米仓山地区一种与超基性岩有关的矽卡岩

A MG-RICH CALCAREOUS SKARN RELATED WITH ULTRABASIC ROCK IN THE MICANG MOUNTAIN AREA

米仓山地区发现一种自然界较为少见的与超基性岩有关的富镁钙质矽卡岩。矽卡岩产于晋宁中期超基性岩与中元古代大理岩接触带上 ,并被晋宁晚期中基性浅成侵入体肢解和包裹。与一般产于中酸性侵入体与石灰岩接触带的钙质矽卡岩不同的是除了含有大量透辉石、钙铝—钙铁榴石、硅灰石、符山石等钙质矽卡岩常见矿物外 ,还普遍发育有钙镁橄榄石、金云母富镁硅酸盐矿物 ;岩石中缺乏长石、石英、金属硫化物及其他热液阶段矿物 ,所有这些特征在很大程度上与超基性岩浆的富镁、贫硅、缺少挥发组分的性质有关。

A Mg rich calcareous skarn related with ultrabasic rock,which is rare in nature,was found in the contact zone between ultrabasic rock in the Jinning Period and marble in the Middle Proterozoic Also it was dismembered and captured by a later intermediate basic intrusion that was a hypabyssal one in the Late Jinning Period Unlike other normal calcareous skarn,it generally contains magnesian silicate minerals such as monticellite and pholgopite in addition to diopside,grossular andradite,wollastonite and vesuvianite Moreover,it is lack of feldspar,quartz,metal sulphide and other hydrothermal minerals All the characteristics may be considered to be related to the nature of intrusive and surrounding rocks Evaluated rock forming temperature of the skarn ranges from 666℃ to 745℃