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长江中下游中三迭统层状—层控型铁矿床,曾被传统地视为典型的接触交代型矿床。笔者研究结果表明,此类铁矿床应是中三迭统富铁沉积物经热液改造迭加的产物,并按其赋矿层位和铁的沉积相,可划分为若干亚类。中三迭统地层对本类型铁矿的形成起着以下主要作用周冲村组和黄马青组一段地层同生沉积的富铁碳酸盐及铁的氧化物,为矿床提供了重要数量的铁质,同时起着矿胚层和矿源层的作用;矿胚层可以成为晶芽层,因而最容易接受热液迭加;上述地层中的石灰岩和白云岩为铁质的活化转移提供了交代沉淀的有利岩性;(?)周冲村组膏盐层的塑性形变作用既控制了闪长岩类的顺层侵位或底辟侵位,并为后期热液提供了促使铁质活化转移的Na、Cl、CO等矿化剂。本类型矿床的矿体附近均发育有热液迭加造成的强烈碳酸盐化蚀变带,它是较钠长石化更为近矿的一种找矿标志。岩石化学和地球化学研究表明,闪长岩中铁是在含有相当数量的CO的富钠溶液作用下活化转移的,并在碳酸盐化过程中沉淀;钠长石化与铁的萃取有关,而碳酸盐化则与铁的沉淀有关。铁在热液中可能呈羰基络合物Na_2Fe(CO)_4等形式迁移。
The Middle Triassic stratiform-stratabound iron deposits in the middle and lower reaches of the Yangtze River have traditionally been regarded as typical contact metasedimentary deposits. The results of the author’s study show that such iron ore deposits should be the product of the hydrothermal transformation of the iron-rich sediments in the Middle Triassic. According to the ore-bearing beds and the sedimentary facies of iron, they can be divided into several sub-categories. The Middle Triassic strata have the following main effects on the formation of this type of iron ore: the iron-rich carbonate and iron oxides deposited co-occurring in the strata of the Zhouchongcun Formation and the Huangmaqing Formation provide an important amount of iron Quality and at the same time plays the role of the ore-hosting layer and the source rock; the mesoderm can become the crystal-bud layer and thus the easiest to accept hydrothermal superposition; the limestone and dolomite in the above-mentioned strata provide the benefit of metasomatic precipitation for iron activation Lithology; (?) The plastic deformation of the gypsum salt layer in Zhoucuncun Formation not only controlled the upwelling or diapirism emplacement of diorites, but also provided Na, Cl, CO and other mineral agent. This type of deposits are developed near the ore body hydrothermal superposition caused by a strong carbonate alteration zone, which is more than the long-term mineralization of albite a prospecting marker. Petrochemical and geochemical studies show that the iron in the diorite is activated and transferred by the sodium-rich solution containing a considerable amount of CO and precipitates during the carbonation process. Alkaline flotation is related to the extraction of iron while the carbon Acidification is associated with the precipitation of iron. Iron may migrate in hydrothermal form as carbonyl complex Na 2 Fe (CO) _4.