花垣铅锌矿床成矿流体特征及动态

CHARACTERISTICS AND MOVEMENT OF ORE-FORMING FLUIDS IN THE HUAYUAN LEAD-ZINC DEPOSIT

花垣铅锌矿床是近年来发现的产于下寒武统清虚洞组藻灰岩 -鲕粒灰岩中的大型密西西比型 (MVT)铅锌矿床。根据矿床中大量流体包裹体的详细研究 ,成矿流体为高盐度的低温热卤水 ,流体气相组分中 ,H2 O占有主要部分 ,CO2 +CH4 约为 5% ,lgf O2 稳定在 - 4 8.0～ - 4 9.0 0之间 ,p H为 4 .3～ 5.8,Eh为 - 0 .0 7～ - 0 .1e V,此外 ,流体组分中 ,钠离子的含量大于钾离子 ,钙离子大于镁离子 ,而氯离子大于氟离子 ,这一特点是 MVT矿床所共有的 ,但 Na+ / K+值较低而Ca2 + / Mg2 + 比值较高 ,不同于美国的许多 MVT矿床 ,流体中 K+ 离子较高的原因之一 ,在于部分矿体的寄主岩石中 K+含量较高 ,对流体的成分产生了影响。此外 ,流体的氢、氧同位素组分表明 ,流体来源与建造水有关 ,后期有大气降水加入。大量数据证明 ,在矿床范围内 ,流体的温度与 CO2 、CH4 、K+、Na+、Ce2 +的含量 ,具有从北向南同步下降的特点 ,表明在矿床中 ,流体的运动方向是由北而南顺层侧向流动的 ,矿区外围可能也具有这种运动趋势。

The Huayuan lead\|zinc deposit is a large Mississippi Valley type(MVT)ore deposit in Hunan Province,which occurs in the algal\|oolitic limestone of Lower Cambrian Qingxudong Formation.The ore\|forming fluids are hot brine with higher salinity and lower temperature accroding to detailed studies of some fluid inclusions.H\-2O is the main component,and CO\-2+CH\-4 makes up some 5% in gas composition of fluid inclusions.lg f O\-2 is stable(-48\^0～-49\^0),pH=4\^3～5\^8,and Eh=-0 07～-0\^10 eV in ore\|forming fluids.In addition,the concentration of sodium ions is higher than potassium ions in the fluid,calcium concentration is higher than that of magnerium,and chlorine concentration is higher than that of fluorine.All these are common characteristics of MVT ore deposits,but the Na\++/K\++ ratios are lower and Ca\+\{2+\}/Mg 2+ ratios are higher than MVT deposits in USA.The higher content of potassium ions in fluids is partly caused by higher concentration of host rocks of some orebodies.Hydrogen and oxygen isotopic composition of fluids proves that the origin of the ore deposit is related to the formation water with the addition of late meteoric water.Plenty of data show that the temperature of fluids and content of CO\-2,CH\-4,K\++,Na\++.Ca 2+ decrease from north to south in orefield,suggesting that the mirgation of ore\|forming fluids is from north to south by transverse motion in host rocks,and the same migration may take place in the periphery of the orefield.