02Fe0.01)0.99(Ta1.69Nb0.31)2.00O8;晶胞参数a=0.9534nm,b=1.1482nm,c=0.5123nm,β=91°07',V=0.5607nm3。依据矿物β>91°、V>0.560nm3、对偶面网221与221具强分裂衍射双峰、I021/I220为0.19和Mn/(Fe+Mn)≈1等特征,在锡锰钽矿与锡铁钽矿所构成的同质多像、有序-部分有序-无序这样一个连续系列中,本区所产锡锰钽矿属有序端员矿物,其阳离子在八面体中分布的有序度约为95%。在钽资源的寻找和开发利用中,应重视含锡锰钽矿的锂云母-透锂长石伟晶岩脉。

The wodginite is discovered at the Red Cross Lake (RCL) pegmatite, which as the lepidolite petalite bearing dike intruded into the Oxford lakegreenstone belt in the northeastern part of Superior Province of the Canadian Precambrian shield. Wodginite is both the important ore mineral of tantalum and indicator mineral of extremely differentiated and evolved granitic pegmatite. Itsideal formula is MnSnTa2O8, Z=4. Its structure is an ordering form of the ixiolite structure. It is dark brown to black, and has a subhedral diamond shaped grain up to 0.2 mm. It occurs as dissemination in the silicate mineral stripe constituted by lepidolite and albite. Wodginite is typically associated with minerals such as pollucite, lepidolite, petalite, manganotantalite, amblygonite and microlite, and so on, for extremely differentiated and evolved granitic pegmatite.Wodginite has an average formula: Mn1.00(Sn0.64 Ta0.24 Ti0.04 Mn0.04 Zn0.02 Fe0.01)0.99 (Ta1.69 Nb0.31)2.00 O8, with a suite of unit cell parameter of a 0.953 4 nm, b 1.148 2 nm, c 0.512 3 nm, β=91°07′, V=0.560 7 nm3. It is considered that transformation in structure from disordering ixiolite to ordering wodginite is continuous, i.e. the relationship between βand the degree of order is thought to be continuous and linear. The wodginite in the pegmatite of the RCL area is an ordering end member with 95%order in this disorder order continuous series.