摘要
在宁芜地区中三叠统层状-层控和次火山热液两种类型铁矿床的成矿过程中,深色蚀变、碳酸盐化蚀变、隐爆作用、碳酸盐围岩、围岩中的铁矿胚层、裂隙构造等因素之所以能控制热液矿体的定位,一个重要的原因是这些因素能加速铁羰络合物的分解,从而促使铁质从热液中沉淀。
The Middle Triassic stratiform and stratabound deposit and the Jurassic subvolcanic hydrothermal one are the two most important types of iron ore deposits in the Nanjing—Wuhu area, whose formation owes a great deal to the hydrothermal process.Carbonyl complexes may have been an important form in which iron was remobilized during the post-magmatic hydrothermal process. Based upon the investigations by T. A. Andieva (1977), the authors (1983) propose a modified chemical model for carbonyl complex remobilization, i. e., iron-bearing minerals can be reduced at high temperatures and pressures by carbon monoxide to yield carbonyl complexes such as Fe(CO)_5 which are ready to be dissolved in alkailne solutions to form iron carbonylates like Na_2Fe(CO)_4. The acidification of the solution will change iron carbonylates into carbonyl hydrides, and the typical reaction is like this: Na_2Fe(CO)_4+2H^+=H_2Pe(CO)_4+2Na^+ (1) Carbonyl hydrides of iron are unstable and will easily be decomposed under the oxidizing condition with resultant precipitation of iron oxides: 3H_2Fe (CO)_4+9O_2=Fe_3O_4+3H_2O+CO+11CO_2 (2)Dark mineral alteration, carbonatization, underground explosion, carbonate sediments, iron portore beds, and structural fractures in confining rocks are all well-known constraints on ore formation. In the light of the above-mentioned model, the following explanations can be made as to how these constraints work:Dark mineral alteration favours the acidification of ore-forming fluids, resulting in the acceleration of Reaction (l)j carbonatization exhausts carbon dioxide from the system, leading to the shifting of Reaction (2) to the right; carbonate sediments can also force Reaction (2) to move towards the right by absorbing CO_2 from the systemj either the decrease of confining pressure by structural fractures or the reduction of reducing gases by underground explosion will help the decomposition of iron carbonyl hydrides; protore beds of iron in the surrounding strata will be able to provide the hydrothermal fluids with lots of minute magnetite particles which will act as both crystal nuclei for iron precipitation and a sort of effective catalyst for the reaction CO+H_2O=CO_2+H_2. The reduction of partial pressure of carbon monoxide by this reaction will certainly expedite the ore-forming process.
出处
《矿床地质》
CAS
CSCD
北大核心
1990年第2期112-118,共7页
Mineral Deposits
