The Study Of Jiufengqi-longgongshan Nappe Structure And Its Ore-controlling Characteristics In Southwestern Fujian

The Southwestern Fujian depression belt, its geotectonic location belongs toCathaysia, which has undergone the transformation from Tethys to the circum-Pacifictectonic domain, also a part of the circum Pacific volcanic belt and polymetalmetallogenic belt. After years of research, it proved that the area nappe structure isextensively developed.Jiufengqi-Longgongshan nappe structure is located in eastern part of LongyanCity, Fujian Province, Beginning at east of Longyan, from xinci, to zhongjia,Longgongshan, xiaojingjian northeastward, about km30length, km8width. Theallochthonous, which is mainly about Cambrian-Ordovician low-grade metamorphicsiltstone and Late Devonian with Lower Carboniferous Lindi formation quartz sandyconglomerate, was west or north-west of the monoclinic structure, developingsecondary folding, it was like great klippe. The autochthonous is mainly aboutPermian phyllite, developing complex folds in the main section. Depending onmeasured sections and geologic path, the Jiufengqi-longgongshan performanceoverthrusting mainly from the NW to SE, then from SE to NW because of the latetectonic inversion. According to the stratigraphic unconformity and rock intrusioncontact characteristics, the author speculate that the geochronology from NW to SE isabout in169-156Ma, belongs to Early Yanshanian; Combined with the regionaltectonic evolution, we suppose that the late tectonic inversion should be caused byZhenghe-Dabu fault activation, the SE to NW nappe era is after135Ma, about inmiddle early cretaceous. According to the external source rock series, we think thatallochthonous come from Northwestern Fujian, the maximum nappe distance fromNW to SE up to100km; SE to NW was affected by Zhenghe-Dabu fault activation,the nappe distance is between15to20km.Nappe structure is the main ore-controlling structure in the area, ore-controllingcharacteristics are mainly two aspects, one is to polymetallic belt, the other is to metaldeposit. The controlling to polymetallic belt is mainly about Late Paleozoic carbonatestrata controling. These polymetallic belt are mainly trending north-east. The depositmainly about Late Paleozoic carbonate strata (C1j-P1q) These deposit either exposedin ore-bearing rock of the Upper Paleozoic tectonic window or concealed underore-bearing rock in allochthonous of pre-Devonian, nappe structure is the maincontrol factor in space, which is as shield for the ore-forming hydrothermal andprovides space for mineralization. Controlled source audio magnetotelluric method(CSAMT) has a range of probing depth, and the profile and bathymetric features,according to the the CSAMT technology, we futther confirm that there are lots ofnappe structure in Southwestern Fujian, which lead to formation inversion. The mainore-bearing rock in the area is Lower Carboniferous Jingshe formation-LowerPermian Qixia formation, mainly along AnD/C1l and C1l/C1j-P1q interface, wherebywe establish ore-controlling geological model of the nappe structure in southwesternFujian.