陕西勉县庙坪石墨矿床地球化学特征及成矿机制研究

Geochemical characteristics and genetic mechanism of the Miaoping graphite deposit in the Mianxian County of Shaanxi Province

新发现的勉县庙坪石墨矿床位于南秦岭勉略缝合带,工业类型为晶质鳞片状石墨矿石。本文对该矿床进行地球化学特征研究,并探讨其成因机制。研究结果表明,含矿岩石黑云母变粒岩Al2O3含量为7.32%~15.01%、TFeO为2.28%~8.68%、Na_(2)O为0.17%~3.38%、K_(2)O为1.15%~3.42%、TiO_(2)为0.50%~0.80%,稀土元素总量为106.38×10^(-6)~236.37×10^(-6);黑云母变粒岩具有明显的Eu、Sr负异常,U、Cs、Pb的正异常,Ce异常不明显。通过对本区变质原岩恢复、沉积环境及原岩物质来源分析可知,矿区变质岩原岩应为沉积岩,具有泥质砂岩、粉砂岩的特征,变质岩系原岩主要形成于缺氧还原的海洋沉积环境。碳同位素分析显示,矿石中石墨的δ13C为-23.6‰~-21.7‰,大理岩的δ13C为-7.1‰~3.3‰,石墨中的碳质来源主要为生物有机质,而大理岩的碳质来源为无机碳。本区经区域变质作用,使含碳质岩石富化成矿,矿床成因应属沉积变质型矿床。

The newly discovered graphite ore deposit in the Miaoping Mianxian County is located in the southern Qinling Mian-Lüe suture zone.The industrial type is crystalline flake graphite ore.This paper systematically analyzes the geochemical characteristics of samples and discusses the metallogenic conditions and genesis of the graphite ore deposit.The results show that the content of Al2O3(7.32%~15.01%),TFeO(2.28%~8.68%),Na_(2)O(0.17%~3.38%),K_(2)O(1.15%~3.42%)and TiO_(2)(0.50%~0.80%)in biotite granulite are relatively high.TheΣREE of biotite-granulite is 106.38×10^(-6)~236.37×10^(-6).δEu and Sr of biotite granulite show the negative anomaly,U,Cs,Pb show positive anomaly,butδCe anomaly is not obvious.The protolith of metamorphic rock in the mining area should be sedimentary rock with the characteristics of argillaceous sandstone and siltstone,which was mainly formed in the marine sedimentary environment of anoxic reduction.C isotope analysis shows that theδ13C of graphite in ore is-23.6‰~-21.7‰,and that of marble is-7.1‰~3.3‰indicating that the graphite carbon is derived from biological organic matter,and carbon of marble from inorganic carbonate mass.Regional metamorphism helped to transform the rocks to ore zones.The genetic type of the deposit belongs to sedimentary metamorphic deposits.