岩浆成因矽卡岩的某些特征及形成机制初探

在矽卡岩型矿床中有两种矽卡岩,一是由渗滤-扩散交代作用形成的矽卡岩,另一种是由充填作用形成的脉状矽卡岩。脉状矽卡岩具有以下特点,表明属岩浆成因:1)呈脉状产出,与围岩界线清楚截然,在易于交代的大理岩中也一样;2)脉状矽卡岩中可含有类似花岗岩的矿物组合,并可出现伟晶岩囊,有时可见脉状矽卡岩与脉岩过渡;3)存在粗晶矽卡岩矿物的囊状体;4)发育气孔状构造和豆状构造;5)有流动构造;6)自身熔离现象十分普遍;7)在矽卡岩脉中常见由重力分异和挥发组分向上集中而形成的垂直分带现象;8)脉状矽卡岩常与矿浆成因的铁、铜矿体和由富含挥发分的硅浆成因的含钨石英脉相共生或过渡;9)脉状矽卡岩中已发现熔融包裹体。

A PRELIMINARY INVESTIGATION ON SOME CHARACTERISTICS AND FORMING MECHANISM OF THE MAGMA-GENETIC SKARN

There are two kinds of skarn in the skarn-type deposits. One of them is the skarn formed by infiltration-diffusion metasomatism and the other is the veined skarn which is produced by filling process. That the veined skarn poss esses the following characteristics suggests it belongs to magmatic genesis. (1) it occnrs in vein and its boundary with the surrounding rock is clear and sharp, even in the easily replaced marble; (2) the veined skarn may contain the mine ral assemblage that is similar to granite, and has pegmatitic po'ckets, sometimes we can see the veined skarn is transitional to dike rocks; (3) there are a lot of podiform bodies constituted by coarse-grained skarn mineral in the veined skarn; (4) it develops the vesicular and bean structures; (5) the flow structure is visible; (6) its liquation phenomena are extremely popular; (7) it is common to see the upward gravity differentiation and volatile floating resulting in the vertical zoning; (8) the veined skarn is generally paragenetic or transitive with the ore magma-genetic Fe, Cu ore bodies and the W-bearing quartz vein formed by volatile-rich silicon magma; (9) The melting inclusions have been discovered inthe veined skarn.