凡口铅锌矿区闪锌矿的成因矿物学特征研究

A genetic mineralogical study of sphalerite in the Fankou Pb-Zn ore district

通过野外观察、光学显微镜、X射线衍射、扫描电镜及微区能谱分析、流体包裹体成分及盐度测定、稳定同位素(S、O、H)分析等手段,研究了广东凡口铅锌矿区闪锌矿的某些成因矿物学特征。结果表明,凡口矿区闪锌矿具有3个世代,分别形成于铅锌成矿期的3个成矿阶段。各世代闪锌矿在产出特征,表观颜色,结晶形态,解理发育程度,晶体常数,铁含量,流体包裹体的成分、盐度、氢氧同位素组成、硫同位素组成及同与其连生的方铅矿的平衡分馏温度等方面均存在规律性差别。从早期阶段到晚期阶段,成矿流体的演化特征是:成矿温度和成矿流体盐度从低到高再到低,流体包裹体成分从Na+-Ca+-Cl-型到K+-Ca+-Cl-型再到Na+-Ca+-Cl-型,δ18O、δD及δ34S均由高到低变化,但δ18O、δD及δ34S自中期阶段到晚期阶段降幅显著大于从早期阶段到中期阶段的降幅,反映晚期阶段至少有部分δ18O、δD及δ34S均显著较低的岩浆源流体参与成矿。认为凡口铅锌矿成矿流体主要为燕山早期区域岩浆热事件加热的中低温混合源循环热卤水,成矿中晚期有岩浆热液参与成矿。

Based on field investigation, microscopic and scanning electron microscopic observation, X-ray diffraction, microprobe analysis, salinity and composition measurement of fluid inclusions and isotopic composition measurement of S, O and H, the authors studied some genetic mineralogical properties of sphalerite from the Fankou Pb-Zn ore district in Guangdong Province. The results suggest that there are three generations of sphalerite in this ore district formed respectively at three stages of the hydrothermal Pb-Zn sulfide ore-forming period. These three generations of sphalerite show remarkable differences in such aspects as mode of occurrence, paragenesis, apparent color, morphology, cleavage development, unit cell parameter, Fe content, composition and salinity, δ^18O‰ and δD‰ of fluid inclusions, δ34S‰ and fractionation equilibrium temperature with galena. The evolutional properties of the ore-forming fluid from the first stage to the third stage are as follows： the temperature and salinity varied from low through high to low again; the compositions of the ore-forming fluid changed from Na^＋ -Ca^＋ -Clˉ through K^＋ -Ca^＋ -Clˉ to Na^＋ -Ca^＋ -Clˉagain. The values of δ^18O, δD and δ^34S decreased , but the decreasing was much more drastic from the second to the third stage than from the first to the second stage, implying that a portion of newly-produced solution with much lower values of δ^18O, δ^D and δ^34S participated in the ore-forming fluid during the third stage. It is thus held that the ore-forming fluid should be a kind of mixed-source hot brine heated by Yanshanian regional magmatic event, with a portion of magmatichydrothermal solution participating in the formation of the hot brine at the intermediate-late ore-rotating stage.