豫西石炭纪铝土矿成矿系统.doc

豫西石炭纪铝土矿成矿系统 豫西为我国重要的铝土矿成矿区。本文通过豫西铝土矿区域分布、典型矿床研究、矿区勘查、矿点地质调查、岩石矿物、地球化学、国内外同类矿床对比等方面的工作,对豫西铝土矿成矿系统进行了研究,提出豫西铝土矿形成于石炭纪华北陆地表面、岩溶洼地洼斗富集成矿、豫西铝土矿围绕隆起区分布的规律由后期构造运动形成等观点,认为豫西铝土矿的深部找矿有较大前景。豫西石炭纪铝土矿成矿系统是一个地表的成矿系统,地球系统的各个圈层都在该系统中出现并对铝土矿成矿具有明显的控制作用。控制成矿的因素有沉积作用、风化作用、构造作用、地貌、气候、水文地质条件、生物作用、氧化还原条件、海洋的作用、岩溶作用等。铝土矿成矿系统为一个其它物质带出,铝质残留下来富集成矿的系统。豫西成矿物质主要来源于寒武系-奥陶系碳酸盐岩的红土型风化壳,成矿流体为矿物质不饱和的大气降水,成矿空间为包括豫西地区在内的华北地区陆地表面的岩溶洼地,大气降水的冲积、渗流、溶解、淋滤是成矿系统的动力来源,岩溶洼地洼斗为铝土矿成矿的主要场所。石炭纪,随生物进化,植物在陆地上广泛分布,大气圈从富含二氧化碳转变为富含氧气,植物、氧化作用导致地表化学风化作用强烈;经过晚奥陶世-早石炭世的风化剥蚀,华北地区成为碳酸盐岩古夷平面,地理上位于热带雨林环境,岩溶地貌发育;在矿物质不饱和的大气降水淋滤下,碳酸盐岩地表形成红土型风化壳,铝质富集;大气降水、红土物质、腐殖质汇集于岩溶洼地洼斗,大气降水下渗、淋滤红土物质,通过岩溶排水系统带走包括硅铁在内的其它物质,形成铝土矿,构成一个铝土矿富集成矿系统。由于在成矿体系中的时间、空间位置不同,导致了铝土矿化强度不同,华北地区古风化面上,形成了本溪组剖面上底部的铁质粘土岩、中部的铝土矿、上部的碳质粘土岩,平面上铝土矿相变为粘土岩、粘土矿等不同的成矿系统产物。豫西铝土矿具有以下特征矿体品位和厚度呈正比例变化关系;高品位铝土矿出现在岩溶洼斗底部,在洼斗外铝土矿厚度变小、品位降低;矿体平面上分布具有局限性;矿石化学成份具有高铝、低铁、高硅的特点;矿石颜色主要为不同程度的灰色。这些特征和岩溶洼斗在铝土矿成矿过程中的重要性密切相关。豫西铝土矿广泛分布于石炭纪本溪期华北陆地表面,形成时产状近似水平,其后太原组、二叠系、早中三叠统覆盖,深埋地下。晚三叠世,扬子板块与中朝古板块碰撞,豫西发生强烈褶皱运动,背斜区域的本溪组抬升。新生代以来,豫西进入断陷构造运动阶段,本溪组在隆起区被剥蚀殆尽,洼陷区深埋地下,围绕隆起出露,形成铝土矿床点围绕隆起分布的特征 The bauxite deposits in western Hernan provience is one of the most important bauxite metallogenic region in China. This paper is focused on Carboniferous Bauxite Ore-ing System, Western Henan, based on the study of regional distribution of bauxite deposits, typical deposits, exploration works, geological survey about mining spots, mineralogy and petrology, geochemistry and comparation with foreign bauxite deposits. Study results show that the bauxite deposits was ed on the paleo-surface of North-China Plate, Karst depressions played an important role in ore-ing, the distribution of bauxite deposits around the highlands was ed by post-ore-ing tectonic movements. The western Hernan bauxite metallogenic region has a great potential depth prospecting prediction.It is a paleo-surface metallogenic system in the Carboniferous bauxite deposits in western Henan. Every Sphere of the Earth such as Lithosphere, atmosphere, hydrosphere and biosphere was involved in the system and played an important role. Main geological processes of ore-ing controlling factors included sedimentary, weathering, tectonic movements, physiognomy, climate, hydrogeologic condition, paleontology, oxidation- reduction, transgression, karstification etc.The bauxite metallogenic system was a process that the oxide of Al remained as residues ing bauxite while the other elements were eluviated and extracted out. The bauxite was derived from laterite weathering crust on the Cambrian- Ordovician carbonate in Karst depressions on the paleo-surface of North-China Plate. Karst depressions was the primary ore-ing place.The ore-ing fluid was unsaturated meteoric in mineral elements. The laterite was swashed to Karst depressions and nudergo infiltration, dissolution and eluviation by meteoric water, ed bauxite.Plants were widely distributed on the continent in Carboniferous as the biologic evolution. The previous CO2-riching atmosphere became oxygen-riching. Chemical weathering was very strong on the paleo-surface, under the combined effect of plants and oxidation. The North China plate became a carbonate peneplain after the erosion from Later-Ordovician to Early Carboniferous and located in humid tropical rain forest, karstification was well-developed. The carbonate peneplain enriched Al minerals with the mineral elements unsaturated meteoric water eluviation. Then meteoric water, laterite and organic matter accumulated in Karst depressions. The laterite was infiltrated and eluviated by meteoric water; the other elements including Si and Fe were dissolved and taken out by the Karst-drainage system, bauxite ed.The bauxite ore-ing process was different on the paleo-surface of North China plate as spatial-temporal differences. There were three profile ore zones ferro-clay zone at the bottom, bauxite zone in the center and carbonaceous clay on the top. In the horizontal ore distribution, bauxite was instead by claystone and clay minerals.The features of bauxite ore deposits in western Henan are listed below Ore-grades are positive related with the thicknesses of orebodies; High grade orebodies present in the bottom of Karst sink-holes, the thickness become thinner and the grade become lower outside the sink-holes; Bauxite orebodies were limited in Karst depressions; Ore chemical composition was high in Al2O3 and SiO2, low in Fe2O3; The colors of bauxite ore are mainly in different gray to black. These features indicate that the bauxite was ed in rich organic matter, reducing ore-ing system which occurred in Karst depressions.The Carboniferous bauxite ore deposits widely horizontal distributed on the paleo-surface. It was covered by Carboniferous Taiyuan Group, Permian, Lower and Middle Triassic. In Late Triassic, Yangzi plate collided with North China plate; horizontal tectonic movement was very strong in Western Henan, the bauxite ore deposits uplifted in anticline. In Cenozoic, tectonic movements was vertical, the bauxite deposits was eroded in highlands and burried in depressions. The outcorps of bauxite deposits distribution were around highlands.;