河北省北部晶质石墨矿层岩(矿)石地球化学特征与成因分析

晶质石墨是一种新兴战略矿产。近年在河北省北部发现了多处大中型晶质石墨矿床,主要赋矿层位于新太古代崇礼上岩群、古元古代红旗营子岩群等,具有良好的成矿潜力。通过系统的野外地质调查与采样、分析测试工作,详细研究了赋矿层位的岩相学、地球化学特征,并对碳质来源进行了分析。结果表明:赋矿岩石主要为含石墨黑云斜长变粒岩、片麻岩与透辉岩,原岩恢复以砂泥质碎屑岩、钙质沉积岩为主。主量元素含量变化较大, SiO₂含量为38.90%～80.42%, CaO+MgO为2.05%～31.93%, Al₂O₃为1.50%～15.34%;稀土元素含量为79.1～321.4μg/g, PAAS标准化分布模式一般具有右倾或较平坦分布特征, δCe略具负异常,部分具有δEu异常。微量元素特征指示沉积环境为滨浅海环境,部分地区存在富氧条件,局部为还原环境或存在热液加入。石墨中碳同位素值为–26.0‰～–20.7‰,主要来源于生物成因有机碳;大理岩碳同位素值为–3.8‰～1.1‰,主要来源于碳酸盐岩成因无机碳。区内晶质石墨矿层分布受到地层、岩性、岩相控制,含矿...

Geochemical Characteristics and Genesis of Crystalline Graphite Ore Bed Rocks in Northern Hebei Province

Crystalline graphite is an emerging strategic mineral. In recent years, several large- and medium-sized crystalline graphite deposits have been found in northern Hebei Province, with great mineralization potentiality in this area. The main ore-bearing horizons are Neoarchean Upper Chonglishang Group and Paleoproterozoic Hongqiyingzi Group. Through systematic field geological survey, sampling, analysis and testing, the petrography and geochemical characteristics of the ore-bearing horizon were studied in detail, and the carbon source was analyzed. The results showed that the main host rocks were graphite-bearing biotite plagioclase granulite, graphite-bearing biotite plagioclase gneiss, and graphite-bearing biotite plagioclase diopsides. The proto-rocks restoration are mainly argillaceous clastic and calcareous sedimentary rocks. The contents of main elements in graphite bearing strata vary greatly, with SiO2 content of 38.90%~80.42%, CaO+MgO of 2.05%~31.93%, and Al2O3 of 1.50%~15.34%. The content of rare earth elements is 79.1~321.4 μg/g. PAAS standardized distribution pattern generally has the characteristics of right leaning or relatively flat distribution. Some samples have slightly δCe negative anomaly and δEu anomaly. The characteristics of trace elements indicate that the sedimentary environment is a coastal and shallow sea environment, with oxygen rich conditions in some areas, reduction environment or hydrothermal addition in some areas. The carbon isotope value of graphite is –26.0‰ to –20.7‰, which mainly comes from biogenic organic carbon. The carbon isotope value of marble ranges from –3.8‰ to 1.1‰, mainly derived from inorganic carbon of carbonate origin. The crystalline graphite ore bed in the area is controlled by stratum, lithology and lithofacies. The favorable ore bearing horizon is sandy argillaceous clastic rock and calcareous sedimentary rock rich in organic matter in the coastal shallow sea facies of the ancient continental margin. The deposit is a sedimentary metamorphic deposit.