湘西北洛塔矿田铅锌矿床与典型MVT铅锌矿床的对比研究

洛塔矿田处于扬子地台东南边缘,矿田内的铅锌矿床(点)分布受断裂、褶皱构造控制,分布在三个背斜的核部.矿体主要赋存于奥陶纪南津关组生物屑灰岩及硅化灰岩中,呈似层状、脉状.围岩蚀变有硅化、方解石化、白云石化、黄铁矿化等,硅化是最直接的找矿标志.成矿硫质主要源于同沉积的海水硫酸盐,铅主要源于造山带,具壳幔混合源性质.成矿流体为含烷类(CH4)有机质地下热卤水,成矿温度介于95~197℃.铅同位素模式年龄指示矿石的形成明显晚于赋矿层位,矿床成因类型属层控型浅成低温热液矿床.通过对比发现,洛塔矿田铅锌矿床在矿床地质特征、同位素地球化学、成矿流体、矿床成因等方面都与典型MVT矿床具有一定相似性,又具有独特的性质.

A Comparative Study of Luota Ore Field Lead-zinc Deposits in the Northwest of Hunan Province with Typical MVT Lead-zinc Deposits

Luota ore field is located in the southeastern edge of the Yangtze Platform, The lead -zinc deposits in the ore field is distributed in three core of the anticline which are controlled by breaks and folds. The ore - bodies mostly present as layer and vein which are mostly hosted in the Nanjinguan group bioclastic limestone and silicified limestone of Ordovician. There are several wall - rock alterations in the ore field such as silicification, calcitization, dolomitization, pyritization, ere, silicification which are the most direct prospecting mark. Sulfur mineralization is mainly derived from the syndepositional seawater sulfate, lead mineralization is mainly from orogenic belt, with the information of contaminating the crust and mantle mixed source. The ore - forming fluids are hot brine from underground containing organic alkanes like CH4. The temperature of mineralization is between 95 - 197℃. Pb isotopic model ages indicate that the formation of ore is significantly later than the Ore - bearing stratum. The deposit type is most like strata bound epithermal deposit. By comparison, the geological characteristics, isotopic geochemistry, ore - forming fluids, genesis of the deposit in Luota ore field have some similarities with typical MVT deposit, but also it has its uniqueness.