河北井陉地区铝土矿地质特征及成矿分析——河北井陉地区本溪组铝土矿成因机制：来自地球化学与沉积环境的约束

Geological Characteristics and Metallogenic Analysis of Bauxite Deposits in Jingxing Area, Hebei Province—The Genetic Mechanism of Bauxite in Benxi Formation in Jingxing Area, Hebei Province: Constraints from Geochemistry and Sedimentary Environment

摘要: 河北省井陉地区蕴藏着典型的“华北型”古风化壳沉积型铝土矿资源，但其精细成矿规律与机理尚未得到充分揭示。本文以该区典型铝土矿床为研究对象，通过系统的野外调查、钻孔岩心观察，并结合X射线衍射(XRD)、电子探针(EPMA)、X射线荧光光谱(XRF)及电感耦合等离子体质谱(ICP-MS)等分析手段，对矿石的矿物学与地球化学特征进行了综合研究。结果表明：(1) 矿体呈透镜状、似层状产出，矿石矿物以一水硬铝石为主，具致密块状和土状构造；(2) 综合地球化学证据表明，该矿床形成于氧化环境下的强烈红土化风化过程：主量元素揭示风化本质，微量元素蛛网图的右倾趋势提供印证，而轻稀土显著富集(ΣREE > 300 ppm)及δ_Ce (1.13)、δ_Eu (0.56)的异常特征则直接指示了氧化的成矿环境；(3) Sr/Cu值(0.96~35.37)与化学蚀变指数(CIA, 85~99)反映了其形成于热带–亚热带温暖湿润的气候背景；V/Cr比值(1.43~3.66)与Ni/Co比值(均值3.33)指示成矿主体形成于氧化环境，期间存在阶段性贫氧过渡；Sr/Ba比值(0.36~4.04)指示成矿期环境以陆相为主导；(4) 铝土矿的物质来源以花岗质酸性岩的风化产物为主，其成矿过程受奥陶系灰岩古岩溶风化及石炭纪海侵事件控制，在潟湖环境中经沉积分异作用成矿。综合认为，河北井陉地区铝土矿属于典型的沉积型矿床，其成因与“山西式铁矿”、耐火黏土共生的“铁矿–铝土矿–黏土岩”垂向序列密切相关。

Abstract: The Jingxing area in Hebei Province is rich in typical “North China type” weathered crustal sedimentary bauxite resources, but the detailed mineralization patterns and mechanisms of these resources have not yet been fully elucidated. This paper takes the typical bauxite deposit in this area as the research object. Through systematic field investigations, observation of drill core samples, and combined with X-ray diffraction (XRD), electron probe microanalysis (EPMA), X-ray fluorescence spectroscopy (XRF), and inductively coupled plasma mass spectrometry (ICP-MS) and other analytical methods, a comprehensive study was conducted on the mineralogical and geochemical characteristics of the ore. The results show that: (1) The ore body is lens-shaped and layered in its occurrence, and the ore minerals are mainly one water-alumina stone, with dense blocky and earthy structures. (2) Comprehensive geochemical evidence indicates that this deposit was formed during a strong redoxic weathering process under an oxidized environment: the major element data reveal the nature of the weathering, the rightward trend of the trace element spider plot provides confirmation, and the significant enrichment of light rare earth elements (ΣREE > 300 ppm) and the abnormal characteristics of δ_Ce (1.13) and δ_Eu (0.56) directly indicate the oxidized mineralization environment. (3) The Sr/Cu ratio (0.96-35.37) and the chemical alteration index (CIA, 85~99) indicate that it formed under a tropical-subtropical warm and humid climate background; the V/Cr ratio (1.43~3.66) and the Ni/Co ratio (mean 3.33) suggest that the main ore-forming process occurred in an oxidized environment, with intermittent periods of reduced oxygen content as a transition; the Sr/Ba ratio (0.36~4.04) indicates that the environmental dominance during the ore-forming period was mainly terrestrial. (4) The material source of bauxite mainly consists of the weathering products of granitic acidic rocks. The mineralization process is controlled by the ancient karstification of Ordovician limestone and the Cretaceous marine invasion events. It forms through sedimentary fractionation in a lagoon environment. In summary, the bauxite in Jingshen area of Hebei Province is a typical sedimentary-type deposit. Its formation is closely related to the “Shanxi-style iron ore” and the “iron ore-alumina ore-clay rock” vertical sequence that coexists with refractory clay.