Study On Orefield Structure In Taochong Area Of Fanchang,Anhui Province

Taochong orefield is located in the northeast of the Tongling-Fanchang oreconcentration area, which is an important segment of the Lower and Middle Yangtzeiron-copper-gold metallogenic belt, and evidently controlled by structures. Fieldinvestigation and measurement have been carried out on the folds, faults, joints andcleavages in the orefield, with determination on the principal stress directions of themultiphase structural activities through deformation characteristics observation andstructural set analysis. On the basis of the study, an analysis has been completed onthe evolution of tectonic stress field in the orefield and its significance in controllingof ore deposits, a model proposed for mineralization in the Taochong orefield, and aprediction done on the favorable locations for iron deposits concentration in theorefield based on the model.The following are major achievements obtained in this thesis:1. Taochong orefield is evidently controlled by structures, and the ore bodyoccurs as falciform. Ores consist of specularite, magnetite and skarn-minerals andwall alteration includes skarnization and marbleization.2. Through the stress analysis and the petrotectonics observation, the principalstress directions in Taochong orefield are determined as northwest, eastwest andnortheast. The stresses have a characteristic of multiphase structural activities, ofwhich the NE stress is most closely related with mineralize.3. Based on structure deformation and Superposition, the evolution processesdivided into three periods, i.e., pre-metallogenic, metallogenic and post-metallogenicperiods. The pre-metallogenic period includes pre-Indosinian (D1-2), Indosinian (D3),Early Yanshanian(D4) phrases, metallogenic period does Late Yanshanian (D5-6)phrase, and post-metallogenic period consists of Late Yahshanian(D7) and Himalayanperiod(D8) phrases.4. The passageway structures for magma and ore-forming fluid and hoststructures for deposits are simple in the Taochong iron deposit. The NE interbedding-fractures occur as major passageway structures for ore-forming fluid, and the sunsidiary-fold as major host structures for deposits.5. A model for mineralization in the Taochong iron orefield is proposed. Thebasement fault development occurred in the pre-Indosinian, followed by the folddeformation with interbedding fractures occuring in the Indosinian owing to NWstress action. Then the pre-Indosinian basement fault and the Indosinian interbeddingfractures were activated due to the Early Yanshanian stress action, resulted inupwelling of magma from a deep magma chamber. To Late Yanshanian phrase, theinterbedding fractures are further extended, the metallogenic materials from themagma rise and deposit in the interbedding fractures and the turn end of thesunsidiary fold.