滇中昆阳群火成碳酸岩的发现及其意义

DISCOVERY AND SIGNIFICANCE OF THE CARBONATITE OF KUNYANG GROUP IN THE CENTRAL OF YUNNAN

在武定西矿带发现的已大理岩化的滇中昆阳群（Ｐｔ２ｋ）火成碳酸岩富含钠长石、更长石、金云母、黑云母等硅酸盐矿物，发育火成结构构造，如斑状结构、隐晶结构，流纹构造、带状构造、气孔、杏仁构造等。与沉积围岩相比，岩石高Ｓｉ、Ａｌ、Ｆｅ、Ｍｇ、Ｍｎ、Ｐ，富Ｋ２Ｏ＋Ｎａ２Ｏ，低钙，轻稀土富集，富含Ｎｂ、Ｚｒ、Ｈｆ、Ｕ、Ｔｈ、Ｓｒ、Ｂａ、稀土等不相容元素，与粗面质、粗安质等碱性硅酸盐岩共生。（铁）白云石（＞５０％）内，含有粗面质、碳酸质熔融包裹体；流体包裹体均一温度可达４５０℃以上。

Marble metamorphismed carbonatite which exists in the adjacent rock of “Daqing sub type” copper ore in Kunyang Group (Pt 2 k ) was discovered recently in the central of Yunnan.The rock contains silicate minerals such as oligoclase (An <35),albite,magnesia,biotite etc,and develops igneous texture and structure such as porphyritic and aphanitic texture,fluxion and banded fumarole amygdaloidal structure.The chemical composition is high in Si,Al,Fe,Mg,Mn,P,low in Ca,and rich in K 2O+Na 2O and incompatible elements Nb,Zr,Hf,U,Th,Sr,Ba,REE etc.The carbonatite intergrowths with alkaline rocks such as trachyte,trachyandesite etc.Dolomite and ferrodolomite in the rock contain varied mineral inclusions and trachytic or carbonatic molten inclusions and fluid inclusions with homogenization temperature over 450℃.The discovery of this rock proves that carbonatite magma was active in middle Proterozoicera in the central of Yunnan,which hasprofoundsignificanceforthe geological studing of the west mineralization belt of Wuding.