川、滇、黔交界地区密西西比河谷型铅锌矿床与美国同类矿床的对比

The Comparison of Mississippi Valley-Type Lead-Zinc Deposits in Southwest of China and in Mid-Continent of United States

我国川、滇、黔交接地区和美国中部地区的密西西比河谷型铅锌矿床的共同特征是 :1)含矿岩系都位于一套红色碎屑岩石之上。它们不但为矿床的形成提供了成矿金属 ,而且由于渗透率较大而为成矿流体的大规模侧向流动提供了通道。 2 )矿床的形成时间都与造山作用的时间相一致。造山作用所引起的挤压应力 ,或者由于造山带的隆起所引起的盆山间的重力梯度为含矿流体的大规模侧向流动提供了动力 ,促进了成矿作用的发生。 3)矿床的含矿岩系大多含有蒸发岩。蒸发岩的存在为成矿流体的形成提供了矿化剂 ,或者为矿质的沉淀提供了硫。与美国中部地区的MVT矿床相比 ,我国西南地区MVT矿床的形成温度相对较高、矿床的分布严格受断裂控制 ,矿体常呈垂向延伸很大的桶柱状产出 ,矿床的蚀变规模较小。这些差别反映出这两个地区矿床形成时成矿流体的通道和沉淀机制的不同。

There are many Mississippi Valley type Pb Zn deposits in southwest of China,in the boundary of Sichuan,Yunnan and Guizhou provinces, and in mid continent of United states, respectively. They shear many same characteristics:① The host rocks, carbonate , of the deposits in the two areas overlay a suit of clastic rock ,sandstone or conglomerate. It has been proved that the clastic rock not only provide Pb and Zn for the deposits but also channeled the ore fluids during mineralization. ② The mineralization time of the deposits in both of the area is coupled with the orogenic phase.It has been suggested that the deposits in mid continent of U.S. formed during the Alleghanian orogeny,and the deposits of the southwest of China formed during Yenshan orogeny(59～81Ma).It was the gravity gradient between the mountains and the basins,which was caused by the orogeny, to drire the ore fluids flowing in large scale. ③There are evaporite beds or evaporite minerals. The sulfate in the evaporite supplied reduction sulfur, by thermochemistry reduction of sulfate, for the precipitation of Pb and Zn of the ore fluids. But there are many differences of the deposits in the two areas also. The deposit temperature of the southwest of China is a little higher than that of mid continent of United states. The alteration accompanying with the mineralization is very large in scale in the deposits of USA, but is small in the deposits of China. And the ore bodies in most of the deposits of China are in high angle faults, but the ore bodies in the deposits of USA are karst caves and the site of different petrology. The driving agent and the precipitated mechanism of Pb Zn of the deposits of both the countries are generally the same. But the channel of the ore fluids are different, the channels in the deposits of China mainly are large faults, while those in the deposits of USA mainly are aquifers.