中国锰银伴生矿床地质特征及成因
摘要：錳银矿是一种Mn、Ag伴生的重要银矿资源类型，但长期以来并未受到矿床学家的重视。介绍了中国锰银伴生矿床的主要类型、地质特征、成矿时代及其与火山活动和构造之间的关系。根据矿床成矿元素组合关系，将中国锰银伴生矿床划分为4种类型：MnAg型、MnAgPbZn型、FeMnAgPbZn型和PbZnAg（Mn）型。MnAg型和MnAgPbZn型锰银伴生矿床数量较多，锰矿规模以中小型为主，银矿规模以大中型为主；FeMnAgPbZn型锰银伴生矿床数量较少，锰矿和银矿规模在湖南后江桥以大中型为主；而PbZnAg（Mn）型锰银伴生矿床仅有辽宁八家子，银矿规模达大型，锰矿规模较小。中国锰银伴生矿床主要形成于侏罗纪—早白垩世，与燕山期中酸性侵入和火山活动关系密切，矿床常产在岩体附近或火山岩中。区域上，锰银伴生矿床沿特定地层层位分布，受富Mn、富Ag矿源层控制；后期岩浆水与大气降水形成的混合热液萃取矿源层中的Mn、Ag等成矿物质；成矿热液沿断裂构造运移，使得矿区内锰、银矿体明显受区内断裂构造控制。根据典型矿床的硫、铅和氢氧同位素特征，锰银伴生矿床的成矿物质为深部岩浆与浅部物质的混合来源，且主要来源于深部岩浆物质，成矿热液也为岩浆水与大气降水的混合来源，只是不同矿床所占比例不同。此外，还探讨了Mn、Ag密切共生的原因及锰银伴生矿床的成矿机制。Mn2+可能是Ag+沉淀的重要还原剂，Mn2+被氧化形成MnO2，Ag+则被还原形成Ag，导致二者同时沉淀富集成矿，因此，可将锰帽作为寻找银矿化的良好标志。
关键词：锰银伴生矿床；地质特征；燕山期；形成时代；物质来源；伴生关系；成矿机制
中图分类号：P618.32；P618.52文献标志码：A
Geological Characteristics and Origin of Manganesesilver Associated Deposits in China
LIANG Houpeng1， FU Yong1，2， XU Zhigang2， GE Zhihua1， WEI Shuaichao1
（1. College of Resource and Environmental Engineering， Guizhou University， Guiyang 550025， Guizhou， China；
2. Institute of Mineral Resources， Chinese Academy of Geological Sciences， Beijing 100037， China）
Abstract： Manganesesilver deposit， which is an important type of silver deposits with manganesesilver associated， has not been paid much attention. The main types， geological characteristics， mineralogenetic epoch and their relationships with volcanic activity and tectonic of manganesesilver associated deposits in China were introduced. On the basis of the intergrowth and associated combination， the manganesesilver associated deposits can be divided into four types： MnAg， MnAgPbZn， FeMnAgPbZn and PbZnAg（Mn）. MnAgtype and MnAgPbZntype manganesesilver associated deposits are dominated； the scales of manganese deposits are often small and medium， while the scales of silver deposits are middle and large. The number of FeMnAgPbZntype manganesesilver associated deposits is less； the scales of manganese and silver deposits are middle or large in Houjiangqiao of Hunan. The PbZnAg（Mn）type manganesesilver associated deposit is only Bajiazi； the scale of silver deposit is large， while the scale of manganese deposit is small. The formation ages of manganesesilver associated deposits in China are mainly in JurassicEarly Cretaceous， which relates to intermediateacidic intrusive and volcanic activities in Yanshanian； the deposits usually form near or in the volcanic rocks. The distribution of manganesesilver associated deposits is in some specific horizons under the control of Mich and Agrich source beds； later magmatic water and meteoric water form a mixture of hydrothermal extraction of Mn and Ag oreforming materials； these oreforming hydrotherm migrates along fault， so that the Mn and Ag orebodies are obviously controlled by fault structure. According to the characteristics of S， Pb， H and O isotopes， the metallogenetic materials of manganesesilver associated deposits are from the mixture of hypomagma and shallow materials， and the hypomagma is dominated； the metallogenetic hydrotherm is also from the mixture of magmatic water and meteoric water， and just the ratios of the source materials are different for the deposits. In addition， the reason for Mn and Ag coexistence and the metallogenetic mechanism of manganesesilver associated deposit were discussed. The results show that Mn2+ is a significant reductant of the precipitation of Ag+， Mn2+ is oxidized to form MnO2， Ag+ is reduced to form Ag， which results in the precipitation of Mn and Ag at the same time； thus， manganese hat is a good marker indicating Ag mineralization.